I have a 16" x 48" piece of 304 Stainless Steel 1/8" perforated sheet
metal, about 1/16" (.065) thick. I want to bend it into a 15"
diameter x 16" high cylinder. Is this something that can be done
(manually) without any special machinery?

Almost. To hand form this without tools, you need a 16x96 inch sheet of sheet.
Aren't you glad you asked us AFTER you bought it?

You can make two 16 inch high by 15 inch diameter cylinders this way, or one
good one that's just about perfect.

Take a sheet of computer printer paper and roll it to a diameter of 2 inches by
8 1/2 inches long. See how the metal goes around more then once?

Now roll it as tightly as it needs to be rolled so that when you let it go, it
can be jigged for "welding" with a very weak 2 inch diameter rubber band. You
have just accomplished

Springback Compensation

but only for the end INSIDE the roll. To get the other end straightened out,
you should first cut off whatever length was damaged by your fingers making a
new roll tightly on the outside, then reroll with that end inside, such that
the whole thing unrolls to 2 inches.

Then, use several bands of paper cut from the piece you removed to retain the
paper in a roll exactly 2 inches in diameter. Test fit this roll where the
finished product must be used. Mark and cut a single straight line with
non-curling nibblers, (ok, you do need a hand tool) along the line, leaving
uncurled edge. If you use scissors on the paper or sheet metal snips (even
aircraft snips) you'll curl the edge and ruin your work.

Now you have a roll of stainless steel (if you followed the instructions at the
desk, then went into the shop), about half an hour of wasted time, a nibbler,
and something ready to be joined. You can apply tape to the paper roll, or go
back and make an overlap, then glue it, and you can stitch weld, or TIG (GMAW?)
weld your sheet steel butted edges, or braze them if you set up a small
overlap.

And it cost you twice as much as the sheet, which the company that runs the
roller knows, which is why they charge approximately the same as the original
sheet cost to do this for you. They know about the hand method, but why should
they tell it to you? You're going to spend twenty bucks either way.

Doing it without a roll machine, with the sheet cut to L on one edge, and pi *
D on the other, requires a lathe with capacity D to turn a forming cylinder, a
large flat place to work, like a clean floor, and MANY expensive, tedious cuts
to make the forming cylinder come out right. You can save on cuts by
calculating the springback using Young's modulus, the percent elongation before
plastic deformation, and the thickness of the sheet. And then after you make
this HUGE cylinder and roll the sheet with it, there will still be an end that
won't lie down flat.

Next time, post your requirements (a sheet steel cylinder 15 inches diameter
and 16 inches long) and let US figure out what you should buy, and what labor
you should pay for, in which process you will determine whether you want to own
a pair of nibblers when it's all over, a couple bits of useless sheet steel
that won't lie flat every again, or a receipt from the sheet metal rolling
company. Me, I'd go with the nibblers, but I am getting the feeling you are
going to end up with a receipt.

The method I had in mind would be to obtain a 16" length of 15"
diameter pipe (or perhaps bolt a few 15" diameter wheels together to
form a 16" high cylinder). This would be bolted or clamped to a fixed
object. I would then clamp one (16") side of the sheet metal to the
pipe with a piece of bar stock and a couple of c-clamps.

Use angle iron for more stiffness than bar stock.

Another
piece of bar-stock would be clamped to the other side of the sheet
metal, and I would then slowly bend the 48" length around the pipe.

And if it springs back on you, you could get whacked in the face with a heavy
pice of bar stock. Ouch. Get some friends for this part.

But then, what can I do to retain the cylindrical shape?

You figure the Young's modulus, % elongation, and sheet thickness before hand,
then build a form smaller than 15 inches, but 16 inches long. Try finding a
piece of pipe that's 13.725 inches diameter or whatever the calculated value
happens to be. Good luck. That would be a coincidence of high order. You could
adjust your thickness to make the form come out to be a standard size, but you
already bought the sheet. Tough titty there.



I've considered using a smaller pipe and bending slightly past the
diameter I need. But I don't know how much smaller a diameter to use.

Mark's Standard Handbook of Mechanical Engineering, or our favorite,
Machinery's Handbook, will probably tell you.

I need to have a reasonably "perfect" circle, and I don't want any
kinks.

Perfection costs (1/tolerance) ^ k where k is something like 5.

Is this a practical thing to attempt,

NO. You'll be injured

should I try to make friends
with someone who has a slip-roll forming machine.

At least you probably know some folks who own leather gloves. Start there, and
see if the three of you can scare up someone with a slip roller.

Any advice would be appreciated.


Sorry if I have been a bit harsh, but I don't want you to be hurt. I hope
you've learned something. There will be a quiz at the end of the thread. Five
questions, two true-false, two caculation, and one essay. Submit medical
treatment bills to your insurance company, not to me. All I did here was talk.

And I believe that in this country, that freedom is guaranteed, and I
appreciate the efforts of our enlisted and officers who keep it that way.

Oh, if you have a tree handy, you can adze it to the right diameter and chisel
a slot to put the metal into, then tie it all up with lots of ropes tied with
blood knots, then weld it, but that would kill a tree, so unless it's YOUR
tree, and you need to make more than one, please don't go there.



Yours,

Doug Goncz
Replikon Research (via aol.com)

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