Instead of making the temporary culet point with the CAM facets, some cutters prefer to make rolled cone culet point first, then cut the CAM facets to It. They feel this assures them of starting out with a point that is centered on the dop arm axis.

To make the culet cone, set your index gear in free-wheeling, set the dop arm angle to a positive stop, and roll the stone continuously on the lap until no sound is heard. To get a nice sharp point you should carry this process to the pre-polish lap stage. To avoid extra grinding, lower the angle a tenth of a degree with each lap change.

At what angle should you make the finished cone ? The steeper the angle used the sharper and better defined the point will be, but if you make the angle too steep, the lines between the CAM facets will disappear before they reach where the girdle will be. There is a maximum angle for each cone. I recently worked out a few of these on my computer to serve as a rough guide. The highest angle you can use corresponds to the lowest-angle ridge-line coming off the culet after the CAM facets are cut. In the list below are given the maximum cone angles for the number of CAM facets at 41 degrees spaced at equal intervals around the stone, as for a round.

Number of Culet Facets – Max. Cone angle
4 – 31.56°
5 – 35.12°
6 – 36.97°
8 – 38.77°
12 – 40.02°
16 – 40.45°

If your CAM culet will be 43°, just add 2 degrees for a new maximum cone angle. I suggest you stay one degree below the maximum, when cutting.