Cutting Commutators
By John Havlicek
Considering how much the comm wears and how important it is to the way the motor runs... a commutator lathe really is a nice thing to have. When winding arms (especially with vintage comms), I can be sure that they're starting out in good shape.
The Integy Xipp lathe I got came with the V-blocks shown and it really was quite easy to set up and came with lots of good information and about all you need to get going.
My first experience with the machine (I'm a newbie to comm lathes) points out a few simple things:
1) Sit down and spend some time looking at how it all works and reading the literature before even starting-in
2) Pay attention to the cutter setup. They do give you a "normal" setup, but in the end you have to go by the cutter's position relative to the front clearance cut on the V-block as well as always being just above the centerline of the arm shaft where the cutter contacts the comm.
3) Take small cuts... as small as you can and do a complete pass at each depth. The cutter may not cut at one end of the comm but it very well may at the other.
4) The arm shouldn't be turning too fast and doesn't need to. I did a couple of test arms and settled in at somewhere around 6v on the power supply as a comfortable speed.
5) Set the travel limit stop to safely avoid contacting the com tabs. I don't know how bad it would be to hit them... but it seems as though it would be a major boo-boo.
6) Use a slow but steady/smooth feed rate.
7) Keep a bunch of arm spacers of different widths handy to set the arm between the V-blocks with a tiny bit of play. The Teflon washers that come with the machine won't work with slot car arms.
8) Take the belts/o-rings that you'll be using to the hardware or auto parts store and get a few extra. They're cheap and just having them in the storage box means you're ready. They seem like they'll last a long time, but everything wears out.
9) Practice on some junk arms... it won't take long to get a feel for what's going on, but better NOT to figure it out on a rare vintage arm.
10) There's absolutely nothing wrong from what I can tell with carbide cutters. Brass is very soft compared to carbide and carbide can be touched-up with diamond hones that are inexpensive, and then tossed when they finally won't produce satisfactory results.
This was a Kirkwood com that was almost a polygon.
I DID also buy the diamond bit. I just figured I'd get a feel for how this all works by using the carbide cutter for a few coms and then ease-into the diamond cutter keeping the carbide cutter as a back-up if I chip the diamond one...OOPS!
So I installed the diamond bit and took a minimum cut (after marking the com) to see what effect if any this would have on a brand new arm I just wound (45T/# 28 AWG). After the cut, the arm sounded better and drew less amps. A positive result!
