Version 1.05 March 2020
25
6.2.4
CUTTING THE GIRDLE
On this step, and the ones that follow, we refer to diamond plated laps as “coarse” (360 mesh) or
“medium” (600-1200 mesh). Use the coarse lap where you are removing a considerable amount of
material, and switch to the medium lap to finish shaping the stone. In general
—on large stones there’s
a lot of work to do with the coarse lap, and on small stones, hardly any (you will quickly learn which lap
is appropriate). This instruction assumes the stone is about ½ inch (12-15 mm)
The first step will be to cut the girdle. Place a coarse lap onto the platen. To preform
the girdle set the Angle Dial at 90.00 . Set the Index at 3 (the first setting of the
Standard Brilliant Design). Start the lap turning at a speed setting about 6 or 7 (yes,
you can slow it down if that speed makes you nervous
—later on, you may be speeding
it up). Set the Water Tank so that it is dripping at a rate of one or two drops per
second, and clip down the edge of the Splashguard so it doesn't interfere with the stone's reaching the lap.
Position the Head so there is no danger of the spindle hitting the lap.
Girdle Facets
– set Angle Dial at 90.00
96 Index at: 3, 9, 15, 21...etc…steps of 6…to 93
Using the vertical knob, lower the stone toward the lap until it makes initial
contact. When you feel it, hear it, and see the Angle Dial readout go over the
90.00 setting, continue to lower the vertical setting a few divisions on the Vertical
Knob, and grind a flat
—the Angle Readout will read 90.00. As you do that you
will be holding the handle, applying a relatively light and consistent downward
pressure as you sweep the stone back and forth across the lap surface. You will
see when the Angle Dial has returned to 90.00 (and, you will feel and hear when
the cutting action stops).
Then index around the Index Gear, repeating the cut 16 times (on a 96 gear
the stopping points are 3,9,15
…..in steps of 6.., to 93. You may have to
lower the vertical position to get the girdle facets to join
—to obtain nice even
facets. As you work, you can see there is considerable material to remove,
but as you reach the stop, come up against it lightly and consistently.
If you want a round girdle
(it has gone a bit “out-of-style” these days), you would now place the machine into the
"free wheeling" mode and round off the points. It is recommended that the series of flats always be placed on
the stone before rounding. (watch the Angle Dial and be sure that the readout finally shows 90.00 all the way
around, as you remove the high points).
