# How much wire do I buy? Elongation calculation post rolling mill

Hi,
I’m making a ring 2mm square x 83mm but have to buy 3mm square wire and mill it down. My question is…is there a rule of thumb about how to calculate how much the wire will lengthen in the rolling process and therefore how much I should buy?
Thanks so much

Hi Liz,.

Yes there are calculations and no I don’t them. What I did was to take notes on every piece of sure I ran through the mill.

I am puzzled why you can’t buy the size wire you need. Or but 2.5 x 2.5 stick and roll that down.

Take a piece of graph paper and Mark it a 3x3 piece of metal in Cross section and you have 9 square units do the same with the 2x2 which is you finished size. You have 4 square units which is slightly less than half the original material in Cross section. When you roll stock you are essentially pushing material along. And since you aren’t destroying anything I’d bet that by rolling a piece of 3x3 down to 2x2 you’d come close to doubling the length.

In any case it would be a fun experiment to try on anything less expensive than gold.

Have fun

Don Meixner

I’m probably going to embarrass myself here by answering this. The way I would approach the problem is to calculate the volume of there rectangular form that you want to get to: 2mm x 2mm x 83mm = 332 cubic mm.
Then 3mm x 3mm x length = 332, 332/9mm = length or 36.8 mm. I would add a bit as a fudge factor and make it an even 40mm and use the remainder later.

Yep, it’s a simple volume question. You’re not going to lose or gain any material, obviously, so the increase in length will be proportional to the ratio of cross-sectional areas.

3x3 = 9
2x2 = 4
Therefore, the length will increase 9/4, or 2.25 times, assuming you roll a perfectly accurate 2x2 square.

And I agree with David. Give yourself some leeway. Just like cheap tools are the most expensive, so is cutting too little material.

Good luck,
Alec

Hello all,
Thank you so much for taking the time to respond. I’ll work with these suggestions and practice on a piece of silver.

I agree that it would be so much easier to just buy the 2x2mm sq but I only buy recycled gold which they only sell in either 1 or 3mm square.

I’ll let you know how I get on!
Thanks again

Liz,

Try Hoover and Strong.

Don

Hey thanks Don,
I’m in the UK so import tax would probably make that prohibitively more expensive…appreciate the recommendation though.

Kind Regards
Liz