What is the best method for bending aluminum square tubing while keeping a tight radius and minimum distortion?

Buy a pipe bender from a hardware store. Then fill the pipe with water and freeze it, this will stop it form compressing.

Frankly, I don’t think you’ll get this to happen. Here’s a table showing minimum bend radii for various tubes. Assuming a round tube (which would be easier), a 1½” dia aluminum tube has a minimum bend radius of 5” on the centerline. Aluminum will stress-crack like crazy if you push it too far. Periodic annealing might help, but I’m still not optimistic.

@usaloveorleaveit Welcome to Fluther!

Have you thought about cutting at an angle and welding a corner into your pipe instead of bending it? that way you avoid disortion altogether, no narrowing, no crimping… and if you do it correctly there should be no noticeable change in the continuity inside or outside.

I agree with Dr_C, although welding aluminum takes some real skill due to its low melting point.

That’s REALLY hard to do, you’re trying to do way too tight of a radius =) Especially with that wall thickness.

Heating & bending may work.

Filling it with sand, capping the ends, heating it, bending it, forging the crimps back into the square shape, then uncapping the ends and draining the sand may work.

These chairs: http://www.target.com/gp/detail.html/175-0120735-4285759?ASIN=B0002VISEC&AFID=Froogle&LNM=B0002VISEC|Cafe_Aluminum_Side_Chair_Set_of_2&ci_src=14110944&ci_sku=B0002VISEC&ref=tgt_adv_XSG10001 have a similar radius to what you’re talking about, but they have a dimple from stretching on the inside, and they are far thinner wall.

I think your best bet may be the welding approach. What I would do is build up a radius from flat pieces. That is, cut the top & bottom pieces, then cut & bend the inside and outside radius pieces, and weld the whole thing together, then chase all your welds smooth.

Notably, the problem you’re facing is that the difference between the length of the OD and the length of the ID is significant. At a 90-degree bend, you’ve got 4.713 inches on the OD, and 2.355 inches on the inside. With your 0.25 wall thickness, you’ve got 0.88 in^3 that you need to ‘get rid of” just on the inside face.

Another option is kerf bending, but that’s far more welding and chasing than just building the corner out of bar stock. In short, you make cuts most of the way through the piece on the inside (if you’ve got a blade with an 1/8” kerf, you make about 19 cuts to do a 90 degree bend), bend the piece, and then weld it all back together, and then grind it smooth.

Fill the tubing with dirt or sand before bending.