What is the best insulation to use when rebuilding a roller
Why insulate it? it need to complete a circuit to earth 4 times in a rotation.
Not the roller the timer cover the roller rolls on.
I think Dean means the composition of the ring inside of the timer case. I'd like to try rebuilding timers and have often thought about how to go about it. I think the perfect material would wear at the same rate as the metal used for the contacts. I was thinking about trying Garolite.
Kerry - The four contacts are bedded in the insulation. The contact posts are also insulated from the timer case. The roller provides the ground. You want it ground only when the roller touches the contact. Otherwise, the coils will "buzz" all the time.
Dean - Some were a hard fiber type insulation and some were a hard plastic.
Richard and I were typing at the same time. I couldn't remember the name of fiber material. Garolite is it. It comes in several densities. McMaster Carr carries it.
How about Delrin?
I had contemplated the same idea. I'm just not sure how one would mill the recess for the curved contacts. Even the smallest gap between the contact and the insulating material would make for a bump in the roller track, probably leading to bounce and wear.
I have often wondered if there was something along the lines of an epoxy or something that could be poured into a mold as a liquid and then harden. If you fixtured the contacts in the proper position, a little lathe work would clean it up. However, I don't think regular epoxy would do the trick. Whatever it is, it would have to be non-conductive and wear resistant.
Hal, don't you suppose someone could cut the recesses on the insulating ring on a mill with a cutter and cut the curved contacts on a lathe from bar stock so the curves match. The hardest problem I see is cutting out the curved contacts from the turned bar so you can cut both the ring and contacts on a lathe at the same time. Of course you have to attach threaded studs to the contacts and mount them with insulating washers and nuts to hold everything in place while you cut the race. Like a lot of machine work, it sounds easy until you try it.
There's some mineral filled casting resins that approach the hardness of thermoplastics. I would think those would work. Of course, you would need to make a mold.