Craig,
The idea of the layer of tin is to provide a sacraficial shim around the tapered mandrel to allow the coil to come off after winding. The tin would be removed from the mandrel before being reinserted. Yes, scale could be removed chemically, reinsert the tapered core and probably tig weld the seams closed for welding the whole together.
Another interesting point would be to setup a fixture in the hydraulic press to help with the jump welds. Hammers tend to swell the steel closer to the hammer blows, while a press will make a billet swell from the center. Having both available during the operation would be handy. Being able to hammer or squeeze the sides, and press the barrel lengthwise would allow the smith to get one more angle on the welding.
Peter,
The use of a rolling mill is a great idea, and I've seen them used to weld billets. I wouldn't use them for my own billets because the way I start my billets the rolling mill wouldn't offer any advantage. I like to use 1/4" thick bars stacked at about 4" tall and 4" long by 1 1/2 wide. The idea is to have thick enough bars to hold their hear for the initial weld, and continue to forge weld for three more cycles as the billet is drawn out. The more drawing of the weld the better as the surface area of the weld surfaces is increased and weld heats are repeated, the more sure each weld will become.
I would love to see more movies. It's a shame anyone would think the process needs to be kept secret, but I guess thats the way it is.
Regarding heat treatment, the core is what needs to be heat treated. The riband needs to be stress releived (along with the core of course) to reduce any warping. It would be heat treated using the times and temps for 4140.
Grain refinement is the absolute key to heat treating. Back in my bladesmith days, I tested a couple of smiths whose blades passed the cutting tests, but groaned and almost imediately broke during the bend tests. The grain structure of the blades were like pyrite. HUGE!! I asked what kind of grain refinement they did and I got the cocker spaniel look.....My Mastesmith test blade went a little past 90 degrees and came back to a 15 degree set. The bottom 2/3 of the blade measured 57 Rc, the spine 1/3 measured 42rc. I did three cycles of subcritical anneals and then hardened the blade and drew a higher temper on the spine.
