zHow to bend 1/4 inch plate steel into 14 inch trunion shape?

[entsminger]

  You may or may not remember that I'm the fellow who is trying to make a fake non shootable 13 mortar from a large propane tank? Since the trunions will be a little undersized from the origional 15 inches and I can't find any roughly 14 inch pipe anywhere so I need to make them myself. I got some 1/4 or slightly thicker plate steel and cut them to the right lenght and width but can not figure out how to bend or shape into a round tube of roughly 14.2 or whatever it is that I need ? I forget at the moment?  My welding torch won't get hot enough to heat it up enough to bend it. Any suggestions how I might bend the plate into a round shape with out a blast furnace or forge which I don't have? I'm trying to do this myself, not take it somewhere to have it bent.

  Scott

[seacoastartillery]

      Entsminger,   You could use the method that Mike and I used to make the radiused sine bar for our gain-twist rifling set-up.  We placed our stock, a piece of .500" X .750" 4142 30 Rc pre-hardened steel in the Kurt milling machine vise between three 1.000" dia. pins, two on one side and one on the other, and tightened the vise with moderate pressure.  Spacing is everything here, of course.  It was trial and error, but only took about an hour to get a beautiful radius that matched our trammel-traced pencil line perfectly.  Make it in thirds or quarters and you can avoid vise jaw interference and then weld together.  Sounds like an interesting project.  Any In-Process photos yet?

Good luck,

Tracy and Mike

[GGaskill]

How wide is the 1/4" plate?

[seacoastartillery]

      Original trunnions were 4.5" long.

[GGaskill]

Is that the length at top and bottom or the maximum length on the sides?

[seacoastartillery]

     Scott and George,  we are only talking about the trunnions here; the info that we posted is correct for them.  The rimbases which project in a very minor way are 17" O.D. and the amount of projection is unspecified per the drawing copy taken directly from the Mordecai plate, but appears to be approx 3/8", at center, slightly more as you get away from their centers.

Tracy and Mike 

[GGaskill]

Basically you need to make a set of slip rolls that are strong enough to deal with 1/4" material.  For a short span, this should not be too difficult.  You may need to do the rolling in several stages before reaching the final size.  Here is a webpage with some info.  Yours probably wouldn't need to be more than 6" wide.

[dominick]

Scott,  why 1/4".  Since it is a non-shooter, it would be alot easier to use 1/8" steel and a 14" car rim.  Tack weld the plate to the rim and roll the plate around it.  You may need to weld a piece of bar stock  to the plate for leverage.  Tack the plate to the rim as you work it around the rim.  You will also need to figure a way to fasten the rim to something to keep it from rotating.  Just a suggestion.  Dom

[kappullen]

entsminger,

You can make saw cuts across the bend area leaving about 3/4 inch of material intact.

I'd make them every 3/4 inch of so and alternate from what side.

***On second thought all cuts from one side may work better.***

You may need a tack weld at the start of the saw cuts as well.

That leaves a 3/4 inch long area to heat and bend.

When bent, restrain, and weld the saw cuts.

Than grind to blend.

This procedure is quick and dirty, but will work for a non functional reproduction.

Otherwise, a sheet metal shop can "bump" the job on their brake.

Bumping means bending in small increments similar to the procedure above.

Kap

[entsminger]

 I don't have access to a milling machine or slip rollers. I guess I could try and make some kind of roller? I thought since the propane tank is close to 1/4 inch thick I'd try and use as close to the same thickness metal but I guess 1/8th metal might work? A friend has an old 4 foot tall propane tank that is roughly 15 inches in diameter and as a last resort I thought I might slice it up with my plazma cutter and use it but I don't know if the thickness is sufficent? Even though it won't shoot I want it to have the feel of solid iron. The thicker the metal the more it would sound like solid iron if you were to bang on it.
  I came across this large plate of thick 1/4 inch steel ( it may be thicker?) and cut it up into roughly 4 foot lengths of around 5 inch wide strips. I had hoped that by securing one end to a train track piece I had and then heating a small area I could slowly bend it into a round shape but I can't even begin to make it bend.Too tough.My torch won't faze the metal.
  I really have nothing to show in the way of progress as money is tight and time non existant and I want to weld on the trunions before I cut the tank in half so I can mount the barrel on something to make it easier to work on but I just can't get the trunions made yet. I've looked at junk yards several times for pipe close to 14 and a half inches but have found none. Since my tank is slightly under actual size of the 13 inch mortar( 41 1/2 vrs 43 inches) I'm going to make all components reduced slighly so it will at least look accurate. A friend who is good at math made all the reductions for me but I don't have them with me at work at the moment.   
  You guys all seem so knowledgable and equipped with the finest shops I know it's hard to explain to someone like me ( Fred Flintstone technology) who has little real knowledge of metal working but thanks for trying!

[GGaskill]

Don't be upset about the limitations of your equipment.  All of us find projects that are difficult due to limitations of our shop equipment.

[entsminger]

I may give Dominick's idea a try with the 14 inch wheel and trying to roll it around it. I'd still rather go with the 1/4 inch over 1/8th as the trunion will hold all the weight of the barrel and the tank. While the tank is hollow it is pretty dang heavy, especially when I get the 3 foot long 12 1/2 inch pipe barrel/tube and front face plate etc etc welded on. If anyone has any more ideas please don't hesitate to send them to me.

  Thanks
  Scott

[GGaskill]

The thicker the metal the more it would sound like solid iron if you were to bang on it.

As long as it is hollow, it will ring when struck.  You could fill it with expanding urethane foam to damp the ringing.  Not cheap but cheaper than iron.  Easier too.

[dominick]

Scott, You can go inside the trunion and weld a flat rib to reinforce the trunion ring.  A  criss-cross shape would be better and weld it to the sides of the barrel to tie it all together.  Dom