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Old 10-11-2020, 04:28 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 22,177
Pete VanderLaan is on a distinguished road
There are two primary things that can go wrong with a lap. If yours is a later model, it has holes partially drilled in the grinding face. As the tool gets dished, which it will fairly easily, lay a good straight edge across that face. You don't want to see any daylight- none. If you do it means a trip to a good machine shop preferably with a blanchard mill. A blanchard will grind it flat fast and then when you get to look at those holes in the grinding face, a bunch will seem a lot smaller. They are. But the good news is it will work again for a while but the same thing is going to happen. You can do this until the holes have essentially disappeared. What you have to be really careful of is chucking it up in a lathe. Cast iron is soft enough that an overzealous worker will chuck it down too hard and it warps slightly. Then it gets ground flat but is warped once the pressure of the chuck is released. How might I know that you could ask. That's when I converted mine into a cerium polisher with a rodel pad. That seems to work forever....
Unless... there's a bearing in the bottom of the tray and there's a bearing surface that those little nylon .625 balls ride on, and there are the little bearing cups that get lightly oiled and those nylons sit on a little steel plate that gets grooves worn in it. When the grooves get bad, flip the plate and you will get more life out of them .

The nylon balls will go bad pretty quickly and develop a flat spot. They will need replacing sooner than later. The net effect of the wear is that the machine begins to speed up, skipping along the defects. A good lap is a slow machine. Now it's important to look at the bearing surface of the actual plate. It should be baby's butt smooth, no grooves at all.

The last thing to go bad is the center bearing which you can get at any machine shop. You will need a keeper pulling tool to get the bearing race out but it's not really difficult. If you wait too long to do that, then the bearing is no longer going to fit in the bore in the big polishing plate and it will slap around. Then, you would need to overbore the plate to fit an outsized bearing.

Everyone of these issues is serious and needs regular attention. The parts can be gotten from HIS or from Covington. At one time, I was running a buying club from Jack Rose who designed these things. Jack sold out to Covington and I set up the club with them. Robert Stephan at HIS complained loudly to them since he was making money on them and Covington refused to sell to me. That's why Stephan isn't welcome around here. I was running a service and not making a dime.

I have an address for a place that sells the nylon balls. I bought 1000 of them. With all my machine tooling, I just had a machine shop on retainer. The good old days. I'd buy Rodel pad material in fifty yard rolls five feet across. We polished a lot of stuff. Six of them running, 24/7.
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