Australian Facetors' Guild Limited

Concave Cutting

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  • 24 Nov 2019 8:35 AM
    Message # 8136454
    Anonymous member (Administrator)

    To all Facetors would you like a (Concave Corner) put on the AFG web site , here I will put some concave cutting instruction every now and then along with the photo, you can also send me your cutting instruction with the photo to be placed in this area if you wish.

    pass the word around to your club members 

    lets see what happens,  Now over to you


    Ed   Webmaster

  • 25 Nov 2019 3:43 PM
    Reply # 8137801 on 8136454
    Anonymous member (Administrator)

    Great idea Ed,

    I'll kick it off with a photo or two. i didn't cut these, they are test cuts for the 2020 IFC  

    The clear free form has concave pavilion facets, the fan shape one is the Montezuma Concavia. The designs can be found in the 2020 IFC schedule.

    The pink CZ is from the 2019 Annual Comp. cut by Barry Chapman


    3 files
  • 26 Nov 2019 6:20 PM
    Reply # 8139671 on 8136454

    Hi Ed,

    It's a great idea, I didn't know we had a section of the website for information on faceting other than that under Beginners or a couple of videos.

    I think that the forum is also a great place to keep this type of information if it can be subdivided by subject matter.  This would allow members to directly contribute information.

    Perhaps we can encourage the use of both media.



  • 03 Dec 2019 9:39 PM
    Reply # 8164654 on 8136454

    I enjoy the challenge of Concave Faceting and just following any diagram to see the sparkle at the end. There is a real challenge when you cut an ordinary cut then lay some Concave on the Pavilion to change the look and sparkle of the stone. John put a couple of photo's of one of my repair cut's in F.T 229 along with the cutting instructions for the Concave. I did not want or need the original cutting instructions as they destroyed the stone, read the paper through the finished product, read the article. Feel free to contact me for any problems that you may encounter.


  • 04 Dec 2019 12:40 AM
    Reply # 8165975 on 8136454

    Finding this whole aspect of concave faceting info very interesting, while I've not actually done any concave faceting, I do have access to a machine to try it out.

    Looking forward to seeing more information on the whole process, especially for those of us who are beginners in this aspect of faceting.  Thank you for making this available.

    Glenn Wood

  • 04 Dec 2019 7:22 AM
    Reply # 8168721 on 8136454

    Hi Barry,

    One of the challenges for me with concave cutting is alligning the dop to the centre of the cutter.  Any misalignment results in lopsided facets on a brilliant cut.

    I made my cutter so I can adjust the cutter position in increments of a couple of hundredths of a mm and can adjust the mast stop.

    I currently allign the cutter by cutting down a facet on a prepolished SRB and adjusting the cutter position until the facet looks alligned.  But a step cut will produce a tilted facet boundary rather than a level facet boundary.  I suspect this is because the quill might not be exactly parrallel to the cutter.

    I currently allign the quill stop by sighting a laser level beam down the cutter and quill.  It's a course adjustment Method due to the beam width.

    Do you have a method for fine tuning the quill stop position so that it is parrallel to the cutter?


    Gordon Perkins.

  • 04 Dec 2019 4:10 PM
    Reply # 8172167 on 8136454
    Anonymous member (Administrator)


    Why not try aligning it with a long dop? Insert a long rod (twice the length of an ordinary dop) into the mandrel collet and into the quill collet, lock it all down, it should all be aligned? If the collets are different sizes, machine the rod down to suit. As long as it it's machined true to the centres it should work? Slide the mast back then insert the stone dop & away you go? Or two separate rods, manipulate so they line up on a straight edge at the sides & top & bottom. Take a look on YouTube how they set up the Fantasy machines & Poly-metric machines.


  • 04 Dec 2019 6:25 PM
    Reply # 8172948 on 8136454

    Thanks Paul,

    I was afraid that is the only way to be sure.  I'll have to get some 1/4 inch brass and make up a long dop.  My machine uses a cam lock to hold in the dop.



  • 07 Dec 2019 10:05 PM
    Reply # 8204032 on 8136454

    With aligning the mandrel to the facet that is to be cut is easy if you use oil on your mandrel and have a micro adjuster for the quadrant as the hard stop for control of you sideways movement. As I have a VJ machine with a concave attachment and there are lots of adjustments, up, down, sideways and cutting head adjustments left and right by degrees. A good demonstration goes a long way to lifting the fog.


  • 29 Dec 2019 8:29 AM
    Reply # 8408827 on 8136454

    There's a good article on concave cut stones by Suzanne Wade in the Ganoksin Jewellery Community email of 28 Dec 2019.  In it she mentions the light scattering effect of concave cutting:

    - enhances light colours that are otherwise washed out in brilliant cut stones;

    - darkens dark highly saturated stones like many pyrope garnets;

    - reduces the bow tie and fish eye effects; and 

    - reduces windowing in lower RI material like quartzes, berryls, topaz.



    Last modified: 26 Jan 2020 10:06 PM | Anonymous member
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