Sorta bit the bullet here with my 40" chunk, secured one end with a plastic cap & a hose clamp, filled with sand & taped the open end, measured off & marked the center at 1'" increments up to 10" (L) to (R) to allow for the radius. The initial bend began in the center with 5 full pumps & alternated (L)to(R) on the marks with 5 pumps on each, back through again until a true 90 degree achieved. minimal dimpling from the rollers & only slight wavy radius on the anvil side. General consensus is acceptable unless the minor dimpling is of concern, good enough for this old racer & getting it back to square one.
Your .104 wall is a big part of the problem unless you get precision dies for chrome moly and the proper bender to use them in.. With the bender you refer to you'll have better luck with DOM tubing that has .134 or so wall, the minimum wall thickness for a hoop is 1 3/4 x .118 per NHRA spec, the heavier wall will actually bend better. I've bent a lot of tubing.
I have done this use used 1.25 or 1.5 oil field pump barrels If you anneal them before bending they work fine with the bender you have
I bent a lotta tube. I have 1 of those type that uses a bottle jack, 7" radius (I think) and it never failed me. It grabs the tube and pulls it around the shoe. I used to oil the roller and the shoe, no kinks. The NHRA spec is a minimum because all tube gets thinner in the bend. A ch***is cert doesn't measure in bends for that reason. .120 DOM bends the best.
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