I'm sure guys with experience using this tool do repairs quite easily
@ 6000 RPM. I imagine many know how long to apply the disc without turning the metal blue, but I've read some use the blued metal as a gauge. I tend to look at what Timothale wrote as a better starting point.
No need to do more when less is sufficient. I may be wrong, but I think
the 2,000 - 3,000 Rpm range would be adequate. At any rate, the drain cover/plates I've found on-line are roughly about half the thickness of what Wray's discs are. About 20 gauge is the thickest I've found mention of so far. That should be a little easier to increase the indentation for the grinder nut - still pretty hefty for a hammer blow I think. But if using a drill, it should only take a thick washer, maybe double nutted on the backside (toward the chuck) before it's ready to go. Beware, some of those drain plates are chromed plastic.