1. Of the 3 rollers, only the middle one needs to fit the stock, right?
The outer two are just pushing and no bending is taking place there.
Except when bending angle iron with the leg out, or when bending flat
stock the hard way, the outer rollers hold the stock "upright".

2. Grant (I think) posted recently about bending tubing quick-and-easy
by bending around a cylinder whose thickness was equal to the tubing
diameter and sandwiched between 2 flat pieces. I.e., the cross section
of the die was as wide as the tubing, but was square & didn't fit the
tubing at all points (just at 3 points). He reported that this did a
fine job bending and that the tubing was not distorted.

Could this style die be used on large scale benders such as Ernie, Don
(?), and ed_h have built? Such a die would *so* much easier to make,
not having to turn semicircular profiles. Also, dies could be built up
by stacking different thicknesses. I suppose the answer is that if it
would work, somebody would would be doing it, so it must not work. What
do you think?

Bob

1) No bending is taking place at the outside ones but the bending
PRESSURE is applied out there. Only half the force at the point of
bending but that is usually enough to deform the tube. Net: the outside
rollers need to have the correct shape if you plan to do anything
agressive or with round tube.

2) Square die and round tube is ok for very mild bends. Get aggresive
and the round tube will collapse.

3) Stack dies are commonly used for square/rectangular tube, not for round.

Net: nope, ya can't take any shortcuts if you plan to get aggressive

Bob Engelhardt wrote:
1. Of the 3 rollers, only the middle one needs to fit the stock, right?
The outer two are just pushing and no bending is taking place there.
Except when bending angle iron with the leg out, or when bending flat
stock the hard way, the outer rollers hold the stock "upright".

2. Grant (I think) posted recently about bending tubing quick-and-easy
by bending around a cylinder whose thickness was equal to the tubing
diameter and sandwiched between 2 flat pieces. I.e., the cross section
of the die was as wide as the tubing, but was square & didn't fit the
tubing at all points (just at 3 points). He reported that this did a
fine job bending and that the tubing was not distorted.

Could this style die be used on large scale benders such as Ernie, Don
(?), and ed_h have built? Such a die would *so* much easier to make,
not having to turn semicircular profiles. Also, dies could be built up
by stacking different thicknesses. I suppose the answer is that if it
would work, somebody would would be doing it, so it must not work. What
do you think?

Bob

I cut a shallow flat depression in the outside rollers, mainly just to
guide the stock and keep it going straight. I didn't want a corkscrew.

My rollers are 2 inches wide and 5 inches OD, and I've considered
turning a profile in the bottom of the existing 1-1/2 wide one for a
smaller shape.

I cut a shallow flat depression in the outside rollers, mainly just to
guide the stock and keep it going straight. I didn't want a corkscrew.

My rollers are 2 inches wide and 5 inches OD, and I've considered
turning a profile in the bottom of the existing 1-1/2 wide one for a
smaller shape.