[Cothron Theiss]

Vex sells two CIM motor pinions with 11 and 13 teeth that use the center distance for 12 and 14 teeth pinions, respectively. I'd tried to avoid them in the past because I was convinced Vex was using some dark form of witchcraft to make these gears work, but now that I have some familiarity with the concept of addendum modification and profile shifting, I can confirm that Vex uses witchcraft. But it's good witchcraft, so these profile shifted pinions should actually be superior to the non profile-shifted versions.

However, this should theoretically raise issues when mating the profile-shifted pinions with every other gear Vex sells. Looking at the CAD models and drawings of Vex's standard gears, it doesn't look like they have any sort of negative profile shifting to match these two specific pinions. This effectively means that the profile-shifted pinions have a slightly larger pressure angle than the standard gear they're mating with. Normally, meshing gears of dissimilar pressure angles is a big no-no, but this is so slight that it should be fine.

That being said, are there any caveats or limitations to using gears with slightly different pressure angles or profile-shifted pinions? From what I understand, these pinions will cause more interference and wear when being driven (as opposed to driving) than the standard profile gears. Is that all, or are there additional considerations for using profile-shifted pinions?

tl;dr: Can somebody please get me Buckingham's Manual of Gear Design?