Myth 3 - Anytime you put compound contours in sheet metal, the costs go out of sight

Pure nonsense!

It is a tooling issue, typically relating to fuselage skins. The photos below show a skin stretch die machined out of laminated lumber yard particle board.

The cost was less than $4,000 and is used to form a New Meyers fuselage skin.

It has reversals in the contours (compound contours) and with a little maintenance from time to time, would be good for a couple of thousand parts.

There are probably two to three dozen shops around the country that could stretch these skins.
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Machining particle board stretch die with compound contours.
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Laminated particle board stretch die used to form compound contoured aluminum skins.
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Stretching 2024-0 aluminum over particle board. The top of the die shows the reversals or compound curves.