Steel bending

kdlklm · Mar 27, 2013

I have got some rectangular tubing that I need to bend a tight radius. It is 1x2x.125 Rectangular tube. I need to bend four pieces that are 30 inches long. The image below shows two of the pieces as they will appear finished. Wondering what would be the best way to bend something like this. I would like to do it myself, I did phone some machine shops and they wanted a lot of money. Any suggestions would be appreciated.

jimgerken · Mar 27, 2013

Cut 45 degree angles, flip and weld up, then grind if desired. IF you actually bent them as shown, the outside surface would be really thin. I assume it could be done with heating it and proper fixture. Cold, I doubt if that tight of a bend can be done in tubing.

GLyford · Mar 27, 2013

Similar idea, if you absolutely need a radius and not a sharp corner: Grind a few slots 1/4 to 1/2" apart, with a bit of a wedge shape leaving the outside of the curve intact. Bend it so that all the slots close up, weld, grind smooth. You might have to regrind a few of the slots to get the bend you want before you weld.

You could also grind a slot at the start and end of the curve, and remove the inside surface and side walls completely. Bend the outside to a curve you like, then clamp into position. From the scraps, bend the inside surface to match the new curve and weld in place. Trace the arc shape for the sidewall onto a piece of scrap, cut out two pieces (using any of: bandsaw, grinder, torch, plasma, cnc), weld in place. Grind to match.

CliffordK · Mar 27, 2013

You could try heating a piece and bending it in a vise.
The radius would likely have a bit of a concave look from side to side, and the sides may be pulled in slightly.

You might be able to protect the structure of the piece some by shoving a tight fitting solid bar into both ends, but you would have to plan on getting it out once it is stuck. Or, perhaps filling it with sand.

As mentioned, a sharp right angle bend would likely significantly weaken the tubing.

jimgerken's plan of cutting out a wedge, bending, and welding would likely give the strongest results as long as you can live with the results.

You could also build some kind of a die to bend it around, giving you a small inside radius.

Do you need tubing? Or is a flat bar ok?

sdkubota · Mar 27, 2013

The tubing walls will collapse or buckle without internal pressure. At a minimum I would fill tube with sand if cold bending. I think the cutting/welding option is the most achievable without expensive tubing bending tools.

strum456 · Mar 27, 2013

sdkubota said:
The tubing walls will collapse or buckle without internal pressure.

That is what will happen, guaranteed. Cut and weld.

jwmorris · Mar 27, 2013

All you have to do to keep it from buckling is to displace the metal.

I bend box tube using a common flat iron worker with a die to hold the box and round barstock I bent to displace the inside diameter, the outside takes care of itself. Put the seam either up or down not on the inside or outside, for best results.

flyerdan · Mar 27, 2013

If keeping a rounded corner is important, I would suggest filling with dry sand, as previously mentioned, and building a jig with a piece of pipe (or better yet a heavy bolt) sized for the desired radius. Have a top plate to keep the sides from buckling outward and heat it to bend. Have a stop about 2 degrees past 90 to allow springback. Since you're only doing 4, it should give pretty good results and not take forever to knock up the fixture.

CNC Dan · Mar 27, 2013

fill it with cerrobend and bend it in a press break.

strum456 · Mar 27, 2013

I just reread the question and some of the posts. There is the "cut and weld" group and the "bend it" group. Both groups are correct; it just depends what you are trying to do. You refer to a picture, but I don't see one. Maybe this would answer some of my questions.

1. What do you consider a tight radius?

2. Which way are you planning to bend the tubing? Will the bend run perpendicular to the 2" dimension or perpendicular to the 1" dimension?

3. How many degrees does the bend need to be?

ghenges · Mar 27, 2013

kdlklm said:
I have got some rectangular tubing that I need to bend a tight radius. It is 1x2x.125 Rectangular tube. I need to bend four pieces that are 30 inches long. The image below shows two of the pieces as they will appear finished. Wondering what would be the best way to bend something like this. I would like to do it myself, I did phone some machine shops and they wanted a lot of money. Any suggestions would be appreciated.

View attachment 310193

Very tight radius you are attempting to bend. Won't say it's impossible, you'll need to experiment to see just how tight a radius you can accomplish.
Bends like this are usually accomplished by mandrel bending.
You can "approximate" the mandrel bending process at home by filling the tube to be bent with molten lead (melt down a car battery or two). Lead is way better than sand.
The lead can be removed by simple heating the tubing.

Cerrobend is better than lead, but costs $15.00 - $20.00 a pound.

Make a jig on your shop press or rig a hydraulic cylinder to essentially emulate a press break. It's going to take substantial pressure to bend the tubing.

Another method is enclosing the tube by welding the ends shut, on one end fit it with a 3/8" hex socket screw or pipe plug.
Fill the tubing with water, screw in the plug and bend. The pipe can also be frozen to increase the internal pressure, being careful not to burst the tubing.

Please let us know how you make out.

kdlklm · Mar 28, 2013

Bending the tube was purely cosmetic, but I'm thinking that I'm going to lean more to cutting and then welding it. But you have given me some really good suggestions. I've attached two renderings of what the difference would be, I've just always been a little picky about how things look as well as how functional they are.

It was 107° bend with a 1 inch radius. Really tight.

ghenges · Mar 28, 2013

kdlklm said:
Bending the tube was purely cosmetic, but I'm thinking that I'm going to lean more to cutting and then welding it. But you have given me some really good suggestions. I've attached two renderings of what the difference would be, I've just always been a little picky about how things look as well as how functional they are.

It was 107° bend with a 1 inch radius. Really tight.

View attachment 310305 View attachment 310306

If weight is not a problem, 1"x2" flat bar stock would bend nicely to the radius you desire.

GLyford · Mar 28, 2013

If you make 6 cuts over 2-1/2" (1/2" apart) each about 0.2" wide at the inside of the wedge (mark each at 1/8" and cut outside the marks with an 0.040 cutoff wheel will get you pretty close to that), you'll have a pretty close approximation...and you won't have to hold the metal in place like you would if you did a cut-and-flip.

M E Race · Mar 30, 2013

Sand workquite well in most cases, but if the piece to be bent is short enough I'v found that filling it with water and freezing solid works better tha sand without resulting in a concave area on the inside of bend.