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.

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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Sumpod 3D Printer With Reel Roller Rack

The more improvements and new features added to the Sumpod 3d printer the more I want to use the 3d printer, and adding better filament handling has gone a long way to improve the 3d printer’s ease of use.

The Sumpod’s sturdy construction has allowed me to set up a filament spool rack on the top of the printer, and adding filament feed brackets to guide the filament round to the extruder keeps friction to a minimum during the printer’s operation. This set-up will go a long way to reduce the printer’s set-up and shutdown time because the filament spool can now be left at the printer.

I’ve made the design files available for download from thingiverse should anybody want to use them. The design files might not suit all Sumpod 3d printer configurations, but the designs should provide inspirations to those looking to improve their own filament material handling.

Sumpod 3D Printer outside – are you mad!

Well, to get the best clear pictures, I make the effort to get the Sumpod outside. I have to make sure it’s a dry day though because getting the MDF case damp might upset the printer’s build platform levelling :). I’ve got more features and improvements lined up for this printer so it looks like I’ll be taking it outside a few more times yet.

And the Problems Before - Basically, I had to put the filament spool where I could get it, and that was mostly on the floor in front of the printer. The spool got kicked over a few times due to lack of space and people walking past, and when done printing, I had to remove the filament from the printer and put away the spool until needed next time. I also had to turn the printer side ways facing so that the extruder was a bit more in line with the filament spool. Which made it difficult to check the LCD screen on the front of the printer.

The solution to these problems will allow me to keep the filament set-up on the printer and have a permanent place for the Airtripper’s pocket reel rollers. Having a spool rack on the Sumpod will allow the printer to stay loaded with filament reducing set up and shutdown times.

Sumpod 3D Printer Spool Rack & Guides

Reel roller Rack and support close up

Reel roller Rack anchor screw to keep the Rack from tipping and moving.

Spool Rack - The spool rack legs stand on the ridge just inside the top edge of the Sumpod’s outer casing, and anchored down with small screws. There is an option to have four screws to anchor but I’ve just used one in each leg here. Once the anchor screws are in place there is no need to remove them to take down the spool rack, just slacken off the screws a bit and move each leg inward to remove or to place.

The spool rack shelf is just a scrap piece of 8.6mm ply measuring around 255mm by 100mm, basically the size to fit snugly inside the recess in the top of the Sumpod (after the legs are fitted), and the size to fit the Airtripper’s Pocket Reel Rollers. Having the spool rack stand inside the recess prevent sideways swagger, improving stability. M4 Wing nuts are used to attach the 100mm tall legs to the ply shelf which allows for easy and quick packing for transportation. Due to vibrations from the Sumpod during operation, it was necessary to fix the reel rollers to the shelf to avoid spools or reels toppling over the edge.

3D Printer Extruder Filament Guide

Filament Guide - Now that the 3d printer has a spool rack, I needed to set up a filament guide for the extruder driver on the back of the printer. The plan was to use existing fixtures to avoid drilling new holes or making new screw holes in back of the case, spoiling the paintwork.

I suppose any tube that has very low friction properties will do for the filament guide, I used PTFE tube since I have plenty to spare. Tube brackets are in place to hold the PTFE tube in position to guide the filament round to the extruder from the spool. Without a guide, the filament is at risk of folding or breaking when pulled round sharp bends.

I designed two tube brackets, one to fit on to the Airtripper’s Bowden Extruder and one to fit a case fixing bolt on the top corner of the Sumpod 3d printer. The 4mm o.d. tube is in two pieces where one piece fits between the brackets while the other is used to guide the filament in to the first bracket I call the in-feed. The out-feed bracket is the one attached to the extruder driver.

Conclusion

The spool rack is working very well and it is wide enough to hold more than one filament spool. However, narrow spools are at risk of toppling if the printer is used in an area where it could get disturbed, like people bumping in to the table that the printer is on. For a more secure set up, a spool rack could be made using screw rods that attach to the spool’s hub, similar to whats already out there but made to sit on top of the Sumpod 3d printer.

I can’t guarantee that the spool rack is fit for purpose and regular checks may be necessary. If I had to print these again I would make the rack legs a bit thicker and more robust, and I would also add another 20mm to the height to give the Hot End bowden cable more headroom.

The Files

Get the files from here: thingiverse

Out-Feed Bracket attached to extruder	In-Feed Bracket with Tube Guide for Filament Spool
Filament Reel Rollers on Rack with Spool	Filament reel rollers attached to Rack with one screw in each
Side View of Filament Reel Roller Rack	Sumpod 3D Printer with Filament Spool

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3D Printer Extruder Hot End Close Up

So, this is an introduction to my latest 3d printer extruder system with a detailed view of the Hot End, Cold End and Nozzle. There are plenty of pictures and a detailed illustration that shows details about the 3d printer extruder system I’m currently using. I explain some of the pros and cons, and explain why the latest extruder system I’m using works.

I’m still using a Twin Drive Extruder System I developed to push the 1.75mm Polylactic acid (PLA) filament into, what used to be, a very stubborn nozzle. However, forcing the filament into the nozzle was not the answer and some investigation work needed to be done to make the system work better. A new Hot End is purchased and after much tweaking, the extruder set-up is now working as well as it can be and I should be able to revert back to the single filament drive extruder upgrade, freeing up a stepper motor. I’ve got a new extruder stepper motor drive gear coming from the US which should provide improved grip on the filament giving more pushing power with a single stepper motor.

Airtripper’s 3D Printer Twin Drive Extruder

What was

The Hot End has caused the most frustrations and headaches during the 3d printer ownership, and at first, I was not sure if the Hot End was at fault or the fault was with some dodgy PLA filament. It seemed that some types of PLA filament extruded better than others, but I still had performance issues with them all. Rather than build a collection of PLA filament that failed to extrude, I decided to develop a set-up that was less fussy about extruding different PLA filament types.

After a number of different extruder mash-ups with some endless tweaking and putting new bits together, I finally have a 3d printer extruder system that works. Through tweaking, the Hot End part of the extruder has increased in sophistication due to having better nozzle heat control and active cold end cooling. This has allowed for better filament management during it’s journey through the 3D printer extruder system that is fitted to the Sumpod 3D Printer.

About The Hot End

A slightly altered version of Mendel-Parts V9

Where it’s from

My latest Hot End is a derivative of the Mendel Parts V9. The parts kit I got, shipped from Make Mendel in India, was supposed to be a Mendel Parts V9 copy, but there was an error in the main Peek housing that allowed the tubes to connect together without a thermal barrier between them, this meant the kit could not be used without a fix or part swap. Instead of returning the Hot End kit, I decided to use the parts to build my own derivative version.

How it works

The basic operation of the extruder system is to feed the filament, using a stepper motor drive gear, into the Hot End melt chamber to extrude melted plastic out of the nozzle tip. In order to achieve good extrusion performance for best 3d print quality, Some conditions in the 3d printer extruder system need to be controlled.

The Hot End has two chambers ( M6 threaded tubes), one melt chamber and one cold end chamber. The chambers are separated by a thermal barrier so that each chamber can be controlled to maintain separate temperature targets. The melt chamber is heated to the point where it melts the filament to a level that can be extruded with minimum pressure without the plastic burning. The cold end chamber, to avoid jamming, prevents the softening and swelling of the filament. A fan and heat sink is attached to the cold end chamber to keep the heat off the filament until the filament reaches the melt chamber. If the filament softens in the cold end chamber the filament will swell and become jammed under pressure from the extruder stepper motor drive gear.

Due to PLA’s relatively low glass transition temperature, the heat sink cooling fan needs to be switched on during 3d printing. Without the fan, the cold end becomes very hot which could lead to filament jamming. The Hot End is capable of extruding 1.75mm PLA at temperatures up to 230 degrees C without changing the glass transition of the plastic in the cold end.

3D Printer Nozzle Tube Parts with PTFE Tube Seperator

Hot End Pros and Cons

Pros

• 1.75mm PLA filament can be extruded at temperatures as high as 230 degrees C.
• The Hot End reaches the target temperature easily because heat transfer to the cold end is kept low by the PTFE thermal barrier.
• Filament swelling, causing extruder jamming, is prevented by using cold end heat sink and fan.
• M6 threaded cold end chamber allows for easy attachment to heat sink.

Cons

• The Hot End is difficult to assemble and has a lot of parts.
• The PTFE thermal barrier is difficult to get right because it deforms very easily, under pressure, when the M6 threaded tubes are screwed against it.
• The PTFE thermal barrier needs to be drilled on each assembly to align with the M6 threaded tubes. This causes extra wear on the inside of the tubes.
• The cooling fan adds extra noise to the 3d printer.

Conclusion

If I’d have got this Hot End from Mendel Parts instead of Make Mendel, I’m sure I would have had a few less problems. However, Make Mendel was the only company that had the parts and could deliver quickly.

1.75mm PLA is probably the most challenging Filament to extrude due to it’s relatively low glass transition temperature and of course being really thin as well. The Mendel Parts V9 Hot End derivative I created works well with this filament, and I’m sure Mendel Parts V9 original does work just as well if set up correctly. Anyway, working with a faulty Hot End has been very educational and has made me a bit wiser for my next purchase.

As it happens, I have a new Hot End on backorder, a Makerbot MK7/8 and Makergear Plastruder derivetive, so looking forword to getting that in the near future.

3D Printer Bowden Cable Extruder System	3D Printer Extruder Cold End with Fan Cooler
Sumpod 3D Printer Y Axis Top View	3D Printer Extruder Hot End Close Up
Old 3D Printer Extruder Nozzle with PTFE Tube Inner Lining.	Old 3D Printer Extruder Nozzle with Fan on SS Block Insulator

[bodyadsrich1l] More Hot End posts to follow as experiments continue, also a new belt driven gear stepper motor extruder is coming up.

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.