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Cutting Opals - Glass Wheel


#1

Hi folks,

In the thread on crazy opals someone mentioned cutting sensitive
opals on a glass wheel to prevent the formation of grinding cracks.

Unfortunately I deleted the post. Did I get that right: “glass
wheel”??

This comes as news to me. I’ve never heard of such a thing.

What is it? How does it work? How is it different, (and presumably
better)? Do you apply abrasive slurry to it or is it pre-loaded? How
much do they cost, who makes 'em, where can I get one or at least
learn more?

Cheers, Hans Durstling Moncton, Canada


#2

All, Technology of glass laps and wheels has developed in many
industries for grinding materials. Glass laps can be bought from
Dyna Systems company. I have used them for many years and they are
very hard to beat. You can also buy low impact diamond wheels from
many different companies. Nova wheels are probably the best I have
ever used. These wheels and laps grind stone with very little
subsurface fracturing. They are the best I have ever used for
cutting opals, soft and materials that undercut.

Gerry Galarneau


#3
    In the thread on crazy opals someone mentioned cutting
sensitive opals on a glass wheel to prevent the formation of
grinding cracks. 

What you want is to cut the opal on a “soft” wheel or belt for the
course grinds. I prefer the Diamond Pacific Nova wheels. They have a
sponge underlayment with a flexible diamond band. They start at
around 280 grit which works very well for rough grinding. The
problems come from a course grit carried on a unyielding surface, IE
a steel rim wheel. A rule of thumb that I use is to never cut opal
on a hard wheel or lap that is courser than 600 grit. Anything
courser is courting damage.

A friend of mine teaches opal cutting at Cobber Pedy at the Technical
institutes there. He uses Silicon Carbide wheels with a lot of water
for his rough grind. Then progresses through the silicon carbide
belts on expando drums, again very wet through the 1200 grit before
polish.

There are a number of successful process to cut opal. The one common
thing in all of them regardless of cutting medium, is to prevent
physical shock and the prevent thermal shock. Either will ruin a
good stone.

Don


#4
There are a number of successful process to cut opal. The one
common thing in all of them regardless of cutting medium, is to
prevent physical shock and the prevent thermal shock.  Either will
ruin a good stone. 

I can attest to the thermal shock. I recently went through my late
Dad’s collection of stones. He had saved a really nice opal cab he cut
nearly 35 years ago. When he got sick and went to a nursing facility
his things were stored in an unheated garage. The temperature
fluctuations caused the opal to crack badly. The stone was absolutely
perfect before it went into storage and is absolutely worthless now.
Makes me sad to look at it.

Henry