bending sheet metal into a cylinder

Hi,
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?
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. 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.
But then, what can I do to retain the cylindrical shape? I assume
that 1/16" stainless will want to spring back with a vengeance. I've
considered clamping it in place and then hammering and/or heating it.
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.
I need to have a reasonably "perfect" circle, and I don't want any
kinks.
Is this a practical thing to attempt, or should I try to make friends
with someone who has a slip-roll forming machine.
Any advice would be appreciated.
Reply to
cdg
Loading thread data ...
To form a cylinder from sheet, you need to first bend the few inches on end of your sheet to the correct curve, using either a press brake or cornice brake, then use a slip roller to roll the rest of the sheet into the proper curve. Doing it any other way is just too much damn trouble.
You could have this done by a sheet metal shop for maybe $20 - $30.
You could form the cylinder in 2 pieces by using over length pieces, bending them around a curved object with a smaller diamter than your finished size, and then cutting the curved bits from the middle of each bend.
It is always better to over bend and then un-bend than to under bend and then try to force the edges together.
For a 15" diameter curve try something 12" - 13" diameter.
Reply to
Ernie Leimkuhler
glad you got your cylinders made. i've been thinking of making my own slip roller. Not that i need one right know. Any chance you could put photos of your one hour model up in the dropbox.
-- Doug Arthurs Kent Bridge, On
Reply to
Doug Arthurs
I'll take some photos as soon as I can find a camera.
Reply to
cdg
Thank you, and cheers! I have not expressed any such a concept, nor do I think it.
I asked a simple question. No one was required or coerced to respond. Two members provided helpful advice. Another was simply abusive. I thanked the first two, and I told the third that his input wasn't helpful, appreciated, or accurate (as presented).
Be my guest. If you can construct any number of cylinders based on Mr Contz's response, you are far more innovative than I.
As do I, if they are decently presented.
a way you had never considered.
The reply to which I objected did not endeavor to, or accomplish, that goal. Nor do I believe it was intended to do so, but rather to scoff and strut.
Terrible enough that I've received numerous supportive emails from other members of this newsgroup that were equally or more critical of the post in question.
Some of us did not find the post in question amusing, helpful, or informative.
Please supply usable details of the procedure involved (which your colleague did not --- he simply suggested rolling it up very tightly, without a hint as to how this was to be accomplished --- which was the question he was supposedly addressing). And, when you suggest a procedure, remember, the material we are (or were, or should have been) discussing is .065 thickness 304 stainless, not paper, nor aluminum flashing. The 1/8" perforation will make it somewhat more flexible, but it is still quite rigid.
Furthermore, what about the "springback compensation" with which your colleague was ostensibly so concerned, while rolling his 8.5 x 11 sheet of computer paper and magically producing a metal cylinder from it? How did it suddenly disappear, as we are rolling twice the material in an even tighter circle?
YOUR problem of the moment.
I am open to learning about anything, if the material is presented in an amicable matter.
Reply to
cdg
Dear cdgoldin,
I checked my Statics and Strength of Materials to see if there was a formula for bending sheet metal around a curve. The best that was there were the parabolic deflection beam formulas. I don't think they apply. However, with a distributed load on a straight beam, the apex of the parabola does have a computable radius after the material gets bent.
So let's say the Young's modulus of your stainless is known. Use the Young's modulus calculator, the bend radius, and the sheet thickness in:
formatting link
to get the force required to hold the material in a 16 inch diameter circle. Apply an adjustable strap, slowly working up to that much tension in the strap, more or less, and your desired bend radius. The strap should be right down the middle. Use one of those endless hose clamps, available in lengths of up to 10 feet, if you don't have a two ladder lock buckles and a 5 foot length of nylon webbing. Use your judgement.
Then apply something a little stronger and resistant to heat, like two pieces of 3 mil aluminum tape 2 inches wide, and at least a foot long, along the edges, over the joint. The extra length is so the adhesive at the ends remains strong while the brazing or welding is done. Remove the center strap, if you used nylon, or leave the endless hose clamp in place. Either way, your choice.
Then, tag weld the seam, be it lapped or butted, one half the way from the center to the edge. Two weld nuggets about 1/8 inch diameter should do. I don't weld much at all. I am probably not as good a welder as you.
If having the seam lapped and then having the upper layer stubbornly remain, say, 1/16 inch from the lower, preventing a sound weld, is a problem, then clamps must be applied to a bar over the seam, leaving the weld area free, and using a more or less identical bar diametrically opposite. For instance, I'd think two pieces of 1x1 inch steel 18 inches long with a 1/4 inch hole through at each end 3/4 inch from the end would do, in combination with two pieces of 1/4-20 threaded rod about 18 inches long, and four matching nuts.
Once two tag welds are made, you can make several more to hold that edge down if it is a lap joint, or a few more if it is a butt joing, and then grind them all smooth. After that, my choice would be to braze rather than weld. Handy & Harman will provide a small sample of stainless compatible braze filler, about 3/16 inch diameter, which is an excellent color match and very strong. You'd use a hell of a lot of flux for stainless and try to work quickly, because the chromium in the steel becomes chromium oxide, a ceramic, at brazing temperatures, and even a large amount of, say Anti-Borax brand flux can only dissolve so much chromium oxide before turning black and forming an insoluble glass. This is an indication that the flux has been "burned". The material is very tough.
If you finish the joint and the flux is insoluble, you can add lots more flux and reheat the work to dissolve the chromium oxide. Then, soaking the seam in a tub of hot water overnight will dissolve all the flux. If necessary, set up a tray with vinegar and water or a solution of hydrochloric acid. This will dissolve the remaining flux. Be careful with HCl, you already know it's dangerous shit.
Now to finish this, you can use a sanding belt to smooth the braze and remove oxides from the metal that got hot but wasn't protected by the flux, and you're done.
I switched to decaf all day yesterday, at well, did a little work, and felt OK. I'd still like to know if when you read my first post in reply to your original post, whether you got the impression I had had too much coffee?
Yours,
Doug Goncz (at aol dot com) Replikon Research
Replikon Research researches replikons, which are self-reproducing configurations of non-living matter in environments that support replication, analogous to organisms living in ecologies.
Reply to
Doug Goncz

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.