Novice Single stone competition

[PINO43]

I would like to know if I am doing the calculations right for the Novice stone competition:
If the size of the stone that I plan to cut is 10mm (10mm-12mm)
Based on the measurement given:
L/W = 1.155 = 10 x 1.155 = 11.55 L=11.55mm
H/W = 0.776 = 10 x 0.776 = 7.776 H=7.776mm
T/W = 0.5 = 10 x .5 = 5 T=5mm
P/W = 0.506 = 10 x 0.506=5.06 P=5.06mm
C/W = 0.250 = 10 x 0.250 = 2.5 C=2.50mm
Adding P + C = 7.56 mm – and H= 7.776 mm I am left with 0.216 mm for the griddle.
And the griddle size is suppose to be 0.5mm +/- 0.03mm
Are this calculations right?

[Frankwood]

You don’t need to worry about the girdle thickness till you start cutting the crown. Just make sure there is plenty of height in the piece of rough to leave plenty of material after transfer dopping. That applies to every stone you cut.
There is a loupe you can buy with a measuring scale on the lens. Forgot the name of it, but I would recommend getting one if going into competitions.

[Lowjiber]

@PINO43… You didn’t provide the height of your pre-formed rough. Attached is a little spreadsheet that I made to do the math quickly… Just fill in the six yellow boxes.

Good Luck with the cut. 🙂

John

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[Alan Balmer]

The height ratio on the diagram is based on an arbitrary girdle thickness of 2% of width. Ignore it, as Frankwood says, and cut to the thickness specified. For measurement, there are magnifiers with measuring reticles available. I have an excellent Bausch & Lomb Lenscope, unfortunately no longer manufactured, but they may be available used. They’re pricey. I got mine many years ago, at employee price.

What many people do is find a wire or drill bit of the proper thickness for visual comparison. That’s plenty accurate enough.

[PINO43]

Thank you for your response.
The measurements I provided are the ones given for the novice competition this year. I will cut a 10mm stone (the competition instructions are 10mm-12mm)
The competition’s guidelines are:
H/W = 0.776 H= W x 0.776. H = 10 x 0.776 = 7.76 mm
C/W = 0.250 C= W x 0.250 C = 10 x 0.250 = 2.50 mm
P/W = 0.506 P= W x 0.506 P = 10 x 0.506 = 5.06 mm

I assume that H = C + P + Griddle

H = 2.5 + 5.06 + 0.5 = 8.06 mm
Competition’s height – 7.76 mm. 8.06 – 7.76 = 0.3 mm
So what you are saying is that I can be off 0.3mm in the total height of the stone without being penalized during the competition.
Thank you

[Alan Balmer]

The only size criteria for the stone is width to be 12mm+/- 0.3mm, girdle thickness to be 0.5mm +/- 0.3mm. The L/W is also calculated, but if your width is right and you cut to the diagram, that’s automatic. Total height will not be a factor for judging, but that too is automatic if you cut to the diagram and get the width right. Study the sample judging sheet.

[PINO43]

Thank you. I’ll do that. 🙂

[Author]

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