Forums Article Discussion Incorrect angle

6 replies, 4 voices Last updated by  gemcutter1 1 month, 2 weeks ago
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  • #5342

    gemcutter1
    Participant
    @gemcutter1

    I am trying to cut the Antique Oval by Nancy Attaway. The #1 cut on the pavilion is wrong. I tried a number of angles and 45.93 seems to work. The 52.93 is wrong.

    #5343

    gemcutter1
    Participant
    @gemcutter1

    I was continuing to cut and the #4 cut came out wrong. The angles for this stone are wrong. If the # 1 cut is correct, then the #2 & 3 angles are wrong.

    #5344

    JTheesfeld
    Participant
    @JTheesfeld

    Gemcutter1

    GemCad typically does not lie. This cut works as shown, with the angles listed, but you may need to use a different process to get it right. This is not at all uncommon.

    This design is the perfect example of the value of using the CAM method to cut a gem. CAM is “Centerpoint Angle Method” CAM for short. The sequence listed for this gem results in an estimated facet length when going from G1 to 2. It is not “meet-point” faceting friendly as shown. In order to cut this gem in 100% meet-point fashion, you would need to re-sequence (not the best way), or use a CAM preform.

    CAM Design

    If you learn to use the CAM preform, you will establish the exact girdle outline first, by using temporary center-point facets, which will be eventually, cut away. I use this method all the time, to avoid the situation you seem to be describing with your efforts. This does require you to use GemCad, or GemCutStudio, to create a CAM preform design first. I completely recommend this to everyone.

    I suspect that when you cut your #2 tier, that you had to estimate your G1 length, which is inherently inaccurate, thus causing the angle issues you describe.

    I hope this helps.

    #5384

    gemcutter1
    Participant
    @gemcutter1

    I tried three times to cut the Antique Oval by Nancy Attaway. The pavilion cut #2 at 45.64 makes the cut too narrow. I tried 48.64, still too small. I then went to 47.64 and it seems to work. I cut the stone and everything looks correct.

    #5385

    Hi, for those that trust their faceting machine and like meet point, re-sequencing is an easy fix. I left the old sequence numbers. It would also be very easy to create the preform steps to create the Girdle Outline first. Then all the GMPs and finish up with nice meetpoints.

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    #5388

    Alan Balmer
    Keymaster
    @alanbalmer

    Dennis, do you know whether Nancy has released this to the public domain?

    Never mind – it’s already in the USFG database, so the answer is yes.

    #5389

    gemcutter1
    Participant
    @gemcutter1

    I give up. I am not the sharpest tack in the box, but I spent 2 days trying to cut this stone. It is a good thing that I used synthetic to cut it so It doesn’t cost much to throw it in the round file. I learned meetpoint faceting 8 years ago and I think that I will stick to it. Thank you for all your help.

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