4 ms·
So what does 'lapping' actually mean? There's a lot of lapping in that process.
by codeulike 6y ago
So what does 'lapping' actually mean? There's a lot of lapping in that process.
- rriepe 6y agoRubbing two surfaces together
- SamBam 6y agoI'm still a little confused. In my mind, if I hold one surface still and rub the other surface on it, it's exactly the same as if I reversed their roles -- the surfaces shouldn't know which one is moving and which is stationary. For example, if I was sanding a block of wood, it wouldn't matter if I moved the sand paper on the wood or the wood on the sand paper. Yet several statements in the article make it clear that my understanding is not correct (e.g. "Next, the Green plate acts as the control and the Red plate is lapped against it," or "Next, the Green and Blue plates are lapped against each other in an alternating manner.")
- mauvehaus 6y agoI'd you look into the community that hand grinds and figures telescope mirrors, you can learn a lot about how which piece is on top and what motion you use influences the shape you get. Of course, they're going for a curved surface, not a flat one, but I suspect some of the same applies. To be clear, I haven't done either :-)
- mhb 6y agoI have ground a mirror and that doesn't provide the answer to his question. Yes - the top glass becomes concave and the bottom convex, but this is symmetrical and doesn't explain what a control surface means in this context.
- bacon_waffle 6y agoBoth surfaces do wear, however any high spots will wear faster.
- SamBam 6y agoSure, but any high spots on either surface should do that, right? I'm still missing why it matters which surface is doing the moving.
- bacon_waffle 6y agoSorry, I must admit to not reading the OP before replying. Not sure what the OP is on about; of course both surfaces wear, the important thing is the sequence of which surfaces are compared/lapped against each other, and how they are oriented. The orientation is quite important - if each pair of plates are always at the same orientation relative to each other (or I suppose 180 degrees from that) then the plates may meet evenly, all having the same twist. Foundations of Mechanical Accuracy is a great book if you're in to this sort of thing.
- mhb 6y agoIt doesn't matter. This will produce three flat surfaces. It looks like he's just using the word control to denote whichever plate is on the bottom. The top plate will become concave and the bottom one convex due to the overhang of the top plate as it is being ground, but that is not relevant here.