simply, from knowledge in the aerospace and bondo car patch business, ohh I mean auto/motorbike bodyman and customization business, it wasn't too difficult to repair a handful of dented and slightly bent booms I had waiting for one day. That day came last weekend when i ran clean out of fresh and bright new 450 booms and the one on the heli of concern looked even worse than what I will soon show you.
Here's da ding, or in plain English "the thing", da ding is sort of eyetalioni for cha-ching, like I gonna save-a me-a suma monee.
I took a metal steel rod large enough to fit in the boom, tapping/pushing it past some of the deeper dings, then took a piece of maple hardwood 1"x1" and flat face tapped the dings out while also rotating the boom with the metal rod in it to even the inner impacts pushing the dings back out of the aluminium booms.
Works like a charm, if the dings aren't so deep they pass the halfway mark of the boom's diameter. A need to straighten the boom a little first will be in order prior and if the boom is banana shaped badly it may not work. Often the boom is slightly bent where it went into the tail block, that's a little tricky but I carefully use the chassis when the boom is on it and recheck a few times by eye and then ruler.
It's what I had to do on a Sunday when no hs was around, none that had any stock, none nearby and I want to fly. Stripped a servo gear besides so never got to fly it after the fixer. Belt drive is not critical, torque tube it may not work very well if it isn't arrow straight,
I used a drill bit extension as my inner rod and would ultimately have inserted a rod just under the id to perfectly even everything out. If you can do that then it'll end up that much better.
Doesn't work on cf.