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What compounds for lapping plates?

Mud

Diamond
Joined
May 20, 2002
Location
South Central PA
I have a surface plate gage that isn't perfectly flat, and I'd like to lap it flat. I have a set of 3 lapping plates, but no compound. What compound(s) do I use, and where do you buy them?

The instructions in the lid of the box the plates are in specify dry lapping compound for one plate, Bon Ami for the second and to use the third plate clean and dry. Is that the common practice?
 
I lap small parts occasionally, usually with a grooved cast iron plate and clover 2a silicon carbide compound. It's a oil abrasive mix. Mcmaster Carr carries Clover as well as many other suppliers. Flatness is relative, I don't have a optical flat to test with, my main concern is removing machining marks. If you use dry compound on that first plate it should be at least 400 grit.
 
The only compound I've ever used is Fel-Pro 'Clover Compound.'
A 'grease' compound and a water based is available.
I have a pair of large heavy hand laps.
Used the finer grades of compound to lap in bearing eccentrics in large machinery frames.
John
 
I use dry 600 grit silicon carbide & water based carrier with a planetary lapping machine. That's a 12" diameter cast iron plate, so hand lapping with that same grit and water would do the same. Material removal is very slow, so you might want to start with 400 grit. You can get it from Lapmaster or various others.
 
Whats a surface plate gauge? You mean like a repeat reading gauge?

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One of these.

surface_gage.jpg


I have 2 that are slightly worn, I can make them rock .0001 or so. I think lapping would be easier and surer than fixturing them on a surface grinder, and give a better surface finish.

Thanks for the replies.
 
One of these.

Oh okay, well depending on if it has a V groove in the bottom (less material to remove when lapping) clover compound should be fine.
Or if you want to be real cheap, get some polishing compound sticks, grind them up and mix them with a solvent. Ghetto, but it works in a pinch.
 
Are you going to roll the grit in, dump/brush off the loose material, and lap with what is left embedded in the plate?

If so, you may have a good shot at eliminating a small amount of rocking.

If the idea is to put down loose grit and work with it floating/covering the surface, i'm not so optimistic. Loose grit tends to cause convex surfaces to develop on the work, on flat laps.

smt
 
Wet/dry sandpaper wetted on a small surface plate has worked for me. I start with 400 grit and down to 1200 if needed.
Use a pattern that uses the whole sheet

not saying it can't be done, but I'd like to see a very faint blue hit on a good surface plate on the finished result.

Best if the work overhangs the lapping matrix most of the time, but in a very random pattern.
smt
 
Paper on plates is not a good idea. It bows up, rounding the edge of the work and has never produced even a decent flatness for me.

You can also use knife sharpening oilstones and whetstones for flattening the surface gauge.
 








 
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