# Sheet metal bending



## stevenreich (Jul 29, 2017)

I am looking for ideas on how to make cylinders in each of the four corners of a square sheet metal box.  This is part of a stove sample that the old time stove salesman used to travel around with.  The existing piece is rusted out but the rest of the stove is in great shape. The four circular columns mate up with the top and bottom castings, and enclose the long screws that hold the top and bottom castings together. They are about ¾" in diameter and 12" long. Any ideas?


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## hman (Jul 29, 2017)

That's a pretty small diameter to be bending out of sheet metal.  Might you be able to start with 12" lengths of ½" or ¾" gas pipe (black, not galvanized) and mill away part of the circumference?


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## stevenreich (Jul 29, 2017)

Well thanks for the reply,  the original sheet steel is fairly thin and seems to be dead soft. Probably hot rolled. I've thought about using thin tubing and welding or silver soldering/ braising the flat sheet at the four corners but that takes away from the original design. 


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## Firestopper (Jul 29, 2017)

conduit work?


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## francist (Jul 29, 2017)

Oddly enough, I have done this before. Not for a travelling display, but to make reproduction "speaking tubes" for an 1890 Victorian mansion.

I don't have the dimensions here at home, but I recall very well how we made them:

-sheet metal hot air ducting, tin plated from the 1950's, about 22ga maybe, three foot lengths
-wooden 4x4 with a half-round groove routed down the length of one side
-ball peen hammer
-wooden broom handle (of the right diameter for finished tubes, about 3/4" or so, maybe a bit larger)
-14 gauge copper wire
-butane torch with flux and solder

Compute the desired circumference, including an allowance for a soldered seam overlap. Cut the ducting into those widths and as long as you feel like trying. We were able to do full 3' lengths. Lay one strip over top of the grooved 4x4, and using the peen end of your ball peen hammer, forcibly work it lengthways on top of the sheet metal to start forcing it into the groove. This gives you a start in getting a tube shape established.

After you've got kind of a tube going, move to the broom stick which should be either mounted in a vise or clamped to a sawhorse. You want it horizontal, and with clearance to work around it. Put your rough tube shape over the stick, have a buddy clamp it firmly with his hands, and you take the copper wire and tie it in various intervals around the broomstick to keep it closed. When you're happy that it's even and as snug as you can safely make it, flux the joint and solder the seam closed. With any luck, it will slide right off the stick afterwards and you'll be holding a very nice, soldered-seam, lightweight tube.

Make sense? I've still got some at work so I could check dimensions as well as metal gauge that we used when I go back if you want. Possibly get a picture or two, but I'm not sure how much I have left over that's not installed into the walls already.

-frank

I should probably clarify, a "speaking tube" was the residential equivalent of shipboard communication tube systems. Allowed servants to (supposedly anyway) communicate throughout the house by talking through these things that were stationed around. My gut feeling says they were probably not very effective, but I can't say for sure.

-f


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## Steve Reich (Jul 30, 2017)

Frank,

I believe you have a good approach,  I will try it.  The exact gage of sheetmetal I don't remember, the stove has been in storage and I am just now setting up shop again and know the stove is in a box somewhere close, I will find it and check the thickness.  Also the diameter of the tubes.  I have attached a schematic drawing of the part looking down from the top of the stove.


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## chips&more (Jul 30, 2017)

A small three bar roller would work. I know they make them. I have one somewhere in my piles in the shop? Have not seen it for a while? Or you could make one. Good project for the HM. Maybe share with us.


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## Steve Reich (Jul 30, 2017)

The 3 bar roller sounds like it might work.  Do the rollers have to be smaller than the cylinder diameter?  I worked at a plant thAt had a brake but don't recall seeing a 3 bar roller there. 

I think it would be an easy tool to build. I just need to get an idea of the roller diameters to use.


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## francist (Jul 30, 2017)

Like this, maybe.


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## mzayd3 (Jul 30, 2017)

Yes, the rollers must be smaller than the desired cylinder.

Maybe you could find a bar the right diameter and hammer the sheet into shape...


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## hman (Jul 30, 2017)

Well, It looks like I misinterpreted how the tubes were used.  I'd assumed they would be ¾ cylinders (thus the machining suggestion) placed outside the walls and used to hold the corners together.  My mistake.

Is this stove just for show-and-tell, or is it actually intended to hold a fire?  If the former, you _might_ be able to repurpose the frame tubes of some lawn furniture.  What I've seen (and used on occasion) is about ¾" diameter and (based on your diagram) suitably thin wall.  Hope this helps!


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