NEMA17 & Bowden geared extruder for the SmartrapCore, V 0.95b

by BrunoBellamy, published

NEMA17 & Bowden geared extruder for the SmartrapCore, V 0.95b by BrunoBellamy Feb 12, 2015
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Warning : this is the OLD version of my geared extruder. You might want to get the new (and very much improved) one, at http://www.thingiverse.com/thing:1359717 ;)

Yet another geared extruder… ;)

This one is specially designed for my SmartrapCore printer, but it can certainly be adapted for other machines.

I made its body in 3 parts that you have to stack together, so it can be printed without using material support. It's really easy to assemble, though, and it allows for a convenient way to attach it to the printer's wall.

It works with a Bowden and a NEMA17 step mottor. The list of extra parts and assembly tips are in the "Instructions" section.

General idea is obviously derivative from the famous Greg's Wade Extruder, and gears are exactly the same, with the very effective good old Citroën chevron design. :)

Update (07/30/2015) : I made minor modifications on the gears…
Update (10/12/2015) : fixed some minor issues on body & latch parts…
Update (10/13/2015) : added body-front and body-back alternate versions for a different installation method in the printer box, that could fit much better the aluminium SmartrapCore.
Update (01/25/2016) : slightly modified small and big gear, mostly by making teeth corners less sharp.
Update (01/27/2016) : modified a few things on body parts (V. 095b) to improve bearings rotation freedom & things like that…


You will need :

  • a NEMA17 step motor ;
  • a M8 hobbed bolt with the hobbed part at 25mm under the head ;
  • 2 M8 washers and 2 M8 nuts ;
  • 3 608ZZ bearings ;
  • 4 M3x25 bolts ;
  • 4 M3x10 bolts ;
  • 2 M3x50 bolts with hex head ;
  • 7 M3 nuts ;
  • 1 M3 headless screw ;
  • 2 M3 washers and springs ;
  • 2 short M3 screws for wood.

Assemble the 3 parts of the extruder body with 2 M3x25 bolts and their nuts, then the latch with the 2 other M3 bolts and nuts, and one of the bearings.
Install the hobbed bolt with the big gear through the assembled body with a bearing and a washer at each side, and tighten it with the 2 M8 nuts.
Put the little gear on the motor with an M3 nut and the headless screw (don't tighten it too much, it's fragile). Install the motor on the body with the 4 M3x10 bolts. You can then tighten the little gear at the right height (there's an opening in the body front to make it easy for you).
Insert an M3 nut in each of the holes that are on the path of the long bolts meant to tighten the latch. Put the knobs on the 50mm hex-headed M3 bolts, then the washers and springs, and insert these to tighten the latch. Don't tighten it yet, you'll do that in the end when the filament is on its way.
Then you can install your assembled extruder in the SmartrapCore where it suits you, with the 2 screws for the wood, and plug the motor wires in.

I recommend you use it with the cables holder and filament guide I also designed (http://www.thingiverse.com/thing:755862) for the SmartrapCore, they really well complete each other. :)

Suggestion : print the knobs with a different color from the extruder itself, it'll be more fun. ;)

VERY IMPORTANT! You must set the following variables in the Configuration.h of your Marlin firmware and recompile/upload it, otherwise your new extruder won't work, and will only make scary noises without extruding anything :

define INVERT_E0_DIR false

define DEFAULT_AXIS_STEPS_PER_UNIT {80, 80, 80, 790}

define DEFAULT_MAX_FEEDRATE {500, 500, 70, 70}

Enjoy! :)

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So I updated the feedrate and steps per mm. They work when trying to extrude, but when I try to retract/back up in Repetier host the motor just buzzes and does nothing. Any ideas what setting I am missing ?

I have worn out two sets of gears, should I be printing them with abs?

Do you by any chance still have the original files ?
I need to modify the big gear a bit as my hobbled bit is a bit lower than 25mm.

It's a Blender file, and the source file doesn't differ much from the STL actually (I don't have the original shapes before boolean operations), so I'm not sure it'll be very useful, depending on what software you're used to…

No worries. I'll try and import it into Solidworks and edit it.

Just to let you know : I made a series of minor updates today, mostly fixing issues with the size of nut cavities in the extruder body parts and small gear. No change to the big gear, though.

Thanks for the warning. I've already printed all the parts and they all seem to fit fine so no need to reprint.
Managed to modify the big gear in solidoworks, will post it as soon as I print and test it.

Cool ! I really hope you'll like this extruder. Mine is working quite well at home, and I'm now printing a second one (hence the recent small improvements) to (try to) do dual extruding with my home-designed twin head for the SmartrapCore : http://www.thingiverse.com/thing:995640 :)

SmartrapCore Twin Head project (V5.1)

Why wouldn't you eliminate micro-stepping, to utilize the full torque of your motor? The gearing allows for higher torque with the same precision.

Well… why not? How would you do that, exactly? Is it something that can be set in Marlin firmware, or does it have to be done with the hardware?
This extruder works really fine on my printer, so I must admit I didn't search for any further improvement… ;)

With most boards, it is done with jumpers on various PINs. On RAMPS specifically, they are the PINs under the stepper drivers.

You have to reduce the steps per mm accordingly afterwards. So 160 steps/mm at 1/8th steps = 80/mm at 1/4th steps.

Is this extruder compatible with flexible filaments?

i found some other faults with this design after printing all the parts.

hey, i updated one of the pieces. the hole on top was not threadable using an M5 0.8 PTC for 4mm PTFE tube.


Fixed thread-able piece for SmartRap Core Extruder
by jesse

I have no idea what the official standard size for the most common pushfit connectors is, but if you started out building a Smart(Rap)Core, M6 is mentioned in the original BOM, so in that sense it works as it is. I would think of yours an M5 remix instead of a fix. :-)
Great to have a choice, though. While I already had M6, I also have some even larger ones around somewhere, which could be but to use with yet another mod some day.

Is this for 3mm filament or 1.75mm?

It's designed for 1.75mm.

All your files are mirrored from your pictures or the other way around, I'm not sure. The fact is they don't match up.

I don't understand… I reloaded everything to be sure, opened them in Blender, Cura, and Repetier-Host, and they perfectly match the pictures (and the reality). What software do you use ?

Posted as a make, realized there must be something wrong with how I have my axis configured vs. what the software believe. My mistake. You can see my print is mirrored, unintentionally.

Which is really all weird since I've printed things like phone cases and those worked...