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 Post subject: Re: Preforming - How much do you do
PostPosted: Thu Nov 30, 2017 2:46 pm 
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Precision Gem wrote:
I use wax too, for the same reasons mentioned, and it's always simple and quick to remove the stone from the dop.
For preforming, I'll use depending on the size of the rough, anywhere from a 100 ripple lap to a 360 lap. Once on the dop, I'll spin or very roughly cut a tier or two with the 360 before doing all the finial facet placements with a 1200 sintered lap.
I don't use 3000 diamond, but prepolish with 8000. A heavy charge of 8000 will certainly move facets, yet gives a bit better finish than 3000. Finial polish is with either oxides or diamond.

I think 600 to preform is way too slow, and using 3000 for facet cutting would take way too long unless you preformed to the extent where the stone was pretty much final cut. I know many cutters overseas do a preform that look almost like a finished stone.


Whether you know it or not, reading about your experience with wax was the reason I initially tried it. Started from the beginning with black wax and have been a happy camper ever since. So thanks! :D

thomas.adamas wrote:
Precision Gem wrote:
I think 600 to preform is way too slow, and using 3000 for facet cutting would take way too long unless you preformed to the extent where the stone was pretty much final cut. I know many cutters overseas do a preform that look almost like a finished stone.


The cutting speed would depend on the concentration of diamond in a sintered lap. Low concentration = low stock removal
I use a hard metal bonded 34 micron (close to 600 mesh) sintered diamond lap with 100% concentration. Preforming goes very quickly, even on corundum.


Using your 600 has been a similar experience for me as well. I find the finish is fine enough to go straight to a 3000 (old diastik) batt, but the cutting is fast enough that I can start from this lap. I only just recently had a piece of rough that I could have probably shaved 30 mins to an hour of cutting time off with something a lot rougher, so I've added that to the wish list haha. I'm gearing my whole setup to corundum and most are small enough that the 600 does one hell of a job.

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 Post subject: Re: Preforming - How much do you do
PostPosted: Thu Jun 07, 2018 11:38 am 
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I don't like preforming.

To do it correctly takes experience and very good understanding of the angles involved, as well as superb hand-eye coordination.

I find that whenever I try it, I end up dopping the thing a bit off, and have to cut to get it squared up, so it seems a bit wasteful.

It's also kind of hard on the fingers, though at least the speed control keeps the stone from flying, generally.

I think one would have to have a really efficient grinding lap for it to be much fun, and rough over 1 cm or so, or it's too much hassle.


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 Post subject: Re: Preforming - How much do you do
PostPosted: Thu Jun 07, 2018 12:00 pm 
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Preforming and doping is where most money is made or lost in stone cutting. In most shops I know where high value rough is cut the owner or a preforming specialist does this work. More and more scanning planning machines that were originally designed for diamonds are being used. I preform pretty close to my desired shape, and depths. This allows me to accurately work with the rough shape, position inclusions, and deal with any color issues. Then you can reliably position the stone on the dop within a few 100ths of a millimeter in accuracy. This saves a lot of weight.

Do you use your target dop when dropping your stones?


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