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?
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
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
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
Afterwards, you will need to heat-treat the tubing if you wish to restore
the strength. That's a whole other science.
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.
I did investigate the muffler shop approach. However, every one that I
visited had a 1 1/2" OD setup, but none at 1 5/8". I was hoping that I had
a simple solution with the 'pipe bender'. Still, you have all given me food
for thought. Maybe I can create a shell for the tubing that will allow the
use of a larger setup at the muffler shop.