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Metal Forming smooth contour bracelets


#1

My students are making bracelets out of sterling #1 triangle wire,
to be inlaid with stones. Prior to forming the bracelet on the
mandrel, we have removed 5 - 7 rectangular sections of metal,
approximately BC inch to BD inch long each (depending upon design),
from the apex of the triangle to about BD way down the thickness of
the wire. The ends of the wire are left at their original thickness
for about an inch on either end. The wire is annealed prior to
forming.

Due to the sudden change in thickness, when we form the bracelet on
the mandrel, we are getting rather sharp buckles and crimps instead
of a smooth contour, especially at either end where the original
thickness suddenly changes at the first cut-out section. Other than
using expensive forming dies or a hydraulic press, either of which
would evenly distribute the load over the entire bracelet during
forming, is there a way to prevent the buckling at these stress
points? The triangular shape precludes using round tube-forming
sheathes.

Thanks!
Emie Stewart


#2
is there a way to prevent the buckling at these stress points? The
triangular shape precludes using round tube-forming sheathes. 

Shape the curve of the bracelet before you put the cutouts in. Since
the cutouts are causing the problem with bending, bend it before they
are there. Or is there some crucial reason why you cannot cut them
after the metal is bent?

Peter


#3
Due to the sudden change in thickness, when we form the bracelet
on the mandrel, we are getting rather sharp buckles and crimps
instead of a smooth contour, especially at either end where the
original thickness suddenly changes at the first cut-out section.
Other than using expensive forming dies or a hydraulic press,
either of which would evenly distribute the load over the entire
bracelet during forming, is there a way to prevent the buckling at
these stress points? The triangular shape precludes using round
tube-forming sheathes. 

There are several ways to deal with that. The easiest is to form the
bracelet and than remove the metal.

If it is not possible, the bending should be done in swage block
using punch with triangular groove and face curvature fitting the
swage. The force must be applied to avoid sections where metal was
removed. Flat sections where metal was removed can be cajoled into
shape by burnishing from inside after the shaping is completed.

If you do not have swage block, a groove in a piece of hardwood will
do, and pulley of the right diameter will serve as a punch nicely.
Select the pulley so grove would match wire profile and use wood
mallet to strike the pulley.

Another way is to remove the metal leaving corners rounded. In
another words, the profile of removed section is not rectangular, but
like a segment cut out of an ellipse (looking from the side ). You
should be able to shape such wire on a mandrel without any kinks.
After shaping is done, you can refine the profiles to required
rectangular shape.

Leonid Surpin
www.studioarete.com


#4

Emie,

I would have removed the material AFTER forming the bracelets (if
I’m understanding your query). Triangular wire is very tricky to work
with; it wants to take on a life of its own, so you’re adding one
more element into the mix. Anneal it well before forming, and then
again before you remove the material to make the removal easier.

Good luck and let us know what happens.

Kay Taylor
http://kaytaylor.ganoksin.com/blogs


#5
Shape the curve of the bracelet before you put the cutouts in.
Since the cutouts are causing the problem with bending, bend it
before they are there. Or is there some crucial reason why you
cannot cut them after the metal is bent? 

It’s easier to cut the slots while the wire is flat, but we didn’t
foresee the problems (and probably more work) that that would cause.

Emie


#6

Depending on what sort of bracelet configuration they’re making,
another good reason to cut after forming is that you can control the
angles of the cut. If you cut then form, the ends of the cutouts will
do what they want to do, meaning your ends will not be parallel, they
are going to splay outwards. You could conceivably undercut the
silver and slide the stones in from the side. I’m envisioning from
your description a bracelet with NO flex. Any flex and the stones
will pop out at some point.

If you’re going to key the stones to the cutouts it might be easier
all around to cut the stones first, then cut the metal to fit.
usually less work to file metal than grind stones.

BTW what does this mean? approximately BC inch to BD inch long each
What’s BC and BD? Yeah I’m dumb sometimes.


#7

Thanks so much for all the responses. BTW means by the way. BC and
BD must have been a computer conversion of numerical measurements. I
don’t remember what I sent, but it was probably one eighth to one
quarter inch, respectively.

Emie


#8

Could you fashion some mandrels to match the size of the holes? With
a mandrel in the hole the surrounding material wouldn’t collapse to
readily, somewhat like filling a tube with sand when bending it.
Depending on which direction the metal is moving when bent you may
have areas that stretch away from the mandrel when bending though.

Mike DeBurgh, GJG
Henderson, NV