[Jewelry making - Article 00228] - Re: [Orchid] Making a Two Piece Ring

[Peter W . Rowe]

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>        about bending rings with a wood block and mandrel:  tell us
>     more about the wood block. 

    Jean, don't turn it into rocket science.  the wood block can be
    almost anything you like.  If you prefer half round grooves which
    will conform to the mandrel and band, then fine. Occasionally this
    will be useful, though more often for forming short bits of metal to
    the desired curve, than for just bending around ring blanks.  I have
    a block made from maple, and another from phenolic that are exactly
    this way, made by using a large set of forstener wood bits (these
    bits drill flat bottomed holes, and can be had quite large, up to
    several inches in diameter) drilling a line of graduated holes, then
    sawing the blocks in half along the line of holes.  gives you two
    matching blocks.  These are useful when actually forming the needed
    curves in various, often smaller, pieces of metal that don't bridge
    the gap across the depression. 

    But for just bending ring blanks around the mandrel, it's the
    mandrel, not the wood block, that actually determines the shape, as
    the metal bends up and around the mandrel.  for this, one can just as
    easily use a block that has a V shaped groove in it, rather than a
    half round groove.  With that, the mandrel simply presses down into
    the groove till it meets the mating width of the groove, so the one V
    groove works with any ring size.  All that's needed is that the two
    sides of the block contact the metal before the metal that's under
    the center of the mandrel bottoms out.  If the metal under the
    mandrel is over a gap, supported on each side of the mandrel, then
    hitting the mandrel down into the gap will bend the metal.  You can
    get this effect in any number of ways. it doesn't even have to be a
    groove in one piece of wood.  Can even be two pieces of wood just
    placed near to each other, with a gap between,  though if the metal
    is already bent and you do this, it will just drive the wood blocks
    apart... The reason it's wood, or similar, is just so it's softer
    than the metal, and won't mark it. 

>           ...t the edges of the band were flared upward. ... ... what
>     caused this problem?  what could i have done to correct it? 
 

    One of the things about bending sheet metal (any shape, actually) is
    that in bending, the inner curve of the bend is metal that's being
    compressed in on itself, while the outer curve is being stretched,
    and only the centerline of the stock stays the same length.  But at
    the edges, some of the metal that's being "upset", a term for
    compressing in itself, which makes it thicker, by the way, instead
    takes the easier route of squeezing out towards the side a little. 
    What that does is to require the outer surface to stretch less as
    well, and it slightly flares the outer edges of the strip.  Now,
    added to that, if you forced the ring up on the mandrel and malletted
    it hard, then yes, you also flared the edges a bit this way too. 

    You CAN correct it as you describe, but annealing the band, and
    holding it over a mandrel at a position where the mandrel is slightly
    smaller than the inner surface.  this lets the band sit flat down on
    the surface of the mandrel without being forced out at the ends. 
    malleting just along the center of the ring can slightly stretch the
    center, making the band flatter.  Easier to do with a steel hammer if
    you can afford the hammer marks. 

    If you've got a steel forming block in the shop, these are steel
    blocks with half circle grooves cut (much like the wood ones we
    discussed above).  If you put a mandrel slightly loosely into the ring
    and mallet on the mandrel (not the ring) to force the ring down into
    th groove, this can also planish that surface flat again. 

    and a final, somewhat more drastic means is to support the mandrel
    in a vise or something, so you can hold the ring right at the end,
    with about a third of it off the end of the mandrel.  Gently hammer
    the edge of the ring over air like this, and it will bend down a
    little bit.  Try not to let the inner edge of the mandrel scar up the
    inside of the ring too much.  You might want to round over that edge.
    once you've gone all around a couple times and reduced that outer
    edges average diameter, then hold the ring fully over the mandrel,
    but in a not quite tight position, and mallet the whole width to even
    out the kinks. 

Peter


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