Before I do something daft I thought I’d check on here….

I’ve got a strip of aluminium (19mm wide x 4mm thick) that I want to bend 90 deg. Can I just slap it in the vice and bend it or might it crack? Should I heat it first?

Should be fine. Remember to protect the aluminium in the vice with cardboard or similar and use a soft hammer. To gain a nice bend you will be best hitting it near where you want the bend or putting a larger section of wood over the bit you want to hit so you keep it in tact.

Are you trying to put a sharp bend in it?

4mm thick will probably crack on the outside edge I reckon, if you just stick it in a vice & whack it round the edge of the jaw.

If you could use some pipe or something as a forming guide to bend it round and give it a larger bend radius you should be OK.

Sharp preferably …. basically making a U shaped bracket for holding a gauge in. It will be hidden so looks don’t matter too much.

Arent they doing a live lounge session soon?

Very little chance of it not cracking, especially if you start whacking it with a hammer, and then a high chance of failing in use if it does survive the forming.

Either use a curved former, the larger radius the better or try it with a minimum of two 45 degrees bends each side.

A lot depends on the grade and heat treatment state of the aluminium to be honest. The cheaper it is the more likely you’ll get away with it as there won’t be so many alloying elements in it to give it strength. A 6000 or 7000 series will almost certainly crack at 90 degs.

Vice Brake

Is what you need.
I’ve got a smaller one – does a grand job and very controllable (unlike battering it with a hammer)

Done it ….. tidy bends but it cracked at bit – may reinforce the joints with some epoxy.

You rub it with a bar of soap then heat it with a blow torch. When the soap blackens you bend it.

Learnt that in school i did.

Agh, too late. Always bend against the grain when forming Aluminium(s).
I used to do a little of this for work & against the grain is the general rule.

Arent they doing a live lounge session soon?

Tomorrow night, Dublin Castle, £6, £5 concessions.
😉

Bend it 45 degrees. Get blow torch on it. Heat it up. Bend to about 70 degrees. Heat it again. Then to 90.
By bending it, Alu work hardens. By heating it between bends you normalise the grain structure again.

I googled this, loads of info. You need to anneal it first.

You rub it with a bar of soap then heat it with a blow torch.

Or it gets the hose again.

Correct, it has to be annealed.
Heat it up slowly, aluminium melts from the inside out, as mentioned a bit soap is a good pointer.
Allow to cool and then bend.

Depends on the grade of alum. Different grades with different tempers.

Forming to 90 degrees isn’t the issue, it’s the radius of the bend that counts. To put it in driving terms, you go round a 90 deg turn on a single track road at 20mph, but can hit a motorway 90deg at 70mph. Both are 90deg turns

G