Cutting by Ear
by Bob Keller

I learned to facet on a Facetron in an Old Pueblo Lapidary Club faceting class. I also worked in class on an Imperial outfitted with a dial indicator. The machine that's been may favorite for several years now is well used Mark I Graves that I acquired cheap. It has been modified and updated by a previous owner with a reversible speed controlled motor, and I like cutting on it.

You can cut a respectable stone on a Graves. I entered the 2001 USFG novice single stone comp as my first faceting competition and won it with a quartz cut on my Mark I. I've come to appreciate it's the faceter who cuts and polishes the stone, not the machine. The Mark I does not incorporate a needle or dial indicator to monitor the depth of cut and after learning on the Facetron and Imperial, I didn't know how I could get along without one. The Mark I is often faulted as slower to operate than a machine with a visual depth of cut indicator, but after learning the technique of cutting by ear I have found that not to be the case. Visual indicator or ear, I seem to get to the 'cut a little - look a lot' stage just as fast either way.

Establishing an initial center point or set of reference facets is one of the first skills every new faceter has to learn. That task essentially boils down to a task of cutting a set of like facets to a uniform depth. There is a fundamental and time honored technique for accomplishing that with 'hard stop' type machines such as the Graves and the Ultra Tec that works very well and requires no depth of cut instrumentation.

To 'cut by ear', the first facet in a course is cut in and the elevation adjusted so that the final swipe just shaves off the remainder of material in contact with the lap. If you're not pressing the stone into the lap (and flexing the machine), what you hear is a diminishing tic-tic sound as you approach the final swipe.

You're "there" when the tic-tic *just* quits. Once the elevation (depth) for the first facet in the course is established, you simply change the index to the next facet in the course and you stop cutting it when it *just* quits ticking.

I use this cutting technique generally and not just to establish initial center points or reference facets. It can be employed to produce very consistent and uniformly cut set of facets around a course.

I have sometimes heard 'cutting by ear' described as cutting each facet in a course until it makes the 'same' sound as preceding ones. My own hearing is still a little better than normal for a 49 year old guy who attended a few rock concerts in his prime, but it just isn't anywhere near resolute enough (or my memory persistent enough) to pick some arbitrary level of grinding noise and consistently cut facets to that as a reference.

However, by adjusting and using the machine so that the cutting noise (ticking) *just* quits at the desired depth of cut, you're listening "digitally" rather than trying to judge when the sound has reached some particular level in a continuously varying analog range of grinding noise. The key to extracting the maximum consistency and repeatability from this technique is no machine flex - you should not be pressing on down on the stone *at all* when you're listening to tics. I've learned a related technique that helps with this which I think is worth passing on to those unfamiliar with it.

I shim under the front feet of my machine so the whole thing is leaning very slightly back. The shim is adjusted so the head swings slowly on its own towards the back of the machine due to the influence of gravity. The idea is to shim until gravity just overcomes the bearing friction. When there's a stone in the quill and it's in contact with a spinning lap, the friction from the contact pushes the stone/head towards the front of the machine.

I cut by sweeping the stone across the lap and periodically releasing my hold on it, so that the only force pushing it into the lap is the weight of the head/dop/stone. If the stone wants to move towards the front of the machine, I know there's still a 'coarse' amount material to remove and I continue cutting. When enough material is removed that the stone just "floats" in the same position on the lap - at equilibrium between lap friction pushing it forward and gravity pulling it backwards - I know I'm getting close, and at that point I begin listening critically.

Most machines and laps are less than 'functionally perfect', with the result that various positions on the lap aren't at the same effective elevation - this is easy to hear as a change in the tic-tic sound from one position on the lap to another.

So, much as when polishing, I reduce the arc of the sweeping during the final stage and finish up cutting each facet in a course at a consistent position on the lap.

Using the shimming I've described, the head/stone wants to swing towards the back of the machine under the influence of gravity when enough material as been removed that the stone is barely ticking on the lap. I've found that attaching a clothes-line pin to the rim of the splash pan on my machine creates a handy stop for the rearward movement of the head, providing consistent, hands-off positioning on the lap.

So, it goes like this - I cut each successive facet in the course, releasing my hold on the stone periodically to see if it's still being pushed forward by the lap. When it starts to get 'floaty' I quit day dreaming and start listening. As it gets closer yet, the stone quits floating when released, and gravity swings it back until the head comes to rest against the clothes-line pin stop on the splash pan rim.

Ever smaller sweeps are made just off the stopped position on the lap using an extremely light touch - just enough to control and move the stone. At the end, the sweeps cover about a 1/4" and the stone is released after each sweep to listen for the tic-tic after the head swings back and stops against the clothes-line pin.

If you have a 'hard stop' type machine, this technique is fundamental and simple, and much easier to demonstrate first hand and use than it is to describe. It is also fast once you are accustomed to it.

My experience is that I can get to prepolish and the eyeball work cutting by ear just as quickly as I can watching an analog gage or digital readout. I'm not out to start a debate or controversy with the bells and whistles guys who are into gizmotrons and instrumentation on their machines. I just haven't found all that to be necessary or even a functional advantage on 'hard stop' type machines such as the Graves and the Ultra Tec.

One further consideration is you need to work in a quiet environment when you're cutting by ear, so this approach won't be appealing to someone who likes to listen to music or watch TV while they're cutting, or usable by someone sitting in a faceting class next to a student who is roughing in a stone on a 100 grit lap. I prefer to do my faceting away from distractions in a quiet environment where I can fully concentrate on and enjoy what I'm doing, so my Mark I and 'cutting by ear' works for me.

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Bob Keller