Lapping: What, Why and How?

[Empire]

A belt sander is faster

[lieber_Scholli]

@relic38

@Ouchyfoot

I suppose two polished surfaces with compound would create a sort of surface tension.

It does, and that’s why I ‘wiggle’ the star around some to spread the TIM underneath. A good portion will squeeze out the sides, which is a good thing.
I have a few different types of TIM, and I find the thicker, pastier ones harder to get thin.

This is Why We Lap by TheInformationator

You don’t even need TIM to make it sticking for a short time. Once i found a better video with much better surface tension effect, but i can’t find it anymore.

[mattthemuppet]

lapping stars falls under the class of things we do that probably doesn’t make any difference but makes us feel better for doing it

[Gurthang]

Matt,

I almost agree w/ you…. BUT after many pills w/ craters or peaks at the center I wholly endorse at the very least a careful pill sanding to insure at least some degree of “flatness”. I’ve used wood dowels to make sanding sticks w/ a small sandpaper disk glued to the end. Only takes a few minutes to remove peaks or begin to level craters.

[cheaplite]

Maybe everyone can relate to lapping by the ceramic washer-less faucets that are available nowadays. 2 pieces of ceramic are lapped so fine that stop water from flowing without any washers or o rings.

[mattthemuppet]

@Gurthang

Matt,

I almost agree w/ you…. BUT after many pills w/ craters or peaks at the center I wholly endorse at the very least a careful pill sanding to insure at least some degree of “flatness”.

yeah, I was being slightly facetious

I think that for badly machined pills it’s worth doing, although if it’s that bad then sanding isn’t really going to make much difference as sanding is a pretty inefficient way to remove material and there’s a tendency to deepen the low spots by accident. You’d be better off using a cylindrical roughing stone on a Dremel first, followed by sanding to remove the coarse marks.

For two relatively smooth surfaces, I think the difference will be largely undetectable by eye, even if it does help by luxmeter. That said, it’s not going to stop me from doing it

[lightme]

@benz

We lapped on a machined piece of stone (granite?) with a full sheet of very fine wet-or-dry sandpaper and heaps of kerosine to stick the paper to the stone, and to stop the sandpaper clogging.

+1
A small granite surface plate is overkill but a nice investment if you use it often. I bought mine years ago for fixing gasket surfaces on small parts. I don’t know about using kerosene. Granite is somewhat porous so I only use tape and water.

[lieber_Scholli]

This star i lapped today with 1500 grit, 6000 with abrasiv toothpaste, 6000 without toothpaste and finally 8000 grit paper (yes, the toothpaste is more abrasive than the 6000 paper, you can hear and see it). I made this photo and you see the blades of the shutter are not perfectly parallel to eachother, so still not a perfect flat surface.