This is the GBJ Faceting Accessory Story behind the Gems By John Faceting Accessory Dial Gauge.
In THEORY, cutting should stop when the quill contacts the angle stop block. That would be true IF no pressure were applied to the quill or to the stone after the quill contacted the angle stop block.
In the summer of 2009 when John was giving a faceting lesson at his studio in Lexington, Kentucky, one student seemed to be over-cutting facets. The student could not tell when to stop pushing on the stone. She was using a Graves Mark IV faceting machine. John observed how difficult it was for the student to determine when she reached the target depth of cut or target angle. Hard stop faceting machines such as the Graves Mark IV require the cutter to listen to the cutting sound to die down. Then when the cutting sound slows from a constant grinding -- grrrrrrrr -- to just a whisper -- pssst, pssst, psst -- the facet is cut and it's time to stop and move on to the next facet. On a hard stop machine, depth-of-cut is limited by a stop-block. The stop-block is set at the target angle and then the stone is pushed into the lap until the quill hits the stop block and cutting stops.
In PRACTICE, however, a cutter unknowingly continues to push the stone into the lap because there is NO VISUAL FEEDBACK warning when the quill approaches or contacts the angle stop block. This situation causes facets to be over-cut. And that happens due to flex throughout the machine. Flex in the faceting machine allows the stone to be pushed past the target set angle. Flex occurs between the stone and glue, glue and dop, dop and faceting head, faceting head and mast (on mast-type machines like Graves), and mast and base faceting machine. So, it is rather easy to push the stone past the target angle -- deeper into the cutting lap -- after the quill hits the stop-block.
Unfortunately John's faceting student just didn't know when the quill hit the angle stop-block. And, she is not alone. As a professional gem cutter, John has the same difficulty. So, John thought other cutters might be having the same problem with their Graves Mark I and Mark IV faceting machines.
This inherent problem with hard stop machines got John thinking about a solution. The problem with using a hard stop is lack of VISUAL FEEDBACK. Relying on audio feedback ("cutting by ear") listening for the sound to stop is slow and not very easy to repeat. Or, cut-look, cut-look, cut-look constantly lifting the stone to monitor cutting progress is a slow process indeed.
One of the keys to faceting is repeatability. So how useful might it be to add a repeatability control device (Soft Stop feature) to the Mark IV Graves faceting machine making these old workhorses much more repeatable? And, easier to use, speeding up the cutting process! After all, soft stops work great on other faceting machine. Why wasn't there a soft stop feature for Graves faceting machines? So, John developed this much needed Soft Stop feature to add on to any Graves Mark I or Mark IV faceting machine. Then after he got the soft stop working on his machine he thought maybe other faceter with old Graves Mark I or Graves Mark IV machines might like to add a soft stop to their machines too.
After field testing the prototype GBJ Faceting Accessory Dial Gauge, John was convinced this accessory would be very useful for other cutters. When another student used the same Graves Mark IV faceting machine retrofitted with the new Soft Stop, he commented “I don’t know how I could have cut the stone without the GBJ Faceting Accessory Dial Gauge". His first faceted stone was beautiful.
That's The Story Behind the GBJ Faceting Accessory Dial Gauge and the reason behind why John developed it as a retrofit accessory for all Graves Mark I and Mark IV faceting machines.