by PCCLDideafactory, published

Libro-Struder by PCCLDideafactory Dec 19, 2015
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The Libro-Struder is an original 3d printer extruder created at the Pueblo City-County Library District. It is part of the RepRap Libro project but is a general purpose filament extruder for all your filament-pushing needs. It uses plastic-on-plastic friction forces rather than toothed-gear biting forces to grip and advance a plastic filament. The Libro-Struder is less prone to jamming and slipping than the more common Wade or Bowden-type extruders. It can also be created with fewer specialized parts. The design explores the idea of using taken-apart pop rivets as tiny bushings on shafts. The current model does require a stepper motor that has an orbital gearbox attached. I have had much success with a Nema 17 stepper with a 27:1 gearbox, Part No. 17HS19-1684S-PG27.

Hackers encouraged to print their own gearbox. :-)
Original design by David Hartkop, Technology Trainer PCCLD.

Nema 17 motor, 27:1 gearbox #17HS19-1684S-PG27
4 x M3x8mm screws
Push-in pneumatic fitting for 4mm od nylon tube
18 gage steel wire, 3 inches
22 x 1/8” x 1/4” long pop rivets, steel.
nut #10 (M5)
set screw #10 x 3/16" long (M5x5mm long).

Printed Parts:
smallGears (11)


-> Movement of the central gear is slow and continuous while movement of the smaller gears undulates as they periodically engage and the spring arms flex slightly.

-> The center hub of the big gear is held tightly to the motor shaft with a set screw in an inserted nut. The hub is reinforced by wrapping some bare stranded copper wire around its groove 6-8 times and then soldering around it. This creates a metal band that is fused into the plastic.

-> Print Settings for Parts: All were printed in ABS 1.75mm filament
Big Gear: 4 shells, 75% infill, 0.3mm/layer, no supports
Small Gear: Same as big but just 2 shells.
I/O Module: 2 shells, 25% infill, 0.3mm/layer raft & support
Galaxies: 3 shells, 25% infill, 0.3mm/layer, raft, support for motorGalaxy

-> The Big Gear's nut and set screw are #10 and #10 x 3/16" long (M5, M5x5mm long).

YouTube Videos:

See video the Libro-Struder power loading here: https://youtu.be/CCGOJw2fUM8
See video of the Libro-Struder extruding here: https://youtu.be/b2AEpmFmc_0
See video of dragging filament out of the Libro-Struder: https://youtu.be/2r9iNOMyIR0

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can you explain me if there is a mechanical reason for this extracomplex estruder?

is there a 3mm filament version?

Nice! Can it handle retractions?

Have you thought to redesign it so the drive motor will be attached to one of the small red-gears. Then you could use it without the planetary gear set.

Could you post up a solidworks file (or step file) if possible, thanks! Great design :)

This object was created in tinkercad and lightwave3D. The final version was created directly with mesh tools, so what you see is what you get! Thanks for the feedback.

could it be made to work for flexible filament?

I think it would work well for flexible filament. Most of the refinement has been in the spot just after the last small gear but before the filament enters the I/O module. If the filament is too flexible, it may buckle there instead of being pushed down the tube. With ordinary PLA and ABS filaments, it is not a problem.

good luck with retraction :)

It seems to be quite responsive; the filament is pretty much just attached to that big gear, and the stepper motor gearhead has relatively low backlash so it hasn't been a problem.

Too bad this can't be used with standard nema, i've got some high torque ones over here.

I have been working on an improved design that has a gearbox built into the big center gear. This will allow it to work with just a standard Nema motor. Stay tuned!

It would be an interesting experiment. I suspect that the torque required is just a little too high. You could do it with a printed shaft adapter and a nema 17 plate adapter.

I'll be printing one in the coming weeks, i'll make sure to post some kind of feedback here.

did you ever get a chance to try this?

What's the size of the set screw and nut for the big gear?

It is a #10 nut and a #10 x 3/16 inch long screw.
Metric substitute would be M5 nut and M5x5mm set screw, but the nut may need to be edge-filed.

Will it work with resin instate of plastic ?
It seem cool.

It may not work if the resin is too brittle. It is important that the arms of the 'galaxy' parts are able to flex like springs.

This has got to be one of the prettiest/coolest/over engineering extruders I have yet to find. Awesome.

Thinking out of the box.

I would like to try this on my XYZ Jr. as I have a lot of difficulty with it slipping.


The more gears it has, the less energy it will give , but otherwise a nice design! Thanks for sharing

So 1.75"mm or 3mm filament? I run 3mm..is there a .scad file?

i dont think it matters... all the red wheels are on springs.

True. It DOES accept larger filament. After you mentioned that, I fed some 3mm through. I had to enlarge the holes in the I/O module, but the gearing works unchanged. The pneumatic tube & fitting, however, is another story. You would need to use a tube for larger size filament.

Forgot to say that! I printed it with 1.75 mm. I created it as a polygon mesh using LW3d so there is currently no .scad file. It would be awesome to have an ultra-clean parametric version of this model. You are welcome to build one & post here if you are into modeling etc.

Hi there, interesting approach. Can you add some pictures of sample prints created with your extruder? Is the friction of the bare plastic parts enough, is it possible to do some tests how much force can be generated by the extruder? I also wonder if the feed rate is constant, from the video, the whole extruder seems to be moving under the tension of the arms.


Plastic on Plastic friction:

FeedRate: It does push filament continuously. Here is a video of printing some infill using the LibroStruder: https://youtu.be/4nDmSsaxJCU
The peripheral gears, do not move continuously, but it is the central gear that counts. They undulate against the spiral spring arms as the springs flex and the teeth engage.

Yes, I noticed that too...

Nice work! Im sure this will solve my slipping issue.

That was our main issue too. We have a couple Makerbot Replicators and also are experimenting with RepRaps, and everything was jamming or slipping.