Days late, dollars short, etc., here is the bender I was talking about above. It was inspired in twain by a Matt the Maker instagram post of FDM 3D printed bending dies sandwiched in steel plate and my need for identically bent 3/4" chainstays. Can you guess whose great idea I totally ripped off?
When the only precision tools you have are a lathe and a computer, all of your designs start to look axially symmetric or like a 3D puzzle piece. Thus, this is made from laser cut 0.188" mild steel, 4 separate PLA bending “dies” in the body of the bender which are sandwiched together (to avoid overhang that would occur if printing a semicircle in that orientation), lots of bronze bearings, some leftover stainless round bar, and some 12L14 hex bar with turned down bearing surfaces. It uses tab-and-slot (Pettis?) joints for most of the 3D geometry, and these are either poorly flux-core welded or poorly brazed together. Its a 4" CLR, and technically you can print different size dies, follower, and clamp for different size tubing, but I haven’t. Lots of through holes for lots of long screws to hold everything together, possibly in different configurations.
Like my other 3D printed benders it gets the job done, if only just barely. It lacks some crucial features that the original has, and this makes it very annoying to set up. Even so, it does just good enough of a job to where I don’t consider the 3/4" x 0.035" tubing I’ve bent with it to be scrap. 3/4" x 0.028" is better left to real benders. I’ve used it enough to feel a lot less proud of it - there are a TON of simple revisions I would make if I I made another one, but I have already sunk a ton of time into this project and I have almost no intention of making another. I actively discourage others from making something like it. Seriously, just buy Joe’s bender or make friends with someone who has one.