DanG wrote:

I haven't seen anyone talk much about backing off the break and
putting in a sacrificial spacer. It increases the radius of the
bend and helps prevent that fracture line from forming. I am not
a tinner, but our tinner has done this on aluminum shapes when the
material wants to shred or crack.

I was taught this procedure under the name of "packing the brake". We
used strips of .063 1100 about 3 inches wide. If you are careful with
them you can build yourself up a set of nesting packing strips that work
well.

Better is to have radius nose blocks on the brake, but ya gotta do what
ya gotta do.

It's pretty much a given that you will not be sucsessful bending a
radius smaller than a certain number of thicknesses (3?,4?). Temper and
material cause variations, but IIRC thats about the normal minimum for
aluminum.

Cheers
Trevor Jones