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mtbkym01

Modelling and printing gears

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This is a question that I’m asking to know if it is relatively easy for someone with the skills and equipment to do. I have no idea of any CAD methods myself.

I tracked down a new set of “Venom Creeper” rock crawler gears after a few years of looking (they have been discontinued for a while and are obviously quite consumable).

what I’m thinking is id like to get some made using the originals to model off before they also get used up, but is this “easily” done?

Cheers

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Coming from robotics where I print virtually all my transmission components for lightness and cheapness I can add the following:

You can get gear generating plugins for basic software like SketchUp for sure, and more complex engineering programs like AutoCAD and Solidworks have it built in. Just be careful your tooth profile is correct. 

I think there is a limit to how small you can go without going to SLS prints. Any smaller than mod 0.6 you might have a bad time. 

For finding out what your gears are, if that is unknown this is a helpful calculator.

https://www.technobotsonline.com/gear-size-calculator.html

There's also the 3dp strength and suitability discussion but we can burn that bridge when we get to it

Perhaps not much help but maybe a start

H

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I'm thinking the design details of gear teeth are not very reproducible or durable given the typical 0.4 mm nozzle size of home 3D printers.  Even with a smaller 0.2 mm nozzle, the available materials are not that great in printed form.

If these are really rare and you want to make copies, I'd consider making a silicone mold of the original parts and then pouring a resin to cast copies.  This article, in particular, caught my attention with the properties of resins available:  https://makezine.com/2014/03/21/resin-casting-going-from-cad-to-engineering-grade-plastic-parts/

Instead of CNC milling the positive parts and making molds from them, just make the molds from the original parts you have.  Just a thought to consider.

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CAD

YouTube has a healthy selection of gear tutorials for nearly every CAD program ever offered... some are sketched out manually and others deploy a plug-in (wizard) that merely asks for the parameters before instantly spitting out the 3D model. Onshape for its first few years had been free to use, now apparently has done away with their free tier. Grandfathered free users can only continue use by making all works publicly accessible to the community. Autodesk Fusion360 remains as one of the last free-to-hobbyists CAD program that has a decent amount of polish to it.

My own CAD tool of choice is McNeel's Rhino 3D and according to a few forum threads, seems to have at least two plug-ins devoted to gears.

Then, there's a stand-alone webpage that creates a 2D gear profile from just entering parameters:

http://hessmer.org/gears/InvoluteSpurGearBuilder.html

The resulting 2D DXF file (while originally an AutoDesk format) is easily ingested by almost any CAD program out there. Once imported, have that CAD program to extrude the 2D profile to the desired 3D depth. Boolean-subtract a shaft-hole in the middle and that's probably one of the fastest ways to make a spur gear.

PRODUCTION

3D printers that squirt its layers from a nozzle (FDM Fused Deposition Model) would be the worst application for producing a finished product. As Speedy indicates, 0.2mm nozzle width still results in a coarse surface where layer lines are easily visible.

Stereolithography resin printers (SLA) will do the trick. They typically print at resolutions of 0.050mm and layer heights of 0.025mm! My B9 Printer is configured for a 0.030mm resolution (XY flat direction). In this thread, I 3D printed a custom-modeled Tamiya wheel in B9's Black Prototyping Resin:

https://forum.b9c.com/viewtopic.php?f=22&t=371&start=20#p32950

Another post to show that it takes a Stereo Zoom Microscope to detect layer lines in SLA 3D printing:

https://forum.b9c.com/viewtopic.php?f=22&t=235&start=120#p32491

Properties for all the different types of resins used in all types of SLA printers vary across a huge spectrum. Where the original Tamiya ABS plastic wheels can deform when squished by fingers, the B9 Black Resin is at least an order of magnitude more resistant. Not sure about its abrasion properties (constantly rubbed against another resin gear) but I do know that it only gets scuffed when I break out the coarse sandpaper or hand file.

Formlabs has around 11 types of resins for their SLA printers and I would expect at least one of them approaches the toughness I've seen in B9 Black. Then there are all the aftermarket resin makers that offer their mix of formulations.

So far, all of this is going with the intent of directly using the 3D printed part as the working object.

The SLA printer can be loaded with a castable resin. This is what jewelers use. Look up "investment casting" on YouTube to dive down that rabbit hole, but the point is that a castable resin model can be used to cast a brass gear.

The other non-printer possibility would be to just hand that CAD file to a service bureau that offers CNC Milling. From here, the custom gear can be cut out of aluminum, brass, or steel. In capable hands, this would offer the sharpest detail, uniformity, and smoothness.

I believe Shapeways is the place to investigate. They quite a large range of materials that their motley crew of machines churn out.

 

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Afaik gear teeth also come in many different profiles...?

If you're drawing from scratch & you're drawing both gear sides then that's easy, choose one profile & cut both from that. Long as they only drive each other, no problem.

But if you're wanting your 1 new gear to mesh with another existing gear, then you'll ideally need to trace the correct tooth profile.

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Hmm, I don’t mind the making moulds idea, might look into that further

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