Quote Originally Posted by Tooly236 View Post
I am building a die to bend 1" square, I have a 8" O.D. x 2" Round die that I have machined a 1.05 inch wide by .5 inch deep groove. *I was going to make the back plate 4" long and machine the same groove into it. *But the truth is I am just guessing, I want to know if anyone could tell me if you machine in exactly 1/2 of the thickness of the material you are going to bend or something I dont know about. * Thanks to anyone that can send me in the right direction. * *I also wanted to know if there was a formula to how long the back plate has to be in relation to the material you are bending and the O.D. of the bending die. *I attached some pictures so you can understand my rambling.

Click image for larger version.  Name: back plate.JPG  Views: 251  Size: 90.0 KB  ID: 18758

Click image for larger version.  Name: side v iew 8 inch bender.JPG  Views: 266  Size: 83.1 KB  ID: 18760

Click image for larger version.  Name: top v iew 8 inch bender.JPG  Views: 274  Size: 96.5 KB  ID: 18759
My experience in that industry is that the friction of sliding the material through the backing block causes problems. It is better to let the backing block travel with the part. So my answer to your question is to figure out the number of degrees you want for a max bend. Then calculate the distance of the Outside Diameter of the bend and add three Diameters or part thickness in your case to that.