Turning down the OD of a gear

[EricH]

Originally Posted by Rauhul Varma

Is it really that common in FRC to add 2-3 thou? (I honestly don't know) For every gearbox I've designed I've only added half a thou and haven't had any problems with wear.

It's been pretty common in the past. Part of the wear thing is that our gears are only running for about an hour per event, give or take a bit (some teams will put more on practicing), which is only about 300,000 cycles for anything going at about CIM free speed, and most gears will be going slower than that. That's not a lot for a typical gear. Even factoring in sudden reverses and the fact that not all gears will be going all the time, it's not a lot of cycles. Once you start getting through a district schedule plus a full round of post-seasons plus demos plus driver practice... Then you might start seeing more wear.

Also, it's a lot easier to add 2-3 thou than 0.5 thou, something about the latter being much harder to do reliably, and needing better measuring tools. (Back in my day, a lot fewer teams had CNC capability. Then again, there were a lot fewer teams.) I'd go into a discussion of tolerancing and its effects, but that would be pretty far off topic, so if you're interested drop me a PM. Short version, X.000 vs X.0005 is probably going to be more expensive and time-consuming one way than the other. Take a wild guess which way is higher cost.