Ned Simmons wrote:

I came up with this technique for folding aluminum without a brake
after learning a similar technique that jewelers use. The grooves in
the 1/8" sheet are cut about 1/16" deep with a 90 degree single flute
countersink. You can see some cracking on the outside of the bends in
the second photo - annealing or a different alloy should take care of
that in cases where it matters.

Neat. Where do you get that single flute counter sink at?

Wes