Introduction:

This is not a Beginners' Project. By its very end use, the machine is intended to produce faceted gemstones of high precision, and it cannot produce something more accurate than itself. Familiarity with mechanical principles is needed to complete this project. A familiarity with mechanical assembly practices and the use of common shop tools is a must.

For those unfamiliar with the operation of machine tools such as lathes and milling machines, it is best to get help from a machinist, toolmaker, or other skilled craftsperson. Often, a local trade school can help greatly..sometimes they are grateful for a "special" challenging project. Of course, you will have to pay for materials and supplies at the least. Another possibility is to enroll in a basic machine shop/ metalworking course. The skill will not be wasted (No skill ever is..), as later on, you can make your own laps and other tooling, saving many times the cost of the course.


Design Principles: The baseplate can be aluminum tooling plate ("Jig Plate"), 5/8" thick, or Plexiglass, 3/4" thick. If the latter is chosen, it should be drilled and tapped so extruded aluminum channel can be bolted to the back surface as stiffeners. In either case, the materials must end up being better than 0.005" flat per foot. Plexiglass is very easy to work with common woodworking tools, so many would prefer it. It is cast to sufficient flatness so it can be used. It does scratch easily, of course. Both materials are illustrated later on.

A DC motor with sufficient torque is used so it does not slow down under load. A solid-state controller with feedback may be used for controlling the motor speed. However, faceting does not put great demands on the motor, so a simpler speed control, such as a Variac, a rectifier, and a capacitor may be used with good results. Very inexpensive controllers are available based on Triac or SCR switching, like a lamp dimmer. The output of these devices may be wired to the appropriate transformer for the motor's voltage, rectified, and connected to the motor. For example, a 24 Volt permanent magnet motor can be run very well by buying a 24 volt transformer of sufficient current rating, connecting the output of a "dimmer" to the input, and connecting the output to a bridge rectifier and a capacitor,(Rated 30-50 VDC, ~10,000 MFd.) through a reversing switch, to the motor.

Ball-bearings are used everywhere, of the sealed type. Should any diamond dust or grit get into them, they can be changed quickly and cheaply. The use of ball bearings eliminates most "slop", and the accuracy of the unit does not deteriorate over the years. Also, all the close tolerance work is done by the bearing manufacturer...all for less than ten dollars.

The faceting head and quill assembly is all ball bearing. The bearings used in the trunnion assembly should last forever, as they are not exposed to spray. The gears are off-the-shelf precision stainless steel, and are assembled to an accurately machined shaft adapter, so they can be changed in seconds. Because the gear is silver brazed to the adapter, there will never be any indexing errors caused by slippage.

The mast assembly consists on a stainless steel centerless ground 1" rod, chilled into an aluminum baseplate. A Thompson or Barden ball bushing with Zero "slop" is used on the head assembly for smooth and error-free adjustment and travel. The depth is set by a micrometer spindle which rests against a coarse adjustable aluminum clamp, so a wide range of depths is possible whether cutting a table or girdle. The Base is straightforeward, and will be built first. If you decide to stop when you are finished with the base, you can always build the faceting head and mast assembly later on if you want, and buy Wykoff's "Calibrated Jam Peg", and with skill and practice, probably turn out better stones than I do, and still be far ahead in cost.

Materials Needed: 1 Sheet 3/4" plexiglass, or 1 sheet 5/8" aluminum Jig Plate 18" X 14", or whatever dimensions you might prefer. These are a judgement call by the builder. Some might want to build it into and existing cabinet or countertop, others may wish to build a base for it so it will be "portable", and will sit on a counter.

Construction details

Revision "H"!...In Stainless Steel.


Motors used are DC, either Permanent Magnet or wound field types, having a shaft diameter of at least 1/2" (12.7 mm), and using sealed ball bearings, rated at least 1/5 HP (~150 Watts).

Here is the c-face motor mounted to the underside of the acrylic base. Note the bolt pattern, and the machined splash and dust guard (Made from an old wire spool). The face of the motor was machined dead perpendicular to the shaft, to remove errors caused by the manufacturer's paint. To do so, the motor shaft was mounted to a live center on the lathe's tailstock, and the motor was chucked, after its wires were carefully taped to the body of the motor. This step may NOT be neccesary in most cases. I just did not like the looks of the paint application, and I like to run the lathe, anyway. A "bump" of paint will affect the perpendicularity, just as a shim would.



Here is a simple fixture, accurately bored, which mounts on the spindle, and measures wobble relative to the top surface. Since the faceting mast assembly mounts to this surface, and the motor is mounted to the opposite side, this is the datum plane from which measurements are derived, and the plane which is the angular reference for every stone which will ever be cut. The parallelism specs for cast acrylic sheet are very tightly controlled.



The faceting head assembly, plopped onto the base. It is secured with a single 3/8-24 bolt and clamping nut and washer, so it can slide in and out towards or away from the centerline of the spindle.

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Last Revised 12-26-96.