Compact Bowden extruder, direct drive, bearing bloc, auto load 1.75mm filament

by scarou Feb 6, 2015
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Good morning, I've assebled the extruder but online I've found only 20mm long spings wich are very very much longer than the ones I see in your pictures...20mm seems to be the default length for the bed leveling springs, could you tell me where you bought your shorter springs? Thanks

I assembled this extruder today and it works great so far, even with flexible materials.
Thanks for the model :)

Glad you like it ;)

Hey scarou, I'm really interested in printing your extruder!
Unfortunately, I got a E3D Hobb Goblin here, that doesn't quite fit the standard MK8 drive gear size.
(See here: https://e3d-online.dozuki.com/Document/59/)

Do you think it's possible to get this extruder to work with the drive gear?
Or, would it be possible to upload a version to support it? I feel like it's not exactly an uncommon drive gear to choose :)

Here some calculated specs about it:
Outer diameter: 8mm, Inner hole diameter: 5mm, Height: 11mm, Distance from bottom to the teeth center: 7.5mm,
Teeth outer diameter: 7.5mm, Teeth inner diameter: 6.5

//update: I quickly built an assembly in SolidWorks to test out the compatibility of the MK8 base,
and as I expected, the inner diameter is somewhat smaller, resulting in the filament either bending towards
the drive gear in the extruder, or just plain slipping completely. I attached two pictures so you can see it yourself.
If reediting step files with complicated shapes wasn't such a pain in the butt, I'd just do it myself, but in this case,
I'd really love to see an alternative version posted, please, that should be less of a hassle..

Hi AnukWolf !
Sorry, I made a test with the design of your HobbGoblin drive gear, and it seems to be slightly too wide for all the design I have.
You can still make a try with the MK8 version, but the auto load function will maybe not work properly. Actually changing the design is a big mess... So maybe it would be easier to change the drive grear. If it's not an option that you are considering, I can try to make a new design, but You will have to get the "small" pushfit with (M5 / M6 thread) because there is not enough room for the 10mm one.

Hey scarou!
Thanks for your reply and your tests, I really appreciate it!
Unfortunately I just recently got the Hobb Goblin a month ago, and I pumped a lot of money into my printer recently (completely new hotend + duet wifi + lots of small stuff..) so I‘d rather not change it out again anytime soon, if possible.

If you can somehow find the time to do it, that would be awesome! I was just about to go buy some high quality Festo brand pushfits today, so I‘m good on that one. I‘d probably go with M5 since it‘s the most used one I think. I also got a tap for M5, not M6.

I've been using this extruder design for 3 years now on multiple printers. It's still my favorite! I just wanted to say thanks!

You're welcome buddy ;)
Thanks a lot for this compliment !

Hi scarou,

is it possible to get the step files? Or even solidworks? I want to redesign the tolerance to my needs.

Thank you for your design!

The extruder has been running great so far! Thanks for the design!

Any chance you could create a mirrored version of MK8 pushfit (non labeled)?

I printed all pieces mirrored, but a couple holes are off, and the others aren't recessed where they should be.

Thank you!

Hey, so I just got this together and for some reason I'm getting a ton of friction when extruding... I think the surfaces inside the bowden fitting are sharp and acting like a one way valve. Any ideas to get around this?

1- make sure you have properly cleaned the filament hole of the extruder with 2mm diameter drill bit.
2- Don't put lot of pressure on the filament (don't over tight the screw + springs)
3- make sure your bowden tube inside the hot end is right angled cuted and completely pushed at the end bottom of it (any play between ptfe tube and the extruder let the plastic making "a bead" that block the filament)
4- Inspect all the extrusion line step by step from the extruder inlet hole to the hot end extrusion hole.

Hope It will help ;)

Thanks for the tips! I was able to re-angle the bowden fitting (wasn't 100% perpendicular), and also ream out the end of the fitting to help the filament slide through easier. I will be posting a Made One is just a couple mins.

Thanks again, this was a pretty straight forward build and thanks for all the pictures, a lot of people are jerks and don't provide instructions like you!


Everything printed okay but I did have a problem with the push-fit. I used a tap to thread the part (printed in PETG), it does not have it enough "meat" to keep the push-fit in well. Is it possible to extend the part a bit so that I can have more thread ?

Hi electronlove,

I'm not sure to understand your requirements... But if you encounter problems with the pushfit, try to not use a tap to thread the part. Personally, I don't use a tap, I just screw the pushfit directly into the plastic. If it is too tight in tour case, just use a small bit to enlarge the hole.

I just want to say, this is an awesome extruder. i tried a few and this is the best i've used. I've since purchased a Bulldog xl clone and while it works well, I don't care for the tensioner design. I wish i knew CAD because I'd love to see one of these modified to work with a 5:1 geared stepper motor with an 8mm shaft. But again, kudos on your design, it rocks!

Thanks for comment budy ;)

Hello Scarou! Do you think I could use it with 3mm filament, just making bigger the hole for the filament?

Sorry, I'm a bit late I'm afraid... And the answer is no. The design is tuned to apply a small amount of pressure on the filament. If you make a bigger hole for a 3mm filament, it will bend the filament and the auto-load will no longer works.
If there is enough demand for that, I will try to find a bit of time, to modify the design for a 3mm filament.

Hello Scarou! I have printed your design and I like it very much. I have a similar problem as Skimmy because my stepper shaft doesn't reach the 625zz bearing. In my case it's due to the smaller shaft length of my stepper motor (only 20 mm). Is it possible to make any modification in the design for this case? I will try to make a modification cutting the stl file (I think I could gain about 3 mm, but I am not sure yet...) and I will show you the result so you can tell me your opinion about the modification and if it could penalize the right working of the extruder.

Thank very much for your design!

Hello, Please can you post a version with m6 PushFit, MK8, with support? Thanks for this awesome design.

Hi khnshkr (bless you)

Done ! ;) (C_BE MK8_M6 pushfit_builtin support.stl)

Thanks, you are awesome! :)

Scarou Hello, thank you for sharing your achievements I have one small request I will start a Bowden on P3steel but I would need a left and a right Bowden. it would be possible to reverse all the editing. Thanking you. Patrick

Hi Patrick,
You do not need a new version. Just mirror it in repetier before slice it. ;)

Hey Scarou! I added another "made" to your design. I works excellent and looks like a charme. Thank you again for customizing this model for my needs! That is a very nice habit!
If you have a little time to spare, maybe there is a way to get the extruder a little slimmed down? I'm short of 4mm on my motoraxis, because of mounting the extruder on a 4mm-thick sheet of metal. Therefore the bearing cannot be reached, look this pic for example: https://thingiverse-production-new.s3.amazonaws.com/renders/ff/9d/b8/2c/61/92790a95171f23bf4c1ff06cc5789b02_preview_featured.jpg

So, if you feel for it, I would appreciate it very much!

Thank you and keep the good design on working ;-)

HI, Skimmy,
Sorry I can't do that. There is not enought space available to slim it more...

Hi Scarou!

I have an idea to get this excellent extruder a bit user-friendlier: How about giving the idlerparts a little more grip for fingers? Just extend them like 10mm further, so one can grip this to lift the idlers up a bit. Would be a super help while changing or feeding filament.

Hi Skimmy !

Done ! Enjoy it ;)

Thank you. They get printed, currently :D

Hi! Would you mind to put the sourcefiles online? I would like to modify this excellent extruder a little. Or, if not, would you be so kind, to modify the extruderbody to a version without the bracket to mount the extruder?

Hi Skimmy,

Which model do you need exactely (1 or 2 pusshfits, MK7/ MK8, with or without builtin support) ?

I would need the MK8 with 2 pushfits. If I can do one more wish, pls without the MK8-text and without support, but either is fine... It should look like this: https://dl.dropboxusercontent.com/u/46522094/IMG_0892.jpg
But please with nicer looking corners ;)

Ok, may be you can try this
C_B_E_MK8 - 2 pushfit - no braket - no builtin support.stl

Tell me if there is something to change.

Great work. This runs in my printer for some month.
Yesterday I've got some flexible filament and it works without any modifications.

I haven't flexible filament, so I am delighted to know it ;)

Thanks for your comment !

I also just picked some ninjaflex up. First little while was fine, then it got all tangled up in the extruder. Still working on perfecting it.

Any tips?

i have a tiny problem slicing the extruder with my 0.5 nozle setup, the support that is already in the file is incomplete and hangs in the air.
Basicaly no problem, could ad extra support in Simplify3D thougt but no this wont work cause befor slicing the preconstructed support is present and mine attaches to this. But after slicing it hangs in the air.
I think it has to do with my 0.5 nozle, is the support you constructed to thin?

Hi Marcus,

I have to check it, but you may be right. My nozle is a 0.4 mm and I think that the thickness of the support is 0.4 mm to avoid wasted time and material.
What version of the extruder you have choosen ? I will try to make a thicker support for the 0.5mm mozle and you will be able to test it.

I cheated Simplyfy3d told it it has a 0.4 Nozle. But dont think that it will work like mentioned.
I have to print the "Lenght 13mm - Outer dia. : 8 mm - Hob. dia. : 7.1mm - Bore 5mm" Bowden in and Bowden out one.

Hi Marcus,

The built in support is not attached to the main part of the extruder. I can publish a version without any built in support if you want.

yes please this would help, thanks

Sorry for the delay. Finally done it ;)

(Compact bowden extruder MK8 - 2 pushfit - no builtin support.stl)

Hi, I'm liking your design, but am wanting to make some modifications to your idler parts (add lever arm so that I can compress springs to load filament). Will you post your DSM files for this so that I can make these changes? Thanks.

nice design with nice features.
Will you share the source files? Which software did you use to design this?
I'd like to add push connectors on both ends. Also I want to use a MK8 but I don't want the MK8 logo. Could you made these changes?
Thanks you.

Hi ionniskar,

The changes have been made ;) I have added the fils "Compact bowden extruder MK8 - 2 pushfit.stl"

I use DSM (DesignSpark Mechanical). It's free and an amasing powerfull tool !!!

I think you forgot the support for the new part I requested. Slic3r adds a lot of material and I don't know if I could remove it easily.
Also if it's not big trouble make grooves for the heads of the left screws holding the stepper.
Thank you.

Sorry buddy !
You are completely right ! I forgot the support !!! Let me arrange that and I'll re-upload it ;)

So, are there any specific setting for printing the idler parts? I am using Slic3r at 0.2 mm per layer with a 0.4 mm nozzle, and infill of 80% and the 1st layer is 0.3. I also have support on. But, what I am noticing is that the parts come out somewhat tight in fitting onto the motor mount. It also seems that a 10 mm M5 is not quite long enough to mount the bearing between the two idler parts. I am printing in ABS, FYI. From your image, you seem to have a couple of washers in there for good measure so maybe your M5 is 14 mm or so?

Just follow instructions given in the "Instructions" tab. I use 25% infill ans it works well. For the main body, do not enable support because the stl file is already with support that you can pill off at the end.

Print each part of the idler separatly and enable support on Silc3r. Dot not forget to flip the idler part 2 before printing.

"About the M5 x 10 ... your are completely right ! You need a M5x15 mm (or as me a M5 x 20 and some washer. I use 4 washer of 1mm thick ) " (I already answered that to someone there just a few days, but I have to admit I forgot to change the info on Thingiverse ... sorry ...)

I hope it will help you ;)

Can be used the MK7 drive gear or only the MK8? Thank you!

No, a MK7 drive will not fit to this extruder.

And can it print flexible filaments with the MK8?¿

I never printed flexible filament, so I don't know. But I think that the auto load might be a little bit tricky with flexible filament.

Hi. I have printed the motor mount only to realize that I have the wrong Bowden push connectors. Are you using 4 mm OD x M5x0.8 Male connectors ?

Hello. My push fit does also not fit. It has a 9.5mm thread. Would you be so kind a just resize the diameters on your files? This would be really cool!

Would you mind sharing STL for clips you used to attached this to the threaded rod? :)

Extruder_to_threaded_rod_support.stl file uploaded ! ;)

What size M3 bolt to use ? Is it for the springs ?

I meant 3 x M3 nut and not bolt (bolt = nut + screw).
Sorry for the poor quality of the translation. I correct my mistake immediately.
Thanks for your comment ;)