[Jewelry making - Article 00937] - Re: [Orchid] Watch crystal update and question

[H.Durstling]

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    If you want to hand-make a crystal, I'd recommend using a dental
    technician's Redwing lathe. This is a ball-bearing motor which runs
    very smooth, has two speeds, and a chuck which takes 1/4" or (I
    believe) 3/32" diameter mandrels. Use the 1/4" for its added firmness
    and freedom from vibration. 

    Or you could use an electric drill clamped FIRMLY to the workbench. 

    In any case what you'll end up with is a more or less improvised
    lathe, in which you can chuck up the workpiece (the crystal) and turn
    it down with diamond tools to the shape you want. 

    Get a piece of 1/4" brass rod, cut it to a convenient length, say 2"
    or 2 1/2" and silver solder a brass plate onto it approximately the
    diameter of your watch crystal. Chuck this up and turn it down to
    centre and level it so that the plate surface is flat and
    perpendicular to the shank. You'll need a good solid steady tool
    rest. I use a big cube of brass I got from the scrapyard, about 3x3x3
    inches. Something as massive as that you can hold a tool on it and
    the tool won't vibrate or chatter as you spin the work. 

    Also you'll need one side of the crystal blank flat, because this
    will be the reference when you switch to grinding out the concave
    inside surface. You can do that by hand grinding - wet - with silicon
    carbide grit on a flat metal or glass plate. 

    Warm some dop wax, and the crystal blank, stick the crystal blank
    flat side down onto the brass plate by means of the wax. Make sure
    there is a good flat contact between the crystal bottom and the dop
    surface. Now adjust the blank while the wax is still hot and pliable
    (or reheat the wax, gently, in an alcohol flame or even a candle)  so
    that the blank is centered.  Put it in the lathe & give it a spin
    holding a grease marker or magic marker against it. This will leave a
    mark on the off centre spots. Adjust again, by warming the wax and
    pushing the crystal around in it. It helps here if you have a piece
    of rough glass to start with that has a lot of extra material. You
    just cut that away and it will be centered. 

    Anyway you have your crystal blank centered on the brass dop. Now
    you turn it down to the profile you want by spinning it while holding
    a diamond tool against it. Keep it wet. This gets messy. Again the
    tool should be solid, even massive. For coarse shaping like this I
    use a single "segment" (the diamond bearing metal platelet) salvaged
    from a tile saw blade and silver soldered onto the head of a long
    3/8" machine bolt. 

    With that you can spin it down to profile. Keep it wet and check
    frequently. The surface will be rough & scratched. Switch to a finer
    diamond tool to take the coarse scratches out, always working wet.
    Then finer and finer still. The progression should be approximately
    like this...roughing out, 100 grit diamond, refining and taking the
    rough scratches out 240-280 grit. You can make your own diamond file
    by putting a dab of olive oil on a file-shaped piece of copper (beat
    a copper tube flat but leave one end round to serve as handle, then
    file it flat & smooth) and applying just a minute pin-head amount of
    diamond grit. Spinning the work against the file will press the
    diamond into the copper. 

    When you've done the fining stage you can switch to using silicon
    carbide wet-or-dry paper glued onto something like a paint stick, say
    about 400 grit, followed by 800, still working wet. Diamond works
    better though. 

    You could do this stage also by taking the dop out of the chuck and
    holding the crystal against a rubber backed sanding pad (wet, always
    wet) on a lapidary wheel. The usual caveat applies: cut and look, cut
    and look. 

    By 800 grit you should have a fine satiny sheen. Check for scratches
    remaining from previous stages and re-sand where necessary to get
    them out. Once the you've reached the 800 stage you can go to polish.
    Do this on leather with cerium oxide (wet, always wet) or any other
    stone polishing compound. 

    That done, gently heat the crystal, take if off the dop stick, flip
    it and re-attach from the other side so that you can grid out the
    inside. Here's where you'll need to very carefully center and level
    the piece. Spin it against the grease pen or magic marker to see
    where it's off center and off level, adjust by warming and pushing. 

    The inside is done in the same way, except rounded tip tools are
    helpful. Again, you can make your own with copper, grinding the
    copper to the profile you want and embedding diamond grit with olive
    oil and pressure against the work. 

    For polishing the inside glue some leather on an appropriately
    profiled stick, apply compound, keep it wet, etc etc. Or you can use
    a leather polishing disc in the foredom...or similar...still working
    wet. Polishing builds up heat, and you'll have put so much work into
    the piece by now that you don't want to have it heat-crack at the
    very last stage. 

    Oh yes and you should always carefully carefully wash the thing and
    your hands and under your fingernails between each step so as not to
    carry any stray particles of coarse grit onto the finer stage. 

    That's long, but that's how I'd do it. You see why buying a
    ready-made crystal would be easier...*S* 

Cheers
Hans Durstling
Moncton, Canada 

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