I'm looking for some instructions on how to make a threaded,
screw-on cap (I'll be using sterling silver).
There is a way to fabricate one of these, I think Charles
Lewton-Brain had shown a method, but I don't know if it's in any of
his books. I have another way you could try. Find a plastic container
with a screw on top, as in a toothpaste tube and cap, or a small
plastic bottle, etc. You cut off the male threaded part, and sprue up
that and the cap and burn them out and cast them. Fabricating them
involves wrapping a double piece of wire around a mandrel and then
unscrewing them into two separate coils. You then need two tubes, one
with an inside diameter that the coil will slip into, the other with
an outside diameter that a coil slip over. But the wire thickness has
to just make up the difference. The coils are soldered onto their
respective tubes, and the larger tube capped off. You calculate the
sizes by finding a pair of tubes first, one with an inside diameter
about a millimeter or two larger than the outside diameter of the
other. When you find two tubes appropriately related as such, and
which are pretty much the size of the cap you're interested in
making, then you use wire that will, when wrapped around the smaller
tube, fill the distance between the two. Clear as mud, right?
Hopefully, someone on this forum will have a reference with
illustrations and better explanation.
David L. Huffman