Bending brass tube

[makila]

Hi,

I am trying to create the intake/exhaust tubes for my radial project and not doing so well.

The material is 5/16" brass tube with .014" wall thickness. The issue is that the cerro metal that fills the tube is cracking during the bend process and causing a stepped appearance, see pictures.

I treated the tube by heating it to a red heat color then let it cool slowly, then filled the tube with cerro low temp metal before using a wheeled bending tool. When the bend was in progress, I noticed (felt and heard) that the cerro metal cracked when bending the tube causing a slight stepped finish on the outside diameter of the bend. I did exactly the same on the next piece but not to the same degree. Is it normal that the cerro metal cracks within the tube? I thought it would be mallable to some degree without cracking within the bore.

Has anyone had experience of this and is there a better technique, The tube between the cracks looks okay, but it does affect the appearance of the tubes and these being the intake tubes, they will be very visible.

I would be grateful if anyone has some good advice.

Many thanks

Steve

 

[10K Pete]

I've never had good results with CerroBend and thin wall tubing. It's not
malleable enough.

I've found that lead is much better. If you soot up the inside of the tubing
before you pour in the lead it won't stick and will melt out cleanly. With
small diameters do a test to verify that your lead is fairly pure as things
like wheel weights are alloyed and can be a bit brittle leading to some
tearing that might show thru like the Cerro does.

I've been told that folks who make brass musical instruments use soap
heavy water solution that when frozen is still malleable and, of course,
melts out cleanly. I've never tried it.

Pete

 

[gbritnell]

Steve,
When I first designed my bender I used a round bending dolly. I found that it would put a little imprint in the tube right where the bend stopped. To prevent this I changed from the roller dolly to a rectangular block with the radius of the tubing machined into it. I have used Cerro alloy to make 90 degree bends but in stainless and not in brass with no problems.
gbritnell

 

[canadianhorsepower]

To prevent this I changed from the roller dolly to a rectangular block with the radius of the tubing machined into it.
gbritnell

Hi GBritnell
this is how exhaust pipe tubing jig are done on full size
scale. Works perfect Thm:Thm:

Although when I have reel steep radius "like a coil of tubing"
I take longer of material then needed, cap one end, fill the pipe
with beach sand or fine sandblast sand and cap the other end.
This works fine but take more time :fan:

always enjoying your art

cheers

 

[makila]

Thanks for the advice. I will try Pete's suggestion and soot up the ID, I believe the problem is the cerrobend sticks to the bore and when the outer radius expands when bending, it causes the cerrobend to crack resulting in a stepped appearance. So sooting up the bore with some light oil to prevent sticking will hopefully work.
I like the idea of a forming block and single wheel instead of two wheels, if I am unable to get a good bend, I will consider making this type of tool.
Many thanks for the advice, will post a picture when or if I am successful.
Steve

 

[gbritnell]

Steve,
Drop me a note at [email protected] and I will send you the tubing bender drawings. I think I posted them in the drawing section here.
gbritnell

 

[10K Pete]

Thanks for the advice. I will try Pete's suggestion and soot up the ID, I believe the problem is the cerrobend sticks to the bore and when the outer radius expands when bending, it causes the cerrobend to crack resulting in a stepped appearance. So sooting up the bore with some light oil to prevent sticking will hopefully work.

Steve

Steve, the Cerro is brittle and does not bend well. Use lead as it's very
ductile. Soot or oil won't help with the Cerro.

Pete

 

[ICEpeter]

Makila / Steve,
I am in the process of building an ETW Sealion engine (Need another year or two before being finished) and had the same problem with bending thin wall brass tubing of dia 3/16" / dia. 7/32" and dia. 3/8" thin wall stainless tubing without using any Cerro, lead or other fill in the bending process. Did some research on the internet and settled on a system / process that seemed promising.

Take a look at the attached pictures of the bending device and the pipes I did bend using the bending device. It does make reasonable short radius bends resulting in about 4 times the dia. of pipe as the bending radius. All bends are without noticeable collapse or cross section changes. In addition, I am able to make some fairly compound pipe bends as you can see.

The piece of pipe you see sticking out of the bender is dia. 3/8" OD / dia. 5/16" ID stainless steel. Used to bend it at 90 degrees and it shows in one picture as the piping to the silencer and silencer outlet. As I said, all bends were made without internal support of the piping and did not cause collapse of the piping. Took a little bit of experimenting but the original design worked as planned. Forgot to mention that during experimenting with different lots of brass piping, I found that brass pipe that wasn't tempered to at least the semi / half hard stage the piping would collapse / break during bending. Pipe that was at least tempered to semi hardness gave no problem without collapsing or cross sectional shape changes.

Peter J.

 

[10K Pete]

ICEpeter,

I love that bender! I don't think I've ever seen one like that before. I may
have to copy that idea, with your permission of course.

And the engine is beautiful!! Great work.

Pete

 

[Tony Bird]

Hi Steve,

I treated the tube by heating it to a red heat colour then let it cool slowly, then filled the tube with cerro low temp metal before using a wheeled bending tool. When the bend was in progress, I noticed (felt and heard) that the cerro metal cracked when bending the tube causing a slight stepped finish on the outside diameter of the bend. I did exactly the same on the next piece but not to the same degree. Is it normal that the cerro metal cracks within the tube? I thought it would be malleable to some degree without cracking within the bore.


Have you tried bending the tube for a bit and then remelting the cerro? Might work.

Regards Tony.

 

[t.l.a.r. eng]

I read through the thread and no one mentioned that brass is softened by heating red hot, then quenching in water.

I think brass is backwards from other metals.

 

[10K Pete]

I read through the thread and no one mentioned that brass is softened by heating red hot, then quenching in water.

I think brass is backwards from other metals.

Quenching is unnecessary when annealing brass or copper. Air cooling
is all that's required.

Pete

 

[t.l.a.r. eng]

Quenching is unnecessary when annealing brass or copper. Air cooling
is all that's required.

Pete

Maybe I missed something, how then do you harden brass or copper?

 

[canadianhorsepower]

Maybe I missed something, how then do you harden brass or copper?

this should help you


http://bisonballistics.com/articles/the-science-of-cartridge-brass-annealing

 

[10K Pete]

Maybe I missed something, how then do you harden brass or copper?

By cold working it. A piece of copper or brass (or austietic stainless and
other materials for
that matter) gets harder and less ductile the more it is cold worked. That
may consist of bending, stretching, hammering, etc. It will get hard enough
to crack fairly quickly. That's why the part must be annealed frequently while
forming it.

While copper and brass can be worked while hot, as can most steels, sstl, bronze and some others must not be worked above a certain temperature
as they are 'hot short'. Meaning that if you try to bend something like 18-8
sstl by heating it, the part will just crumble in the hot zone when bent.

It's an interesting subject that many folks don't know a lot about. But it's
fairly easy to get information on.

Have fun,
Pete

 

[10K Pete]

this should help you


http://bisonballistics.com/articles/the-science-of-cartridge-brass-annealing

Good article on brass!!

Pete

 

[Draw-Tech]

Hi Steve & Tony
Years ago I used to bend and twist Brass wave guide, We found that the cerobend was sticking to the brass, not allowing the cerobend plug to slide inside as we were bending it. We got around this by first coating the inside of the tube with dykem blue, metal layout bluing, let it dry, and now coat with mineral oil. Brass stayed clean and dykem washed out with acetone. Don't forget to warm up the tubing, this stuff cools real fast.
Jack

 

[goldstar31]

There is far more on bending tubing on the musical instrument repair and construction side of things.
I am looking at Ferees catalogue and various books belonging to my late wife.

Me, I've never had any bother with Cunifer piping.

As for copper, it softens with heating to bright red and then quenching. The Bronze Age was full of such- but perhaps the Bronze Age never got to the USA. My late father - a blacksmith/farrier, always annealed soldering irons which failed to 'tin' after repeated heatings.

I hope that this information helps

Norman

 

[johnny1320]

I have heard of water with soap can be frozen in the tube and then bent. they bend tubing for musical instruments this way.

 

[makila]

Hi All,

Great info, many thanks for all the inputs.

I had a couple of practice bends over the weekend, both with heat treated brass tube and using a nylon rod as a filler but all failed to produce a uniform bend. I noticed that Cerro-bend is quite brittle, when bending a cool piece it readily snapped in half, which was a surprise. It is nowhere as maleable as lead which can be folded in half without snapping. The only issue with lead is it must reach about 350-370 degrees C to achieve it's liquid state and melting, pouring and filling a small tube seems awkward but achievable with care.

I like the suggestion of coating the inside of the tube with marking dye and oiling when using Cerro-bend so as to not stick, sticking was apparent in my previous attempt which caused the snapped portions to show through the tube. I will give this a try when my re-ordered brass tube arrives as I have managed to destroy my stock with rubbish bends.

Just a thought, as the tube has a wall thickness of .014", could this be the cause for difficult bends. As mentioned, brass work hardens when being cold formed and a thin wall would possibly need more care?

If the above fails, I will attempt to make a new tool, as described in Gbritnels post or try one attempt at using lead.

Thanks again for all the inputs, I have provided a picture of the home made tool used below.

Steve