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Old 01-11-2019, 01:01 PM   #21
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That is, believe it or not, the way that small non-structural cracks are dealt with on aircraft. Drill a hole at the end to eliminate the stress concentration from the sharp point, then if necessary attach a doubler plate.

I have a hunch this is due to the van body flexing while driving. I feel like getting in and out of the bunk wouldn't be enough stress cycles to propagate a crack that far, but I could be wrong. These bodies don't have a lot of stiffness in the roof area, and adding a penthouse top cuts out a lot of the reinforcing members. Westfalia conversions used to have a thick L-channel all the way around the opening for that reason (but those were unibodies, and so subject to more structural load.)

It could easily start at any rough edge or notch where the metal was cut.

1990 E-250 Sportsmobile w/ penthouse top, converted in 1990 by SMB Texas.
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Old 01-11-2019, 02:46 PM   #22
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I was always told to drill holes for the corners and then cut to the holes. That way you don’t leave a weak point for a stressed area to start cracking from.

From the handful of pix posted on this forum of the cuts under smb installs I’m surprised we don’t see this more.

"understeer is when you hit the wall with the front of your car, oversteer is when you hit the wall with the rear of your car, horsepower is how hard your car hits the wall, and torque is how far your car moves the wall."
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