For starters, when you buy a comm lathe, get a regular carbide tool. Diamond tools might sound like a great idea but they're insanely expensive and (ironically) very fragile. Plus, when a carbide tool wears out it leaves a crappy cut. For some reason worn or cracked diamonds still leave a smooth finish on what is really a lousy cut. You can get carbide tools from McMaster-Carr
for about $4, and some of mine have a lot of mileage on them. I bought four or five carbide tools about 4 years ago and I've only recently gone through the second one.
Unless you're going to use the new Reedy Stockstar or Challenger motors, you'll want to get something to align the brush hoods too. Some companies make these H-bar things that just sit on top of the endbell, but when you think about how they work you realize they're useless. All they do is align the brush hoods to each other, what you really need is a tool to align the brush hoods to each other and
to the center of the armature shaft. I think Trinity makes a tool that's just a brush shaped bar and a dummy armature shaft: you build the motor with no armature or brushes, loosen the hoods and slide the bar through them, run the shaft through each bushing/bearing and the hole in the bar, and retighten the hoods.
Shimming the armature is important too, usually the factory job is kinda sucky. Pull the motor apart and remove all the factory shims except the phenolic (sp? I say it all the time but dunno how to spell it
) washer, the one right above the commutator. Put the motor back together except for the brushes, and spin the armature by twirling the output end of the shaft. Make sure it spins freely after you let go, the idea is you're trying to get the armature centered in the permanent magnets' field. When it stops, gently push on the endbell end of the armature and see how much it moves, then take the motor back apart and add shims to the output end. Keep messing with it until you've removed as much slop as possible, then do the endbell end. When you're done, the armature should just barely
be able to slide up and down in the can. The closer you can get to zero movement without actually getting there, the better.
Breaking the motor in is very important as well, but there are MANY different ways of doing that, and the best method really depends on what you have available to you.
Dynos...I've never used one. All you get out of those is a bunch of numbers, and I've seen some motors that did well on the dyno run like garbage out on the track, or go like hell then blow up. When I do motor tuning I always start with two identical brand new motors, go through them both, drive them both, and pick a winner to go racing with. The other one serves as backup and I'll continue to experiment with it until the primary motor starts to wear out. From there on out I just keep going back and forth. I make my motors compete with each other to see what works and what doesn't