Here is a little trick I came across trying to make seamless tubing
for a gold bead necklace-
Prepare a symmetrical ingot (round, square, what have you) say, 1cm
in diameter, and carefully drill a hole through the ingot’s long
axis (a drill press helps). Insert a brass wire or rod snugly
through the hole, leaving enough to hang out of the ingot at both
ends, and roll the assembly down in your rolling mill. Once the
ingot sandwich has been reduced to an appropriate diameter, you may
solder one end tight and pull it through a draw plate to give it
whatever profile you like. When you’re done drawing, hammering,
sectioning or texturing your tubing, etc, dissolve the brass core
with an acid that won’t harm your ingot material. Voila! Seamless
tubing. It is important to drill the hole for the core precisely in
order to produce uniform thickness of the walls of the tubing.
An experiment with a brass core and silver ingot suggest that
whatever proportion of ingot diamter to core diameter you start with
is roughly the same proportion you end up with in the finished
tubing, however, this may not hold when there is a big difference
between the physical properties of the core and ingot. I’m going to
run a test with an iron wire core tomorrow to see if this can be
used to control the size of the hole more easily.
Guido - I find the question you pose at the end of your post very
interesting. Does the relationship (proportion/ratio) of wall
thickness to “hole” or, in your case, core, change by reducing the
diameter of the tubing. My experience in drawing tubing is that it
does not. I know I have tried to create thick walled tubing in
copper, sterling and gold tubing by drawing tubing down in a
drawplate. It didn’t work. The relationship of tubing wall to tubing
ID always remained the same. I have been told that metal is very
plastic - much like clay. I don’t have much experience with clay but
I have done some workwith Fimo and equivalent substances. One of the
facinating things about this “plastic clay” is that in drawing down
the images, the ratio or proportion always stays the same. That is
how you can do a large “face cane” and draw it down to 1/10th its
original size, or even smaller, and the face always remains in
proportion - just smaller. I believe the same happens with metal and
would happen with your drilled ingot technique no matter the
difference in size between the ingot and the core.
I would love to hear the views of others with more experience or
education in the physics or mechanics of this issue.
I have found that the ratio of wall thickness to hole size stays
fairly constant in drawing tubing. You do get some thickening of the
wall in relation to the hole but not that much. This relates to tube
where typically I am not changing the outer diameter by more than a
factor of 3 from start to finish.
Jim
Jim Binnion
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
@James_Binnion
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