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Posted by Chriscase [76.201.17.56] on Sunday, October 04, 2009 at 09:52:16 :
In Reply to: Double the thickness is 1/4 the width. posted by Chriscase [76.201.17.203] on Sunday, October 04, 2009 at 01:02:07 :
When bending metal precisely, work to the outside dimensions. Subtract 1 1/2 times the material thickness for each 90° bend. With a press break, you want to center the upper die at a compromise location, 3/4 material thickness shy.
Here's a press break tonnage chart. Note that thicker material takes a wider bottom die. Tonnage goes waaaay up if you use a narrow die and try for a sharper bend.
I used a piece of angle iron for my bottom die. It was a left over bit from replacing the top angle iron on my winch. 2x2x3/8, sawed the edges off to 1 1/2 wide. Upper die is a piece of 1/4", ground to 45° from each side.
http://www.americanmachinetools.com/pressure_table.htm