W.E.T.Re: [CAD_CAM_EDM_DRO] Bender DRO question some OT

Hi John and All:
I can answer some of your questions and I want to warn you about
overloading the unit in the middle. At a place I did work we used
one of these units to bend up special brackets out of 1/8' thick
aluminum. The bend was about 7 or 8" long and everytime one of the
production worker put the die in to press brackets they would put it
in the middle. WRONG ! ! ! As you all ready know the bridge casting
over the top is too light as it will not bend a long piece with an
even bend. If you try to push it heavy in the middle the bridge will
break. The workers broke two before we made a new one out of steel
so we could do the job with unqualified workers. If you want to you
can add a straight steel reinforcement bar bolted to the bridge and
it helps. (wonder how I know Ha Ha) Also if you set the depth at the
middle where it springs the most the ends may be a little tighter in
the bend but you can easly pull it back if it is bent a little extra
on the ends of a long piece.
On the shears I have worked with in the last 30 years that have
automatic back gauges they all had a chain between two sprockets.
They also would go back past the locating point and come forward
towards the shear blade to the final diminsion. This includes the
ones with DRO.
On the stock thickness I worked on a smaller 48" 20 ton press
brake that had micrometers on the end of the upper ram that could be
adjust to equalize and limit the travel. I sure wish I had this now
as it was a nice unit.
I have a 4' and 8' standard leaf brakes that were my uncles but
they are in good condition. I still think if I get rich or start
selling machines I will buy a 24" or 30" unit for doing box work as
they are much quicker for that type of work.

Hi everyone,

On Thursday one of those 3 in 1 30" sheet metal tools followed me home. I
didn't have the heart to shoo it away so it now resides in my shop. The
original plan was to put a stepper motor on the back gauge and dial in the
lengths to cut or bend.

Turns out that the back gauge is moved to either the bender or the sheer
when used. On the sheer, it sits attached to the bottom knife assembly
which doesn't move. On the bender the die part moves up against the fixed
anvil to bend the metal so the back gauge has to move with it.

This means the stepper controlled back gauge will have to be easily
transported between the two mounting positions and some sort of repeatable
calibration approach used.

My plan was to use the ELS (Electronic Leadscrew) electronics to drive the
stepper motor since it's not a really heavy or co-ordinated operation.
Taking into account metal thickness and whether it should be an inside or
outside bend should allow the back gauge to be positioned without problems
and prepunched or drilled holes in the sheet metal should end up in the
correct spot relative to the bent edge. Just key in the bend length, press
start and when it's finished moving the back gauge, it would beep and tell
you to insert metal and bend or cut.

OK. So that's the plan. But like most far east products, this tool is also
slightly wanting. Adjusting it for 90 degree bends on small 1" wide 22g
coupons at the ends results in an under bend of a 30" wide piece of 22g.

So here's the question. How do the large commercial CNC based benders set
up the depth for metal thickness? Do they have a leadscrew with an encoder?
Do they use a chain or belt drive between the two ends much like my surface
planer has leadscrews on all four corners connected by a chain?

Or do they have a setup for thickness at all. Instead do they just have a
zero reference when the anvil touches the die and then back off from that
for metal thickness?

Thanks.

John Dammeyer