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Compact Bowden Extruder, direct drive 1.75mm

by schlotzz Mar 19, 2014
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Anyone could set the perfect retraction settings for this extruder?

Hi JoaquinPicci. The “perfect” retraction settings are not only related to the extruder, but e.g. to the length of the bowden tube, your nozzle, the material used etc.

Did you modify the firmware to get this working?

Hi sniper23. I’m using Marlin with an LCD, so setting the E-steps/mm did work without changing the firmware. If you are using the same hobbed gear as the original extruder, no changes should be needed.

Thank you, it is simple and works well (I am using PLA for now). :)

Thanks for your feedback.

Hola muy wenas, queria preguntar si alguien lo a usado para poner filamentos de 2.85 i de 3.00mm.
I gracias voi a probar de ponerlo i adaptarlo si funciona to comentare.

Hi xoye. Please have a look at older comments about this topic. tl;dr: the OpenScad-file could be changed easily to 3mm due to the almost fully paramtric design, but your stepper motor will probably have too less torque to handle the thicker filament.

hi! great work! how can i make this work for a 3mm filament? thanks

Hi carlosmci. Please have a look at older comments about this topic. tl;dr: the OpenScad-file could be changed easily to 3mm due to the almost fully paramtric design, but your stepper motor will probably have too less torque to handle the thicker filament.

This is the best extruder I ever assembled.
Thanks man for the collaboration!

hi will a standard mk8 non hobbed gear work?

If you use the 608 bearing with a non hobbed gear can work, but you have a high risk that the filament displaced and get out during the print, the correct couple needs to be: Hobbed gear - plain bearing or plain gear - hobbed bearing.

Hi Lamacon5. Basically yes, if it has enough grip on your filament... Please keep in mind that you have to adjust the gear dimensions in the OpenScad file to suit your one.

what does it mean by the hobbed offset?
What is the drive gear tooth death

Сломалась такая же деталь на принтере FLSUN Cube. Отпечатал, всё совпало!

Hi uncle_grin. Would you mind posting your message in English, so others can read and answer it? I used google translate and it said: "The same detail broke on the FLSUN Cube printer. Printed, everything matched!". I'm not sure, if your original part broke and you printed a spare part, or if the printed part broke.

Anyone tried to make it work with ninjaflex tpu?

What are the values of the esteps/mm that you use after using this design?

I had to use 147steps/mm, is it to much?

Hi danabr87. There isn‘t any specific value for E-steps/mm. It depends on your driver‘s microsteps, stepper motor and drive gear’s effective diameter. The easiest way might be by calculating a raw value and adjusting iteratively by extruding and measuring e.g.10cm.

Yep, i made that and i had to use 147 Steps/mm...i just wanted to know if it is a reasonable value, or is too high!!Before i used the ANET A8 original extruder and i use 100steps/mm

Thanks for a great design, however i don't know if it is just me as i cant see anyone else with this problem in the comments, but when i install the bearing it is very tight and does not spin. I know i can file this back i little but i was just wondering if it was something that i was doing wrong. Keep up the good work..

Hi fizzyfish. I'm not sure about what exactly does block your bearing. You may post a photo of your assembled extruder setup, so I can have a look at. One possible reason could be a wrong size of your drive gear. Did you adjust the dimensions of the extruder via OpenSCAD according to your drive gear before printing?

Thanks for sharing, I printed the extruder and it works great. However I'm having a little problem, I'm just not able to find an easy way to of loading the filament. Currently I use a flat head screwdriver which i put between the two parts of the extruder, in order to keep it open so I can push the filament in. On the other hand, if I reduce the tension from the spring to make it easier to open by hand, then the gear starts slipping on the filament and it fails to push it as a result. Am I doing something wrong? I did quite a few prints using it and after calibrating the e-steps I'm getting pretty great results, however loading the filament is just a nightmare. Any help is greatly appreciated.

Hi magkopian, thanks a lot for your comment. There are some different solutions for this problem. On the one side some people redesigned the idler and attached a small lever to help them releasing the pressure from the spring. On the otherside I prefer replacing the spring with a knurled nut or wing nut, so I can fine tune the pressure as well.

Thank you for the suggestions, I found this remix and printed the example part for the idler that includes a lever. I tried it and it works great, I can now push the filament very easily even when the spring is very tight. So I guess problem solved.

Customizable Bowden Extruder | Mount for ANET A8 & Others
by TNS

Can you give any source for the spring? Amazon or eBay possibly.


I am printing this model right now. I want to use a Pre-Extruder for my Wanhao Duplicator i3 in order to give less stress to main Extruder motor ? If i want to sync this Stepper motor with Main Extruder motor ? what steps to be taken ?

Need some advice.

Hi asking. Thanks for your comment.
Doing a pre-extruder setup seems to be a fiddly task. Both stepper motors will run the same rotational speed if connected in parallel, but I wonder if the drive gears effective diameter will always be equal on both extruders. Minor differences in the filament diameter or idler pressure could change the effective diameter on the drive gear and therefore the extruding speed. Under some circumstances this could lead to a "breaking" pre-extruder, putting a bigger load on the regular extruder than without. But I'm interested in your results. Did it work as expected?

Well Actually i printed parts.... But still waiting for Stepper Motor Driver board to arrive. I don't want to wire parallel to one Driver. So fingers crossed will update once i finish it.

This might be a strange question, but do Bowden tube couplings connect to where a hotted would normally thread in on a extruder? This is so I can skip one of the prints here.

If I am just using the stock A8 drive gear, do I need to redesign anything? Also, which bearing holder do I use? I will be using the standard 608zz bearing. Thank you. I just get confused when there are multiple parts for the same thing. Also, which base do I need to print if I am using a bowden style push adapter?

I would advise you to pick up another drive gear the stock one on the A8 is terrible for grinding filament due to its spikey design I'm using a mk7 style gear i got for €2 in sclotzz's design and its a big improvement from when i modified the stock extruder to work as a bowden set up with my lite 6

That is good to know. I do have issues once in a while with the gear slipping. Any chance you would have a link to the gear that you bought? I just want to make sure I get the right ones. Thank you!

I ordered from the link provided by Tech2c (same as above i think) but the actual gear was only 9mm in diameter, making it an MK8. As such it doesn't work work with the Tech2c remix. The specs on the banggood.com page are for the MK7 so not sure what's going on. I got a refund and had to order from Amazon.

Sorry to keep bothering you man but with this new gear, what extruder mount did you use from this model? I am not familiar enough to modify one of these STL's in order to adapt for the different gear. Thank you!


Hi I used this remix by tech2c for the mk7 gear

Compact Bowden Extruder, 1.75mm Filament for MK7 Drive Gear
by Tech2C

Thank you so much. I will definitely make the order. I appreciate the help.

Hi brothainchrist06. I'm not sure which dimensions the original Anet A8 drive gear has, thus I can't make any comments on that.
There are two different types of bodies and two different types of idler arms, which can be combined to your needs. Both bodies use M5 push fit connectors, but one uses a connector on the inlet side, too. Each of the idler arms is suitable for a 608 bearing, but the version consisting of two parts is a little bit stronger...

could this be designed for 2 push connectors and the space in the middle filled in so that it can be used with flexible filament?

Hi warham. There's already a version for two push fit connectors, one on each side. Just have a look at the different extruder bodies. Furthermore there are a lot of remixes out there optimized for flexible filaments, e.g. http://www.thingiverse.com/thing:1728411, http://www.thingiverse.com/thing:1676931 or http://www.thingiverse.com/thing:1084109

Semi flexible TPE bowden extruder modification
by Wolraad
Extruder for flexible filament
by kona
Compact Bowden Extruder for Flex filament
by Billie

Anyone remixed for mk7 drive gear?

Compact Bowden Extruder, 1.75mm Filament for MK7 Drive Gear
by Tech2C

Really nice extruder! I'm planning to install it on all my printers! It's on my OrdBot now, printing out a couple more...

Thanks for your feedback. I'm looking forward to seeing some photos of your OrdBot with this extruder design ;-)

could this work with flashforge creator pro ?

I'm not sure, because I've never seen a flashforge creator pro in real world. As I can see on photos on the interwebz, it uses two direct drive extruder. So maybe, but heavy modifications will be necessary...

Can anyone help me with open scad? I need to increase the frame plate holes up to 8mm with a 13mm head hex screw and 8mm of depth.

Hi BerniApple. I'll try to help you with customizing the OpenScad file to your needs.
At first, the mounting plate should be wider and longer to give you enough room for 13mm screw heads (see line 44/45, base_width/base_length). I set it to base_width = 20 and base_length = 80. At second, the position of the holes must be adjusted to shift a little inwards. Have a look at lines 132/133 and change -6 / +6 to -10 / +10. At last adjust the size of holes itsself. In lines 164/165 change the radius from m3_wide_radius / m3_head_radius to the radi of you screw / screw head with a little extra margin. For example a M8 screw with a 13mm head should go with "8/2 + 0.3" instead of m3_wide_radius and "13/2 + 0.3" instead of m3_head_radius.
Hopefully you get along with this short guide. Please feel free to adjust the parameters to your needs and get back to me whenever there are any further questions according OpenScad.

Awesome thanks! What about the thickness of the plate for mounting extruder on frame? It should be 10mm

Comments deleted.

You should make a base that is capable of holding larger diameter gears.

i can make a different version of the bearing idler that can fit your needs

Hi EstSom. Thanks for your feedback. It's a pity, but currently I'm engaged with a lot of other projects. Therefore probably there won't be any changes in the near future.

Hm, I'm not sure if the diameter of your drive gear is too large. Do you have any dimensions for your gear?

The outer diameter is 11mm, inner is 5mm and the "height" of the piece is 11mm aswell, what do you think?

hi scholtz, i went through the comments so that i can get an idea to adapt the scad file for my mk7 12x12mm sized so these are the settings that i used
// drive gear
drive_gear_outer_radius = 12.00 / 2;
drive_gear_hobbed_radius = 11.00 / 2;
drive_gear_hobbed_offset = 3;
drive_gear_length = 11;
drive_gear_tooth_depth = 0.2;
but i am facing a problem that i have to fully tighten the idler to make it work and still the extruder skips a lot so if i could just tighten it 1mm more than that would have been more than enough. Can you please guide me what do i need to change to get the desired results

H ishaan,
thanks for your message requesting help with the setup. A MK7 drive gear with 12mm OD and 11mm D on the hobbed part seems a bit strange, but decreasing drive_gear_hobbed_radius to, for instance 9.00 / 2, and reprinting the idler could do the job.
Regards, schlotzz

Hi, schlotzz!

Would you be so kind to publish OpenSCAD file for the alternate idler? Top plate of the alternate idler seems too thin to me and I can't find M5x14 screws, have M5x16 only. So I have two reasons to make top plate thicker. :)

Hi Lazyyy. Please have a look at the scad-file. The alternate idler is defined there as a separate module. You can change between both idlers at the end of the file by setting proper comments...

Oh, sorry. Didn't notice it. Thanks a lot!

Looking for a m5 push fitting but I can only find m6, will this work?

There are a lot of M5 push fit connectors around here in the interwebz, e.g. on ebay. Just search for "m5 push fit connector". Maybe you want us to tell where you are from? So it's easier to look for some vendor in your country.

Isn't it just easier to adapt the object itself, rather than spending so much time finding the right screw?

There are some remixes using other push-fit connectors. Maybe there's one for M6.

Everything is printed but I may have printed the wrong base. The filament hole for the tube is small. I guess this one is for the tube only? If I want the push in bowden, I need to reprint the base?

Hi Ctx32. Please note, that there are two versions of the base. One version has a bowden outlet on one side and a simple filament inlet on the other. The other version has bowden inlet and outlet.

Yep, I printed the wrong one.
I'll print the other one and I found the bowden inlet.
Thanks for responding it helps allot.

I'm preparing to print this extruder, Any tips?

I'm using a nema 17 with the gear it came with, Sorry I don't know the gear type.
The printer is a Hictop that I'm converting to use the E3d V6.
Cross your fingers I get it right.

Hi Ctx32. I'm not sure which drive gear comes with your Hictop, but probably you want to measure it and change the dimensions in the scad-file accordingly. Therefore your base and idler will match the sizes...

What an absolute simple yet effective design, has been in daily use for the last 7 months!
Thanks @Schlotzz
The idler arm has eventually broken BUT I was not even using it with a spring, just a careful amount of tightness on the adjuster screw, was printed at 30% infil at 0.2mm layer.

Highly recommend printing this part in solid PLA which only add a few minutes and will probably last the lifetime of the printer :)
Will be fitted with a tension spring this time when I rebuild it, FYI, use a 4mm drill to clear out the filament exit (top) port then insert a small section of PTFE tube to run against the Bearing/Mk8 wheel which will be held in place by the tube connector, this allows for perfect use of Flexible Filament! without any chance of wrapping around the Mk8.

Hi Taritec. Thanks for your great feedback about using my extruder design on a daily base. Personally I'm still using my first printed version without any spring on my Kossel Mini. The idler hasn't failed, yet, but I changed it to v2 anyway. Using a short piece of PTFE tube for decreasing the gap between filament path and drive gear/idler bearing is a really nice idea.

What I write now
apsoluut is not meant negatively !!!
(I'm afraid that it gets misunderstood) therefore.....
It looks really good!!!

but wonder if this design perhaps what could be more universal?
the circle around the motor A bit wider,
Screw houses as a trench so your engine can go Slightly back and forth
so that he be able to slide back and forth (for example if you have a larger or smaller gear)

Also, the space between the gear and the holes is large.(where the filament passing through it)
maybe is it possible to have less room there?

not right now but I will also try to print this design.
maybe there are still come some adjustments? ;-)

myself I am still a beginner I have two printers self-made.
the software and my English are the biggest problem! step-by-step......... you know how it goes :-)

I wish you all the best!
Regards from the Netherlands.

Hi 3drob3d. Thanks for your very constructive feedback. You're absolutely right. There are still some details that could be improved, especially with the large amount of space between filament path and drive gear. I'm still very busy with a lot of other projects right now, but (hopefully) I'll do an update someday... ;-)

You've got some good points, I was actually thinking the same thing about the inner circle diameter when I was assembling it!
It's a really good design and has been extruding really well for me, with couple of improvements it could be even better!

Thanks for this! Excited to put it to use!

Thanks for your feedback. Looking forward to seeing some photos of your print...

Simple and nice design. This came with my Kossel XL assembly kit. Now I can finally do some spare parts.

Thanks for your feedback. Hopefully nothing broke with the first extruder of the assembly kit, yet.

would it be possible to get a list of the screws/hardware needed, thanks!

Hi Andy1122. You can find a list of all hardware needed at the "What you need" section.

I see it now, thank you!

Can I drill both sides for push fit connectors for double PTFE tubing on both ends?

You don't have to drill the sides, just cut the M5 thread with a screw tap. There are two versions of the base. One is called compact_direct_drive_extruder_base_bowden_inlet.stl which uses PTFE push fit connectors on both sides.

What % did you print at 20 and it Brakes like a China with HIPS

Hi ijhcs1. Usually I print at 25% honeycomb infill with PLA. I had no issues so far...

I really like this design, but I'm having an issue with it. It extrudes plastic perfectly until the plastic reaches the nozzle of the hot end. At this point, the extruder will just begin to grind at the filament. Sometimes I can push on the idler more and it moves about an inch, but then it refuses to go any further. Do you have any suggestions to fix this?

Hi molmsted98. Thanks for your feedback about my extruder design. If your filament gets stuck, even if you're pushing by hand, something else might be an issue.
Is this the first extruder in this setup. If not, did you experience any problems with other extruders? Which material and hotend do you have? Sometimes PLA gets stuck if the hotend is not cooled properly. Did you check the hotend temperature? Maybe it's too low due to a misconfigured firmware or faulty thermistor. Or maybe your hotend nozzle is clogged. Did any material exit the nozzle? If not, maybe your hotend is not assembled properly and the filament path is blocked by a misalignment.
Please feel free to get back to me for further consultation. Hopefully the problem can be solved.

I previously used a different extruder, which caused no issues. I tried pushing the filament through the hot end by hand, and it went through with no problems. Is it possible that my extruder motor doesn't have enough torque to overcome going through the hot end?

Hm... If the drive gear grinds at the filament, the motor seems to have enough torque. Otherwise the stepper would stall and loose steps. Did your last extruder have a MK8 drive gear, too? If you push on the idler, it moves some more and then stops. Does the motor stall in this case?
Could you post a picture or two of your extruder loaded with filament (e.g. as a make) for further inspection?

My previous extruder was a Greg's, so direct drive is all new to me. I think the motor stalls, if by that you mean begins to make a different sound. Here it is loaded with filament. https://imgur.com/a/no2az

The filament does not get bend. That's good. If the motor stops, makes louder humming noises or makes kind of click noises while the drive gear turns for some degrees backwards out of nothing: that's stalling. Maybe it does help to increase the idler pressure and the power of your stepper driver.

It stalls very infrequently. It's now even having a hard time retracting. I adjusted the idler to various pressures with no increase in performance. I also raised the voltage of the stepper, and that did not help either.

How much torque (Ncm) does your stepper motor have? Maybe its to weak?

The motor has a torque of 47 N/cm. Does adjusting the voltage do anything to the torque?

Yes, indeed. The higher the current, the more power will be transfered to the stepper motor, which will result in higher torque and more heat. So basically it's a trade off situation... Just have a look at these sites: http://reprap.org/wiki/StepperMotor#Purchasing_a_motor and http://reprap.org/wiki/Stepper_torque

Hello. I've been printing for a bit now using your simple design. However I cannot print above 40mm/s without skipping steps. Can you let me know what current (vref) and micro step you run. Also do you have a "high torque" stepper? Thank you.

Hi Telly. Thanks for your feedback. Currently I'm running at 1/16 microsteps with an 48Ncm stepper (Wantai 42BYGHW811). I've never measured my vref/current but adjusted it "by feeling". Some more factors could be a problem, too. Maybe you're using a smaller nozzle, your temperature is set too low or maybe you're overextruding. Hard to tell without further information.

Thank you for the rapid reply! I'm running an e3d .4 at 1/8 and 220 deg for PLA. What speed have you printed upto? I'm not to sure how to tell if it's over extruding but my prints look good to me. Haha. I'm using the same stepper as you!. Thanks Telly.

I haven't cranked up the printing speed too much, but after changing the filament extruding in air with over 200mm/min is not a problem.

hey, where do you put that on a prusa rework

This is the worst extruder on the thingiverse I've ever seen. Don't waste your time printing them and using. There are plenty of extruders much more suitable.

Hi slenderguy79. Sorry to hear that you're not happy with this design. Did you experience any problems with it?

The main problem is that I mostly use 8mm fitting for PFTE tube, which doesn't fit to this extruder. The second one is that it's pretty hard to tighten the idler perfectly - either the motor slips or it just doesn't push the filament.
The only benefit I saw so far - it requires much less plastic than other extruders to print :)

Sounds like you are the problem. Don't talk shit about the design if you don't know what the fuck you're doing.

Hm, I see your concerns. There are some remixes using 1/8 pipe thread, e.g. http://www.thingiverse.com/thing:835542 or http://www.thingiverse.com/thing:676687. The design is easy to customize, so please feel free to change it for your type of fitting if you don't have a common 5mm OD push fitting.
Did you use a second hexnut on the idler screw to adjust the pressure? I never had any issues with a stalling motor so far. Maybe your stepper driver current is adjusted too low?

Compact Bowden Extruder 4mm
compact bowden extruder using jhead normal push-fit

Is it possible to modify this for 3mm filament?

Hi marshalltjones. Please have a look at older comments about this topic. tl;dr: the OpenScad-file could be changed easily to 3mm due to the almost fully paramtric design, but your stepper motor will probably have too less torque to handle the thicker filament.


I need use 3mm filament do you have STL for it?

Hi dinizhobby. Please have a look at older comments about this topic. tl;dr: the OpenScad-file could be changed easily to 3mm due to the almost fully paramtric design, but your stepper motor will probably have too less torque to handle the thicker filament.

Is it possible to adapt this to use a 688zz bearing?

Hi Spark111. The extruder is designed for M5 threaded push-fit connectors and therefore cannot be used without further modifications with the bowden coupling you linked. Maybe this remix could fit your needs: http://www.thingiverse.com/thing:835542

Compact Bowden Extruder 4mm

New idler ist just perfect. Many of my earlier idlers broke. Thanks for editing that.

Thanks for your feedback.

Do you require a spring to make the pulley push as closely as possible to the drive shaft? Or is it fine? Thanks

Hi T1GGE. No, a spring is not important for this extruder. Just tighten the screw enough to give the drive gear a good grip into the filament, but don't overtighten it. I've used my extruder a long time without a spring and it went fine...

The SCAD file has some flaws if set for MK7 gear and 3mm:

  • 4th hole for Nema17 is now covered, make it useless hole.
  • The idler plate is more smaller = more weaker design. Bad design.
  • The hole above idler plate is broken (open side), MK8 has it closed.
  • The splitted idler v2 is broken. It has unwanted parts.

I must say, this is not correct automatic build in SCAD. You can move idler a bit up for MK7 / 3mm, but SCAD keep it in same place and that has some issues in idler design.

Please rebuild SCAD script to avoid weakness in idler design when using 3mm/MK7. Make sure everything is correct build.
It's nice you have option in script for 3mm filament, but it causes some build flaws.

Compact extruder is nice, less parts. But you have not tested properly script for build 3mm/MK7 and checked on strength idler / good and clean idler parts.

Hi mrdummy. Thanks for your feedback according MK7 with 3mm. Could you post your settings for the used MK7 drive gear? It would make things easier to reproduce the issues your facing with. I did some tests but haven't seen any error so far with my settings...

Btw, I wonder if a MK7 drive gear is able to push 3mm filament with a direct drive extruder anyway...

I tried this on my Kossel Mini. I have a MK7 gear, and it just did not have enough torque with a regular NEMA 17 to drive 3mm filament bowden style reliably. The slightest back-pressure and it was stripping out filament. I really like this simple design, and wish I could have made it work! Bravo on the good design and support of this thing.

I used to use a full bowden setup with 3mm filament and it is certainly possible. Now I use a suspended extruder.

Hi cycliste737. Thanks for your compliment about my design. It's a pity that 3mm filament does not work. Once I tried 3mm filament for a bowden setup on my Kossel, but it was too stiff. Therefore I did not investigate on this any further.

The settings are:
// drive gear
drive_gear_outer_radius = 12.50 / 2;
drive_gear_hobbed_radius = 11 / 2;
drive_gear_hobbed_offset = 3.2;
drive_gear_length = 13;
drive_gear_tooth_depth = 0.2;
// filament
filament_diameter = 3.00;

The bigger MK7 pushed the filament guide more to right, so the idler is more smaller.
The 4th hole is now covered, you cannot put something inside...
When enabled for v2:
translate([20, 0, 0])
there is strange effect on generated item.
And i see only 1 half part, but there is no another half. It looks incomplete.
See image: http://imgur.com/909epAA

I re-design your extruder again to solve the problems. I will post it later when ready.
You have right MK7 might heavy for 3mm pushing. But someone reported it you need 2A version with high torque. It can generate 3KG push weight, and it worked.

Thanks for posting your settings. Yes, one of the four holes is covered too much to be usable, but some people reported three holes to be enough to hold the stepper motor.

If you cannot see the second part of the idler v2, please try to disable idler v1 by using //
// translate([20, 0, 0])
// idler_608_v1();
One part of idler v2 has exact the same position as idler v1 and therefore is covered by its "ancestor".

The whole extruder hasn't been designed for these large combination of MK7 and 3mm filament due to being compact was a main goal.

I'm looking forward to seeing your remix suitable for MK7 and 3mm filament.

Hi! Can I find on ebay the pulley you have used? Because I have already printed the parts the same as you....Thanks...

Hi StelMex, I haven't tried it by my own, but a MK8 drive gear (11mm length 9mm dia) could work, too. Just search for "mk8 drive gear" on ebay...

Thanks very much! Finally I'll print this again by changing the pulley dimensions in openscad to be sure...

I do not see how so many people are having problems with the v1 idler? I printed one with ABS at 50% infill and (4) vertical walls… it’s a tank. Ditch the PLA, it is useless when it comes to using it in mechanical ways.

Me neither... I printed my whole extruder with PLA and haven't had any troubles so far...

Honestly, I believe the people that are experiencing idler breakage might be using lower quality PLA… which is very susceptible to less-ductile characteristics. I still recommend ABS (engineering grade) when used as a part of a mechanical system. This design has exposure to both heat and high pressures which PLA (commodity) was not designed for.

This is a great design and I do not believe the v2 idler was necessary. v2 idler just adds more parts …which allows more things to go wrong. Get over the fear of printing with ABS… It is a great material once the “Cons” are overcome. It took me 8+ weeks to figure it out.

I will be releasing my own revision of you design soon 

Addy rant end.

Hi is there a 3mm version of this extrudeur ? Thanks

Hi drepou. Please have a look at older comments about this topic. tl;dr: the OpenScad-file could be changed easily to 3mm due to the almost fully paramtric design, but your stepper motor will probably have too less torque to handle the thicker filament.

Ok Thanks i Will try to play with parametric value to adapt it for a nema23 .... 6kg of torque should be enought

Hi drepou. A NEMA23 as extruder sounds really interesting. Hopefully you'll publish some pictures of it. I'm looking forward to seeing it :D

printed 4 times in all....firs time the holes for everything were way to tight.. couldn't find a M5 bolt so i tries a M6 and it broke so i modified the the holes and it work for some time until i had to take to bearing off to clean it and it broke again i tried to make the holes a bit bigger then had an idea if you change the hole for the screw to 1.45mm a M3x12 or M3x8 fits perfect with a washer and now the part where it breaks is a lot thicker just thought i should let you know :)

Hi hambobolubia. Thanks for your feedback according the idler breaking too easy. I'm aware of this problem. It seems to get a common problem and I'm developing a solution but haven't finished, yet. As soons as there's a new version of the idler I will post it here.

Printed 3 of them with 100% infill but the idler keep breaking on me :)

Hi skelator. Sorry to hear that. Would you mind posting some photos? Maybe I could improve the idler, if I know where it broke...

Could you add a filament extraction handle?.. Just printed out this thing and that's the first thing that I kinda miss already.
Like a small tab on the lever part mear where the springed bolt comes in. Thanks!

Hi toxuin. Thanks for your feature request. I'll give it a try the next time I do an update on the design.

Here's a printable part that takes the place of the hex bolt to secure the 608zz bearing. http://www.thingiverse.com/thing:961968

Extruder nail
by jesse

Hi jesse. Thanks for sharing your design. It might come handy for other people not having the described M5 bolt.

Stupid question: for some reason I'm in the possession of 100+ 8 inner diameter x 16 outer diameter x 5mm width ball bearings, and a grand total of 0 608s, and I can't find a local store that sells them, would it be possible to tweak the design to work with a 16mm instead of 22mm bearing? Or would printing a "sleeve" to adapt the bearing work?

Well took me like 10mins in modo to modify the idler to have the bearing post 3mm closer to the mk8 gear and added some additional material around it for strength, seems to work well, assembles nicely at least, haven't tried it yet properly.

Hi KriLL3. Thanks for sharing your feedback about using a smaller OD bearing. Would you mind sharing your idler design?

I'll be happy to do so, I want to properly test it and refine the design somewhat, turns out my bearing is slightly narrower as well so I need to move the wider section of the bearing peg up a bit, it's not much so even if the bearing slips all the way down on my original version it's still in the filament path but eh took seconds to correct in the model once I noticed, need to come up with a similar solution for the top, perhaps a printed washer kind of affair?if I make the peg shorter you an even shorter m5 screw. give me a day or two, I need to design and print a way to mount it to my i3 before I can test it properly. There doesn't seem to be any i3 mounts for this design, a bit weird.

Is this mountable on a M5 T slot 2020 extrusion?

Hi Fractle. Usually it is meant for being mounted on smaller 1515 extrusions with M3 screws, but you may change a few parameters in the OpenScad file to adjust it for M5 screws. Please change the following parameters:

  1. lengthen the frame mount by some mm by changing base_length in the header of the file on line 44
    "base_length = 60;" should be changed to "base_length = 65;"

  2. adjust the frame mount holes by changing its diameter and removing the hole for its head in the module "frame_mount" on lines 164/165
    change "r = m3_wide_radius" to "r = 5 / 2"
    remove "cylinder(r = m3_head_radius, h = height + epsilon, $fn = 16);"

  3. compile and export your stl

Hopefully you get along with these short instructions. Please feel free to come back with more questions.
I'm looking forward to hearing from you.

Is there a version of this that lets you easily switch filament? There is this design http://www.thingiverse.com/thing:287287 which is actually made for QU-BD but I like the design of the idler.

Compact Bowden Extruder Derivative

Hi bilalasd. I'm not quite sure what you mean with "easily switch filament". For switching filament there exist two methods.
I usually let the extruder run backwards by the length of the bowden tube, enter the new filament and extrude by the length of the tube. All work is done by the stepper, you don't even need to release the idler screw. Easy as pie.
If you like to change the filament by hand, all you need to do is releasing the idler screw. The filament can be removed by pulling it out. Due to the funnel like design the new filament enters the bowden tube by itself. Just slide it in and tighten the idler screw afterwards.

Thanks for the reply.

It is true that you can retract the extruder to remove the filament. The problem is that if you retract using marlin through the lcd, the speed is really slow. There probably is a way to make it fast but I haven't looked into it. I usually connect my computer and use repetier but that involves connecting a computer.

What I wanted was a little lever on the side of the idler that let's you lift it up the bearing while compressing the spring and you can easily change the filament by hand. Just like the in the remix that I linked.
I will see if I can make something like that using my limited knowledge of openScad.

whats meant with bowden inlet? my pushfit doesn´t fit in "compact_direct_drive_extruder_base.stl" the hole is too loose. does it fit in the other?

Hi sobo84. There are two different versions of the extruder body. One is used for a push fit connector on the outlet side (towards the hot end), the other one is used for push fit connectors on both sides. The inlet side means the side the filament is fed into (towards the spool). Some people use bowden tubes on both sides...

and the spring should be between the screw and the printed part?

Yes. As you can see on the first photo, there is a nut sitting on the screw between its head and the idler (the printed part holding the bearing). Just remove the nut and add a suitable spring instead.

thanks for the answer.

Hello. I'm confused. Why are you using 5mm (hard to find) OD Push Fit Bowden Connectors since the most popular size is 4mm? Does the 4 mm ones that i've got fit in? Where did you get the 5 mm OD? Thanks in advance.

Hi juandavidbarrada. The 5mm OD size is for the M5 thread on the push fit connector. The bowden tube OD is 4mm as usual. I should update the BOM to turn that out more clearly. Thanks for your hint.

Can I print this out of PLA or must use ABS?

Hi StelMex. I have printed mine with PLA more than a year ago and it still works fine.

Hi , schlotzz :

I tried your design , it is perfect . But , after 40 meters , the bearing mount crashed by deflection : The bearing slope and stop to round with driver-gear .

I printed it with PLA .

Could you tell me how to fix ? Thanks .

Hi Shazoo,
thanks for your feedback. It's important for the M5 screw to go all through the idler to stiffen it. Maybe this could be a possible mistake. Did you fasten the idler too much? I think the idler needs some rework, but I'm still quite busy at the moment...


Thanks for your reply . I follow your suggestion , now the M5 screw have been fully go all through the idler .

But , the bad news is : after about 10 meters , the idler's M3 adjust screw make the idler to slope ....

I did not fasten the idler too much ...

so , should I use ABS to print it and test it again ?


I have not tested the idler in ABS, therefore I don't know if it would help. Maybe adjusting the overall height of the extruded in the OpenScad file could result in a more stiff extruder.

Thanks very much! :)

Hi, your driving system is simple and works excellent. I would like to ask for a modification to make it even better.

I found that if I add a tension spring on the M3 screw to have a constant pressure on the filament, the print quality will be even better.
However, the current M3 nuts holder and the M3 screw position on the bearing arm is quite thin. Although adding a spring can be done, but I can see the plastic near the M3 nuts is elongated and turning into white colour.

Would you please do us a favour and update the design for me?

Thanks for your kind help in advance.

Hi yungamos. Thanks for your feedback on my compact extruder and your proposal for modification.
I haven't had any problems with my extruder printed in PLA so far, so I'm not sure about where exactly the plastic gets elongated. Would you do me a favour and post some images of your stressed extruder/idler as make?
Hopefully I can find a solution...

Hi Schlotzz. Thanks for your reply. At the end I found out the "slipping" was due to my Delta DIY kit has not been calibrated (ha ha.. because I was a "CAN" Up! Plus printer user.). Now I calibrated the thermistor and adjusted the POT on A4988, and the machine is working quite stable now.

The "tension spring" that I mentioned in the last post is something similar to below linked image:


I thought the spring can press the filament constantly, but indeed the plastic body of your design already achieve the same as it can be blended slightly as always.

Thanks again.

Getting close to the old 35 mm snap close film advance like old projectors and film editors used back in the '40's and '50's. All it needs is a Cam to release the roller pressure..

Hey, I'm using an mk8 pulley but the filament slip and if I squeeze too much the screw the NEMA17 loses steps.
Obviously this only happens when the filament reach the Hot end. Have you any idea? I really can't figure out

Hi BerniApple. If your NEMA17 looses steps while extruding during a print, are there any visible marks in your print?
You may try to increase your nozzle temperature or crank up the extruder motor driver power. Some people use a DRV8825 stepper driver instead of the 4988, because it's able to deliver more power to the motor.

@schlotzz Hey, where do you buy the 5mm OD push-fit bowden connector?

Hi BerniApple. I ordered them via eBay Germany. A search for "push-in m5" should get you some good results, e.g. the following one: http://www.ebay.de/itm/Pneumatik-IQS-MINI-gerade-Steckverschraubung-Verbinder-Push-In-Verschraubung-/321597847071?pt=LH_DefaultDomain_77&var=&hash=item4ae0b9b61f

Hi schlotzz,
thanks for your project ... but I have a question for you ..
Since I already have a MK7 bore brass hobbed pulley thing I have to change in your project to adapt it to my DA 5MM MK7?

I have this at home

thank you

Hi CaptainX / Manuel,
You can adapt this extruder design for your MK7 style drive gear easily by changing according parameters in the OpenSCAD file. A few minutes ago I uploaded a new version of the file, which is now further optimized for using a MK7 drive gear. Just download and install OpenSCAD, open the .scad file and change the drive gear parameters. Compile the design and export your STL for slicing...

The following parameters should work for your drive gear:

// drive gear
drive_gear_outer_radius = 12.00 / 2;
drive_gear_hobbed_radius = 11.00 / 2;
drive_gear_hobbed_offset = 3;
drive_gear_length = 11;
drive_gear_tooth_depth = 0.2;

I'm looking forward to hearing from you.

Thanks for the directions @schlotzz .
Next week I should have finished the repairs of my printer, and then try to print the version of your extruder with the changes that you have shown me .

I hope everything works to be able to operate my new delta ; )
thanks a lot

I am the following adjustments after three times printing to fidlle with the right sizes.

and it seems there is no room for the idler to manouver,
any ideas on how to fix, or could you fix it ?
my bowden tube connector is m10
these are the specs of my gear:

so i hope you can help me out :) been printing all day no results and this design is the most suited for my setup.

Hi Duality. I can see your problem clearly in the OpenSCAD rendering. Some parameters have to be changed to make the extruder suit your needs. I did some quick changes (see comments "@CHANGE") and pasted them on http://pastebin.com/iJApXQLB
Please give it a try. I'm looking forward to hearing from you and see some pictures of your print.

cool looks nice! what did you change ?
I'll try and print this in a few mins i'll keep you updated.

Hi Duality. Thanks for your quick feedback. I decreased the size of the idler by tweaking some parameters. Furthermore I added several comments, each beginning with "@CHANGE", describing what has been changed. Just have a look at the OpenSCAD file and do a small search for "@CHANGE".

hey I printed it. but uh on the idler the bottom is to thin it's really flexible now.

Hi there. I thought you changed the dimensions of the idler by purpose... :-(

Here is another slightly modified idler version with a higher base: http://pastebin.com/J4tu0xpG

Hopefully the bearing will have enough contact with the filament...

Hi there, thank you so very much for helping me out !

Is there a way to decrease the distance between the idler and the drive gear? When I printed this, there is too much space and the filament slips. Below are the values I used for the drive gear:

// drive gear
drive_gear_outer_radius = 12.00 / 2;
drive_gear_hobbed_radius = 10.35 / 2;
drive_gear_hobbed_offset = 2;
drive_gear_length = 13 + 0;
drive_gear_tooth_depth = .2;

Hi osgibson. You could try to decrease drive_gear_hobbed_radius by 2 millimeters and reprint the idler. By decreasing this value the 608-bearing is moved nearer to the hobbed gear. Just have a try at OpenSCAD and have a look how the bearing position changes accordingly to the drive_gear_hobbed_radius value. I'm looking forward to hearing from you and your results...

That fixed it for me, thank you so much.

This may be a silly question (newb here) but with Bowden extruders is there any preference between mounting it to the side of the printer or overhead feeding down? Seems like the required bend in the filament/tubing would be minimized by mounting overhead in the center?

Hi John10. I mounted my extruder on the side of my kossel mini, the outlet facing upwards, so that the bowden tube has only one wide loop (180° turn) without getting a sharp kink. Mounting it on the top, the outlet facing sidewards, should be an option, too, but I haven't tested it by myself, yet.

Thank you for your reply schlotzz. I don't know why but I had been thinking of either mounting on the side directed at the hot end or on the top pointed straight down - it never occurred to me to put it at right angles so you may have saved me a lot of grief - thanks again!

I was only able to find 9mm thread inlet (M9?) . Is it possible to change settings in SCAD model to accommodate that? Thanks! :)

Hi bratan. Thanks for your feedback. For using a M9 connector additional changes have to be made. An update is planned, but I haven't got time to implement them, yet. Sorry :(

I'm about to print this myself but I'm considering modifying it to replace the pneumatic connector with a couple of embedded M4 hexnuts. That hasn't been done already by any chance, has it?

Hi Myndale. I haven't seen a remix with two hexnuts, but one with one embedded on the output side. Maybe http://www.thingiverse.com/thing:579385 is suitable for your needs?

Bowden direct drive extruder
by fjriosp

Thanks Schlottz, that's exactly what I was after. To be honest I still prefer your general design though, so I might see if I can modify it myself to embed a single hexnut.

Would there be any way to change this to use a Nema 17 Geared motor?

Hi flux83. The mounting hole dimensions from geared stepper motors usually differ from NEMA17. Therefore the extruder design won't work without major changes. Maybe an adapter plate could work?

Could you please make a version for a bigger inlet? Maybe something like this http://www.thingiverse.com/thing:321523
I know I could buy a smaller inlet very cheap, but I'd like to use the one that came with my E3D v6 (I think it is 1/8").

I would try to do it myself, but I'm not very good using openSCAD.
Really nice design by the way, I like the idea of not using springs.

Motor Mount Extruder
by paenian

Hi Makarov_sl. Thanks a lot for your feedback.
Due to not owning an E3D-hotend I'm not 100% sure about what you mean with "bigger inlet". I assume you're talking about the push-fit bowden connector. The connectors used in my design have an outer diameter of 5mm. You mentioned your connector has OD 1/8" (3.175mm) and therefore is smaller. Are you sure about the size of your connector?

I am in the same business, that is creating an extruder for my E3D v6, and I guess he means this coupling:
The dimensions got me a bit confused at first as well, but it does say thread size 1/8" BSPT (British Standard Pipe Thread), not plain 1/8" measurement. According to http://en.wikipedia.org/wiki/British_Standard_Pipe 1/8" BSPT means a thread major diameter of 9.728 mm, and a minor ditto of 8.565 mm. Mystery solved.

Thanks for this useful hint. I haven't thought of BSPT... :)

Those darn confusing Brits! (... says the weird and crazy Swede)

That was what I meant, thanks

I was told that I'm not goong to be able to use this kind of extruder with 3mm filament and the nema17 stepper motor. I will be losong steps due it does not have enought strenght. Do you know if this is true ?

The BNC3D Sigma machines use 3mm filament, with a bowden tube and direct drive! Richrap has a few reviews of the machine. You'll see the stepper motors in there are rather long for high torque. So it certainly is possible. Personally I've been able to do it too, but the motor wasn't the strongest available and only worked well for lower speeds.

Hi manu123. Yes indeed. Direct drive extruders (like this one) struggle with 3mm filament. Maybe you could use a geared stepper motor.

schlotzz, i dont have the still to use opens cad. can you make me a BIGGGGG favor and probably other guys, and make this for filament of 3mm.im using the following drive gear


I Have just installed openscad . i did find the parameters. i will be uploading the version with my gear drive.

THis are the parameters that i need to update with the size of my gear

// drive gear
drive_gear_outer_radius = 8.00 / 2;
drive_gear_hobbed_radius = 6.35 / 2;
drive_gear_hobbed_offset = 3.2;
drive_gear_length = 13 + 0;
drive_gear_tooth_depth = .2;

This is the one that i allready updated with the 3mm filament
//// filament
filament_diameter = 3.00; // 1.75, 3.00

Comments deleted.

Hi tatubias. Sorry for not answering earlier, but I had a lot on my plate during the last week... I didn't test my direct drive extruder design with 3mm filament, but I'm sure it won't have enough torque and will skip steps... Maybe a geard stepper will do the job, but I haven't tried. I'm looking forward to hearing from you with your results ;-)

I Bet I'm gonna sound stupid, but this doesn't use pellets to make filament right, what does it do, straighten it?

Hi Jamchef81. No, this is not an extruder for creating filament out of pellets, like the Lyman filament extruder, nor it is used for straightening. It's a part for 3D printers used for pushing the filament into the hot-end. Some people also call it cold-end.

I bought this extruder in kit http://www.aliexpress.com/item/K800-Self-assembly-3D-Reprap-2014Newest-kossel-3D-printer-DIY-kit-The-pre-sale/1990522179.html where it was made from molded plastic. It broke after 20 hours of printing. Later I've printed it from ABS, but it became loose after approximately the same time. Design would be OK if bearing would be attached to metal, but to plastic, the shaft needs support from both sides....

Hi igi79. Thanks for your report about the weakness in the idler. I'd like to inspect this problem further, because I've printed for more than 6 months without any problem with a PLA version of my extruder design.
Where did the bearing shaft exactly break? Did it snap off the base? Is the M5 screw for retaining the bearing long enough to reach the bottom? Did you use a M5 manual screw tap before inserting the screw? Would you mind posting an image as make for further investigation? Maybe I'll get some spare time to design an enforced version of the idler.
I'm looking forward hearing from you...

so tried with ninja flex ... NO GO.. i think it can work but the hole that the gear is pushing the flex into has to be nearly flush with the mk8 gear. otherwise it just bends down and forces itself past and out of the hole. . any way you would be willing to try to get that hole as close to the hear as possible?

Thanks for your feedback according the use of flexible filament. On Nov 4th I answered crunchtime2k's comment about decreasing the inner hole to match the radius of the drive gear. It's just a small change in the OpenSCAD file that can be done by hand easily, but I'm going to add a parameter the next few days... Btw, would you mind posting an image of your print?

I just built a spool holder for my bowden set up.. I have angled the motor mount so that your extruder with the bowden tube on both sides dips down to grab the filament right off the spool .. take a look!

and by the way your mounting holes are available on the top. so your extruder mounts perfectly. as soon as I get a new motor and gear I will mount this up and start using it!

Bowden spool holder for with extruder mount many spools supported

Hi danman1178. Nice to see my extruder design incorporated in your spool holder. I'm looking forward to seeing your setup as soon as your missing parts have arrived ;-)

Take a look at the design of http://www.thingiverse.com/thing:147705

Some of the pictures show the extra little tunnel very clear.

Notice how the tunnel extends up to the hobbed gear to eliminate any chance of the filament popping (bending) out of its natural path

Direct-drive hinged extruder for E3D/J-Head hot-end (Prusa i3)

Can the filament outlet area be made closer to the drive gear so soft/flexible filament does not pop out of the side. Using some of the softer ABS it has bunched up and popped out many times from the side.

Hi crunchtime2k. Thanks for your feedback according my extruder design. The inlet/outlet areas can be made closer easily by changing only one value in the OpenSCAD file. Please open the file and look for the comment line "// middle cutout for drive gear". Continue two lines after this comment and adjust "cylinder(r = 11.25 + extra_radius..." to "cylinder(r = 6 + extra_radius...". Change the radius according to your needs. Please note, that you have to add proper support via your slicer software.

It is a excellent working design by the way

So it can push flexible filaments with a little modification?! :D !!

Yes, these modifications should work for flexible filament, but I haven't tried them myself, yet.

Better still, get a pass through bowden connector, increase (or drill out) filament path to 4 mm, and let the PTFE-tubing go all the way to the gears. Less friction than drilled through plastic; also makes for fewer junctions in which filament can get stuck. I made this yesterday: https://www.dropbox.com/s/jinvs396ew5yh9g/bowden.jpg?dl=0
(I'm still waiting for my MK8 drive gear, which should arrive tomorrow.)

Sort of like what the E3D people suggests you do: http://e3d-online.com/index.php?route=extras/blog/getblog&blog_id=21 (and more specifically http://e3d-online.com/image/data/v6/626%20done%204web.jpg)

I like the approach of passing the bowden tube completely through the extruder, especially for flexible filaments. Maybe I should implement a more modular concept of how the bowden tube gets connected on each side, so it can be changed according to your needs easily. I should do some shopping for different tube connectors ;-)

The couplings I used are
which fit in a 12 mm hole, at least 7 mm deep. (I missed the last part on my first try, making the holes only 5 mm deep, resulting in the tubing sticking since you couldn't unlock the connector because it struck the back end of the hole.)

E3D also sells
wich has the aforementioned 1/8" British Standard Pipe thread.

Both of these are drilled through, and are really easy to work with, which suits this usage perfectly.

You can probably get the same type of connectors elsewhere. I just happened to add a bunch when I was ordering a new hot end from them anyway.

Do you have a 3mm version?

Hi tabubias. Thanks for your interest in this extruder. User ipblythe asked me the same questions some months ago. Please have a look at the conversation in the comments below.
The OpenSCAD file is almost completely parametrizable and the filament diameter can be changed easily. Although I didn't make any tests.

Hi! I wanna ask you how does it block the push-fit for it does not move, I do not see it clearly. Also, does any of you have the stl for the MK7 drive gears? I would apreciate if you send me it please

Hi jjuasjjuas2. The push-fit has a M5-thread, which is inserted in the manually tapped hole on the extruder plate. The instructions say: "Use M5 screw tap to cut thread for push-fit bowden connector on base plate..." ;-)
Currently I don't have STLs for MK7 drive gears, because I haven't got any reliable dimensions of it, sry :(
You may download and change the .scad file according to your dimensions and export suitable STLs. Just use the free software OpenScad.

Ohhh, I understand ok. Thanks!

what size you are using for (M3 allen head screw of suitable length with washers and a spring to apply pressure on filament) ?

thank you for your contribution i like the extruder

Hi labidus. The size of the screw mainly depends on the spring you are using. Currently I am using a M3x20mm screw with a washer and 12mm long spring (uncompressed). Alternatively you may use a shorter screw without a spring.

Quick question, what kind of motor is this setup to use?

Hi DocNasty. This extruder setup uses a NEMA 17 stepper. I achieved good results with a stepper from Wantai with 4800g/cm holding torque, type 42BYGHW811, but every other stepper with enough torque should do the job...

Thanks, I'm going to try to fit a NEMA14 on it to see if it will work. I have a small space i'm working with here... so i'm going for minimalist.

Is this thing fully operational as is?

Hi dowhilegeek. Yes, the design is fully operational now. After a lot of testing with my Kossel Mini, positive feedback from the community and some minor changes I removed the work-in-progress flag.

Dude. Excellent design. Truly works wonderfully. I love how open the design is so that I can actually see the area of compression! I found the default configuration works exceedingly well with this direct drive gear: http://deezmaker.com/store/#!/~/product/category=0&id=36429224http://deezmaker.com/store/#!/...

Thanks for the commendation and your feedback about the drive gear from Deezmaker. Indeed, I tried to create an open design to be able to clean the drive gear easily. Btw, would you mind uploading a photo? I am interested in your build with the TatsuMini drive gear.

Slicer is reporting the stl file not water tight. I tried to go into the scad file to export out but the two parts were not separated out, but one assembly instead. Help!

I'm having the same slicing issues with the extruder base- it slices but is missing the extruder idler mount geometry in the print, even though it shows up in the repetier-host object viewing window. Any suggestions? I'm using 1.1.7 slic3r. Thanks!

Hi pefozzy. Thanks for your feedback regarding the missing extruder mount geometry (filament tunnel). I tried slicing the base via RepetierHost/Slic3r, and Repetier keeps telling me, that the object was non-manifold. I inspected this issue with MeshLab and changed my OpenScad file accordingly. Please download the new files (scad/stl) and give them a try. I'm looking forward to hearing from you.

I changed the OpenScad file and placed base and idler beneath each other. Furthermore the file compact_direct_drive_extruder.stl has been added, that contains both base and idler.
If you like to enable/disable parts, you may have a look at the end of the OpenScad file. Each part has its own module and therefore can be commented in or out.

I'm using 1.0.0RC2 which is built in to Repetier-Host v0.95F.

Have you been able to slice the model with the new files, yet?

Hi Could you make a version for 3mm filament as well?

I have found 3mm does not work well direct drive remote hot end because it requires more force to drive the filament the longer distance. I kept experiencing my MK7 gear skipping making using 3mm filament virtually useless.

Thanks for sharing your experiences with 3mm direct-drive bowden extruders. Have you ever tried using a smaller hobbed pulley, like the MK8 instead of the MK7? Does the lower radius increase the force on the filament enough to make it useable? I haven't used the MK7 or 3mm filament on MK8, yet. So I wonder if it would work...

I haven't tried a MK8 pulley yet. I set my stepper motor to half steps which gives me 90% of original holding torque. I was pushing it with 4.95kg/cm. I sure a planetary gear stepper would work or a beefy NEMA 17 from Anaheim Automation would be able to push the 3mm.

Hi ipblythe. The OpenScad file is almost completely parametrizable. You just may change the parameter "filament_diameter" to 3 instead of 1.75, although I'm not sure if a 3mm filament will work with a M5 bowden push-fit connector. I once tried drilling one up to 3.2mm ID, so that a 3mm will fit through, but I had to be carefull no to damage the M5 thread.
Please give it a try! I'm looking forward hearing if it'll work or not.