I have a Covington vibratory flat lap. Can you show a pic of what it looks like? I may be able to help.
Mine works by a pan that has diamond pattern grooves in it. I start with the pan cleaned and put a little water in. about a 1/4 cup.
I sprinkle some 60/90 grit on that and let it vibrate for a bit to make a grit soup. Then put the flat surface of the rock on the mix. Keeping it the right consistency is the trick and you will learn it over time.
I have some "Old timer" powder that helps make the mix a bit thicker so it gets some better adhesion to the flat surface as it grinds. Not needed but it helps somewhat.
How do you know when it's flat? I take and aluminum rod, 1/8" in diameter that is sharpened to a point. Works better than pencil. You can use a brass rod the same way. You use them to mark a tic-tac-toe grid on the surface of the rock you are grinding. The process will grind away all the marks in a matter of a minute or 2 if it is flat. if any of the marks are still there the grinding needs to continue at that stage
if it is not flat continue grinding with 60/90 until it is.
Once flat then you will move on to 220 grit and repeat the process. check for flatness the same way. You grind at that grit until the surface has a uniform look to it where the surface of the first stage is now uniformly smoother.
Repeat with 400 grit
Repeat with 600 depending on the material and how hard it is.
Repeat with 1000 grit.
Last stage is cerium oxide on the polishing pad.
It is important to clean each stage thoroughly between stages.
do not contaminate the polish pad. Keep it in a bag away from other grit material.
While you are grinding each stage it will become like a slurry. Good! It adheres to the surface better to grind better. Just add more grit.
As it grinds you simply sprinkle more of the same grit as it gets worn out and makes a slurry.
Use your ears and listen to your machine. You will get to know the sound when it is grinding correctly and when it needs more grit.
Don't use too much grit. It doesn't help. About 2 tablespoon maybe. You get the feel of it with trial and error.
Do not walk away from your machine and let it go. If it dries out, your rocks will get tossed around kinda violently. Not good.
You can work on other things at the same time but keep and eye on it. I get my rock saw cutting, my cab machines going and vibe lap going all at the same time. I use my ears for all for them
I use ABS and rubber "Fernco" sewer pipe couplers of different sizes to separate rocks that will be damaged by rubbing together as they grind.
I made some lead ingots as an experiment on larger thin slabs for some added weight (I don't know if it's the right thing to do and I haven't tried it yet.
Good luck
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