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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3D Printer Extruder Filament Drive Gear Review & Benchmark

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