How Should A Gemstone Contact A Faceting Machine Lap?

Question

I have a question I hope you can answer for me. Recently, I was cutting a stone and watching it contact the lap of my Graves Mark IV faceting machine. As I moved the stone, I noticed that contact was not consistent across the width of the lap. While the stone wasn't making contact with the lap toward the center, near the arbor, it was contacting the outside portion of the lap.

I thought the stone being cut should make contact across the entire width of the lap. Is that correct? If I need to adjust my faceting machine, can you give me some tips for completing that task?

Thanks,

Phil DeHart

Answer

Here are two IGS lapidary articles that will help you. The first, "Scratches From The Master Lap," is quite lengthy. Nevertheless, it covers just about everything you'll need to know about adjusting your Graves faceting machine. The other, "The History of the Beale/Woolley Depth of Cut Indicator," covers an inexpensive accessory that will make your faceting machine more accurate.

Regarding how a gemstone should contact a lap, let me point out that a flat lap to dop swing isn't necessary. I learned to cut that way, but when my Ultra Tec faceting machine developed a slight tilt, I left it alone. I actually prefer it that way! The trick is to always finish cutting at the same point on the lap. I use the spindle nut as a reference. I finish cutting with the dop pointed at the center, using just short swings as it gets close. This is a good practice no matter what you are cutting on.

When it comes time to pre-polish or polish, set your height so the stone contacts the lap in the center. Bring it on to the lap from the low end, and just give it a gentle swing into contact. You get great control this way.

Happy faceting,

Donald Clark, CSM IMG