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Author Topic: Just to get you thinking - Funny L/W Ratio  (Read 1630 times)

FlashGP

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Just to get you thinking - Funny L/W Ratio
« on: December 01, 2017, 09:16:01 PM »
Here's a question about the Gemcad Ratios. 

I designed a long rectangle in blue corundum (MM).  it is 5.9mm wide by almost 16mm long.  I dopped the rough at 45 degrees to the horizontal figuring it would force me to rotate the design to suit the stone.  I then rotated the design to give me the correct cutting indexes.

When I went to check how much to leave for the crown, I noticed the ratios were very small, the C/W ratio being 0.013 and P/W being 0.042.   The volume/W ratio was under 0.03 and L/W 1.0.

Anybody care to explain what happened to my stone?

PS. I know the answer, but had to stop and think about it last night.
Yours Sincerely
Flash (Gordon)

Rej

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Re: Just to get you thinking - Funny L/W Ratio
« Reply #1 on: December 05, 2017, 11:15:56 PM »
L/W are lined up with up/down. By turning a long rectangle by 45 degrees you made it diagonal and thus both extents (X-Y) became equal.

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FlashGP

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Re: Just to get you thinking - Funny L/W Ratio
« Reply #2 on: December 06, 2017, 06:45:10 PM »
Spot on. 

A nit of a trap for the unsuspecting.  I had to think about it at first.

For the same reasons rotating a gem in Gemray gives different results.

 I have yet to test if non round designs need to rotated to the direction they are likely to be set before optimisation.
Yours Sincerely
Flash (Gordon)

Ghost

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Re: Just to get you thinking - Funny L/W Ratio
« Reply #3 on: December 07, 2017, 08:35:10 AM »
Hi FlashGP.
Need help producing a perform.   Don't have Gemcad.   If I give you 12 index numbers; 3 pairs that will produce triangle points and 3 pairs that will produce the flats between the points, (looks like a cushion triangle), can you provide two fairly low angles that will produce equal length girdle facets from a central culet?
The pre Gemcad instructions are to cut the girdle at 90 degrees and measure as you go for equal length.   This method is both tedious and not very accurate.
Thanks.   Regards,   Ghost.

Tags: Gemcad Ratios 
 

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