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Posted in response to Graves Mark IV from Justin on September 18, 2010 at 16:23:21:

Re: Graves Mark IV

Hi Justin,

Here is an article on faceting machine alignment you may benefit from:

http://rockhounds.com/oplc/cd_online/faceting_articles/paul_head/alignment.html

Peter Erdo at Graves should be able to give you an idea of when your particular serial number was manufactured.

If your transfer fixture is the original Graves unit that came with the machine, it may not hold dops concentrically. The casting on mine warped, I assume after the v-grooves were machined in it, causing an alignment issue with the transfer. A more robust transfer fixture is something you may want to consider if you are working with the original fixture.

One of the most critical alignments you need to check is that the plane of the sweep arc of the head is parallel to the plane of the lap surface. If not, you will suffer a spiraling effect as you cut.

You can check that alignment by dopping a piece of practice rough and grinding a small face on it with something in the neighborhood of a 240 grit lap. Then adjust the elevation until you can just barely hear a tic-tic sound of the rotating lap contacting the stone. If that tic-tic remains constant as you sweep the stone across the face of the lap from one side to the other, you are probably good to go. It's important that you do not exert any downward pressure on the stone with your hand as you execute this test (which will flex the head, dop and even the mast if you press down hard enough).

Another article you may find useful regarding cutting technique applicable to the Graves is:

http://rockhounds.com/rockshop/gem_designs/cutting_by_ear.shtml

There are a number of issues that can cause the sweep arc to be out of parallel with the lap face. If you are having that issue, or others, I strongly encourage you to join us on the USFG Faceters List to discuss and solicit advice regarding them:

http://www.usfacetersguild.org/faceters_list.shtml

May all your scratches be little ones!

From Bob Keller - September 19, 2010 at 11:42:33

Message: 69388



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