Confused about rough.

[Gregory]

1. Evaluate the rough for best return of the cleanest part of your rough.
2. What shape is the rough going to cut to achieve #1, round, oval, etc.
3. Cut your temp table say on your 600 lap for later doping. If you need to remove a lot, start with a 180 or 260 then use the 600 just to give a good surface for the doping. (By hand on your machine) if that’s all you have to preform a table surface.
4 After you have your temp table, measure how much height you have for the finished stone. Calculations are always done by the narrowest width of a design (Rounds or L/W 1 to 1 are the width from side to side), ( a 7x5mm oval (L/W 1.4) 7 divided by 5, 5mm is the width of the finished stone.) Use you calipers using your best judgement, and the temp table to estimate the size of stone. Best to stick to sizes or L/W ratios commonly used in published gem cad designs if your beginner.
5. Calculations can be done by using the cad design figures usually in the top section of the design page.
Paper designs, GCS, and Gemcad have slight variations, but generally the same info above the cutting sequences.
Cutting a 7x5mm oval as the example, using the design figures below to evaluate if there is enough material to cut the design.
P/W = 0.423 C/W = 0.167
Formula for calculating: H/W = (P+C) /W+ 0.02 = (Total height)
0.423 + 0.167 + 0.02 = 0.610 (P+C+Girdle(.02)
0.610 * 5.0 = 3.10mm is the absolute needed amount of material form the design at width of 5mm on a design with the above mathamatical calculation vales for pavillion, crown and .02 averaged estimated girdle thickness here would be .02 * 5.0mm = 0.1mm.
I need at least 3.10mm, I typically add 20 -30% to this number for uncalculated issues encountered along the way, surface reaching fractures, inclusions, girdle sizing +/-, just for arguments sake.
Happy cutting, and remember as you get better at the evaluation part of gem cutting you will find that these numbers do not lie and are reliable. You will get the most of valuable rough.