Working with marble.

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michdad

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Apr 24, 2007
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I have some large pieces of one side semi finished marble slab that I would like to lap together and use as precision working surfaces. The slabs ain't square, big one is 38X19, small piece is 16X10, and one in between. What I want to do is hand finish the top surface of each slab.
What should be used as a lapping coumpound to get a nice finish?
Matt
 
I am not sure how to finish, but in town here there is a counter top place that regularly throws away big pieces that are already finished. I think most counter places throw out drops and you won't have to do any work to them. I have picked up several large pieces that are very nice.
 
marble is probably too soft for extended use, granite would be a better choice. look for some tropic brown as it is an especially tough stone but most any darker granite should work for you.
 
Yeah that is what I picked up is granite. The shop is called something like Granite Tops Plus. Hard stuff can't scratch it when using a razor knife on it.
 
You are taking on a big job with uncertain results, but if you want to try to lap the smaller piece on the larger one:
use loose grit silicon carbide - get it from a lapidary supply or on Ebay.
Start with 100 grit and put a small amount on the plate and add a tsp of water and a squirt of dish soap. spread out and start lapping. Apply even pressure, and don't go beyond the edges more than 1 inch.After the surfaces are evenly frosted, clean well and switch to 220 grit. Repeat. Then 400 grit ( or finer). If the plates are for lapping with sandpaper and such, they don't need optical polishing.

Another way that might work for just making then fairly flat is to use a ceramic or diamond flatting stone. They are used to true up water stones and come in 3X10 inch sizes. Use lots of water and work the entire surface with the flatting stone until it is evenly frosted. They are usually 100 grit or so.

Your post brings back memories of grinding and polishing an 8" parabolic mirror for a telescope back in the 80's. It took many weeks.
Stacy
 
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