Drawing epicyclic/internal gears

I want to draw an involute gear with both external and internal teeth.

I’ve found the SPGear plugin on SketchUcation, but as far as I can see, it can’t draw internal teeth, just external ones.

I can no longer find a source for DHGear3 or DHGear4 which have been referenced in Forum threads from five years ago and which used to be available on Jim Hamilton’s Spirix website Some of his site still works, but links on it to these plugins no longer work.

Apparently one or both used to be available on SketchUcation plugin store, but they aren’t there now - a search for “gear” just returns one extension - SPGear. And a similar search on Extension Warehouse returns nothing either.

Can anyone point me to a source for one of the DHGear plugins, or even just upload an rb or rbz file?

It doesn’t matter if it only works on Windows, or even only works in older versions of SU - I have access to both, though I mainly use Mac (Monterey) and SU 2023.

I’m afraid I don’t know of a source for those old versions. Unfortunately Jim withdrew most of his extensions after some false accusations from someone.

How accurately do the gear teeth need to be modeled?

At this stage, not very. I could draw external teeth with the SPGear plugin, then take one, turn it 180° then copy/rotate it.

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You might have a look at some gear manufacturer or seller sites for downloadable CAD files. I didn’t hunt very hard but since I already had the McMaster-Carr site open I downloaded a couple of randomly selected CAD files and put them together for this.

Modeling decent gear teeth from scratch isn’t terribly difficult. I did a chevron gear from scratch for 3D printing a few months ago. It worked quite nicely for the competition robot built by our FIRST robotics team in the spring.

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Good idea. I may resort to that if I have to. But made first shot using the process I described earlier, just shrinking the inside tooth a bit before rotate/copy.

Now have to draw a matching internal and external pinion gear to mesh.


external tools (no plugin, you’ve got this and that


you can generate vector files, and from there, 3d models.

Thank you. I’ve had a quick look. Looks useful for many purposes.

It doesn’t seem to do internal teeth. Am I missing something?

Well the second link makes either external or internal gears.
(click on your gear, and tick the “int” on the left)

I suppose you have to combine both ext and int yourself, using two radiuses.

The one time I needed gears (and found this site), a colleague ended up giving me the needed files, so never really used either site.

The first link is simpler, only two gears at a time, and is one of Mathias Wandel woodworking tool.

The second (blue) one is a “for fun” project.

It has a V2 in beta with more gear options

My plugin is still available, but it doesn’t do internal teeth (as I recall). However, here’s a mating set of gears that I somehow made, but don’t recall how I did so. Maybe it will come back to me. Or maybe not. Maybe you can make use of these by scaling or whatnot.

wankel2.skp (2.6 MB)

Thanks, Jim.

I’ve managed to draw an acceptable approximation of a circular track with both external and internal teeth, and (more or less) matching pinions.

Need to have around 96 teeth on the track, in and out. It’s good enough for the moment, though not accurate enough for manufacture.

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I believe that Mark J. Grundman’s SPGear was a massive rewrite and expansion of Doug Herrrman’s DHGear for Mark’s needs with Sketchy Physics. (See comments in code)

But it needed to be properly wrapped and packaged as a true SketchUp Extension, which I myself did with v1.3, and TIG updated to v1.4, which is posted here:

However, I see nothing it the code (with a quick look) that implies it draws internal teeth.

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@DanRathbun thank you.

I couldn’t see anything about internal teeth in the parameters of SPGear, but haven’t looked at the code at all. Indeed, I don’t know if the profile of an internal tooth is just a rotated external tooth (though a bit smaller for the same number of teeth), or the ‘negative’ of an external tooth (an external tooth subrtacted from a circular face). For my present purposes it doesn’t matter, though, which it is - I just need gears that look as if they could mesh.

I downloaded v1.4 of SPGear from SketchUcation earlier - that seems to be the current version. It says it fixed a small typo in v1.3 and looks like an update of your version 1.3. It has installed as an extension, not a plugin. It has a loader rb file and a same-name folder.

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Ah, okay I don’t have v1.4 in my local archive. Okay, I see it now @TIG fixed a path booboo in it a few days later.

(Updating my link above.)