Quote:
Originally Posted by freebeard
That would be a shame considering how you've done so far. I suggest cutting 'darts' in the aluminum. To save me drawing or hotlinking a picture, look at the Goode Homolosine and Waterman Butterfly map projections here.
If you use the Goode Homolosine, the single seam could be lapped, or trapped in an aluminum or brass H-channel (model making parts). 
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Cutting 'darts' to effectively shrink had also crossed my mind, I might even try it but I'm not real optimistic about that route. For one thing I've never seen any 'real' part implemented that way. But sometimes try it and see is worth a thousand conjectures.
Quote:
Originally Posted by freebeard
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A person who's better than me with a hammer and dolly could make that corner flat again. Maybe that's why the planishing didn't work, it wasn't pre-smoothed enough. You could try shrinking with a hair dryer and dry ice, if the aluminum wouldn't lose its temper.
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Sorry for the confusion, when I say 'bungled' and 'scrap' I mean that the aluminum in the corner zone is well on its way to the fatigue limit. I didn't shoot the picture close enough so you can't really see, but there is even one spot where I've worn a crack right through the metal. I can continue practicing on this piece, but I won't want it on my box even if I fix my shrink method. That's why this piece is scrap.
But overall the reason I got stuck is my methods failed to shrink the sheet. I'll be making one or two more attempts before the end of the week. I think I know what's wrong.
I'm also at a point where my timeline is in jeopardy. I was hoping to have it road-ready before spring-time vacation travel, but that may or may not happen now. My wife is being phenomenally supportive: an offer to watch the kids double-time so I can pour on the shop hours. (Jealous?) I also have some vacation time I could 'squander' on even more hours.
However, I'm prepared to leave it sitting in the shop for a few months if that's what it takes, and I feel like I should also stop and thank
Tango Charlie: even a project that didn't pan out had lessons that influenced my project and were a big help to me in getting this far:
- Fab a separate frame instead of building onto existing hitch rack, thus we can still travel in the middle of the project (also for my project the existing commercial hitch rack didn't fit the aero envelope very well). I can resell the existing commercial hitch rack version after aero version completion.
- Use better load-bearing materials instead of coroplast.
- Don't get emotionally invested in completing before a deadline, even though, to paraphrase MetroMPG recently, the lack of an aero tail bothers me literally every. time. I. drive. (especially on a long haul).