I know there are two schools of thought on the beds of press brakes. Some
manufactures machine the bed under the dies flat. Others machine it with a
crown. Several years ago I saw a unit that had a crank handle on the
bolster under the bottom die. By cranking the handle the operator could in
effect crown the bolster under the vee die.
For bottom dies most sheet metal shops use individual bottom dies that
have a key protruding that matches the keyway machined in the bolster block.
In shops doing plate work four way dies are more common. They are not as
versatile when making complicated bends.
Your boss is correct in that a vee die set flat will produce a tighter
bend at the ends than the middle when bending sheet longer than say four
feet. I started on an old verson built in 1947. The crank had about a 1/8
slop on one end. You learned how to bend on that unit. My next machine was
a new Acushear 250 ton hydraulic. It was a dream after using that worn out
old mechanical. The manual on that new machine called for four inch wide
shm stock stips under the main bolster to create the crown. I don't like
that method since I have done a lot of right hand/left hand box units and
you have to shim your dies just in from the ends with these fancy bends.
I used to do door panels: eight separeat die changes and fifteen hits.
I found some of the best shim material is the strapping that your sheet
often is wrapped with. You will need many lengths ranging from six feet to
a foot long. If I was to bend 1/8th material in a one inch vee die and the
sheet was say six feet long I would use two three foot strips, one und the
front and one under the back of the bottom die. After my fist bend I would
check the angle along the length. I might have to add two one foot pieces
in the center area.
e-mail me if you have other questions. There are several tools you can make
to speed things up.
Randy


"Lane" lane (no spam) at copperaccents dot com wrote in message
...
I've recently started using the press break at work. This thing is old,
worn out and very difficult to get set up to get decent repeatable bends.
Aluminum is all ours every sees, and not very thick either. I have some
questions for those professionals here who use one.

My boss says that even new CNC press brakes can be troublesome to set up.
He says that they often need shims under the dies or on the back stop to
get good setups. Someone please tell me that this isn't so. I can't
believe that a brand new break press would be like that.

My boss also says that the center of a part will always bend different
than the ends, and therefore you need to shim accordingly. True?

Is there an online tutorial for press break setup? I've been going by the
seat of my pants and have been very frustrated. Today I literally spent an
hour on setup to bend 8 pieces of aluminum into "L" shapes the long way.
Even after that I had to manually adjust some of them at the bench
afterwards.

Lane