Experience users with sheetmetal BD

[marbien]

I am looking for a good formula for sheetmetal bend deduction with hand brake or power hydroulic brake
I cant seem to fiqure it out with so many out there, So I am just looking for that quick formula no need for precision just close to get by
Thanks

[weldnman]

There isn't really a formula, it's tied to the radius of the punch and the thickness of the metal.
I have a bend allowance chart that will get you close.(do a search for bend allowance chart)
However the best way is to shear a small strip of metal measure it with callipers bend it to a 90 and measure each leg. Keep a notebook by the brake with this info in it.

[-Chris-]

What i do when bending quick little jobs is first i'll convert any ID to OD demensions to OD dims. then add up all the bends to be made. Picture a hat section with 1" feet 2 " legs and body of 4" all od dims, made out of say 16ga mild steel lets say .062 thk matl I would add all those dims 1+1+2+2+4=10" for a pretty sharp bend in mild steel you can get away with not much inside bend radius so for a bend deduction i use about 85% of the material thickness so i use .052 for each side of the bend or .104 per bend so the shear size is 10.00 -.104 4x i cut the pc @ 9.584. then when you go to bend the foot you take the 1" od foot and subtract .052 and make the bend @.948" in from the edge you should get a close dim to 1" do the same for the 2 " legs . but as mentioned before a good way of finding what your machine does is take a pc of matl that your bending cut a 2x2 square bend in the middle 1" and see how much it grows use that number for your bend deduction. this is ok for 90 deg bends with no inside bend radius to speak of. But when you add large bend radius's its a whole different routine. there is a whole bunch of formulas for bending that take into account the matl thickness type of matl K FACTOR , BEND ANGLE, SET BACK and such but for a hand brake you can make this work pretty easley. Setting up a hand brake has a few steps to follow in itsself to get good bends. I hopr this made a little bit of sence