Rostock (delta robot 3D printer) fitted with Airtripper’s bowden extruder

About The Airtripper Extruder

The Airtripper’s direct drive bowden extruder for 3d printers has been a large success, which has allowed makers & builders to easily add an extruder to their custom 3d printer. Its simple bracket design means the extruder can be attached to most surfaces and T-slot type extrusions, and its compact design easily allow for multi hot end set-ups. The bowden extruder’s popularity was especially boosted when it was used on the first Delta Robot 3d printer called Rostock by Johann C. Rocholl. The Airtripper’s bowden extruder was originally designed to replace the Sumpod 3d printer extruder.

After writing the “3D Printer Extruder Filament Drive Gear Review & Benchmark” there is no longer any doubt about the capabilities of direct drive extruders when using recommended stepper motor and drive gear. With better stepper driver tuning, the MK8 drive gear could probably push more force than what I’ve recorded, and if you are only going to be using 1.75mm filament then a direct drive extruder is all you need for most 3d printing operations.

Available On Ebay

The Airtripper’s Bowden Extruder V3 BSP Edition is sold on Ebay by me as a kit with plastic parts and fittings, with optional PTFE tube and extra BSP fitting. The extruder kit is also offered without the plastic parts which allows the purchaser to get the bits from one place in needed quantities and 3d print the plastic parts themselves. My Ebay listings.

Airtripper’s 3D Printer Direct Drive Bowden Extruder BSP Edition

Additions & Tweaks

The latest batch of additions and tweaks was driven by requests to adapt the extruder to accept a BSP push in fitting. Other makers had successfully adapted the extruder to accept a type a of push fitting, but I wanted to use the most popular and most widely available push fittings and made my own adaptation. So the bowden extruder can now be fitted with the 1/8″ BSP 4mm straight fitting.

A view of the 1/8″ 4mm BSP Fitting With Set Screw, and a view of the 4mm Pipe Connector

The second addition to the extruder, after the BSP socket add-on, is the pipe bracket. The pipe bracket allows a 4mm tube to be connected to the extruder so that filament can be gently guided from the spool to the extruder. A separate tube bracket, the new additional part, is used to fix the other end of the tube near to the filament spool. The tube bracket was a separate add-on with the last extruder version but now the tube bracket is integrated in the latest extruder body design.

Some tweaks was made to the extruder fixing bracket so that it 3d printed more neatly; you can use the Thingiverse STL viewer to compare this extruder version to the last version. Another tweak was made to the  idler housing. It was found that the idler housing was prone to cracking when printed with brittle filament. So the tweak included widening the idler housing and thickening the walls; this has led to a shorter axle. The axle now drops to rest into a deeper sockets so that once the axle and bearing is pushed into position the axle does not constantly push into the idler housing walls, reducing stress and cracking over time.

3D Printer Bowden Extruder – Parts

Airtripper’s Bowden Extruder 3D Printed Parts

Four 3d printed parts are required to complete the bowden extruder plus an optional part called the tube bracket. The tube bracket allows for a PTFE tube, or other 4mm outer diameter tube, to fit between the bracket and the bowden extruder; this allows the extruder to pull filament from the spool, guided by the tube, from different possible spool location around the printer.

3D Printing The Parts

Skeinforge had been my first choice for printing the bowden extruder parts for some time but Cura has shown to do a better slicing job – and much faster too, and with the ability to print a tray of parts one part at a time, means Stringing is kept to a minimum. I have used Slic3r in the past and found that the extruder body thin walls don’t fill correctly, however, the latest Slic3r versions may provide better results.

I’ve 3d printed the bowden extruder using only PLA filament and can’t really comment on how well the extruder parts will print using other filament materials. There have been reports that ABS filament works well enough but there have been a couple of reports about issues with printing the idler bearing housing correctly.

A print layer height of 0.25mm is always set with my own extruder parts print, with top and bottom layers set to 0.75mm. The fill density is normally set to 25 percent, and with the print speed set to 24mm/s, all the parts will take around three to three and a half hours to print.

Non 3D Printable Parts

Airtripper’s 3D Printer Bowden Extruder Metal Parts

A full description and quantity of the parts that are shown in the image above:

• 1 x M3 x 25mm S/S Cap Screw Allen Bolt.
• 2 x M3 x 30mm S/S Cap Screw Allen Bolt.
• 2 x M3 x 45mm S/S Cap Screw Allen Bolt.
• 1 x M3 x 6mm S/S Button Head Allen Bolts.
• 1 x M3 x 10mm Screw
• 4 x M3 Stainless Hex Full Nuts.
• 2 x M3 washers.
• 1 x 22mm of 1/4″ 6mm id Rubber Diesel Hose Tubing Line.
• 1 x 608 ZZ [8 x 22 x 7] Roller Skate Ball Bearings.
• 1 x 1/8″ BSP Male to 4mm Straight Push In Pneumatic Fitting

MR105ZZ Ball Bearing for the stepper motor axle is optional with drive gears such as MK7 and MK8

The above parts are required to assemble the bowden extruder to the stepper motor and allow for the bowden tube to be attached. If you own a Dremel type tool you can cut the 6mm and the 25mm screws from the longer versions if desired.

I’ve continued to use the rubber tube as the idler bearing pre-loader because it allowed for plenty of space to remove the idler housing from the extruder for filament changing. I’ve tried using springs and it was difficult to get the springs over the idler housing hooks.

Caution needs to be taken when fitting the BSP fitting to avoid splitting the extruder body. The threads on the BSP fitting provide a good grip inside the fitting socket on the extruder, so there is no need to tighten the set screw too much. The set screw only needs tightening just enough to hold the fitting in place.

3D Printer Bowden Extruder – Recommended

PTFE 4mm x 2mm Tube Preparation For Bowden Extruder To Reduce Filament Snagging.

Since this is a bowden extruder, you will almost certainly be using a length of PTFE tube between the extruder and the hot end. The extruder is designed to take PTFE tube (4mm OD x 2mm ID) and 1.75mm filament, 1/8″ BSP Male to 4mm push fitting is used to connect the tube to the extruder.

As shown in the picture above, to avoid snagging when loading new filament, it is recommended to taper the end of the tube which can be done with a drill bit. Some snagging will occur occasionally but changing the PTFE tube alignment inside the fitting with one hand while loading the filament will help get the filament through the connector.

Before loading new filament into the extruder, straighten the end of the filament as much as possible so the end of the filament does not snag inside of the BSP fitting. Snip the end of the filament if not cut square.

3D Printer MK8 Extruder Filament Dive Gear Benchmark, Recommended For Direct Drive PLA Extruder

Along with a high torque stepper motor, the MK8 drive gear is recommended for the direct drive bowden extruder. As shown in the tests here, a good stepper motor / drive gear combination will provided plenty enough torque to drive 1.75mm filament. It will be difficult to solve 3d printing problems or even to calibrate the printer properly without the correct stepper motor and drive gear behind the extruder.

Extruder Stepper Motor SY42STH47-1684B

The stepper motor I use with my own extruder set-up is the SY42STH47-1684B (Holding Torque (Kg.cm) 4.4) and you will find this stepper on the RepRap NEMA 17 Stepper motor Wiki page.

Due to the grip provided by the MK7 and MK8 drive gear filament pulleys, it is no longer necessary to have the extra bearing on the stepper motor axle. The MR105ZZ Ball Bearing was previously used on the axle to take some load of the stepper motor internal bearings, but since the MK7 and the MK8 drive gears have excellent grip on the filament, it is not necessary to apply a heavy load on the axle with the idler bearing. These same stepper motors are used to drive pulley belts and may put a higher load on the axle than the extruder idler bearing itself.

Airtripper’s Direct Drive Bowden Extruder V3 BSP – Files

OpenSCAD Script File Code Snippet: preview_part = 1; // [1:Extruder,2:Idler,4:Strut,5:Axle,6:Tube Bracket]

However, should the STL files need to be compiled again, the OpenSCAD script file for the extruder is also available for download. At the minimum, you would only need to change one line of code to compile an STL file for each of the bowden extruder parts.

preview_part = 1; // [1:Extruder,2:Idler,3:Idler with brim,4:Strut,5:Axle,6:Tube Bracket,7:All Parts]

You’ll find the above line of code in the OpenSCAD script file at the top of the page after a few lines of comments. Basically, to select a model to edit or compile to STL, change the number assigned to the preview_part variable with the number assigned to the model; the image above shows a number assigned to each bowden extruder part model.

File Downloads

Thingiverse

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3D Printer Extruder Filament Drive Gears: a, Plain Insert; b, Raptor Filament Drive Gear; c, MK8 Drive Gear; d, MK7 Drive Gear

Probably the most important part of the 3d printer direct drive extruder system, at least after the stepper motor, is the filament drive gear pulley. Basically, the choice of drive gear could make or break the quality output of the 3d printer. Without a good drive gear, it will be difficult to begin to troubleshoot or solve hot end issues. So, with the help of the Airtripper Extruder Filament Force Sensor, I’ve reviewed and bench-marked four drive gears and provided graphs for a quick visual comparison.

All the benchmarking and the drive gear reviews in this topic are based on PLA filament only, softer filament might provide very different results, so a separate review would be needed for different filaments. Since PLA filament can be difficult to extrude, this was a good filament to do the first drive gear benchmark with.

It’s almost certain that some of the drive gears will perform much better on geared extruders, but for this topic, only direct drive extruder is used. I think the benchmark results for drive gears are more interesting when the torque limits of the stepper motor are also shown.

Filament Drive Gear Review & Benchmark

3D Printer Extruder Drive Gear Pulley Benchmarking Kit

The Benchmark Testing Procedure

The benchmarking is done with the Sumpod 3d printer fitted with the Airtripper Extruder Filament Force Sensor; an introduction to the filament force sensor can be found here. Filament is extruded through the hot end nozzle in air away from the build platform. Enough filament is extruded until filament force has reached its peak, and then continue extruding to be sure that the drive gear can push against the force without filament slipping or stepper motor stalling.

Screen capture is used to capture the Processing application graph at the point of interest. The extruder flow rate is either increased or decreased depending on the drive gear performance. Flow rate is increased to cause the filament pushing force to rise to the point of failure, of either the stepper motor (stalling) or the drive gear (slipping). Adjustments are made to the extruder idler tension to try to compensate for failures and to fine tune for better performance.

Each drive gear pulley is calibrated for the correct value for E Steps/mm. A starting value is entered into the Marlin firmware before extruding 100mm of filament for measurement. 100mm of fresh filament is extruded from the printer interface with the driven filament length being measured for length accuracy. E Steps/mm is updated as necessary to satisfy calibration test accuracy before benchmarking.

Plain Insert Coupling

Brass, bore 5mm, length 15mm, effective diameter 7.66mm approx. E step calibration starting point for 1/8 micro stepping 67.16.

Plain Insert Coupling showing good grip on the filament pushing over 3.6kg of force.

Plain Insert Coupling Stalling the stepper motor at around 4kg of force. Good filament grip here.

Plain Insert Coupling stalling the stepper motor with the idler tension overloaded.

This gear was originally supplied with the MDF Sumpod; my first 3d printer. It’s usually called a Plain Insert Coupling, used for connecting universal joints to motor shafts in model boats. A quick google search “plain insert joint” found a number of suppliers with prices around GBP 2.00 (USD 2.64). Similar to the Plain Insert Couplings, a range are also sold under the brand Raboesch Couplings. The prices for the range are slightly more, GBP 2.26 (USD 2.97), and sold by Boots Industries as a drive gear for CAD 14.99; so shop around. Plain Insert Couplings and Raboesch Couplings look very similar but can’t tell how closely matched the teeth are without having both types in hand.

If the Plain Insert can seriously be used as an extruder filament drive gear then this would be the cheapest drive gear available by far, and graph one confirms that this gear has some pushing power. I can’t say that my experience with the Plain Insert has been good, I had a lot of other issues with the Sumpod extruder and with my inexperience at the time it would not be fair to judge the gear by past experience. So, my opinion of the Plain Insert Coupling will be derived from the benchmarking test.

The teeth are triangular shaped, slightly flattened on top, and angled at the bottom between each tooth; a design that will mostly prevent the gear teeth from fully penetrating the filament. So, because of the shape of the teeth, and as confirmed by the teeth marks on the filament, the effective diameter will be determined by the filament type and idler tension. It is likely that there will be flow rate differences between filament types and E step calibration.

Extra care needs to be taken to setup this drive gear, getting the correct tension on the filament, and checking the E steps/mm and flow rate. Over tightening the idler tension can have a negative effect on performance as shown in graph three, and this is due to the stepper motor torque being used to compress the filament between the teeth of the gear; making the extruder stepper motor work harder.

Graph one and graph two show that the extruder idler tension is optimized for best filament grip with graph two being influenced by increasing hot end flow rate to the point of stalling the extruder stepper motor. Graph three shows the extruder stepper motor stalling under increased idler tension.

Although the the Plain Insert as shown good performance for this benchmarking, achieving the same result will be difficult without an extruder filament force sensor. This gear does not have the same high level of grip as the MK7 and MK8 and so hitting the margin between filament slips and stepper motor stalls with idler tension tweaking will be more difficult at higher forces.

Raptor Filament Drive Gear

Brass, bore 5mm, length 11.2mm, effective diameter 9.67mm approx. E step calibration starting point for 1/8 micro stepping 49.7.

The Raptor Drive Gear holding steady at around 1.85kg of force.

The Raptor Drive Gear loosing grip on the filament with increased extruder flow rate.

The Raptor Drive Gear stalling the stepper motor with best idler tension

The Raptor Drive Gear was offered by QU-BD alongside their new MBE Extruder V9 at a time when 3d printer parts was much less available than they are today. During that time, filament drive gears for direct drive extruders was quit rare and expensive to import. So when the Raptor Drive Gear came to market with favorable shipping costs, I ordered two to replace the Plain Insert Coupling that I was then using. Unfortunately, my extruder woes didn’t end.

I’m not sure how the QU-BD company did the benchmark for this drive gear but I could not get it to work with PLA filament; so I’m assuming the performance claims was made against ABS filament. Even with the filament force sensor, I could not get a reliable flow rate above 2kg of force. Graph one shows the best force level I could achieve without filament slipping or stepper motor stalling.

With increased filament flow rate, graph two shows the filament slipping on the drive gear leading to under extrusion. When attempting to compensate for the slippage, graph three shows the result. The flattened teeth on the Raptor causes more work for the stepper motor as the teeth get pressed into the filament under increased idler pressure. The harder the teeth get pressed into the filament the less force is available to push the filament, eventually leading to stepper motor stalls.

The Raptor Drive Gear has deep teeth which may effect flow rate calibration accuracy between filament changes and E Step calibration. If the drive gear teeth don’t fully sink into the filament then the effective diameter of the drive gear might not be consistent between different filament types. This would complicate filament set-up and you would have to set-up the idler tension correctly as before when reinserting filament previously calibrated.

The grub screw was a problem for me while using this gear, the Raptor often come lose on the stepper shaft. Personally I thought the wrench required to fit the grub screw was too thin for the tightening toque needed, and sometimes it slipped round in the screw head. In the end, I manage to fined a grub screw with a larger hex socket to insert into the Raptor; which did the trick.

MK8 Filament Drive Gear

Machined stainless steel (304), bore 5mm, length 10.1mm, effective diameter 7mm. E step calibration starting point for 1/8 micro stepping 75.7.

MK8 Dive Gear showing good grip on the filament pushing over 4.2kg of force.

MK8 Dive Gear loosing grip on the filament while pushing over 4.7kg of force.

MK8 Dive Gear Stalling the stepper motor at over 4.6kg of force. Good filament grip is demonstrated here.

When I ordered the MK8 Drive Gear I had doubts about its ability to grip the filament with performance on par with that of the MK7. This was due to the reduced diameter, giving 35% more power as claimed, which I thought would compromise the effective grip on the filament. But it turns out that the MK8 Gear can maintain excellent grip on the filament right up to the point of stalling the stepper motor. It’s reduced diameter, compared with the MK7, makes better use of limited torque provided by 3d printer direct drive extruders.

The MK8 Drive Gear’s fine milled teeth allows the filament to be held against the effective diameter easily by the idler bearing; allowing for consistent flow rate calibration between filament changes and E Step calibration.

Graph one shows the level of force that can be achieved with the MK8 when the extruder idler preload is optimized. Achieving this level of set-up will be difficult without a filament force sensor and this is due to the filament slippage, shown in graph two, being difficult to detect. However, since this drive gear is capable of stalling the motor as shown in graph three, cranking up the feed rate fast enough to see if you can stall the stepper motor will indicate if the idler is tight enough to prevent filament slippage.

Even without a filament force sensor, for a well maintained 3d printer extruder system, this gear is easy enough to set-up without special considerations or set-up exercises; since the high level of forces achieved by this gear may never be needed for normal 3d printing conditions.

MK7 Filament Drive Gear

Machined stainless steel (304), bore 5mm, length 11.1mm, effective diameter 10.56mm. E step calibration starting point for 1/8 micro stepping 48.1.

MK7 Dive Gear showing good grip on the filament pushing over 2.8kg of force.

MK7 Dive Gear Stalling the stepper motor at over 3kg of force.

Purchased from Ebay, the MK7 Drive Gear turned out to be the most important update to my 3d printer extruder system. After struggling with the Raptor Drive Gear for some time, with the MK7 fitted, I was now able to solve extruder issues rather than manage issues. My extruder suddenly became more reliable and I was now getting the correct feedback needed to calibrate settings to get the best looking 3d prints.

The MK7 with its large effective diameter provided excellent grip on the filament which meant less care about idler tension set-ups. Like the MK8, consistent flow rate calibration between filament changes and E Step calibration was possible due to the gears’ finely milled teeth. Also to note, the MK7 grub screw worked well and its hex socket took a decent size wrench to lock the gear on to the stepper motor shaft with plenty of torque.

NEMA-17 Bipolar 5.2:1 Planetary Gearbox Stepper Motor

Although the MK7 performs well in the grip department, its large effective diameter means there is less torque to drive filament through the hot end. Compare graph one to the MK8 Drive Gear and you’ll see a performance gap between two similar designed gears but with different effective diameters. Looking at graph two the MK7 stalls at around 3kg of filament force, probably not ideal for direct drive extruders but there is enough torque for a good hot end set-up. It’s only when you start having hot end issues that this gear will show it’s torque limitations, and that’s what prompted me to change to the MK8 Gear.

The MK7 Drive Gear would work better with geared extruders or even NEMA23 stepper motors. But options are limited while the MK7 is only available with 5mm bore, an 8mm bore version to fit Planetary gear stepper motors would be welcome.

Filament Drive Gear Review & Benchmark Conclusion

MK8 Filament Drive Gear Pulley

The drive gears may provide very different results for different types of filament, but for PLA filament at least, the MK8 Drive Gear came top in this article. I would recommend the MK8 Drive Gear for direct drive extruders, especially when paired with the stepper used for this test. The MK8 Drive Gear provides a good balance of grip and torque to push the filament with force that easily exceeds 4kg.

The MK7 Drive Gear would be my second recommendation, it has excellent grip on the filament and the idler tension is easy to set-up. However, the gears’ large effective diameter may not provide enough torque when nozzle and filament troubles occur. If you’re looking for serious pushing power from a geared stepper motor, the MK7 should be first choice.

The MK7 and the MK8 have been engineered for the purpose of extruding filament and have provided good all round performance; both easy to set-up with the extruder idler tension.

The Plain Insert Coupling deserves a mention for its good pushing power. However, the gear can be difficult to set-up without the help of the filament force sensor. If you have good experience with 3d printing and have a well oiled machine, you might get some good performance out of this cheap drive gear.

And finally, performing very poorly, the Raptor Drive Gear. As proved with the MK7 Drive Gear, bigger gear teeth don’t mean better grip. However, the Raptor Drive Gear might perform better on a geared extruder where idler tension can be increased, but at the expense of causing more damage to the filament.

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Documentation for the electronics and software is currently being edited and will be published shortly.

The Load Cell Bracket

The current force sensor bracket is designed to be configurable to suit a common load cell size configuration with small variances in screw hole positions and sizes. Only two revisions of the bracket have been printed, to test different load cells, and no failures have developed with the plastic parts after many hours of use. A few tweaks have since been made to bulk up the bracket design to improve stiffness and more 3d printable for other makers.

The force sensor bracket design and the OpenSCAD model file was made to be as distribution friendly as possible to allow other makers to get involved in the project as easily as possible.  For now, the current bracket configuration only supports 1.75mm filament but 3mm filament support is on the way with a new extruder design. While the force sensor bracket uses the Airtripper bowden extruder, other direct drive extruders that support 1.75mm or 3mm filament could be made to fit.

It was decided, for a bowden extruder set-up, that a 5kg load cell was sufficient. It was found that an extrusion force of more than 2.8kg (approximately) over a long periods of time would strain the push fit fitting holding the PTFE tube. One push fit fitting had failed, but after many hours of use. However, as well as the high extrusion force, the pushing and pulling of the retraction operation may be a high contributing factor of the fitting failure.

A normal working filament extrusion force has not been defined that I know of but some of the better filament I’m using requires less than 2kg of force at 24mm/s, 0.25mm layer height and 0.4mm nozzle. While I’ve been using the filament force sensor I’ve noticed that the filament is requiring more force to extrude as it ages. Probably a good time to think about my filament storage strategy.

Choosing a Load Cell

The load cell required for the Airtripper Extruder Filament Force Sensor should have a 5kg load rating and be at least 75mm in length. How you’ll get the load cell will depend on the resources you have to get the load cell calibrated. A guide about acquiring load cells can be found here: Electronic Kitchen Scales Teardown Versus Load Cells.

5kg Load Cell Bought from Ebay

The above load cell is similar to what you need and the dimensions you see are used in the OpenSCAD model file to configure the filament force sensor bracket. As long as the load cell is at least 75mm long and about 13mm wide then the load cell should fit the bracket after some configuration.

Load Cell Bracket – Configure The Parts

Since load cells from different sources have features with measurements that vary, it is necessary to configure the OpenSCAD file to produce the correct STL files. This should be easy to do even if you are new to the OpenSCAD application, there should be enough information in this guide to successfully reach the 3d printing stage of the project.

OpenSCAD Application Window View

Getting Familiar With Model File

At this stage you have the load cell you are going to use and measured up similar to the example shown above. You’ve got OpenSCAD installed on the computer, running and got familiar with the software interface. Press F5 to refresh the model window after editing code, and press F6 to compile the model before choosing to export to STL file.

Before configuring the OpenSCAD file with the load cell measurements, we need to get familiar with some code in the file in order to get the model view we want in the render window. Loading the project file into OpenSCAD will automatically  render any object that is configured in code to show in the render window.

The OpenSCAD model file supplied for this project, if I remember to set it correctly, should show by default the assembled model (1:assembled) of the Airtripper Extruder Filament Force Sensor. The models in the file are partly parametric and the assembled model should adjust itself to reflect the entered dimensions of the load cell. The load cell should correctly fit the brackets as long as the assembly screw holes line up. After entering new load cell dimensions, it will be a case of rotating the assembled model in 3d view to check screw holes are aligned.

Selecting A Model To View in OpenSCAD

The bracket part reference guide above shows the models available for selection to view and edit in the OpenSCAD filament force sensor project file. A number is assigned to each model and is used in the OpenSCAD project file to select which model we want to view in the render window. The following code from the project file is used for selecting a model to view in the render window; it’s the first bit of code in the file.

//– Select Part To View –//

view_part = 1;    // [0:nothing, 1:assembled, 2:load_cell, 3:bowden_bracket...

//-- END Select Part To View --//

In the code file, anything after the two forward slashes " // " are just comments to help describe some code.

The above line of code shows that 1 is assigned to view_part variable and this will cause the project file to display the assembled filament force sensor kit. Changing the assigned 1 to a different number that is associated to a different model in the part reference guide will cause the OpenSCAD render window to update after a compile command (F5) is issued.

Tip: When exporting the rendered model to STL, it is recommended to use the model name as the file name.

Load Cell Configuration

5kg Load Cell Size Variables

//—— START Load Cell Configuration——-//

lcl = 80;        // (80) Load cell length
lch = 12.7;        // (12.7) Load cell height
lcw = 12.7;        // (12.7) Load cell width
lclhs = 4;        // (4) Left side screw holes size – screws 1 & 2 (load cell bracket side)
lcrhs = 4;        // (4) Right side screw holes size (load cell stepper bracket side)
lchle = 5;        // (5) Measure from left edge to center of first screw hole (load cell bracket side)
lchln = 15;        // (15) Measure from first screw hole center to second screw hole center (load cell bracket side)
lchcd = 40;        // (40) Measure distance between the second & third hole centers
lchrc = 15;     // (15) Measure distance between the center of the third and fourth screw hole (load cell stepper bracket side)

//—– END Load Cell Configuration —–//

The above code is found in the model file and allows you to enter new load cell dimensions so that the extruder filament force sensor can be configured to fit the chosen load cell. The load cell image above the code shows the variables at positions where measurement values are taken from; this serves as a simple and quick reference to identify each variable association.

When making changes to the load cell dimensions, render the 3d view (F5) to review the changes. With the assembled model in view (1:assembled), rotate the model to check that the changed feature is still aligned correctly.

Configure Bracket & Screw Holes

After the new load cell dimensions have been entered in to the project file we now need to sort out what screw sizes to use to attach and assemble the brackets. Refer to the image below to quickly identify variables used.

Please Note – Screw Sizes

Default screw hole sizes are oversized to allow for shrinkage when 3d printed, and the measurements have been fine with my particular 3d printer & filament set-up. When reviewing the screw hole sizes you will need to determine how much shrinkage allowance you want to add in order for the screws to fit.

Hex nut capture sockets for screw heads will be most sensitive to filament & 3d printer configuration, and so it is advised to do a test print using a small part with the screw sizes you want. Hex head socket being the wrong size could render your newly printed part unusable; wrong size hex nut sockets could make it difficult to assemble the parts.

To avoid complications, the filament force sensor bracket has been designed not to rely on load cells having particular screw hole designs. This means in most cases the default settings for lcbhs, sbsd & sbsdh will not need to be changed.

Variable lcbhs will be an M4 screw with 2 fitting options:

• Screw into the load cell from underneath the bracket – load cell screw hole is M4 threaded.
• Push all the way through the bracket and load cell, and fasten with a nut – load cell screw hole is not threaded or the screw hole is M5 threaded.

Variables sbsd & sbsdh should always be at the default setting for M3 screws which allow for a wider stepper motor position adjustment. M4 Screw size can be used if more convenient but the load cell screw holes must be big enough to allow the screws to drop through for nut fastening.

The load cell bracket attachment screw holes lcbfh are adjustable and are used for attaching the bracket to the printer or other surface. The default size is 8mm, for M6 screws, to allow for 3d print hole shrinkage and screw hole misalignments.

Variable lcbss can be updated to adjust the distance between the lcbfh screw hole centres. If you are replacing the Airtripper extruder with the bracket, setting lcbss to 60mm will allow the bracket to fit the holes used for the extruder; saving extra drilling.

The bracket is designed to fit NEMA 17 stepper motors and the variable smw allows some adjustment to the stepper motor clamp width. It is important that the stepper motor is fitted loose enough inside the clamp so adjustments for alignment can be made before the clamp is finally tightened. Adding 1.5mm to 2mm to the stepper motor width when updating the smw variable will reduce the chances of the stepper motor snagging inside the clamp during set-up.

Load Cell Bracket Variables

Load Cell Bracket Variables

Variables stbsd, stbsdh, lcbbss & lcbbssh are available to fine tune for your 3d printer & filament set-up.

Find the configuration code, shown below, in the model file to make the necessary adjustments as described above.

//—- START Load Cell Bracket Configuration —-//

// Configuration for part 4:load_cell_bracket
lcbhs = 4.5;    // (4.5) Bracket screw hole size for load cell attachment
lcbfh = 8;        // (8) Bracket screw hole size for attachment to printer
lcbss = 46;        // (46) Bracket fixing screw holes distance apart, hole centre to hole centre
lcbbss = 4.5;    // (4.5) Bowden bracket attachment screw size
lcbbssh = 8.4;    // (8.4) Bowden bracket attachment screw Hex head size

//– END Load Cell Bracket Configuration–//

//—- START Stepper Motor Bottom Bracket Configuration—-//

// Configuration for part 5:bottom_stepper_bracket
smw = 44;    // NEMA 17 stepper motor case width
// Stepper motor bottom bracket load cell attachment screw size
sbsd = 3.5;        // (M3 = 3.5)(M4 = 4.5) Screw size
sbsdh = 7.5;    // (M3 = 7.5)(M4 = 8.8) Screw Hex head size

//– END Stepper Motor Bottom Bracket Configuration –//

//—- START Stepper Motor Top Bracket Configuration—-//

// Configuration for part 6:top_stepper_bracket
// Stepper motor Top bracket load cell attachment acrew size
stbsd = 3.5;        // (M3 = 3.5)(M4 = 4.5) Screw size
stbsdh = 7.5;    // (M3 = 7.5)(M4 = 8.8) Screw Hex head size

//– END Stepper Motor Top Bracket Configuration –//

3D Printing & Building The Parts

Skeinforge has been my number one slicing application and it has worked great in producing g-code for the Airtripper Direct Drive Bowden extruder parts. Between Slic3r and Skeinforge, Skeinforge is still the better slicer for the extruder. Other slicers may work very well, but for this project, I’m just going to report what I used successfully with good results.

While Skeinforge worked great for the Airtripper extruder parts, it was not the best choice for the load cell brackets. I found that Skeinforge added too many solid layers in the larger parts which caused poor 3d printed results where there was many consecutive solid layers. Not sure why Skeinforge adds the extra solid layers, but decided that slic3r worked better for the filament force sensor brackets; only putting in solid layers where needed.

Export The Parts

//– Select Part To View –//

view_part = 1;    // [0:nothing, 1:assembled, 2:load_cell, 3:bowden_bracket...

//-- END Select Part To View --//

Once you are sorted with the OpenSCAD file configuration, locate the above code in the scad file and change the number assigned to view_part to the next model you want to export to STL file for slicing. Use the part reference image above to quickly identify the parts to be 3d printed. In the OpenSCAD application menu "Design" select Compile and Render, and then select Export as STL under the same menu. Use the model name as the file name as you export each model.

The 4:load_cell_bracket and the 3:bowden_backet can be printed in one piece if desired. The one piece bracket, 7:full_load_cell_bracket, was too big for my 3d printer platform.

3D Printing The Parts

Below are some bullet points about the set-up I used for the brackets and the extruder. The settings are more of a starting point than recommendations set in stone.

• All the parts set to 0.3 infill density.
• Minimum two perimeters.
• Solid layers, three top and three bottom.
• Set a cooling threshold for parts 3:bowden_backet & 7:full_load_cell_bracket. The BSP push fitting socket can spoil without adequate cooling.
• All the parts printed with 0.25 layer height.
• Solid infill every 6 layers for parts 3:bowden_backet & 7:full_load_cell_bracket. This was to add stiffness to the bowden tube bracket.
  

Electrical Tape Added For Padding & Protecting

Building The Parts & BOM

The force sensor bracket assembly will be detailed here while the Airtripper bowden extruder assembly is covered here: Airtripper’s Bowden Extruder V3 – Updated Design. Also note that the bill of materials is based on the default set-up of the OpenSCAD file. However, note the lengths of the screws required when ordering the screws you have configured for your set-up.

Tip
For the purpose of prototyping, I usually keep a stock of screw sizes of the longer lengths and cut them down with a Dremel to the required length. This saves on storage space and keeps the stock of screws to a minimum, and also cuts the cost of getting screws of all sizes.

Six steps have been defined to assemble the filament force sensor bracket and by using the image above against the numbered bullet list below the assembly should go smoothly.

1. First, if the two part version was printed, attach the bowden tube bracket to the load cell bracket with M4 screws pushed through the back. Tighten the nuts and attach the load cell bracket to the printer or other chosen surface.
   • 2 x M4 x 40mm Hex Head Bolts
   • 2 x M4 Full Hex Nuts
   • 2 x M4 Washers
   • 2 x M6 Screws, length & type chosen by user
   • 2 x M6 Nuts
   • 4 x M6 Washers

    

2. Attach the stepper motor bottom bracket to the load cell. Check that the load cell is attach the proper way round with the load cell load direction arrow pointing downwards on the stepper bracket side. The extended square bit should be pointing towards the back end of the stepper motor.
   • 2 x M3 x 25mm Hex Head Bolts
   • 2 x M3 Full Hex Nuts or Wing Nuts
   • 2 x M3 Washers

    

3. Assemble the extruder and attach it to the stepper motor. Make sure the stepper motor wires come off the correct side of the extruder for your set-up.
   • 1 x M3 x 25mm Socket Cap Head Screw Allen Bolt.
   • 2 x M3 x 30mm Socket Cap Head Screw Allen Bolt.
   • 2 x M3 x 45mm Socket Cap Head Screw Allen Bolt.
   • 1 x M3 x 6mm Button Head Screw Allen Bolts.
   • 3 x M3 Full Hex Nuts
   • 2 x M3 washers.
   • 1 x 608 ZZ [8 x 22 x 7] Roller Skate Ball Bearing
   • 1 x 22mm 1/4″ x 6mm id Rubber Diesel Hose Tubing Line
   • A suitable drive gear for direct drive extruders

    

4. Place the stepper motor into the load cell bracket (2), and then clamp the stepper motor in place with the top part of the bracket. Insert all the screws from the underside and slide the stepper motor until the edge of the bracket is about 2mm from the back edge of the extruder. Finally clamp the bracket down evenly until the stepper motor is just about secure and does not move.
   • 4 x M3 x 30mm Socket Cap Head Screws Allen Bolt
   • 4 x M3 Full Hex Nuts
   • 4 x M3 Washers

    

5. So, with the load cell bracket attached to the 3d printer (1), attach the load cell and stepper motor assembly (4) to the bracket. Use a piece of filament to thread through the bowden tube holder and the extruder to align the force sensor assembly. Some screws might need to be undone to allow more adjustment before finally tightening all the screws.
   • 1 x M4 x 45mm, Head type optional
   • 1 x M4 Full Hex Nut
   • 2 x M4 Washers

    

6. The final part is to attach the 1/8″ BSP push fitting and PTFE tube. The fitting is held by a screw and the screw only needs to be turned just enough to grab the fitting securely. The PTFE tube end should be tapered to reduce snagging when loading the filament. Tapering the tube end can be done by hand using a drill bit. A tube is required between the filament spool and the extruder so a place needs to be found to attach the tube bracket (12_tube_bracket).
   • 1 x M3 x 10mm Socket Button Head Screw
   • 1 x M3 Full Hex Nut
   • 1 x 1/8″ 4mm BSP Push Fitting
   • 1 x PTFE Tube for Bowden Feed
   • 1 x PTFE Tube for Filament Reel Feed

    

Airtripper Extruder Filament Force Sensor – FILES

A snapshot of the OpenSCAD file will be put on Thingiverse which this topic will support to keep things in sink. A development version of the file will be available on GitHub.The version on GitHub will be develope to support 3mm filament with a new extruder design with possible changes to the bracket. Documentation on GitHub will detail the updates as they happen.

Files

Thingiverse file links will be updated as soon as the electronics and code documentations are complete.

Thingiverse: Airtripper Filament Force Sensor – On thingiverse

GitHub : Airtripper Extruder Filament Force Sensor – On GitHub

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Related topics

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Airtripper’s Bowden Extruder V3 – Updated Design

Airtripper Extruder Filament force sensor – Introduction

This is a project with a lot details to cover so there will be three articles including this one. This article is about selling the idea, then the next article will be be about the load cell bracket construction. The last article will then cover the electronics with load cell calibration and software interface. I would advise not to go out and buy the load cell or supporting electronics until advised by this project. This is just to make sure that your load cell will get the best start for successful calibration.

Airtripper Extruder Filament Force Sensor

Airtripper’s Load Sensitive 3D Printer Filament Extruder Using A 5KG Scale Load Cell

You probably get an idea of how this Airtripper load sensitive extruder works by looking at the picture above. I don’t expect it will look great on every 3d printer but it looks good on mine and I shall be fitting a second one soon. The attachment footprint is small which should suit many 3d printer set-ups. All the load sensor bracket components have been designed to provide good stiffness to the complete assembly. More details about the bracket assembly and other options will be covered in the next article.

Airtripper Extruder Filament Force Sensor

How It Works. It is basically an Airtripper bowden extruder that is attached to one end of the load cell. When the extruder feeds the filament to the hot end, the extruder is effectively pushing against the filament causing the extruder to apply extra load on the load cell. Load cells have strain gauges attached that change in electrical resistance when under different loads. This resistance change provides small voltage levels that can be amplified and then read by an analogue to digital converter. In this project, an Arduino Uno is used to read the analogue output from an instrumental amplifier. The readings taken from the load cell are linear which makes it easy to create an accurate weight table in the Arduino Coding.

Because of the stiffness of the load cell and the brackets, printer wobble has very little influence of the final sensor readings. Any operational lag in the assembly is likely to be much less than the combination of stretching and compression of the bowden extruder system. You’ll notice in the picture above there is a filament guide tube fitted between the extruder and the filament real. This filament tube guide prevents the extruder pulling down on to the load cell when tugging at the filament reel; skewing sensor readings.

Airtripper Extruder Filament Force Sensor Graphs

Set Of 3 3d printed 608-ZZ Ball Bearing Axles

Basically, the purpose of doing these graphs is to find out what sort of information we can get out of the load cell that is used for the filament force sensor. We want to find out if the graphs can be used as a guide for better extruder set-ups. The graphs below is just a start and not a complete test of every set-up situation.

Some Test Conditions. I used the same test print object for all the graphs below accept for graph twelve.  The test print object is a set of three bearing axles used on the Airtripper’s Bowden Extruder.

Skeinforge was used to compile the g-code for each test while Pronterface was used to interface with the Marlin Firmware on the Sumpod. It should be noted that the temperature used in the tests below is the temperature of the nozzle heater block and that the nozzle temperature could be much lower.

Graph One

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 220, Extruder Retraction Speed (mm/s) = 13.3, Retraction Distance (mm) = 0.8, Restart Extra Distance (mm) = 0.

Graph one is a plot of what was my typical set-up for months. The 3d printed outputs were good but a bit of cleaning was needed to get rid of the many fine hairs and the odd clumps of plastic.

a The load sensor shows that a consistent pressure is maintained with the current settings, however, there is a slight climb in pressure after each retraction. b The retraction was not long enough to fully de-pressurise the hot end nozzle which caused some pressure to be lost from the nozzle tip through extrusion. Unwanted extrusion usually causes stringing and clumps of plastic to be left between object cavities and perimeters.

Graph Two

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 220, Extruder Retraction Speed (mm/s) = 13.3, Retraction Distance (mm) = 2.0, Restart Extra Distance (mm) = 0.

b Retraction is increased to 2mm and the change is reflected in graph two. The retraction is long enough to drop the pressure to 0kg but the consistent pressure maintained across the graph a still shows a slight climb after each retraction b.

Retraction was long enough to relax the filament in the bowden extruder system but not long enough to pull the filament from the nozzle tip. Some oozing may have occurred to cause a slight loss of pressure. Graph two looks better than graph one because of the signs of less pressure being lost between retractions.

Graph Three

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 220, Extruder Retraction Speed (mm/s) = 13.3, Retraction Distance (mm) = 2.0, Restart Extra Distance (mm) = 0.1.

Using the same settings as graph two but using Restart Extra Distance of 0.1mm, the graph shows a consistent pressure level across the graph a and also in between retractions b. You will notice that all the retractions b are hitting the 0kg mark consistently. The width of the retraction indicates travel period between plastic filament extrusion.

This demonstrates the sensitivity and the consistency of the load sensor. Adding Restart Extra Distance will add more plastic to the 3d print and alter some dimensions.

Graph Four

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 220, Extruder Retraction Speed (mm/s) = 25.0, Retraction Distance (mm) = 3.0, Restart Extra Distance (mm) = 0.

With this test I have altered a few more settings (shown in bold red above) since graph three. The main change to note is that we now have a Retraction Distance of 3mm. This has brought the retractions b to well below the 0kg mark. Each retraction shown in the graph is consistent in length and the pressure a has maintained a consistent level between retractions and across the graph.

The effect of this change now means that the filament is pulled from the nozzle tip; preventing pressure loss caused by melted plastic oozing from the nozzle tip. The Extruder Retraction Speed setting is almost doubled to reduce the retraction operating time between plastic extrusion.

This has provided the best set-up for my 3d printer, no oozing and no strings. I was able to print a tray of different objects without loss of quality to object walls; no 3d printed parts clean up was needed. A lot of time saved on production runs.

Graph Five

Flow/Feed Rate (mm/s) = 48, Temperature (C) = 220, Extruder Retraction Speed (mm/s) = 25.0, Retraction Distance (mm) = 3.0, Restart Extra Distance (mm) = 0.

Flow Rate and Feed Rate are both doubled to a setting of 48mm/s but all the other settings remain the same as the previous graph. Because the parts being printed for this test are small the printer would not make the 48mm/s speed. However, speed is increased and is reflected in the graph as an increase in pressure compared to the last graph a.

Although the pressure is nicely maintained across the graph, pressure ripple a has appeared as a result of increased speed. All the wider peaks a look to have a similar patten which would suggest that this is caused by a control feature of the firmware as a result of printing a small part at a higher speed. Although the pressure has increased the retractions b still make it below 0kg and the retraction length remains consistent across the graph.

Despite the ripples the graph still looks pretty neat and tidy and as uniform as the previous graph that had good print results. This faster setting also produced the same good print results.

Force Sensor / Load Cell Temperature Detection Test

The following graphs from six to eleven is about what difference the temperatures makes to the force sensor / load cell readings.

Graph Six

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 215, Extruder Retraction Speed (mm/s) = 20.0, Retraction Distance (mm) = 2.5, Restart Extra Distance (mm) = 0.

220 degrees C looks to be the best setting for my 3d printer set-up and may get away with 215 degrees C as shown in the above graph. The temperature decrease as shown a slight increase in pressure a and a slight variance in pressure across the graph. The length of the retraction b shown in the graph look less consistent.

Graph Seven

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 210, Extruder Retraction Speed (mm/s) = 20.0, Retraction Distance (mm) = 2.5, Restart Extra Distance (mm) = 0.

With a lower temperature of 210 degrees C there is an obvious pressure wave showing in the graph a. Despite this wave, each retraction b is still hitting around 0kg and looking a lot less consistent in length. The lower temperature setting is now plotting a graph that is now a lot less uniform.

Graph Eight

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 205, Extruder Retraction Speed (mm/s) = 13.3, Retraction Distance (mm) = 2.0, Restart Extra Distance (mm) = 0.

With the temperature lowered again the load cell is detecting higher pressure a and also the pressure wave that was shown in the last graph. The Retraction Distance setting is reduced to 2mm and the graph now shows a pressure wave on retractions b similar to the upper pressure wave a. The wider peaks between retractions are now showing indications of sharp rise or sharp falls in pressure.

The walls are looking a bit less evenly printed on the test parts now, but no real signs of major print disaster.

Graph Nine

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 195, Extruder Retraction Speed (mm/s) = 13.3, Retraction Distance (mm) = 2.0, Restart Extra Distance (mm) = 0.

At a temperature of 195 degrees C the pressure is now detected by the load cell at well over 2kg. The above graph shows similar characteristics as graph Eight.

Graph Ten

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 195, Extruder Retraction Speed (mm/s) = 25.0, Retraction Distance (mm) = 4.0, Restart Extra Distance (mm) = 0.

The Retraction Distance is adjusted keeping the same temperature as the previous graph. The retractions b are now hitting around the 0kg mark and no longer matching the pressure wave of the higher peaks a between retractions. The retraction length shown in the graph are now not consistent across the graph.

Graph Eleven

Flow/Feed Rate (mm/s) = 24, Temperature (C) = 185, Extruder Retraction Speed (mm/s) = 25.0, Retraction Distance (mm) = 4.0, Restart Extra Distance (mm) = 0.

This is where everything goes a bit pear shaped. The temperature is lowered to 185 degrees C and the pressure peaks at above 3kg as detected by the load cell. The graph is looking a bit distorted because the extruder drive gear has reached it’s filament pushing power limits due to the higher pressure. The test parts failed to print properly under these conditions which was mostly due to filament slippage.

Set Of Three 608-ZZ Ball Bearing Axles. Graph 11 test subject

The graph shows indications of filament slippage c and stepper motor stalls d, e. Stepper motor stalls produce a knocking sound and so is easily detected without the aid of the force sensor. Filament slippage is a lot more difficult to detect but can be seen easily on the graph at point c. The filament slippage seems to continue until a lower pressure is reached where the stepper drive gear can move the filament and get a fresh grip; forcing the pressure to go up again.

Sometimes stepper motor stalls look like retractions like at point e on the graph. At point e a retraction happened just inside a stepper motor stall and we know this because the pressure dropped to 0kg and the retraction return did not fully recover. From the settings above we know that the retraction start and return points should be at around the same pressure level.

Graph Twelve

Flow/Feed Rate (mm/s) = 48, Temperature (C) = 220, Extruder Retraction Speed (mm/s) = 25.0, Retraction Distance (mm) = 4.0, Restart Extra Distance (mm) = 0.

Graph twelve sees a return temperature of 220 degrees C and the Flow Rate and Feed Rate of 48mm/s. But this time we a printing a larger part to encourage a faster print speed.

While comparing to graph Five we have achieved a higher pressure level a and still maintaining consistent retractions that drop below 0kg b. The print still looks as good and you don’t get the pressure wave as shown in graph eight with similar pressure levels.

Conclusion

The Graphs. Since adding the filament force sensor to the bowden extruder the 3d printer is now outputting it’s best print runs. The graphs have played an important role to identify the best extruder set-up, for the first time I have real feedback to work with.

The graphs above are typical of the test part I chose to print and it is important to note that printing more complex objects could produce graphs that look very different. The pressure level will not always be the same across the graph for some 3d prints and this can be due to the firmware printing at varying speeds. Infill is usually printed faster than the perimeters so higher nozzle pressure will be detected during infill printing.

A good graph such as graphs 1 to 5 show a good measure of control over the extruder operation. Settings in the g-code are detected accurately and there is good consistency showing across the graph. Achieving this type of graph from the bowden set-up delivers the best print results.

Graphs 7 to 11 shows how things start to get messed when hot end nozzle temperature is gradually reduced. Pressure waves form across the graphs and retraction lengths become less consistent. In a more serious case of low temperature the extruder load cell (used as a filament force sensor) was able to detect filament slippage and also stepper motor stalls.

V9 Hot End Clone Heater And Nozzle Used In This Force Sensor Test

The Pressure Waves. In graphs 7 to 11 you can see a kind of pressure wave where the pressure seems to go up and down like a sine wave. This has caused elements of the graph to lose consistency such as filament retractions and nozzle pressure.

We know that the pressure wave appears when the temperature is reduced because graphs 1 to 5 and 12 show no wave at all; despite the same test part being printed throughout. We also know that 3d printing at a higher speed does not produce the same wave effect because graph 12 pressure reading compares with graph 8 that has the wave.

On this 3d printer hot end the nozzle sticks out from the heater block by about 8mm which I think is plenty enough to cause a large temperature difference between the heater block and the nozzle tip. My guess is that when extra force is needed to extrude filament at lower temperatures the hot end pressure rises causing the nozzle tip to get hotter until it extrudes filament more quickly. As the filament extrudes more quickly the pressure starts to drop causing the nozzle temperature to drop. As the temperature drops in the nozzle the filament becomes more difficult to extrude causing the pressure in the hot end to rise again. I think this is a temperature rise and fall cycle the force sensor is detecting and producing the pressure wave in the graphs.

The Future. I think at the very least this filament force sensor technology could be used for benchmarking new hot ends. We probably should be seeing test results from the many new hot ends that are now appearing on the market to help our purchasing decisions. If the filament force sensor becomes popular it could certainly be used to help troubleshoot extruder problems with new hot ends fitted. The data collected from the filament force sensor could be used to better prepare new hot end for the market. Having new hot ends backed up with good filament force sensor data would help build customer confidence.

The extruder filament force sensor technology could redefine the reputation of bowden type extruder set-ups and the bowden set-up may even become more popular on 3d printers. The filament force sensor would provide an easy set-up and configuration procedure based on sensor feedback.

In the future the filament force sensor could be used to allow 3d printer firmware to calibrate itself to determining the best speed, the best temperature and the best retraction length settings. The firmware could also dynamically adjust the retraction distance when printing speed is adjusted on the front panel. This kind of 3d printer set-up could be the ideal thing for consumer level 3d printers.

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The next post will be the guide to setting up the Airtripper Extruder Filament Force Sensor brackets and how to adjust the brackets to fit different load cells.

My 3d printer is tied up doing production runs so not yet had the opportunity to study cause and effect with different Skeinforge settings. Basically I’ve been studying live graphs from the production runs; checking for consistency between print jobs and during print runs. The graph below is a 100 second snapshot of a production run I was doing.

3D Printer Extruder Force Sensor Graph Sample

3D Printer Extruder Filament Force Sensor graph

From the graph it is easy to tell when the printer is printing and when it is not. The drops are the retractions and you can see that the nozzle loses pressure after each retraction. The retractions also show a period of travel without printing, and the longer the travel – the more pressure is lost. Also, a bunch of retractions together shows a decline in nozzle pressure with each retraction.

The pressure sensor is preloaded with 200g of force so that the retractions can be absorbed by the sensor without bottoming out. This has not been accounted for in the graph and so 200g needs to be taken off the force sensor graph readings in this case.

By looking at the graph I would deduct that my retraction setting is not long enough. Even after deducing the 200g pre-load, there is  still a round 500g of force applied by the extruder.

Extruder Force Sensor – The Next Step

There is plenty of room for improvement on my 3d prints and I’ll be looking at the graphs to see if the readings can help identify what settings needs to be changed to get the best print quality. Also I’ll be testing the force sensor on printing simple shapes to better judge sensor reading consistency.

How do I get one of these sensor thingies?

I don’t want to reveal the set-up until I’ve got all the support documentation ready to publish. This is because I need the time to focus on the documentation that will allow others to replicate the sensor kit as easily as possible. If I reveal my set-up now, many people will try to build there own sensor kit and I could be bogged down with providing support.

Due to the low investment cost of the hardware and the potential it has for testing 3d printer extruders and hot ends, the force sensor gauge is likely to be very popular. So I’ll be looking to get the airtripper extruder filament force sensor properly backed up with good support documentation.

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If you would like to speculate how the force sensor works and how it is fitted, use the comment section below.

Airtripper’s Direct Drive Bowden Extruder V3

The Airtripper’s Direct Drive Bowden Extruder is now at version 3 with the design files ready to download from Thingiverse. A lot of work went into the design to improve the usabillity and the look of the extruder. The design is stronger with a much cleaner 3d printed finish, and filament changing is now much easier than before.

The bowden extruder was originally designed to fit the Sumpod 3d printer to replace the bulky MDF extruder housing that was awkward to use. However, the bowden extruder can be used for other 3d printers making use of it’s simple bracket, and the extruder has been popular with the Rostock delta 3d printer. A tube bracket is now availble for attaching to the bowden extruder to help guide the filament from the filament spool. more about that here at Sumpod 3D Printer Filament Handling for Bowden Extruder.

You will find more about this bowden extruder on the following page: Bowden Extruder Upgrade Part 3.

The popularity of The Airtripper’s bowden extruder was boosted when the extruder was included in the development of the awesome Rostock 3D Printer (delta robot 3D printer). To see the bowden extruder in action on the Rostock, watch the youtube clip below.

Click here to view the video on YouTube.

Bowden extruder V3 Update Details

A number of updates were made to the bowden extruder design with some minor updates on the strut and idler housing.

To get a better fill between perimeters around the screw holes, the rounded ends on the strut have been increased to 10mm in diameter to improve print quality on wider 3d printer settings.  A small taper was added to the edge of the idler bearing housing to make it easier to slide the rubber tube over the preloader hook.

1. The filament drive gear housing has been filled-in to improve overall print quality by minimizing stringing.
2. Filament guide funnel size increased and angled for (a) a more gentle filament bend around the drive gear and for (b) easier filament threading.
3. Holes opened up and angled to give the idler preload screws better clearance from the idler housing hooks.
4. M4 nut for bowden cable (PTFE tube) now drops in to position much easier than before, also, reduced filament snagging when threading into the bowden cable.
5. Screw column housing lowered and widened at the top to minimize shrinkage and deformation. The M3 screw now drop in without drilling out, although a 25mm screw is now required instead of a 30mm. However, a 30mm screw will fit with a washer so the screw cap does not drop into the recess.
6. Holes removed from the fixing bracket to improve overall 3d print quality.
7. The filament in-feed bracket is re-designed for a much cleaner look and is now attached to a screw column for added strength.
8. A spacer is added so that extra washers are no longer needed.

Bowden Extruder V3 Parts List & Files

Most of the items below can be acquired cheaply from Ebay. The MR105ZZ Ball Bearing is optional but recommended, and the Rubber Diesel Hose can be replaced for coil springs. The M6 nuts, bolts & washers are for attaching the extruder to the Sumpod 3d printer or any other printer with similar fixing arrangement, just decide what length of bolts you need.

Extruder 3D Design Files

All the files for this extruder project are on Thingiverse for download. I’ve Supplied STL files that combine selected 3d objects for printing in one session. This is good for the smaller 3d objects because the printed layers will be given more time to cool. You can download the files from here:

http://www.thingiverse.com/thing:35404

Special Parts

• Nema 17 Stepper Motor. Since this extruder is a direct drive type, a powerful stepper motor will be needed. Point your browser to http://reprap.org/wiki/Stepper_motor for a good source of stepper motor information.
  
• Filament Drive Gear. For direct drive extruders, I can only recommend the MK7 drive gear at this point. If this does not work, you probably have Hot End issues. Starting with a tried and tested drive gear will help with your extruder system trouble shooting.
  

Screws, Nuts & Washers

• 1 X   M3 x 25mm S/S Cap Screw Allen Bolt.
• 2 X   M3 x 30mm S/S Cap Screw Allen Bolt.
• 2 X   M3 x 45mm S/S Cap Screw Allen Bolt.
• 1 X   M3 x 6mm S/S Button Head Allen Bolts.
• 3 X   M3 Stainless Hex Full Nuts.
• 1 X   M4 Stainless Hex Full Nuts.
• 2 X   M3 washers.
• 2 X   M6 S/S Hex Head Bolts.
• 2 X   M6 S/S Flat Form B Washers.
• 2 X   M6 S/S Hex Full Nuts.

Ball Bearings

• 1 X   608 ZZ [8 x 22 x 7] Roller Skate Ball Bearings.
• 1 X   MR105 ZZ Model Miniature Ball Bearing 5 x 10 x 4mm.

Tube

• 1 X   PTFE Tube 4mm x 2mm.
• 1 X   1/4″ 6mm id Rubber Diesel Hose Tubing Line.

Printing the Bowden Extruder

Direct Drive Extruder 3D Printed Parts

As a guide for printer set-up, I’ll list some of the settings used to compile the G-code. The toolchain I normally use includes OpenSCAD, Skeinforge, Printrun/Pronterface and Marlin. The settings listed below will be those used in Skeinforge, just the notable settings are included that works for this 3d print. Printing thicker layers and adding extra shells could create gaps in some surface layers, especially around screw holes that are close to a surface edge.

• Carve: Layer Height = 0.25
• Dimension: Filament Diameter = 1.75
• Fill: Extra Shells on Alternating Solid Layers = 2, Extra Shells on Base Layers = 1, Extra Shells on Sparse layer = 1, Infill Solidity (ratio) = 0.25

The STL files should be all you need to print off the extruder successfully, and I’ve provided extra STL files that will allow you to print a pair of selected items or all the items in one go.

3d model images have been uploaded to Thingiverse to help identify which STL files have multiple objects in them. The STL files rendered to images by Thingiverse don’t clearly show the files with multiple 3d objects.

Assembling the Bowden Extruder

The original assembly instructions are still valid for this bowden extruder update and you can find it here: Extruder Upgrade Part 3.

To add to the original instructions

The bowden extruder V3 bill of materials is slightly different from the last version because of a couple of small changes made to the extruder main body. However, all the parts used to assemble previous versions of the extruder will still fit the new version without buying new parts.

As mentioned above (bowden extruder update details), an M3 x 25mm screw is now required for one of the screw posts for attaching the extruder to the stepper motor. However, an M3 x 30mm screw can still be used if a washer is added to the screw before inserting in to the screw column. This will shorten the screw enough to fit the stepper motor body.

Direct Drive Extruder Stepper Motor with Gear, M5 washers and Ball Bearing. Notice the bearing with electrical insulation tape to increase diameter.

The bowden extruder features an axle bearing support for the optional MR105 ZZ ball bearing to spread the load on the stepper motor shaft. Because of variations in 3d printer outputs, it may be necessary to add a bit of extra diameter to the ball bearing. When assembling the bowden extruder, take note of the amount of contact between the ball bearing and the bearing support. If you don’t think there is enough contact, try a piece of electrical insulation tape to add some diameter to the ball bearing. Add as many tape layers as needed to get good contact.

Some types of filament drive gears, after lining them up with the filament on the stepper motor shaft, will leave a gap between the ball bearing and the drive gear. For proper stepper motor shaft support, the ball bearing should be positioned at the end of the shaft. This position can be maintained by adding M5 size washers to fill the gap between the bearing and the filament drive gear.

Related Topics

Sumpod 3D Printer Filament Handling for Extruder
Bowden Extruder Upgrade Part 3
Bowden Extruder Upgrade Part 2
Bowden Extruder Upgrade Part 1

Airtripper’s Direct Drive Extruder V3 Assembled View from Front	Airtripper’s Direct Drive Extruder V3 Assembled View from Back
Airtripper’s Direct Drive Extruder V3 Fitted without washer on M3 x 25mm screw	Airtripper’s Direct Drive Extruder V3 Fitted with washer on M3 x 30mm screw
Raptor Universal Filament Drive Gear from QU-BD, CNC machined from a brass alloy and shipped with the MBE Extruder.	Airtripper’s Direct Drive Bowden Extruder V3 Fitted to Sumpod 3D Printer

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Airtripper’s Bowden Extruder V3

The new 3D printer 1.75mm filament extruder upgrade is now complete, all the tweaks mentioned in the Extruder Upgrade Part Two are now built in to the unit, plus extra improvements was made to the overall design, including a newly designed idler to accept the cheaper 608 ZZ Skate Bearing to simplify assembly and to keep the overall cost down. All the project files are now on Thingiverse, STL files and the OpenSCAD 3D script file. Check out the rest of this post for bill of materials, printing and assembly tips.

This 3D printer extruder is design to fit the SUMPOD 3D printer without further modification which makes it an ideal upgrade for SUMPOD users. However, due to it’s simple fixing bracket and bowden feed, the extruder can be easily added to the other 3D printer designs.

3D Printer 1.75mm Filament Extruder

The extruder, because of it’s compact size, is an ideal solution for multi-coloured printing, and also ideal for multi-nozzle 3D printers.

Rubber Pinch Roller
I’ve been testing a rubber pinch roller idler for a while now, and after close inspection of the roller, I can’t see any damage or deformation in the rubber. In my opinion, the rubber pinch roller has performed very well and performed at least as good as a bare ball bearing. However, I’m not going to recommend it for this extruder because I can’t yet provide details that proves it offers better performance than a bare ball bearing idler. For the extra cost to implement it, some proof of superior performance over ball bearing is necessary before recommending it. You will find more details and pictures about the rubber pinch roller in Extruder Upgrade Part 2.

Sumpod 3D Printer Extruder Upgrade

SUMPOD 3D Prototyping Printer – View from Rear

I’m recommending this 3D printer extruder as a replacement for the original SUMPOD extruder for the benefits including the following:

• The filament is pushed over a ball bearing instead of a plunger, reducing friction.
• Filament is guided through the extruder mechanism without needing to disassembling the extruder.
• A lot quicker and easier to change filament.
• It’s open and accessible design makes it easier to trouble shoot, and to visually detect signs of filament slippage.
• Easy to mount on the SUMPOD using the original extruder mount points with M6 nuts and bolts.
• The new extruder is much lighter and a lot more compact making the SUMPOD more evenly weighted.
• Improves the overall look of the SUMPOD.
• Easy to attach a second extruder for dual nozzle set up and multi coloured printing.
• Option to add a shaft ball bearing that may extend the life of the stepper motor by reducing the load on the internal stepper motor bearings.

Printing The Parts

3D Printer Extruder Body, printed at 0.2mm layer height.

3D Printer Extruder Printed Parts – Idler Body, Strut and 8mm Ball Bearing Shaft.

Well, there are four items to print, the main body, a support strut, idler housing and an 8mm ball bearing shaft. There will be an STL file for each item so that they can be printed separately, this will produce cleaner parts, especially if you have a bit of trouble with oozing and stringing. For the ball bearing support to be properly aligned with the stepper motor shaft bearing, the 3d printer build platform needs to be as level as it can be for printing the main extruder body.
All the printed parts were printed slowly with a fast travel feed rate with the layer height set to 0.2mm, this helped to reduce the working pressure in the nozzle which made cleaner prints, stringing and oozing kept to a minimum. For these 3d prints I used Skeinforge and Pronterface, and for the 3d printer firmware, Marlin Ver. 1 RC2.

Bill of Materials
All the parts are available from Ebay apart from the brass gear insert, if you are a SUMPOD owner, then you will have the brass gear insert already. The small shaft support ball bearing (MR105 ZZ) is optional but may improve the life of the stepper motor if fitted, also the M3 6mm screw is also optional since three screws is enough to attach the stepper motor to the extruder base. SUMPOD users require two M6 30mm screws to attach the extruder to the 3D printer, longer screws provided with the printer could be cut down to fit.

1.75mm 3D Printer Extruder Parts

The extruder requires M3 Allen Bolt Cap screws, three of 30mm and two of 45mm, these come with a smooth shaft and a limited amount of threaded shaft. To reduce cost, and you have a Dremel and eye protection, you can purchase all M3 screws at 45mm length, then cut three of them down to 34mm length (not including the cap) and fit them with M3 washers so that the caps don’t sink into the cap recess on the extruder body. Please note that the M3 45mm screws have been sized to fit the idler that is preloaded with 6mm i.d. diesel hose. You could use springs instead of diesel hose, in which case, you’ll need to size the M3 screws to fit accordingly.

Part sources and price is provided as a guide only and I’m not affiliated with any supplier on this post. Shopping around should help to reduce overall cost.

Full BoM List

1. 1 X   MR105 ZZ Model Miniature Ball Bearing 5X10X4 – Ebay
2. 1 X   1/4″ 6mm id Rubber Diesel Hose Tubing Line – Ebay
3. 1 X   5mm Plain Insert – Maritime Models – 1.80 + p&p
4. 3 X   M3 x 30 S/S Allen Bolt Cap Screw – Ebay
5. 2 X   M3 x 45 S/S Allen Bolt Cap Screw – Ebay
6. 3 X   M3 Stainless Hex Full Nuts – Ebay
7. 3 X   M3 washers – Ebay
8. 1 X   PTFE Tube 2X4mm – Ebay
9. 1 X   M4 Stainless Hex Full Nuts – Ebay
10. 2 X   M6 30mm Stainless Hex Head Bolts – Ebay
11. 2 X   M6 S/S Flat Form B Washers – Ebay
12. 2 X   M6 S/S Hex Full Nuts – Ebay
13. 1 X   608 ZZ [8 x 22 x 7] Roller Skate Ball Bearings – Ebay
14. 1 X   M3 x 6 Stainless Button Head Allen Bolts – Ebay
15. Files for 3d printable parts – Thingiverse

3D Printer Extruder Assembly

Some basic tools are required to complete the 3d printer extruder including, a file, drill bits to clean out the screw holes, and allen keys to assemble the extruder. Pliers may be required to grip the drill bits when reaming screw holes, and also to hold nuts while tightening screws and threading PTFE tube. The drill bits are used by hand for reaming so no power drill is required. Pictures are provided below to help with extruder assembly.

When preparing the PTFE tube to accept the M4 nut, file a taper around the end of the tube to make it easier to screw the nut on. Twist the nut back and forth a few times to get a good thread on the tube, and with the nut in place, used a 2mm drill bit to restore the tube’s inner diameter if necessary. Fit the nut, with the tube connected, in to the slot on top of the extruder and screw the tube one turn in to the nut to lock in place after testing for hole alignment with a piece of filament.

To prepare the idler preloader, cut a piece of diesel hose tubing to about 22mm long, then make two holes about 12mm apart for the M3 screws to go through. You can make the holes by pushing a thin shafted plus head screw driver through the rubber, and then move a drill bit back and forth to open up the holes enough to push the M3 45mm screws through. You may have to use pliers to hold the drill bit. Refer to the pictures below for further assembly details.

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3D Printer Extruder Base and Stepper Motor Assembly	3D Printer Extruder Strut Assembly
3D Printer Extruder Idler Preloader Assembly	3D Printer Extruder 608ZZ Ball Bearing Idler
3D Printer Extruder Bowden Tube Cable with Nut	3D Printer Extruder and Stepper Motor Assembled

3D printer bowden extruder with brass insert and support ball bearing

3D printer bowden extruder with pinch roller idler

Improvement
The new 3D printer extruder works great, very pleased with the design, and now the extruder is a lot easier to work with. Changing the filament is not such a big deal anymore because now, it’s a lot easier to feed it through the mechanism and in to the bowden tube. All the extruder’s inner workings are now visible making the 3D printer extruder a lot easier to trouble shoot.

My old 3D printer bowden extruder

My new 3D printer bowden extruder

Not only is my 3D printer looking more sophisticated, it’s now 700g lighter on the back side. The most important improvement I was looking for was the extra filament pushing force. I achieved that by using a rubber pinch roller instead of a bare ball bearing, a bare ball bearing common with other extruder designs. Unlike bare ball bearings, the rubber pinch roller has a much wider contact along the filament length, forcing the filament to wrap slightly more a round the brass gear insert. This allowed the brass gear insert to have better contact with the filament which reduced slippage and improved reliability in constant extrusion rate at higher speeds. A small ball bearing has been added to the stepper motor shaft to further support the load and to help extend the stepper motor life.

Tweaking
During the the use of the new 3D printer extruder, I made a few notes to further improve the design and reliability. These improvements will be applied to the files and tested before being made available in Extruder Upgrade Part 3.

3D Printer Extruder without Idler

3D Printer Extruder Idler With Pinch Roller and Scews

• Change the in-feed filament guide hole to an in-feed guide pipe. This is to stop the filament from bending out of line and moving out of the idler’s grip. Only a problem if using a bare ball bearing but not so much of a problem if using the rubber pinch roller, since the pinch roller now has a deep grove filed in to keep the filament in line.
• Modify the out-feed bowden tube bracket so that the tube can be released without unscrewing the tube from the capture nut completely. This will help prevent spoiling the thread made on the tube by trying to screw the tube back in the capture nut, making it easier to remove and replace the bowden tube.
• Replace the M4 screws with M3 screws that hold the extruder idler in place. This will allow me to spread the screws wider apart to hold the idler more squarely. Also, the thinner screws will allow the idler to be removed without removing the screws completely.
• Widen the pinch roller bearing housing in the idler to prevent the rubber roller from scraping the walls. Build in ball bearing spacers in to the wall to keep the bearings centered in the idler housing.

The brass insert gear on the extruder stepper motor is not ideal for 3D printer extruders, but it’s cheap and easy to get hold of. I don’t have a better solution at the moment with out the high cost, so I’ll be leaving this for another day.

Design
I looked at a piece of 3mm glass that I use on my heated build platform and decided that’s a good thickness to start with in the extruder design. So, all the walls of the main body of the extruder and the stepper motor mount is 3mm thick except for the fixing plate, which is 4mm thick. To minimize the amount of plastic used and to cut printing time, I just built plastic in to the design where it was needed, I just used enough  plastic to add support and rigidity. I also put extra holes in to the design to help reduce warping during printing and to improve the overall look of the printer extruder.

OpenSCAD 3D printer bowden extruder assembly model

OpenSCAD 3D printer bowden extruder base model

The 3D printer extruder has three printable parts, the main body that attaches the stepper motor and the printer, an idler pivot support strut and the idler housing. All the parts are created with OpenSCAD 3D modeller and exported to STL to be converted to GCode by Skeinforge. The printer extruder currently under test was printed with 0.2mm layer height at 16mm/s and with hot end temperature set at 190 degree C.

Signing Off
I guess that will do for now until Part 3 of the Extruder Upgrade. Part 3 will include all the files including STL files, for those not familiar with OpenSCAD, so that you can print your own. A bill of materials will also be included which all items can be obtained from Ebay.

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3D Printer Extruder Idler Showing Rubber Pinch Roller	3D Printer Extruder Idler Parts, Ball Bearings and Rubber Roller
3D Printer Extruder Idler Parts, Rubber Pinch Roller	SUMPOD 3D Printer Extruder Idler Hack

I had planned to do a post about adding a dimmable lighting feature to the SUMPOD 3D Printer but had difficulties in extruding some of the 1.75mm filament I was using to print the lighting fixtures. I opted to buy the cheaper filament that was available around Europe which in most cases, can be less than half the price of the filament that can be sourced in the UK or America. As far as I can tell, the SUMPOD community appears to be getting better 3D printing performance out of using the more expensive filament. However, I’m not ready to give up on the cheaper filament just yet. I’m going to do some upgrading, starting with the extruder, and hopefully be able to continue using the cheaper filament with more reliability. I should point out that the SUMPOD extruder plunger modding I installed was a replacement for the plunger I lost that was delivered in the SUMPOD kit. The original plunger may have worked much better than my modded version.

Instead of just downloading a design from thingiverse.com, I decided to have a go at designing my own 3D printer extruder. For my first extruder upgrade, I’m just going to keep it as simple as possible and go for the Stepstruder style design. This design will offer improvements such as the use of a bearing instead of a plunger to reduce filament friction. Another welcome improvement will be for easier filament loading. So, without further ado, lets get started on the new 3D printer extruder.

To make it easier to design the 3D printable components of the extruder, I’m going to also include the non printable components of the extruder in to the design. This includes the stepper motor, bearings, screws and insert  which are created easily using primitive solids. Each of these non printable components will be created separately, and then added together to produce a partly completed 3D printer extruder. In part 2 of the Extruder Upgrade I will be going over the process of designing the printable component to complete the 3D printer extruder. Continue reading to learn more about the design process of the individual components and how the components are put together.

In OpenSCAD I usually start with a template to save typing and it takes the form as what you see in the image on the left. The first line starts with two forward slashes which tells the compiler not to execute this line. This is known as comment out, and usually used when adding descriptive text about lines or blocks of code. The forward slashes are commonly used to activate or deactivate modules in a OpenSCAD script. This allows you to compile only the parts of the 3D model you want to view and export. After the first line there is a block of code declared as a module. This module will only be compiled when the first line has the comment out forward slashes removed and the module name matches.
The above image represents the insert that will fit on to the stepper motor shaft to grip the filament. Only 3 lines of script is needed to be added to the template script shown earlier to create the insert. This 3D part is contained in a module called insert and it is called by using the first line in the above script. Three primitive solids are used to create the insert, the first two combined in the first union block and the third, while not required to be in a union block, is used to subtract from the first union block because both union blocks are contained in the difference block.
The above script is a bit more complicated because parametric equations are used to construct the 3D model – in this case a ball bearing. This allows me to reuse the same script to create different size ball bearing models just by passing three values when calling the bearing module. The three values required are the ball bearing measurements which include inner diameter (id), outer diameter (od) and width (w).
The Nema 17 stepper motor OpenSCAD model is shown above with the script which contains some parametric equations. The purpose of the equations are just to align primitives in relation to other primitives along the z axis. The screws in the 3D model are there as a guide while the printable part of the extruder is being designed. The OpenSCAD script will be altered once the length of the screw has been determined.The final OpenSCAD script, shown above, assembles all the different components to make a partially completed 3D printer extruder. The 3D printable components can now be designed around this assembly and having an instant view of the complete assembly at the same time. This script is a module that calls other modules for each component required for the 3D printer extruder assembly, it also positions and rotates the different components so they fit together correctly. I’ve made the OpenSCAD file available to download so that you can mess with the script yourself.

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Download Zipped OpenSCAD file: stepper_kit OpenSCAD file.