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Old January 24th 08, 07:42 AM posted to rec.crafts.jewelry
Peter W.. Rowe,
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Posts: 355
Default Disc cutter - oval and other shapes

On Wed, 23 Jan 2008 22:16:03 -0800, in rec.crafts.jewelry gloflyer
wrote:

I recently purchased a disc cutter. I love it, and it is easy to
use! The one I bought goes from 1" on down by 1/8". I had a bit of
trouble finding one in stock. It sure is a time saver. I still have
to file the edges, but that is nothing compared to the time it takes
to saw a circle.


they vary in quality. The best made ones leave the edge with a clean sheared
surface. You don't generally need to file these. minor sanding or polishing if
you require, but nothing enough to need a file.

Does anyone know where I can purchase a similar item for ovals? I
think that someone must make one, because there are bezel formers that
start with an oval "washer" shape.


Oval punches like the common circle cutters aren't made. Producing such a punch
is a much more complex machining task that making the round cutters, since for
the round cutters, a lathe simply trues up the punches, and a drill or milling
machine or reamer cuts the precise hole. In short, round is easy. ovals or
other shapes require much more complex (think costly) maching methods to get the
required accuracy. That doesn't mean they wouldn't still be straight forward
for a good maching manufacturer to make, but it does mean these would be nowhere
near as inexpensive to buy, and that greatly reduces the potential market for
the tools. Thus they aren't currently made.

You can, however, get slightly different punches. The profiform combination
shear and bending brake tool, made in switzerland or copied by the chinese in
much lower quality and sold by harbor freight, offers (in the original swiss)
optional die sets that are sold singly as a set of cutter and die. it's
intended to mount onto the bending brake part of the profiform to power it. They
cost, if i remember right, around a hundred dollars for each set. Offered in a
variety of shapes, not just ovals.

There are several other manufacturers who similarly make punch and die sets to
cut various shapes, including ovals. As above, these usually are sold singly
for each cutter and die, and range in price from somewhat under a hundred
dollars per set, to several hundred per set. I seem to recall Roper Whitney,
the firm that first came up with their popular little plier style circle punch,
also have die sets in other shapes.

By the way, don't infer oval punches just because you can buy oval or other
shape bezel punches. The main uses of disc cutters is not to prepare blanks for
a bezel punch, and bezel punches of various shapes don't mean someone is making
a matching shaped sheet metal punch. In contrast to the funny little tool tip
in the rio grande catalog, most pros don't use those punches with a flat washer
as the starting shape, and they're not really intended or optimized for that
method. Usually, a flat strip is bent around and soldered, just as for a
standard straight wall bezel, and it's then pressed into the bezel former to get
the taper. For higher wall bezels, one can lay out a curved arc shaped blank to
bend around, so by the time you're done, the bezel punch is used to true up and
finish the shape of the bezel, rather than totally forming it all the way from
scratch. Starting with either a vertical walled bezel, or an already partially
cone shaped blank deforms the metal a lot less than starting with a flat washer.
Among other things, the flat washer method gives a bezel with the greatest
thickness at the upper edge. That's often not as useful as one that's thickest
at the bottom which is what you can get if you start with a straight walled
blank that sits partially up above the bezel punch, and you hammer or press it
down into the depression. And starting with a flat washer will tear the metal
a good deal more easily than starting with a straight walled bezel. Rio's tool
tip is still a good trick, and a time saver when it works, which means you're
needing a shallow enough depth of the bezel and can start with thick enough
metal and are using a soft enough metal, for it all to work. But even with
Rio's trick, you still have to get the center hole right, and most disc cutters
aren't so good at centering a hole in a washer (I say most, because there is one
type available that's intended to do just this) and if the center hole is off
even a hair, your bezel won't be so good. (another advantage of starting with a
straight vertical walled bezel is that it's much more forgiving of starting
conditions.)


HTH

Peter

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