We try and mark our gears that do not come from the vendor marked. We have used:
Inspired by our nut and bolt size checker, I created these models to avoid counting teeth on gears. Printables
Looks great! My team has been running in to the same issue but never thought of this. Thank you.
This is great!
We’ve always used a caliper to check the diameter of the gear and cross checked that with the spec. It has worked well, as long as you are reasonably careful with your measurements, and know how to find the gear spec on the vendor website. Having templates like this that are clearly marked seems like a much quicker and more reliable solution.
We used to print out the identification charts from VEX back in the day, but just eye-balling gears with them didn’t work well (and it may not have printed at exactly the right scale or something).
I look forward to printing some of these off (lord willing my printer won’t under-size them).
Yo this is an awesome idea! Definitely going to start up printing some of these if i’m able to tomorrow
You could also multiply the pitch diameter by the DP of the respective gear to get tooth count
For 20DP gears - (Measured OD-0.1") x 20 = tooth count
For 32DP gears - (Measured OD-0.062") x 32 = tooth count
This is the way. The 3D printed size checkers are a novel idea, but you’d need to print a lot of them to cover all sizes. They are also going to get pretty big. It is not unusual to run 20DP gears with tooth counts in the 60s and 70s.
It may be simpler, especially with 32DP gears, to use equivalent formulas:
32DP tooth count = (32 x OD) - 2
20DP tooth count = (20 x OD) - 2
Be careful with 20DP pinion sizes (probably 14T and below). Some FRC vendors sell pitch-shifted versions of pinions so a given OD might have fewer teeth than expected. Same heads-up applies to the 3D printed sizing guides. For example, you might need a standard 12T checker as well as 10T with 12T diameter checker.
I like the simplicity of the 3D printed size checkers, it makes it pretty clear, and can also work on addendum-modified gears that would give incorrect results if you measured the OD.
But to reduce the quantity of gauges, I wonder if you could combine some together nested like the shape of an inverse wedding cake. Maybe increment the gears by like 10 teeth per layer, and then print the different gauges in different colors of plastic. E.g. the red one can measure, 20, 30, 40, 50, 60, etc teeth, the orange one can measure 22, 32, 42, 52, etc teeth, etc. and then maybe print a big blocky one for all of the pinions.
Or, maybe reserve the difference in 3DP color for different gear pitch / sprocket pitch / timing belt pitch.
I thought about sprocket version as well. I can’t think of how to do one for pulleys. I don’t think the flange diameter would reconcile to tooth profile close enough.
Print a “Half Moon” shape and slide it over the pulley.
Use a set of metal number stamps and hammer the tooth count into the gear or sprocket. This is also a good thing to do if you are broaching your own sprockets so they are “paired” and lined up for any use.
I will let you know how it works.
This is a Gear Counter/Bearing Checker I made last summer/winter for a few of the Steel City Robotics Alliance teams. This seems like a good opportunity to share this with the CD community 
This design works for 20 DP (very common, at least for 4467) and 32 DP (much smaller teeth, not very common for 4467). The plate can also double as a bearing/shaft checker, using any shaft you want - 1/2" ThunderHex, 1/2" Hex, 1/2" Round and 3/8" Round are depicted in this model, but you can put any size standoff on the plate.
Note - The plate shown in Onshape is very overkill, and truthfully not simple to make. I made scribe lines every 5 teeth and used a die set to put labels directly on the 20 DP rack (the 32 DP rack is too small for the die set, so it’s marked with scribe lines every 5 teeth).
Note - In the final product (not reflected in Onshape), the 32 DP rack is attached to the plate by 4 #10-32 x 1/2"(?) screws with washers on them, all tapped into the plate; this was easier than drilling and tapping into the 32 DP rack we used. We also considered using glue to attach this rack to the plate, but screws were easier at the time.
As for permanently marking the gears, I highly recommend using an alphabet die set to punch the teeth counts into the gears (where possible). Sharpie works, but isn’t a long-term solution.
Feel free to make modifications as you see fit
Onshape File: Onshape
20 DP Gear Rack: McMaster-Carr
32 DP Gear Rack: (I can’t find the right MMC part number, but it was 2ft. in length)
Plate: 1/4" Polycarbonate
I went ahead and printed one of these off on my dual-extruder (because why not?) Snapmaker F350 just to test it, overall I’d say it came out pretty good, but my main suggestion would be to, where possible, use font that is larger/bolder, as the lettering on some of these can be a bit hard to read, even when using two different color materials.
Now I just have to see if it will fit a gear the next time I’m in the shop, or if I’ll have to scale it up a bit.
I feel like this is something that ML/Image recognition would be good at…
Another thought occurred to me - all we are doing is counting teeth. So one simple way to do that would be to have something like a strip of belting material that had correctly sized/spaced teeth that would engage with the teeth of the gear. on the back side of the belt, you mark numbers of teeth. Then you just wrap the belt around the gear and you just read the number where the belt intersects/overlaps with the initial end of the belt that you placed at the first tooth.
With some of the materials that people are printing with these days, is there a material that would be suitable for printing a measuring belt like this?
We just write on our gears the number of teeth at the moment we get them.
Thanks for the files!! I printed a batch to try out and they work great. I think I might make a rigid “Tree” for them to fit on that can live near our storage area so you can quickly try out sizes and they are easy to manage.
McMaster-Cupp 
