Introduction: Aluminum Dome

Picture of Aluminum Dome

I made it at TechShop!  www.techshop.ws 
I just took my first class at TechShop, entitled Organic Sheet Metal, Safety and Basic Use.  In it, I created this aluminum dome, or bowl from a square of about 20 ga sheet aluminum.  Here’s how...

Step 1:

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Using a paper plate for a guide, I drew a circle on the sheet. I then used a Beverly Sheer, which cuts using a hand lever and a scissor action, to cut out the circle.  After filing the edges, I was ready to start shaping the dome.

Step 2:

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On the workbench was a sand bag that resembled a small round throw pillow, but filled with sand.  After making an indentation in the bag with my fist, I placed the edge of the disk of aluminum on the bag and began striking it with a kind of a glancing blow using plastic hammer, about an inch from the circumference. After going all the way around, I started in the center and worked outward in a spiral.  At this point, I had an ugly dented workpiece with some curvature that was warping into a taco shell shape.  The aluminum was getting work hardened, too.

Step 3:

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Next, I took the piece to the English Wheel, and began working it back and forth between two rollers in a radial pattern. This did three things.  It smoothed out the hammer dents, it eliminated the “taco shell” warping, and it relieved the work hardening.

Step 4:

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I then moved on to a pneumatic planishing hammer to further hammer out the dome.  This hammered the piece between a flat die and a curved die, at several hundred blows per minute.

Step 5:

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Another tool I used was a shrinker, which had a slot about an inch deep and 1 1/2 inches wide that you put the edge of the workpiece into.  Then as you push on the hand lever, two pairs of jaws grip the workpiece and then come together slightly to shrink the edge.

Step 6:

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Going back and forth between these tools, I formed a dome about 9 inches in diameter with almost a 2 inch dome.

What’s it for?  Well, you could use it as a bowl, make a clock out of it, use it for a hub cap, or wear it on your head to shield you from alien mind control rays.

Comments

avenger22 (author)2015-01-30

This is pretty cool. One could even use this method for a captain america shield.

skreft (author)2014-02-23

Now for the red white and blue paint and the crime fighting.

al_packer (author)2014-01-31

Nice if you have access to all the fancy tools, but the old-time metal workers did it pretty much all with just the hammer and sandbag. We had to do a bowl project that way back in 5th grade (60 years ago). Some kids' bowls were pretty sad, some were OK, and a couple were excellent (mine was in the first category).

rimar2000 (author)2013-04-04

Very nice!

ironsmiter (author)2013-04-04

Your final product looks WONDERFUL for a first attempt.
Nice and symmetrical, smooth, the whole 9 yards.
Any DeSoto would be proud to wear that on it's rims.
When you do your next sheet metal project, take more in-progress photos.
I'd suggest, every 5-10 min, put down the hammer, and pick up the camera ;-)

the English wheel did NOT relieve any stress :-(
Without knowing what type of aluminium sheet you are using, I'll give you a GENERAL rule of thumb.
2 hours at 650F. Cool 50 degrees every hour till you hit 500F. then air cool.
This should work for MOST aluminium. 7075 is 'special' but odds are pretty good you're not using that.
The "quick and dirty" method is to rub bar soap over the work, and heat it with a torch JUST till the soap turns black. Then let air cool.
Not as precise, or accurate, but it works, and is a LOT faster and cheaper to do.

What you then have is an annealed aluminum work piece.
This will form like gold. at least till it work hardens again.
This is what we call "dead soft" and is a dream to work with.

You said it "taco shelled" on you... do you mean like a taco shell bowl(wavy edge) or tried to fold itself in half, like a hardshell taco?
The first is expected, and part of the process. When you get that, you go back, and hammer between.
This pushes the extra material to the sides a bit, thickening the edge. Technically, this is upsetting.
Don't go TOO over board trying to get it back perfectly flat, since the next time around with the hammer, to increase your radius,
it'll happen all over again :-) for a simple overview, see https://www.instructables.com/id/Learn-to-Dish-by-building-a-Buckler/
They did a fine job(make sure to "view all thirteen images" in step 3)
The "hard shell tacoing" is a different matter. Not sure exactly what would cause this,
other than someone bending it in half for you, and ending up with a potato chip shaped piece.

There's a youtube video here (http://www.youtube.com/watch?v=CZLJhdKPwfw) that is a minimal stop-motion view of the whole process.
The metalworker in this case uses the "soot it up, and burn it off" annealing method.
Works OK, if you are comfortable with oxy-acetylene, and can avoid spot-melting your sheet.
Don't be scared of it. it's pretty easy, but practice on scrap sheet first.

Looking forward to your future 'ibles.