The general rule of thumb is that the material, any material, needs to be properly supported on all sides. This does not mean that the tooling should be too tight on the material as that will only create drag on the machine and increased wear on both the tooling and the material.
A good starting point for square tubing is approx. 1/8” of clearance on both sides of the tubing. This will allow for some expansion of the tube without completely squashing it. If it is too tight, the tooling will begin to shave the material, evidenced by actual metal filings being removed and the machine struggling to bend the metal. It can also lead to the thermal overload on the drive system kicking in, shutting down the unit. Should the tooling have too much clearance, the finished material will not retain its “square” shape.
No matter how the tooling is set, square tubing will always cave in on both the inside and outside radii surfaces. This concave look cannot be avoided without the use of a mandrel style bender.
Roll bending square tubing is a trial and error process, as certain materials and sizes will require the tooling to be adjusted.
In certain instances, the material may require rolls which are designed specifically for the material size. This may incorporate larger diameter side plates or differing diameter rolls to keep the material in check.
View Baileigh Roll Benders.