Gear Teeth Clearance

So my team is building a gear system and we had to make the solidworks for the individual gears ourselves. What should be a clearance between each tooth for the robot to function? The gears are small, 1.5 inch to 0.75 inch. Can we get away with 0.017" of clearance after running them for a while so they set oooor nooo…?

Pitch Diameter?
Number of teeth?
Spur Gear?

What are you using to lay out your gear geometry in solidworks?

Can you provide more detail like material, intended use, or how the gears will be made?

It sounds like you’re trying to design your own gear tooth profile, which is a really bad idea. Instead, try using existing gear pitches/modules.

Spur Gear, Pitch diameter=1.5/16? 13 to 12 tooth, then 12 to 32 tooth, Aluminium (or maybe steel) CNC milled or waterjet

Intended use is our little rookie secret but it’s for a major part of our robot which will see alot of motion

This should help with some of the clearance (backlash?) questions you have, as it would have been what I would use for reference. If you have a copy of the Machinery Handbook it would also help and provide guidance. I had said Pitch Diameter, but really the Diametral Pitch you choose for the gears determines what diameter you have, as well as the amount of backlash you should expect, though the criticality of the backlash is only if you are going to move the mechanism back and forth often.

Also keep in mind manufacturing tolerances tied to the machine you are making them with. The teeth may grow or shrink due to this, either increasing or decreasing the clearance you experience.

I would also recommend not making gears out of aluminum unless you plan on anodizing them. Aluminum on aluminum tends to gall.

I’ll see what we can do for steel then, thanks

I am definitely not an expert at gear design. I have designed some limited gear systems for FRC in the past, but not with custom made gears. I do have some experience with custom made sprockets, which I used the Machinery/Machinists Handbook as guidance (back in 2001 when I was still in high school). I think most CAD programs tend to have “canned” operations to make gear/sprocket profiles now.

Yeah I think so, we just used the circular pattern to line the gear teeth around the base radius then went from there

Brass is a reasonable alternative if strength is not a big issue

I would strongly recommend reconsidering this approach. Your rookie year is hard enough (even if you have some experienced mentors). Don’t screw around doing something exotic you’ve never done before. Get COTS gears. Modify them if you really need to.

You will not be able to mill or waterjet a true involute tooth profile. If the gears in question only mesh with each other, an approximation would be fine. The best way to do this yourself is to get involute tooth cutters for the mill and a indexer so that you can cut them. This requires a series of cutters to cover all possible tooth sizes.

Second what Cory said. If you really want to stick to it though, Solidworks Toolbox should be able to generate you a gear model without having to sketch an involute profile.

We’ll Show you WE’LL SHOW ALL OF YOU.

See you at worlds

With love: 5870 <3


Making gears is work, I mean legit work. Would recommend just buying some off the shelf.

Listen to the smart people above.
To get gears that are as accurate as any COTS Vex or Andymark gear you would need involute gear cutters.
CNC mills would need a tiny endmill to do gears, and waterjet is inaccurate and has an extreme taper. If you buy a COTS gear, the two pitch circles should be tangent to each other exactly. But using your method, I would want 0.004" or more of clearance depending on how you are making them.
Your gears will be less efficient and more likely to bind than any COTS gear, not to mention will take far more hours than COTS.

Consider what you’re getting from making your own gears. I find it very hard to believe that you can’t just find a gear with the right gear teeth from Vexpro, WCP, Andymark, SDP-SI, etc and modify it to fit your design. Unless you want to make gears just for its own sake, I don’t see any reason to try it. It wastes a lot of time and labor resources on something that won’t give you any competitive edge.

You have been warned by many others smarter than me above.:stuck_out_tongue:

That’s not strictly true. A good waterjet will produce little taper on a 1/4" or so thick part. One with a tilting head will effectively produce zero taper and hold .001-.002" overall tolerances. You certainly can cut a gear that will run at relatively low speed, but it will only be an approximation of the involute tooth profile and it will mesh relatively poorly with a COTS spur gear. I had some very large ring gears waterjetted for a project at work and they worked well.

That being said, whatever the OP is trying to do can almost certainly be done faster, easier, and with higher quality by adapting the design to use COTS gears, even if they are steel Martin gears that require putting a custom bore in.

Put bluntly, there is a VERY good chance that you are wasting your time with endevour. If your team has the massive skills to design their own gears and gearboxes in your rookie year, then you can definitely turn that skill towards building innovative and robust mechanisms that blow everyone else out of the water. Seriously, consider using a couple COTS parts instead.

For the love of all that is good, don’t waste your time making your own gears. It is your first season, and frankly, I have never heard of any team that has made their own gears and used them successfully on a high-load mechanism. This doesn’t mean it can’t be done, but you can save yourself a ton of time and money and just buy them online. You will be much happier.

I agree with all those who encourage the OP to find another way but if you won’t be discouraged, I say more power to you. Live and learn. Either you learn or you show us and we learn.

I would ask the OP not to bet the entire season in it if you can help it. Have a back up plan, another source for the product or another option. Something to keep from having your robot be a box of rocks bot.


Dr. Joe J.