Bending Metal

I'm going to get out my new bender that's been in the box on the shelf for
years now. I used to have one made by Breakdown Industries. It's just one
of the common ones with the dies that mounts on a stand.
When figuring the bends, and doing so as not to make three incorrect copies
while arriving at one acceptable one, how does one calculate the amount that
any given piece of metal will "grow" during the bend, so you can cut stock,
make the bend, then have it come out right.
Or do you just make it, then cut the excess off, or stretch it if short?
Is there a guide of this kind on line? Also, figuring out and marking where
to start the bends, and in general things that can help me rather than the
old trial and error method, particularly at today's steel prices.
Reply to
Steve B
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Machinery's Handbook, find "Bend Allowance" in the index and then look it up to determine for specific material, radius, and thickness.
Reply to
Terry mentioned the bend allowance tables. But.....
It's helpful to look at how the metal behaves; A couple of things: First is that the neutral line is pretty close to the center of the material: the outer edge gets stretched (and thinner), the inner edge gets compressed (and fatter). So if you you do a half inch radius on 1/4" stock, the material in the bend will see a 5/8" radius.
The other ugly part is the springback. Some springback will always be there: not all the metal is stretched beyond the yield point, any that is not is in the elastic range and you will get springback. You can minimize springback by making sure your dies are adjust to put all the bending action at a single point. If you have any gap at the point of bend, you will have more springback.
I did quoting for various bent tubing parts. It was always safer to bend first and do trims as a second op. Ditto for any holes. Drilling might be easier on flat stock but getting the holes in the right spot was always dicey that way.
Steve B wrote:
Reply to
Draw the piece, label the bends in order and on which side, bend thin pieces of stock to dial it in. Measure everything possible in the brake, and cut off after the bend if practical.
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