Bending chrome molly tube?

Hi All, I have tried to bend a 1 5/8 " x .058 " wall chrome-molly tube, but have had poor results. I used the 12 ton hydraulic press from Harbor Freight, with 1 1/2 " shoe (measures very close to 1 5/8 " OD). The shoe has a radius a little over 5 inches. The bends that I tried resulted in the inside radius being wrinkled. This happened even though I filled the tube with compacted sand. Any ideas where I am erring? Thanks, Jim Burns

Reply to
Wizard of id
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Back in the late 50's - early 60's, my profession was tubing bender for Todd Shipyards. I bent a LOT of chrome-moly pipe.

  1. 5" is a very tight radius for 1-5/8 OD tubing. You would be better off doubling that.
  2. Sand doesn't prevent wrinkling, just flattening and then not all of that.
  3. A proper tubing bender uses a "bullet" or mandrel on the inside of the tube to counteract wrinkles.
  4. 0.058" wall is very thin tube. Thin tube is harder to bend than thick walled tube.

In short, with that small of a radius, it's going to wrinkle. If you absolutely need the tight bend, you're going to have to use a bender with a mandrel and you'll be lucky if it doesn't still wrinkle. You can remove most of the wrinkles, if they aren't too deep, by heating the pipe red hot and beating on it with a hammer. Do this before you remove the sand. It won't be pretty, but you can reduce the wrinkles by judicious application of a BFH. It's much like bodywork on a car. You have to work the excess metal around to the outside of the bend. Bring your lunch, 'cause it's going to take a while.

Afterwards, you will need to heat-treat the tubing if you wish to restore the strength. That's a whole other science.

Good luck, Rich S.

Reply to
Rich S.

I love reading this group. Nothing beats experience, eh?

Reply to
Jon Grimm

Years ago in my midget racing days (Badger Midget Racing Association--1950s) we made race car frames from heat treated chrome-moly tubing. tubing was 2" OD and about .0625 wall if my memory is correct. We bent the frame elements to the proper shape using what we called a wrinkle bend. We had a template for the bend shape. We used a oxy-accetylene torch with a fine tip to heat red a narrow band on the tube radially around the inside of the bend and then bent the tube slightly. A small wrinkle appeared alone the heated zone as we bent. This was done repeatedly moving the heating zone as we developed the proper bend radius. Bend radii were always several times the tube diameter however.

Not that this helps you with your problem but what the hell, it was fun back in those days when race cars were built in ones own home shop and with only your ownskills and iginuity.


"Wizard of id" wrote:

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Well, for starters you're trying to use a *pipe* bender to bend *tubing*. To bend tubing, you need a tubing bender, very different animal from a pipe bender. It *draws* the tubing around the bend. Go to a good muffler shop and watch a tubing bender in action.


Reply to
Gary Coffman

Last time I needed some thin walled stuff bent I went to a muffler shop and they did a nice job with no wrinkles. It was thicker wall than what you're using, though. Might be worth a try. Greg Sefton

Reply to
Bray Haven

Reply to
Wizard of id

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