how to charge plates, substrate
Bill Tindall, E. TN
>It would be good if someone that does lapidary work would answer this question as they would have more experience. I'll say what I do but it may not be best, or even normal.
For the paste, I squirt about a 1/4" "worm" on the top of the plate and pull it down the plate with a gentle stroke of that to be sharpened. after sharpening a while it gets "dry" and I add a drop of mineral spirits to float some of the gunge away.
I have yet to use the powder as I have not run out of my first 5 mL of pastes. I was told by the company that sells powder that they charge their lapping plates with powder slurried in olive oil. My theory is that diamonds were historically polished in middle east so olive oil was a handy choice, but there my be a more scientific reason. Anyway, olive oil is an essential ingredient of pizza dough so I will always have some available. So, I guess when that day comes I will add a smidgen of powder to the plate plus a drop of oil and grind away. It takes but an astonishingly small amount of diamonds to be an effective grinding media which is why my tubes of smaller grit paste will last forever.
Substrates: I have used cast iron, copper,a worn out diamond "stone" and a piece of beech. there are all kinds of cast iron surfaces around the shop and I have employed several of them in addition to real surface ground cast iron plates made from cast bar stock. Historically cast iron is what has been used for a substrate for cutting diamonds so I presume it best.
the worn out diamond stone seems to be a bit too hard, at least for coarser grits.
the copper(an old circuit board) was not sufficiently flat but it worked ok
the beech took a lot of diamond to charge it. Compared to cast iron it cut like it was charged with a 2-4X smaller grit size. theory- diamonds embed deeper and hence "appear" smaller. I suppose MDF would work similar to beech but I have not tried it.
When I can get some I want to try plexiglas, or polycarbonate sheet, but I expect the embedding effect I saw with beech will show up here too.But I expect it will take less to charge.
I have not explored these issues thoroughly. I'll bet the lapidary folks know all that is needed to know about the topic. I can say that compared to anything else I have tried, diamonds on cast iron is very fast and very cheap, discounting the cost of the cast iron (I got my plates for free). We are investigating a source of long wide plates that we think will cost about $20 each. Will post results when we have them.