Spirit of St. Louis Cowl Question

What was the reason for the spiral pattern finish?
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This was actually discussed "to death" a few weeks ago. Many theories were tossed out...and I think the most convincing, to most people, was that it was pretty much a decorative thing, to help mask the surface imperfections on what were hand-formed compound curved pieces. It was a techgnique that was "in style" then, and helped illustrate the skill and artistry of the artisans.
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Greg Heilers
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Jack G.
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Jack G
At a guess, I would say that it stiffens the panels to keep them from flexing.
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Jessie C
If you watch the old movie with Jimmy Stewart as Lindy, you'll see a scence in the movie where a guy uses a drill press with a wire brush on it to put the swirls into the metal. It was mostly decorative but also served another function, I'll check with the guys at the restoration shop at EAA to see if I can find out. I was told once, but that was a long time ago.
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The technique is called "engine turning" I believe. I think it's usually done with some sort of fine polishing bit in a motor tool, flexible shaft, or drill and polishing compound. I've been told it can also be done by hand with an appropriately sized dowel rod and compound. Toy might be right about strengthening the panel but I don't remember.
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Bill Woodier
Many '50s cars had the technique used on instrument panels. It's difficult to reproduce in 1/25th models. I really haven't tried too hard as some of those oldies have considerable chrome inside. Today's plastic 'rubber room' interiors could never look as attractive.
Bill Banaszak, MFE Sr.
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If it is done by hand it is called hand tooling or hand turning. If done by a jig it is called engine turning. Engine turning makes a very REGULAR pattern, hand turning makes an irregular one.
I used a bench drill press to do a new instrument panel for my (full-size) race car. I made a jig with two pieces of wood, to allow the row spacing to be adjusted, and with a set of marks on the top piece (and an index pointer) so I could move the top part (which the workpiece was fastened to).
I also used a dowel with valve grinding compound on the tip. One caution. It wears down the dowel VERY fast. I kept getting a weakening of the pattern every so often. I finally found the problem was the dowel was wearing so fast I was hitting the depth stop on the drill press!
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Don Stauffer
Back when I did car models I used to get a rough representation of handturning by roughing it in with a silver paint pen or a gel pen.I recall seeing some of those 70s disco prism decals being used in a model once also.
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