Curved rack and pinion - best practices

My kids are asking me how to build a curved rack interface for a pinion gear.
My first thought was they could use the spur gear generator in onshape and build that into a sketch, but that generates a complete gear.

Is there best option to manually measure the gear teeth of their pinion and manually create the teeth? Or is there a tool or method that makes more sense? Looking for the best practices or documentation. Searched of CD, Youtube, and Google weren’t very promising other than the manual method.


(Coding guy here - not a CAD expert so pls be gentle)


I haven’t used the onshape spur generator, but could you generate a full gear, and then add lines extending from the center to sweep out whatever arc you need, and trim whatever is outside?


That’s a great idea Tim!

As already recommended, we used a spur gear generator for the full gear and cut away what we didn’t want.

Onshape Link



Which direction do you want the rack gear to be curved? Do you want it to be curved like a banana, where the pinion is rolling along the curve of the banana?


Or do you want it to be switch on a cog railway, where the curve is perpendicular to the direction the pinion would travel?

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Thanks RickeyRobot - this is very similar to what they want to do.

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Do not worry, we don’t bite. Also never used Onshape spur gear generator before, but It looks like the suggestions above will satisfy.


It’s the internet…people always bite.
Documenting the use of search tools + admitting ignorance is generally a good inoculant. :slight_smile:

But I am EXCEEDINGLY pleased with these helpful results. If I see any of you guys at an event… a beverage of your choice is on me.


well, now i’m sad we’re not based in michigan!

but yeah, our team uses solidworks, and we do something very simular to the folks above, use the toolbox, grab our gear we want, and just cut off the stuff we don’t need. was very useful when we made a hooded shooter in the offseason after 2022

We used a gear generator in Inventor to start. Then another mentor turned it into an involute tooth. We integrated the rack into our shooter plates.
We did the same thing back in 2018 for Powerup. They worked out really well.

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A really important thing to know is that generating a large gear lags out your part studio a lot. It’s better to generate and cut it in a different part studio and then derive.


I do my best to help those with Onshape but my experience is in Solidworks. And for that we have built a whole catalog of parts that are configurable so we don’t have to make the same thing every time.

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Good luck! Hope you make it to state!

Thanks that’s one of our objectives :slight_smile:

Here is an example of what we did in OnShape: CAD Design The tab is called “Curved Rack”

This is more conventionally called a “sector gear”.

You may have better luck with research using this term.


Can we normalize the use of “sector gear instead”

Curved racks of this manner aren’t a thing, by definition.

This is the correct use of curved racks, at least as far as I am aware.


What material did you make these plates out of?

I had no idea what it was called…… software guy. All this physical stuff is alien to me.

It’s better than: curved part with pokey thingees with wheel thingee with more pokey thingees the same size


We are calling ours a “big gear” but yeah, we’re doing something very similar