Folding brass

[jadboog]

Hi all,

I'm having real difficuly folding brass angle (3/4 x 3/4 x 1/8) over to make saw backs. The first two attempts the brass ruptured and is now unusable. I have one piece left that I don't want to ruin.

I've contacted a few metal fabricators who say the brass is too thick, but I checked the thickness of an old Sheffield saw and it is that thick, so it must be possible. Other forums say I need to anneal the brass first - heat it to just below red and cool it before folding. None of them are interested in the job because it is too small.

Does anyone have experience of this that you could share ? What would be the best way to heat that hot - I'd rather not build a forge or spent £80 on a blowtorch to make one saw!

Thanks

James.

 

[jadboog]

I've just got off the phone with a blacksmith who reckons even with annealing I might have difficulty as there is more material at the intersection of the angle which will put stress on the remaining pieces.

He's given me an elderly chap's number who does small metalworking jobs for him - the best solution might be cutting a slot in a brass bar. Will update later.

 

[Sheffield Tony]

I think you have the wrong sort of brass most likely. Flats, angle etc are often grade CZ121, which is an alloy suited to machining but not cold forming. Sheet stock is more often CZ108, which has better properties for cold working.

 

[jadboog]

Tony - thanks for the tip. The blacksmith also mentioned that I might have the wrong sort, but its good to get clarity on the numbers.

James.

 

[Graham Orm]

Have you tried folding it whilst it's red...or hot at least?

 

[Cheshirechappie]

Wot Tony said. If you can track down any Spinning Brass, that's supplied in the fully annealed condition, and is very ductile compared to even CZ108.

Most of the bespoke makers seem to use machined backs, though you need a fairly rigid machine to successfully mill a thin, deep slot. Another (simpler) answer for a one-off might be to build up the back from three pieces of brass; two flank pieces from flat bar and a strip of narrow shim the same thickness as the bladestock or a tad thicker, between them. Hold together with a good quality engineering adhesive, or by using a row of brass rivets. Done with care, and with the top filed to a crown, it could look just like a folded back without any of the hassle of bending and trying to keep things flat and straight, and would provide the same weight and stiffness as a folded or machined back.

 

[-Matt-]

Sheet stock would be the best way to go. I wouldn't attempt to bend angle around anything.

You want to bend the brass up and well past 90° to as far as 135° then slot another piece of material in (which is the same thickness as the blade would be) and then press it all together to create a nice U section.
A propane torch should get it to a decent annealed temperature, a plumbers one with a nice broad flame will give you a nice even heat over your material.

Hope this helps
-Matt-