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Old 06-26-2017, 09:39 PM
longyard longyard is offline
MetalShaper of the Month September 2013
 
Join Date: May 2012
Location: Winston-Salem, NC
Posts: 1,083
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I need to wrap the nose grille panel around the actual steel tubing I will be using in the Superleggera structure. I hadn't originally planned to do this, but thanks to Mark Savory and Rick Mullin I realize I must do it this way.

Here's how I made the tubing...which I ALWAYS find difficult to work.

I made a template out of aluminum 1/2" air conditioner tubing. It is soft and easily formed.

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I used a Pexto stove pipe stake to shape 1/8"x1" hot rolled bar to the inside shape of the template (careful two handed pushing down over many places). After tack welding the upper horizontal of the bar to the bench near the center, I pulled each leg in about 3/4" and tack welded some more. This was absolutely "by guess and by golly" mixed with a bit of previous tube bending experience. I did this to anticipate spring-back of the tubing.

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I welded a short stub of 1 1/4" tubing on the work table near the left side of the steel bar. I used a length of electrical conduit and slowly bent it around the steel bar. I DID NOT pull on the end of the tubing length, but kept my hands as close to the steel form as possible. This kept the shape closer to form without it bowing out.

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On my first attempt, the finish shape was very close, but the spring-back on the right side was more than on the left side. I therefore decided to try it again, but this time I only bent 1/2 at a time, and once I had the first half bent, flipped the tubing over (after careful measuring) and bent the "right side" of the tube in the left side of the steel form. The result was MUCH more symmetrical.

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After trimming the tube to length, note the amount of spring-back. Fortunately, the steel tubing now matched the aluminum template exactly.

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Painful experience has taught me how nearly impossible it is to get a really tight (2" radius?) in electrical conduit without special dies. Instead of fighting the system, I cheated a bit and cut the 90 degree corners out of a base for a halogen lamp. You see the corners on the table ready to be welded and joined by a straight piece of tubing. Another halogen lamp base is in the center of the photo to show where the pieces came from

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Tomorrow I will weld the pieces together; I'll then curve the grille hoop to conform with the curve of the nose; and then I'll begin to carve out the wooden nose to accept this hoop.
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Bill Longyard
Winston-Salem, NC
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