Boba Debt Posted August 22, 2007 Share Posted August 22, 2007 I have been processing some Uruacu for a Garimpo (Philip). As part of our agreement he said I could have enough material to make a 50mm sphere. I processed a 7kg rock and easily got my sphere rough and it looked like it was going to make an awesome sphere, it was loaded with inclusions and all of the end cuts and slices etched really well. I sent the rough to my machinist and then the project went south. He uses a 5-axis milling machine to turn my rough cube or core into a rough sphere with a clamping nub. Normally he's able to machine a sphere with a single insert, he had already gone through 4 inserts when the sphere sheared off the clamping nub and flew out of the fixture. He tried to epoxy it into his fixture but it didn't hold so with nothing to clamp to he had no choice but to send it to me as is. I contacted John, the guy that makes my Chondrite spheres and asked him if he could finish the job. He said he could grind it in by hand and then polish it on his 3-head sphere machine so I sent it off and waited more then a month. He was able to finish the job but he couldn't keep it to 50mm. The machinist cuts it to .010" over 50mm which is fine for me to polish but it didn't give John enough material to work with so it ended up being 48mm. That doesn't sound like a lot but when every other sphere in my collection is 50mm it makes it stand out A LOT. Another problem was the finish was not up to par for etching, I guess the included material mixed with the grit and caused a lot of scratches. Normally I have the nub on my rough sphere which I chuck in my drill press and this makes the polishing process very easy. Well, John sent back a sphere with no nub and a finish equivalent to what you get from 80 grit sand paper. I thought about it for a while and determined my only option was to epoxy a bolt to the sphere to act as the drive nub, it worked well and I spent about 30 minutes polishing it up to 600 grit and it looks fantastic Which is just another reason to be upset, it's going to finish out to a beautiful sphere but it's too small, so it's not a keeper. Philip was kind enough to allow me to use the only remaining piece that's large enough for a 50mm sphere for a second attempt so now I have to start the process all over again. If it's successful I will try to sell this one but I'll never recoup the money we would have made selling it as slices, but Philip is a great guy and doesn't seemed to be bothered by that. Quote Link to comment Share on other sites More sharing options...
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