Originally Posted by 123pugsy
You'll need to go around 3 sides of the frame with some substantial thick walled tube to make it stiff enough. This is only if you need the metal to change shape quickly. The machine will work right out of the box, you'll just have to keep at each panel longer.
Besides the soft frame, the wheels have been known to be out of round. If they are too far out, they will only put pressure on the sheet for about 1/4- 1/3 rotation of the wheel and this will give you hard time to get the panel stretching at an even rate.
I haven't tried a wheel being out of round before and I sure wouldn't want to.
Pugsy is correct. They will work out of the box just not as quickly. We built mine years ago before they were as common as they are now. Way over kill. It does not require nearly as much pressure as you may think to raise the metal. One thing to watch out for on a cheap wheel is the way the anvils are machined. There needs to be a flat spot on the small anvils. The lower the crown the wider the flat spot. This will affect the smooth finish you attain.