Bending brass strips into semi-circle

[Submachine]

I am trying to bend 1” brass strips (up to .090 thick) and 6 inches long into a semi-circle with 1”diameter. The bend should be close to the middle of the 6” strip with 2-3 inches non-bent tails on either side. This is for the top section holding down trunnions on small cannon.

I bent the bottom ones with a lot of work and a hammer. Not ideal.

I created a mold of sorts of the top section made out of wood. I then used various clamps as a press and got it 80% there.

Ideas on how to do this? (If I have to buy a tool, include instructions on smuggling it past my wife)

 

[just old al]

You're half way there with the mold idea. One of the things I built for my hydraulic press is a bending jig for right angles - a machined steel block with a V notch and a matching knife. One attaches to the hydraulic press ram and the other sits on the table.

Given tooling (a bench vise or the like) you could do that with wooden formers easily. Just make sure to allow for pressing the joint tighter to allow for springback to your 1" need.

 

[JimDawson]

Make a punch & die that has the shape you want, then using a large hammer or press to drive the punch and material into the die. Just a piece of 1'' round bar is all you need for the punch, the die is just a hole bored through a piece of steel then cut in half to create a half circle.

 

[Submachine]

how do I account for spring back.

You're half way there with the mold idea. One of the things I built for my hydraulic press is a bending jig for right angles - a machined steel block with a V notch and a matching knife. One attaches to the hydraulic press ram and the other sits on the table.

Given tooling (a bench vise or the like) you could do that with wooden formers easily. Just make sure to allow for pressing the joint tighter to allow for springback to your 1" need.

how do you account for spring back?

I have seriously thought of using my log splitters a press.

 

[RJSakowski]

This should be relatively easy since you have two handles to work with. I find that my socket sets provide a good assortment of bending mandrels. I would start with a longer strip than required and just bend it around a socket or other suitable round stock and cut the ends to the finished length. The lathe will provide a suitable fixture for your mandrel but a vise will also work. If you are dealing with hardened brass or half hard brass, the brass can be annealked to make bending easier.

 

[RJSakowski]

If you are experiencing spring back, reduce the diameter of the mandrel and over bend to compensate.

 

[JimDawson]

I have used a log splitter for a press, works very well. I have a 7 ton electric that I converted into a broach/break press for small items, and just bought a 25 ton gas powered that will do double duty as a log splitter and assembly press for a product that we build.

Over bending is not needed if you mash the punch into the die hard enough. It actually stretches the metal a bit and will hold its shape.

 

[Al 1]

Submachine, These were done on a 20 ton press in a half circle and rod. You may need some shims when applying pressure.
Do some practice pieces. Al.

 

[Submachine]

Submachine, These were done on a 20 ton press in a half circle and rod. You may need some shims when applying pressure.
Do some practice pieces.View attachment 283474 Al.

Nice cannon. It definitely looks like a machinist made it...very nice
The problem I seem to be having, with all methods, is repeatability. I think the issue is that I am using 1 inch die and a 1/2 inch punch. Should I cut 1 inch bar in half lengthwise and use that?

 

[JimDawson]

I wouldn't bother to cut the bar, just us it as it is. But, the die needs to have the correct radius for the part. With a 1'' ID and 0.090 material thickness, the die needs to have a radius of 0.590'' (ID + the material thickness)