775 Pro Coupling

[Richard Wallace]

Originally Posted by BoilerMentor

We're looking at how to get a 19t 32dp pinion onto our 775Pro shafts for our shooter. My students effectively designed a clone to the AndyMark Cim-Sim, stealing the shaft, cluster gear, and bearings and using a 19t gear from bane bots that was thought to be appropriate. Long story short, that gear has a 5mm bore, but is also 40dp (we think). As of right now the plan is to modify 19t 32dp gears from AM to fit the 775Pro.

My dilemma this morning was related to fixturing the gear, but also whether to use a #10 drill then ream the bore to .1955" or .1960". This gives you either .0007" or .0012" interference. At this size a proper press fit is .0002" to .0014" interference. If I don't have to spend $40 on tooling it wouldn't hurt my feelings though. My only concern is that a slipping pinion might be pretty difficult to diagnose and could be a pretty severe failure mode in a competition environment.

I agree with all your points regarding proper interference fit, and reaming is clearly a better method. I think we just got lucky with the #9 drill. Over the past 30 years, I have press fit a lot of motor shafts from 2mm through 17mm diameter and have developed a feel for the forces involved, so I am pretty confident of the results we got on a few motors. I would not use the same method in serial production.

To your question: I'd go with the 0.1955" ream. We will probably do the same when I need to make more components.