Although this might seem like a long title, but the application is
rather simple, why so?The very first thing is to measure your Cabochon stone in
millimeters. The reason for this is that all burs are all measured in Metric.
For example; a bur number of #050 is really 5.00mm's in diameter.
“THINK METRIC, AT ALL TIMES!”Another
point is please avoid asking the tool-supplier for a “half-round bur”, why not?
The simple answer is because there aren't any, you have to make one yourself
! “I'm going to do what? I'm gonna make a
“half-round bur”, don't worry, I will guide through this whole simple process. All you
need are a few simple tools; a bench-grinder with little bulbs for up-close
viewing! A pair of safety-glasses. A pin-vise to hold your bur while shaping!
Not too mention a cup of water, this is to keep your bur 'cool to the touch'!
Let's start by measuring your stone; Calculate
the distance from the top of the Cabochon to bottom, the circumference of the
base. Now determine the height from the base to the start of the curve. Is this
important? Yes for the first few times, after a period of some weeks, you can
just do this by 'eye-measuring' these distances!
How thick must the bezel wall be? No
thinner than 1.0 mm but high enough to envelope the curve of the stone. I
believe the height of the 'bearing-groove' to the tip of the bezel should be
about 1/3 of the height of the stone.
You've now made all kinds of measurements,
bought all of the burs, reshaped many of them and now you're ready to cut a
bearing-cut or inner-groove!
How many burs would you buy, in case
one bur is not cutting well? Just don't keep it, throw it away, use another bur
that you bought. I always have 'duplicates' or even 'triplicates' of the bur
sizes. I always allow this, in case of a bur getting worn down during this
important bearing-cutting process.
To start, put your new full shaped bur into
you pin-vise, finger-tight the vise! Start your new bench-grinder, put on your
safety-glasses, have your container of water with-in finger reach. The water is
to keep the bur cool, not allowing it to heat up. Sit comfortably & lets
start.
What you must do is to not remove any metal
beyond 50% of the 'round shape'. As this will be the shape of your intended
Cabochon stone, keep your bur cool! If it gets hot, it will change colour &
loose it's tensile strength! Keep rotating your bur & keep the bur flat
underneath, this so very important. Stop your grinding when you reach the
50% being removed.
You must do this grinding, in increments of
2-3 actions, to one dunking in water..gotta keep the bur temperature cool to
touch! The second photo below shows how the burned bur looks.