sharp bend

[Gages]

I've been playing around for years making fibreglass boats ect and have recently been playing around making my rudders out of 3mm Al and need to weld a bit and got the hang of that but now I want to make a nice sharp 90deg bend on a piece about 15cm long 20 wide but only 2 cmm down on one side....

so
My question is any secrets to a home made jig that I can make myself to bend this sucker ?

Cheers

[pipeclay]

Trying to decifer your sizes it would appear that you maybe looking for a piece of 3mmx20mm equal angle 150mm long is that correct,if so that can be easily bought.

[Stustoys]

Maybe 15cm x 20cm with a 2cm fold?
Sharp folds are a bad idea in steel, they are an even worse idea in Alum. Does it need to be strong? If so I think you'll have to come up with another design.

Stuart

[joe greiner]

The "sharp" bend you seek will be limited by the minimum safe bending radius to prevent cracking, as Stuart indicates. This is generally on the order of several times the sheet thickness, and there's often insufficient tangent to secure in the brake.

The "secret" is to make the tangent portion over-length, make the bend, and cut off to the required dimension.

For a very sharp bend, an extrusion would be superior.

Cheers,
Joe

[dj_pnevans]

You could put some heat into the bend but it will still be weak.
David

[Hunch]

Here's a bend radius table for various alloys - some not readily available in Oz though and the one you'd want to use in water, probably one of the worst for bending.

http://www.aircraftspruce.com/catalog/pdf/aluminumalloy.pdf

5 series probably easy to source just about anywhere and not too bad to fold on the other hand. When bending, sheets of alloy either side of the piece being formed is the hot ticket to minimise cracking - at least on a brake.

[Stustoys]

I've found on small radius bends in Alum grain is very important. Much more cracking if the fold is parallel to the grain than if its across the grain. Also all settings being the same one has more spring back(cant remember which, I'd guess that the one that isnt cracked). Does anyone know if this effect is effected by which temper is used?
Stuart

[Karl Robbers]

I've found on small radius bends in Alum grain is very important. Much more cracking if the fold is parallel to the grain than if its across the grain. Also all settings being the same one has more spring back(cant remember which, I'd guess that the one that isnt cracked). Does anyone know if this effect is effected by which temper is used?
Stuart
Temper and grade both affect the bendability of aluminium alloys, some like 5183, require a radius top die instead of a knife edge die. Grain direction comes into play far more with these alloys as well.

[rusty steel]

Hello Gages,
You could try to buy a piece of extruded rectangular tube either 150x50 or 200x50(x3.0). The full length is 6.5 metres. Capral will usually cut the larger sections in one metre lengths .
Russell