I recently swapped out my non-geared Z motor for a 10:1 geared version. While doing all the calculations for my unit values, I ran across something that I never realized.

Most all Shopbots have either a 20 tooth or 25 tooth pinion gear for Z. A 20 tooth pinion moves your Z rack 3.14 inches for every one revolution. A 25 tooth pinion moves your Z rack 3.92 inches for every one revolution. If you think about it, most people do 80% of their cutting over maybe a 2" range of Z travel. So, on a 25 tooth pinion, especially, you are wearing out only half the pinion.

Every few months, I am going to disengage my Z motor from the rack and then rotate it half a turn. This should help wear all the pinion teeth equally. Possibly giving me 1.5 to 2 times the life of the pinion.