Yay!
I found the technique I used with the 100 grit stone to be frustratingly slow. But considering how alarmed I was at the speed the 100 grit cut when the stone was to form, this wasn't a bad thing.
I'm now sure that a sanding step is needed. I was able to get rid of most of the ridges but not all. Even if the cutting was slower, I found that if I persisted at trying to eliminate the ridges on the 220 wheel, I ended up making more ridges and taking off more than I wanted.
Use of the 220 wheel and a lighter touch prolonged the lifespan of the carbide sanding disks, but not by much.
I found the 400 grit to be too aggressive. I attribute this to all the grinding on the 220 wheel. In general, the closer to form I get the rock the faster any given grit will cut. The 400 grit disk was not anywhere this aggressive when it was dealing with much more carry over work from the 220 grit sanding disk. I have a few more 400 grit disks to test this assumption.
The 600 grit disks worked well. I suspect that they may work better when they are not correcting the problems introduced with the 400 grit disks. I'm irritated that I screwed up my last order and only bought two disks. I will have to get some more.
My question now is: Do I test a grit somewhere between 400 and 600 grit? Or try something between 600 and 1000 grit?
I'm well pleased with the tripoli. After finishing with it last night I brought out a finish similar to the cerium oxide finish I got on my first stone. When I moved to the cerium oxide after the tripoli I achieved a finish that displayed a pleasing depth in the stone. One stone in particular shows clear layers of cream with a window into a transparent center. I can only imagine what these stones would look like if I had worked the bottoms.
So, what is my progression like?
1st stone: Some rounded facet like tables all over the cab with a nice shine
2nd through 3rd: No faceting but not symmetrical. Some stones have a dome that have a full curve on one side and a shallow one on the other. One's edge is a nice oval on one side and has sort of a fatter bottom on the other. Nice polish on all.
4th stone: This was a problem stone that I didn't think I'd do well on but still wanted to try. It was some grayish white soft material with mica throughout. I tried working it from the edge as this caught all the mica chips on the edge giving a glittery appearance. The soft stone cut alarmingly fast and I was only able to bring up a soft luster on the dome. The attractive glitter does not show up in the finished product. The next time I find a rock with many mica chips in it, I'll work it from the side where the full face of the mica chips show as those edges took a better polish.
As I'm concerned about the state of my 100 grit wheel, further grinding will have to wait until my dresser arrives. However, my templates (from a different supplier) have arrived and I'll try my hand with the trim saw.
Update:
After looking around it appears that the finer carbide sanding pads come only in 400 and 600 grit.
So I'm going to order a bunch of 600 grit.
Considering how it is looking like I will be able to get away with one sanding step, I'm also going to order "How to Use Diamond Abrasive" by Riggle.
Hmm, that reminds me, I should mention the books I picked up along with my grinder.
"Cabochon Cutting" and "Advanced Cabochon Cutting" by Cox
"The Art of Gem Cutting" by Dake
All of these books are quite dated (especially the Dake book). However, what modern books I've found on this subject tend to have a great deal of fluff. Even if they are dated they still have useful hints and pointers. I'd have to say both of the Cox books have more useful info on cabs.
The real issue on cab books is that beyond a few specifics, the actual act of cutting and polishing cabs appears to vary greatly between cutters. An example I've seen several times is how cutter A claims one polishing agent is the best for whatever stone. While cutter B is unable to get any luster from cutter A's polishing agent, but gets wonderful results from a different agent.
So it would appear that anyone who wants to learn to cut cabs must put in time and effort actually cutting stones in order to discover what works best for him.
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