I formerly straightened the copper wire into “bus bars” for the astable multivibrators by whacking it with a slide hammer, but someone whose name is lost in the mists of time told me the right way to do it:
Yup, grab a piece of wire at both ends in Tiny Lathe and give it a few low-speed turns while pulling firmly on the tailstock.
No muss, no fuss, no drama, just bar-straight and slightly work-hardened copper wires:
I slide-hammered the top wire before remembering the clue. The bottom two wires have peppermint-stick swirls.
Thank you, whoever you were!
The Smell of Molten Projects in the Morning 
I do it like this: Clamp one end of the wire securely. Wrap the other end around something stout like dowel well enough it won’t slip. Pull on the wire until you feel it yield (it will relax slightly and then tense again but a little longer.) Voila!
Aaaand, I see that’s pretty much exactly what I said on your last post. ‘doh. I guess I’ll add that I usually do it like a dead lift, holding one down end with my feet and using the mechanical advantage of only the last few degrees to standing straight to activate the yield (it only stretches a fraction of an inch over that distance.) I do this with up to about 12ga and am pretty sure 10ga is possible.
My back informs me I should gimmick something mechanical, perhaps involving a crowbar, but that’s definitely the way to straighten wire beyond Tiny Lathe’s capacity.
Or I need a much longer lathe … [grin]
Didn’t you once have a, “much longer lathe”?
Yup. Hadda give it up in the Great Shop Purge.
After four years, the “I know where that used to be” thought still happens occasionally.