There are two basic types of faceting machines: Hard Stop and Soft Stop. Soft Stop machines use a dial indicator, or moving needle aligned to a stationary needle to determine when the faceting arm (quill) is positioned at the angle set on the machine. When you push the faceting arm down toward the lap on a Hard Stop machine, the faceting arm is halted at the angle you set by a mechanical stop.
Hard Stop Machines
There are two types of Hard Stop machines. I refer to these two categories as "Full Hard Stop" and "Spring-Loaded Hard Stop."
Full Hard Stop Machines
When you adjust a Full Hard Stop machine to a particular angle setting, the quill rests against the mechanical stop at the angle you set on the machine. In order to cut a facet to the set angle, you simply lower the mast until the stone just touches the surface of the lap. Then, you lower the mast slightly more and more to accommodate the amount of stone you want to cut away.
Lowering the mast below the point where it just touches the lap, essentially puts the quill at a higher angle than is set on the angle reading of the machine. The idea is to cut from this higher angle until the stone is ground down to the point where the quill comes to a hard stop at the angle you have set.
Theoretically, on a Hard Stop machine, once you have cut to the hard stop on one facet, if you cut all other facets to the same point, all your facets will be exactly the same. This is true in theory, but in reality even the most sturdy of masts can be flexed with too much pressure. This can create uneven facets.
The way Full Hard Stop faceters get around this potential problem is to carefully listen to the cutting action of the stone against the lap. When you hear the point where the lap just stops cutting the stone, that’s when you have reached the proper angle. At this point, you move to the next facet and cut it to that same point (where the lap just stops cutting the stone).
This is how I cut, by ear, with a Full Hard Stop machine. Some people are experts at holding the stone against the lap with a consistently equal amount of pressure. I try to keep an even amount of pressure, but when I get close to the point where the lap is no longer cutting the stone, I stop, hold the quill in place without any downward pressure and listen. When I can no longer hear any cutting action, that’s when I’m ready to go on to the next facet.
There is no such thing as a perfect lap or a perfect machine. Therefore, when you stop to listen to the cutting action of the lap against the stone, always stop at the exact same place on the lap. It’s been my experience that the closer you get to the center of the lap (near the spindle), the truer it runs. You will reduce the effect of any inconsistency from the inside of the lap to the outside of the lap if you are always measuring from the same place on the lap.
I feel I can get a much more accurate cut using the listen to the lap method than by using a needle, light or dial indicator. What works for me, may not be the preferred method of others. In faceting, as in many other crafts, there may be more than one method for obtaining excellent results. Choose the method that you feel the most comfortable with and stick with what works for you.
Ultra Tec, Graves Mark IV, Raytech-Shaw and Lee machines are all full hard stop machines. The Ultra Tec has the advantage that it can be equipped with a dial indicator so it can also work as a Spring-Loaded Hard Stop machine. The Raytech-Shaw machine is a little different only in that it doesn't have a mast. Poly-Metric machines (Xristal-tek 87, Xristal-tek Digital 99 and Scintillator) and the Alpha Taurus can easily be set to operate as either a Full Hard Stop or Soft Stop machine.
Spring-Loaded Hard Stop Machines
Spring-Loaded Hard Stop machines are a hybrid between Full Hard Stop and Soft Stop machines. They have the advantage of a mechanical stop, but also provide the convenience and fast reading of a dial indicator. In order to get the quill of the faceting machine to the degree of the angle you set, slight downward pressure must be placed on the quill. This downward pressure offsets the spring of the dial indicator. A major advantage of the Spring-Loaded Hard Stop is the dial indicator provides a real-time reference as to how quickly your stone is approaching the proper depth of cut. Once the first facet of a tier is cut, you simply cut the rest of the facets to the same dial indicator setting. However, in meetpoint faceting, you still have to look at the stone to make sure all of the facets are lining up exactly.
The MDR 300C comes equipped as a Spring-Loaded Hard Stop machine. When you add the dial indicator to the Ultra Tec, it becomes a Spring-Loaded Hard Stop.
Soft Stop Machines
The Scintillator, Xristal-tek 87, Xristal-tek 99, Alpha Taurus and Facetron are all set up as soft stop machines. Although the manufacturer of the Facetron claims that it can be adjusted to work as a Spring-Loaded Hard Stop machine, we haven't been successful in getting it to work with a hard stop. We consider the Facetron to be strictly a soft stop machine. The Alpha Taurus can be easily set to change it from a Soft Stop to a Full Hard Stop machine. Poly-Metric's Scintillator and Xristal-tek machines can also be used either with a Full Hard Stop or Soft Stop.
When you set the angle on a soft stop machine, the quill rests at a higher angle than the angle designated on the angle indicator. In order to have the quill brought to the exact angle set on a soft stop machine, you must push the quill down against the lap until a needle lines up with a zero point on a dial indicator gauge, or on the Facetron, when the moving indicator needle lines up with the stationary needle.
Once you are satisfied with the cut on your first facet (and the needle lines up), then you proceed to the next facet and cut until the needle lines up again. This seems simple and straightforward, but it is very easy to overcut on a soft stop machine. That’s because there is no mechanical stop to keep you from continuing to cut past the proper depth.
Ultra Tec offers a dial indicator that can easily be installed on their machines. The dial indicator on the MDR or as an accessory on the Ultra Tec provides the same simple cut to the needle style as standard Soft Stop machines without losing the benefit of a mechanical hard stop. Mechanical hard stops make it less likely you’ll grossly overcut your facets.
Comments
Whether you cut with a Hard stop or Soft stop, one thing is universal. Your eye is much more accurate than your machine. Use at least 10X magnification and constantly stop to look at your work. That’s the only way you can be assured you are cutting accurately and lining up your meetpoints.
Remember: faceters, not machines, cut competition quality stones.
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