On larger seams I rarely solder everything at once. I often tack a
portion, use this as a fulcrum and then either close and straighten
things up after pickling and resolder or close seams up while things
are hot. I've learned to do this making cylinders of 24g bimetal.
As soon as you start heating them the seam opens up. I am right
handed and hold the torch in my left, less dominant, hand which
leaves the right available to manipulate a pick, tweezers--whatever.
As I'm heating I apply a gentle closing pressure to the cylinder with
tweezers. This anneals the cylinder in place and I can then solder.
I do this with all kinds of things from rings to big hollow brooches
and from bronze to gold and steel. (I know of holloware makers who
employ this technique when applying "decks" to hollow forms.) I may
use a punch or probe to push with or any variety of altered tweezers.
Anyone who has taken a workshop from me has seen me do some variation
on this. I call it hot bending or annealing in place. Once the metal
gets hot enough, stresses begin to "bake out" or relieve themselves
and the metal responds to the pressure exerted on it from the
tweezers, etc. What you need to watch out for-- especially, I
imagine, with Argentum --is cracking or fracturing resulting from
over heating, spot heating, or overaggressive pressure.
Another thing occurs to me: I make bimetal earrings called "Whelks"
which are confetti like corkscrew shapes. Even if the strips that I
begin with cup a bit when I anneal them the cork screws themselves,
once they are made, rarely move. It has something to do with the
forming and the regularity of the stresses imparted, I imagine. It
really varies with the form.
I also suppose that most forms could be held in place with binding
wire, which would keep things alligned. I rarely ever use binding
wire. But regardless of what you use, I think that it's important on
larger seams to solder a portion at a time so that adjustments can be
made. Soldering is one of those things that is a back and forth.