Anonymous
Sometimes lessons come from the most unexpected places. One of those lessons was an invaluable schooling on how sheet metal parts are made. Not out of a book, or in a video. But from an experienced hand who's been doing it for decades.
A couple of weeks ago, while working my volunteer gig at Planes of Fame in Chino, Ca. I found myself talking to the DC-3 restoration crew.
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| The DC-3 undergoing restoration |
The DC-3 at Planes of Fame is on the road to flying again, but needs to have some work done to it.
Tony, an Airframe and Powerplant mechanic started out working on aircraft in the U.S.Navy. He's been at it so long, some of the ships he's served on are museums now.
He's studying a door gusset that's come out of the DC-3's door.
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| The gusset's location |
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| The gusset after removal |
"This part is finished." He remarks confidently. "See here?" He indicates the ends of the part. "It's been drilled too many times." I can see three holes in the part where one should be.
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| There's a few extra holes that shouldn't be there! |
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| There's an extra one here too! |
But Tony's lesson is just getting started. "We're going to have to fabricate one." His eyes narrow as he studies the part. "The part is made out of 2024-T6, but the bend radii on the flanges are too tight. If we try to use T6 from the start, the part will crack. That wouldn't be good." He smirks.
"So what's the plan?" One of the curious volunteers among us ask.
Tony closes one eye and holds the part up, studying it. "2024-0 will bend to that radius, but we can't use in an aircraft structure. It'll have to be heat treated to T6 after the fact. We'll also have to be careful about how we cut our blank. We want to make sure our flanges are oriented correctly with the metal grain."
"Sheet metal has grain?" One of us asks. (I smile inwardly. This is an answer I knew!).
"Sure does." Tony remarks. "Almost like wood. If you bend along the grain, the bend has a better chance of cracking."
The collected few of us nod. It's been quite a lesson he's taught us. The wisdom of decades of experience, passed on with a casual confidence.
"Yup." Tony smiles. "In the English Wheel for the contours, bend the flanges, we'll leave a little extra on the flanges and trim them back." He makes a casual wave of his hand. "A thing of beauty."
Why relate this story? Because in our age of computer aided calculated nonlinear numerically simulated design, it's amazing to see somebody who is a true artisan of his trade.
I consider myself to have learned a valuable lesson. A lesson I'm going to take back to my computer aided numerically simulated world.
I'm bringing back a lesson on how parts are made in the "real world". And just as importantly, I've relearned a valuable lesson that to be a good designer, you have to understand how those parts are made.
So what are my "treasured" lessons?
- Sure I knew sheet metal had grain, and I knew it could affect a part. But when I was designing sheet metal, we never considered it. Now, I know more than being able to repeat "sheet metal has grain", like a trained parrot. I understand how that grain can affect a part.
- Heat treating was another process I "sort of" understood. I knew that T6 materials won't make tight bends without cracking. But because my sheet metal design work was done in mild steel. I never applied that understanding. If we had a tight bend, we just avoided the material that wouldn't make that bend. I never even considered having to use annealed material, then treating it after the fact. Now that an experienced hand has explained it to me, I feel silly not having considered this myself.
I'll truly appreciate the lessons I've learned. I hope there's a few more in my future!
