Tubing benders

[pkastagehand]

I didn't know if this should go in questions and answers or here in tools. I'll try here...

I bought one of those Horror Freight pipe benders; you know the one with 3 wheel dies and a big hand wheel to turn it. The dies are all for round tubing. I want to bend 1 inch square tubing. I have done this before with a homemade unit built similarly to the HF unit but no hand wheel. Just had to push/pull the stock through it. Also, the wheels were just flat cast iron wheels and I used posts with bushings along the side to guide the tube (relatively) straight.

I was thinking that similar to the round tube dies, if I made wheels with a square walled profile they would guide the tube for me. The wheels started with 4 inch CRS slugs. I have them 1/2 inch deep (on the radius, leaving 3 inch diam.). Is that enough? Too much? I figured half the tube gets me to the neutral axis where no compression or elongation should be happening much.

The bottom rollers are on the outside half of the curve where the tube is in elongation so side clearance may not be much of an issue.

The top roller is on the inside of the curve and is the side that is in compression in both in terms of length as well as maybe some flattening. I started with only about .030 inch side clearance. After starting to curve a test piece I'm already starting to wedge in the top wheel because of the deformation. Any ideas how wide I'm going to have to go and can it only be the top roller that gets widened? I suppose it depends on factors like tubing wall and radius of bend. Other factors?

Paul

 

[Ken I]

Square tubing typically collapses its walls inwards - there's nothing the external rollers can do to stop it.

Professional production tube benders insert an inside mandrel (usually made of Ally-Bronze) held at the bend point and even then there is some collapse.

For a one off try filling it with Cerrobend or other low melting point alloy made specifically for such applications.

Ken

 

[pkastagehand]

Square tubing typically collapses its walls inwards - there's nothing the external rollers can do to stop it.

Ken

I've done a small amount of this over the last few years with my first home made bender and this has not been a problem at the radii I usually bend to. We're talking a roller not a "bender" so to speak.

My problem has been a mushroom capping outward near the top wall (inside wall of the curve) which started it binding in the top roller. I can make more width on the top roller and try again and eventually get (hopefully) something that will work. I had hoped someone might be able to get me harder data.

 

[Ken I]

I meant roll bending - but the problem is still there it depends on radius and tube section.

Try looking on the Addison tube bending site for tables or information - these are one of the foremost manufacturers of tube bending machines.

Here's a link to the Hines tube bending guidelines book in *.pdf

http://www.hinesbending.com/BASICTUBEBENDINGGUIDE.pdf

Most of these will refer to "wipe" or mandrel bending.
Ken

 

[pkastagehand]

I meant roll bending - but the problem is still there it depends on radius and tube section.

Try looking on the Addison tube bending site for tables or information - these are one of the foremost manufacturers of tube bending machines.

Here's a link to the Hines tube bending guidelines book in *.pdf

http://www.hinesbending.com/BASICTUBEBENDINGGUIDE.pdf

Most of these will refer to "wipe" or mandrel bending.
Ken

Thanks for that PDF, good information.

I didn't see anything on the Addison site that seemed like tables etc.

I know I had success down to about a 2 foot radius using flat rollers and guides so I'll just widen the groove in top wheel and see what I get. Or switch to a flat wheel on top and use the grooved wheels on the bottom for guiding.

Paul

 

[pkastagehand]

Well, I got my tube bent. I made 3 wheels for the Harbor Freight tubing roller. I used 4" CRS. I bored the bottom two rollers to fit bearings just like the stock wheels that came with it. I bored the shaft hole, drilled and tapped the setscrew holes for the upper wheel. The square sided cutouts in the lower wheels are 1.030" wide and the top wheel I made 1.125" wide after measuring some 1" square tubes that I bent using the old flat roller that I had been using.

The tube squashes down radially and the face gets wider at the inside of the curve which is why the top roller had to be wider. I find I can get down to or slightly smaller than a 2' radius before things start to bind in the wheels too much again. Also, by this point I'm starting to see some slight buckling on the face of the tube that is the inside of the circle when using 16 guage (approx 0.060" wall). As someone mentioned, buckling starts sooner on some 20 gauge I tried.

For a non-production and infrequent use this is not too bad a tool for the price. I can make rollers as needed for other tube sizes if I need to. I think HF sells a set for 1/2" square bar and tube.

I also rolled some 1" x 1/4" cold rolled with it for part of the same project and it was successful as well.

Paul