pic: 3D Printed Timing Belt

Since we’re showing off 3d printed parts I wanted to share an experiment I did tonight - I printed off a model of a GT3 timing belt using NinjaFlex.

I wouldn’t trust it for most FRC power transmission but for either prototypes or transmitting rotations to sensors it should be solid.

It would also probably be solid for many FTC applications.

I’m going to order a roll of SemiFlex to see if it would be better at some time in the future.


Prusa i3 Original Mk2 stock
230C print temp
60C bed temp with masking tape on it (the TPU sticks to PEI too well)
15mm/s print speed

If anyone can suggest a good method for testing how much torque this can transmit that doesn’t require a ton of resources let me know.

Re: “testing how much torque it can transmit,” set it up to proper tension between two pulleys on hex shaft (e.g. with versablocks on 2’‘x1’’), and use a torque wrench? Keep in mind that it’ll vary with pulley size (obviously).

Guess that’s simple enough and jives with my initial thoughts. Time to order a torque wrench… and print some pulleys.

Now we can 3D print 3D printers, which can 3D print more 3D printers… :ahh:

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I feel like 192 needs to do this for their printed swerve.

I’d be very interested in the results of your testing, if you’re able to get conclusive results. Very cool idea!

Sure beats waiting a few weeks for timing belts from SDP-SI. I’ve heard BB Mann is better, but printing it overnight can’t be beat.


Tensile strength of Ninjaflex: 580psi yield

Cross sectional area of 3M GT3 9mm wide belt tooth root: .0177in^2

minimum install tension of 3M GT3 9mm wide belt ~ 3lb (I don’t have the doc open right now to check actual)

0.0177*580 = 10.27lb max tension

10.27-3 =7.27lb - usable tension for torque transmision
7.27 -3 = 4.27lb - again for slack side tension

PD of 22t pulley = .8271in - size I like to see on a cim for good power capacity

0.413in(radius) * 4.27lb = 1.77inlb = 28.29 ozin max torque transmission with 22T pulley.

I’d be interested to see how close that 3 minute math is to actual before belt deformation. Sorry if there are any glaring mistakes it’s a bit late for this.

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I wonder if you could use a MarkForged to inlay CF or Kevlar into the belt to allow it be used for more demanding applications. Would be fairly cost effective as well considering the small volume of the belt.

I’d love to see someone do this!

Well, I don’t have access to a markforged printer (yet) so I can’t do that.

There’s 3 failure modes that I can think of and I’m not sure what fails first:

  • belt failure (tensile strength)
  • ratcheting (stretch)
  • tooth failure (material failure)

The inlayed kevlar/nylon would help fix the first two. If I see that failure happen it might be worth the time to investigate options of manually placing some reinforcing bands in the belts. Not sure how useful it would be but it could be a fun experiment. Plan would be to pause the print at a few points and add a couple bands of reinforcing fiber that have been either melted or epoxied together and then continue the print.

One issue I was having was with how thin the print actually is and I’m getting two distinct walls that are disconnected.

If you up the number of shells that should make everything adhere. Semiflex is horrible to work with on open air machines, so putting it in a warm, sealed box might give you better results.

The MF software allows you to add additional shells of fiber in certain areas, so maybe more in the teeth? I have a feeling semi-flex or even a new material will work best. Taulman makes a killer soft nylon that could do it. Really great stuff to work with. I believe that our head mentor is trying to get a Markforged. (Why do they have to be so expensive)

I don’t think I’d ever trust it for anything load-bearing, but maybe for intake or shooter rollers. I bet 118 would have a field day for white and gold belts. :slight_smile:

Have you thought about using Cheetah filament? Made by the same company ninja-tek, it has less flexibility than ninjaflex but its also a lot stronger. Better impact strength, and greater abrasion resistance. This should keep the belt from tearing, losing its tension, or even having the teeth strip out. Now I just got the roll in so I still haven’t tried it out but its definitely on my list of things to do.

I thought about it, but I only tried this because I had the roll of filament already.