If you can cast the piece, you could do this pretty easily. Use a
curved tube of polystyrene, uncooked macaroni, or whatever is the
correct thickness for the bar you want to insert. Form the wax around
that core and then remove the core and cast.
As a hint, if you spray the polystyrene very lightly with WD-40,
Pam, olive oil, or some such, it will release beautifully from the
wax. The macaroni should do likewise.
Alternatively, if you have a polystyrene tube/macaroni that the bar
you want would fit into, go ahead and form it the same way (without
the lubricant) but cut off the tube flush with the surface of the
wax. This will leave you with a beautifully formed and supported tube
all the way through.
One additional consideration will be the curved tube and burnout.
Mix a small amount of investment and fill the curved tube with it
prior to investing the rest of the flask. That way, you won’t end up
with bubbles or an incomplete tube. You can fill it (depending on its
dimensions) by using a syringe, or using a toothpick or similar
object to push the investment into the tube.
Hope this helps!
No Limitations Designs
Hand-made, one-of-a-kind jewelry