I read a lot in the internet about using laps made of resin to cut stones. Again there are a lot of vendors offering such laps, but I wanted to try my luck in casting resin myself and in the same time adding diamond powder to have the particles embedded into the surface to have a long living lap. As my coarse laps become worn out too fast I decided to order a 120 grit powder. The coarse grain I thought would also not be too much sensible about accuracy.
As resin I ordered a clear epoxy based one with a hardening time of 48 hours together with the appropriate hardener. The setup was planned as following: First, use a very accurate plane ground as base, where the powder should be distributed upon first. I chose a mirror:
On this mirror I put an accurate ring of tin, which is a left over of the trimming of my tin lap with my mill. Then I distributed the coarse powder on the mirror and mixed resin and hardener:
Here's a short video describing the setup step by step:
Then I did the casting as explained in the video and waited for two days as described in the instructions of the hardener. Indeed the resin was still not hardened out before the second day. Then I started the crucial part, which is removing the mold. And what happened? Nothing, it was sticking like a block of concrete. No movement at all. I tried around and could manage to lift the aluminium plate slightly off from the resin. But for the mirror on the ground there was no gentle way to remove it. So what I did then was just to risk to brake it. And it broke. Still, only single broken pieces of the mirror went away from the resin:
Additionally, I figured out that so much resin ran out that some kind of a bubble was present under the aluminium lap. Meaning, that even if the mirror would have been not sticky, the lap would not have been usable. And a third show stopper was the fact that the diamond particles where not reaching out of the resin's surface, but seem to be fully included into the resin, which sets the abrasiveness to zero.
So to summarize, I need to first find a solution to tackle the following three challenges before doing another try:
- Find a way to make the even base plane not too sticky for the resin. Maybe a metal plate like aluminium would be fine here, or use some substance (like oil or similar) to cover the base first.
- Fix the ring on the plate in a way so that resin can not run out. This issue seems to be solveable.
- How (or when?) put the powder on the surface of the resin? Ideally the particles sink partly into the resin so that they are fixed well and scratch the stone well.
This is where I am right now. I'm hoping to think through to a feasable approach.
Will keep you posted!