The Beale/Woolley Depth of Cut Indicator
by Dave Woolley and Marcus Beale
Marcus Beale and I took classes together at Central Virginia Community College in Lynchburg, Virginia not knowing we shared interests outside the classroom. It was after Marcus and his wife Marie opened up a retirement business, the Amherst County Rock Shop, that we discovered other activities in common. I am a Geologist, and Marcus has a lifelong interest in rocks and gems. Back then, Marcus was perfecting his cutting techniques using an Ultra Tec faceting machine, while I was struggling with a Graves Mark IV. The Lynchburg Gem and Mineral Society was experiencing its rebirth. I volunteered to pen a series of articles for its monthly Journal: the Scratches from the Master Lap articles documented my learning curve. Marcus also contributed ideas that he discovered which made faceting more profitable.
The articles led to experiments in faceting techniques and in fine-tuning machines. Our machines are mast type faceting machines, each with a lock or "hard stop" designed to end the cutting at precisely the same angle for a group of identical facets. Note: a mast must flex when a protractor lock is engaged. A mast flexes an unknown and therefore an uncontrollable amount from facet to facet, thus over cutting some facets while under cutting others, especially when variable hardness facets prompt different hand pressures. The angles of facets vary as the mast tilts. Adjusters are needed when polishing to "find" these should-have-been-identical facets. Precision faceting becomes a labor intensive, time consuming, and sometimes a nerve-racking procedure. I had success with a hands-off, gravity-feed modification that required the "sound-of-cutting" faceting technique. When combined with a slightly tilted base, this method controls mast flex, but it takes much too long to complete a gem. Later, I added a spring loaded Dial Indicator, a "soft stop" depth of cut guide: I could push the cutting until the dial told me when and where to slow down. Accurate faceting was now possible but the techniques were cumbersome and still too time consuming.
To end mast flexing, Marcus and I considered building an electric warning light and later a Light Emitting Diode attached to the protractor lock. The LED system lights up faster and is more accurate because it does not wait for a filament to heat up once a threshold voltage is reached. Construction consists of establishing electric contacts where the pointer (Graves) or the fine angle adjuster (Ultra Tec) touches the protractor lock - one contact is insulated from the faceting head and the other one grounded to it, making a simple on/off switch. Warning lights have limitations: you can't predict when they will burn, and you can't stop cutting soon enough. Once the light begins to burn you have already flexed the mast. Marcus, having worked with a strain gauge, pondered what was going on electronically: he replaced the LED with a Volt Ohmmeter.
In the spring of 1990, Marcus discovered that the Ohmmeter needle makes a full sweep of the dial as the contacts begin to touch. This variation of electrical resistance is measured by the Ohmmeter in the very tiny area where the contacts first begin to touch: the Ohmmeter's needle moves to the right as the very low voltage, electrical resistance goes to zero. From facet to facet the mast can be flexed an identical amount by cutting to the same mark on the Ohmmeter dial: the depth-of-cut and the angle can easily be reproduced for a group of facets. Rapid meet point faceting is now possible even with entry-level faceting equipment. We now have a 'Bio-feed Back Faceting Machine' for rapid, hands-on, precision faceting; a 'High Resolution - Analog - Mast Flex Duplicator'; or the Beale/Woolley Depth of Cut Indicator.
With the Beale/Woolley Depth of Cut Indicator you can push the stone into the lap at whatever speed of cutting the gem will tolerate, slow down the cutting as the needle begins to move, and stop the cutting at any chosen mark. The numbers on the Ohmmeter dial are unimportant. By flexing the mast the same amount and waiting a couple of seconds for the cutting to finish, or as evidenced by the sound-of-cutting, identical angles and depths are achieved for all the facets in a group. "Cut a little-look a lot" to create a controlled, hands-on, meet point facet for the first facet of a group, while noticing the final position of the Ohmmeter needle. The rest of that group of facets is "cut a lot": no additional inspection of the gem is necessary.
On complex cuts, coarse grind only the initial facet groups: the final, small facet groups are cut after the initial facet groups are re-surfaced with a pre-polish lap. If a pre-polish facet is accidentally over cut, all of that group of facets will need to be re-cut to that new needle position to maintain symmetry. Meet points may then be reestablished on a polish lap by re-cutting the previous facet groups a very slight amount. If a facet is cut to the zero mark on the Ohmmeter dial, the mast begins to flex an unknown amount: re-cutting the entire pavilion or crown may become necessary to reestablish the meet points. If using a worn lap, all final cutting will need to be made in the same small area, so that all of the pre-polished facets will have the same lap surface-angle imperfection.
A faceting machine's protractor may "read" to a tenth of a degree or better, but many machines lack the precision from the factory to cut true angles. The fact that a protractor is not quite accurate is of slight consequence: adjacent facet groups will have similar errors, so facets will "fit together". Therefore, slight angle error is unimportant provided the pavilion main-facet cut angle is not too shallow (or too steep): too extreme and light will leak out the pavilion causing a "fish eye" gem. Often, the Design Angles are not achieved in good faceting! Adjustments of angles and depth-of-cuts are routinely made to cause facets to meet at points. Cutting to the precise Design Angles is unimportant because, ultimately, the facets of all hand cut gems are custom fitted! With the B/W Indicator only the initial facet of each group will be custom fitted to meet point perfection: the use of the Ohmmeter needle will duplicate the subsequent facets.
For polishing, the protractor - with the stop locked - will be used only once to get into the ballpark to "find" the facets of a new group. Make a very shallow trial polish. See if the top or the bottom of the facet is beginning to polish. Unlock the stop and move the head slightly up or down the mast accordingly. With the head free floating, trial polish an adjacent facet. Repeat if necessary. While making the polishing trials use the radial "cheater" or adjuster to locate the facet, left to right, to compensate for any cutting-lap-to-polishing-lap slope variation. Once the facet is found "dead on", polish all the facets of the group on the same small area of the polishing lap, without further adjustments. Using this method will prevent any one facet from being miss-positioned by the polishing lap while maintaining overall meet point perfection.
Many faceting machines have benefited from the addition of a Beale/Woolley Depth of Cut Indicator. Applications may function better than an electronic strain gauge. The B/W Indicator functions better than spring loaded and non-spring "floating stop" Dial Indicators: no irregular-friction-generating "lumpy" gears. The B/W Indicator is reported to reproduce depth-of-cuts to less than 100-micron variations. Note that the Fac-Ette GemMaster strain gauge patent is written to prevent other manufacturers from using "any electronic device" for depth-of-cut control. You may, however, modify your own machine for personal use. Caution: you may also void your manufacturers warranty by altering parts. An Ultra Tec can accept a B/W Indicator for trials without any changes being made to the machine by using alligator clips, although firm mechanical and solid electric connections are highly recommended.
Faceting with the Beale/Woolley Depth of Cut Indicator has the following benefits:
- Constant diameter perform cylinders and constant angle cones are cut regardless of variable hardness, even if the cylinders have irregular heights or the cones have irregular diameters.
- Over and undercutting, and variable angles, caused by the variable hardness characteristics of each gem species and the lack of feedback for monitoring hand pressure, are eliminated.
- Accuracy is greatly improved. Girdles are cut to a uniform thickness; perfect rounds are the norm, rectangular facet edges are parallel, and fancy cuts are symmetrical. Ultimately no gem is perfect; but it is more fun to need higher magnification to find and correct slight imperfections.
- A gem can be well cut in as little as 1/4 the time it takes to cut with out the device.
- Except for orienting a damaged gem for re-cutting, or aligning after a poor transfer, adjusters or "cheaters" are not often used. Adjustments are no longer required to polish each facet.
- You will no longer tolerate a machine with a bad bearing or a bad alignment. The B/W Indicator will help you isolate and cure your machines problems. The accuracy of the B/W Indicator is far better than a Dial Indicator for maintaining and aligning a machine.
The B/W Indicator has been added to the Ultra Tec, Graves, Lee OK, MDR, and others, including homemade machines. The addition to an Ultra Tec can take as little as 20 seconds; the Graves, maybe 2 hours of hand tool work to a small part - warranty not voided if you replace that part. Non-mast type faceting machines such as the Raytech have also been fitted with the device. Tube-on-mast machines have not been adapted. Jon Rolfe has incorporated the Beale/Woolley Depth of Cut Indicator in the design of his excellent faceting machine, the J-2, which is intended for home construction. See the Lapidary Journal article in the April and May 2000 issues and his web site. Most applications are made with just the simple addition of an insulated electric contact at the protractor lock, and an inexpensive, analog, Volt Ohmmeter. Short needled, un-dampened meters respond faster. Some applications such as on the Graves allow you to adjust the protractor to cut true angles. See the Scratches from the Master Lap articles for additional suggestions.
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© Bob's Rock Shop Bob Keller