I suppose the advantage to this setup is the high pressure clamping the two dies together - maintaining tube shape. Dis-advantage is that the clamping force is 'stolen' from the bending force.
Just a heads up, these kind of benders are used extensively by 4x4 builders, so you would get a ton of help if you ask on the forums at pirate4x4.com.
Looks like the bending die is asymmetric around the pivot point. The radius of the die must be offset from the pivot point. Did you make the bending die?
This type of bender is designed so there is minimum offset between pivot and force input - thus it needs lots of force but little travel, exactly what a bottle jack provides. Unfortunately this means it's also horribly inefficient with most of the force being exerted on the frame. Look at your design and you'll see most of the forces are in compression or tensions through the steel, except that lower plate that contacts the jack - it's the weakest link. Try welding some 'fillet' plates in a 'V' from jack contact out to top edge.
No I didn't make the die, it's a Pro Tools Portabender die set. Apparently that's what the plans were based on
These photos of a 3/4 front view of the device virtually conceals the geometry of the action. A clear side elevation diagram showing the alignment of the die set and Jack would easily reveal the leverage effects. Is this a copyright design? Can we see the plans?
Does that look right to you? I think that it's in front of the pivot enough to rotate, not sure how to correct that if not
I agree this is the problem too.It looks like your jack is set too far back under the die and needs moving further out towards the end where the clamp is. The yellow one looks to be under the front of the roller.