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Bending Steel Tubing to Small Radii

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wsimpso1

Super Moderator
Staff member
Joined
Oct 18, 2003
Messages
11,357
Location
Saline Michigan
OK, this was not supposed to be so hard to do, but it turned out to be a big lesson for me in underestimating a task. And I have success that I thought I should share.

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First off, I am building four adjustable rudder pedals, each with an "S" tube to allow the cable to slide when we want to move the pedals. Lots of photos exist elsewhere on this, but I had trouble making the tubes with a 1-3/8" radii without kinking. I started with 3/8x0.035 tubes and made a bend jig out of aluminum, turning the "roller"s with 3/*" diameter grooves, and bolted to a plate that I just C clamped to a bench. Plane tube would not go around without kinking. Then I filled with common sand, tamped, and welded on a cap - failed. Then really fine sand, and it failed.

Then I got serious and I bought two pounds of Wood's Metal, and 1-2/8x0.049. Wood's Metal looks like solder, dense like lead, melts at 156 F (or was it 158 F?) and has the neat trait of expanding slightly when it hardens and also produces a fine grain structure that helps with bending when quenced in water 55 F or cooler. The thicker walled tubing should also have better resistance to kinking...

After getting a stainless steel funnel with a small enough neck for this tubing, and a Pyrex cup to do the melting in, I melted the stuff in a double boiler, oiled a couple pieces of tubing, and did my first cast in a piece of 035 tubing. After quenching it in cold water in the bath tub, I made one good S and one that kinked. Upon cutting the tube at the kink, I found that I had a cold shut, where the woods metal did not fill the tube fully. Hmmm. Solution to that problem was to heat the tubing with a heat gun until I could not touch the tube, then pour the oiled tube full of Wood's Metal. I have since formed four very nice "S" tubes.

Next I will recover all of my woods metal from the tubes (back in the double boiler) and buy some more 3/8x0.035 tubing and try again with that. Or maybe I will just use the 049 wall "S" tubes... Anyway, Wood's Metal, poured into preheated tubes, quenched in cold water, and bent smoothly and slowly over a contoured forming jig works great.
 
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