Bender question

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