wide band ring sizing troubles

[Elizabeth]

Hello all,

I am having some problems with sizing metal for making wider ring band.

I've been using the formula of multiplying the thickness of the metal by 3 and then adding it to the circumference, plus 1-2mm for end straightening. This seems to work fine for thin rings of about 1.5mm but when I did exactly the same thing for a wider band (4mm) it ended up multiple sizes too big (an attempted size U ended up a massive size 1 - 6 sizes too big)!

I suspect perhaps hammering a wide ring on a tapered mandrel is stretching as it's being hammered? Is there any other tool I should be using to round a wide ring (i.e. a tool that's not tapered) or is there some other solution?

Still a newbie so apologies if there is something obviousl I'm missing here! Grateful for any help with this.

[ps_bond]

Not sure I quite follow the reason you're adding 2mm? I recently made a ring in 8x2mm silver using the formula pi*(diameter + thickness) and it came out the right size.

If you're using a steel hammer on a ring mandrel then there's a good chance you'll stretch it; I use a rawhide or UHMWPE mallet (yes, I can tell the difference - just depends which is closer) to finish rounding rings, flipping them over to even it out from both ends.

[Elizabeth]

Hi Peter,
Thanks for reply. I'm using a rawhide mallet and fliping it over to even it out so doesn't seem that's the issue.
I'd been told to add 1-2mm to calculation to allow for straightening the ends of the silver before making the ring, but actually I only added 1mm on the one I described anyway so that doesn't account for the massive size increase either.
It seems the mystery continues....

[ps_bond]

Do you have a record of the measurements you used? Just to cross-check.

[Elizabeth]

Hi, sure :
Attempting to make a U size (62.7mm) ring using 4mm wide/1.3mm thick silver wire:
So I did (1.3 x 3) + 62.7 + 1mm = 67.6, rounded up = 68mm length of metal.

[ps_bond]

My charts list U as 62.89 (20.02 diameter); pi * 1.3 + 62.89 = 66.97mm (67 nears as makes no difference).
I still don't follow the need to add on 1mm... If anything, it's preferable to make a ring fractionally small and stretch it.

Can't see how that would land you 6 sizes off - 1, yes, but not 6! Z+1 would need just over 74mm of metal.

[CJ57]

It was my understanding that it is Pi plus the metal thickness only