I need to wind a couple of large-diameter, fine wire springs. (light
force, balancing device. And I cannot find any "stock" springs that fit
the bill)

I have good luck with wire that is larger, and whose elastic limit is
mightily overcome by the radius of the arbor. Then they relax only a
little, and come off the arbor a few percent larger than they were wound.
I have OK luck with very small diameter springs of fine wire.

But with 0.013" music wire, I'm having trouble getting the right arbor
size for a large-diameter spring. At anything near the desired size, the
wire is only slightly bent by the process; so I know I'll need a MUCH
smaller arbor -- but how small?

I need a spring es-aKly 5/8" o.d., 1-7/8" long, of twelve turns of
0.013" phosphated steel music wire.

Anyone have a rule-of-thumb for sizing the arbor for fine wire sizes?

Or, am I stuck trying 15-20 different diameters until something just
works?

LLoyd