# Bending brass tube



## makila (Oct 3, 2015)

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 (Oct 3, 2015)

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 (Oct 3, 2015)

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 (Oct 3, 2015)

gbritnell said:


> 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 (Oct 3, 2015)

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 (Oct 3, 2015)

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 (Oct 3, 2015)

makila said:


> 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 (Oct 3, 2015)

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 (Oct 4, 2015)

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 (Oct 4, 2015)

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 (Oct 4, 2015)

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 (Oct 4, 2015)

t.l.a.r. eng said:


> 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 (Oct 4, 2015)

10K Pete said:


> 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 (Oct 4, 2015)

t.l.a.r. eng said:


> 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 (Oct 4, 2015)

t.l.a.r. eng said:


> 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 (Oct 4, 2015)

canadianhorsepower said:


> this should help you
> 
> 
> http://bisonballistics.com/articles/the-science-of-cartridge-brass-annealing



Good article on brass!!

Pete


----------



## Draw-Tech (Oct 4, 2015)

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 (Oct 5, 2015)

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 (Oct 5, 2015)

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 (Oct 5, 2015)

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


----------



## 10K Pete (Oct 5, 2015)

Heavier tube is much easier to bend. If the higher melt temp of lead is a problem,
try the soap-heavy water I suggested. Every one has a freezer.

Pete


----------



## ICEpeter (Oct 6, 2015)

Hello Makila / Steve,
In post # 8 the thin wall brass tubing I referenced in that post is of a 0.014" wall thickness, same as your dia. 5/16" brass tubing. As I stated, I was successful in bending the 0.014" wall pipe without problems. It is important though to use annealed brass tubing of semi hardness to avoid collapse or breaking. The principal of the little tube bender I built can be looked at by googling pipe bending and there are some videos on youtube that depict a bender of similar design.

The tube bender I built incorporated a provision for a mandrel to be used if the bending without a mandrel had failed. As it turned out, I could bend the tubing {3/16 / 7/32 brass and 3/8 stainless - all annealed) without the use of a mandrel.

I just looked closely again at the pipe bender picture you show in your latest post. It seems you have a gap between the two rollers and it looks as if the pipe you intend to bend is not very tightly held between the two rollers allowing for some play while bending. In my experience, if the pipe is not tightly held without any play, you will have problems when bending because the pipe is allowed to distort in the bending process and will fail. The radius in the two rollers must also tightly match the pipe diameter without play.

Hope you will be successful in bending your brass tubing.

Peter J.


----------



## WOB (Oct 6, 2015)

I used Cerrobend to make 9 intake pipes for my Hodgson radial out of 5/16" OD 3003 alum tubing.  The bends were 90 deg. with an inside radius of 1/2" and there were no problems making them.   Cerrobend expands as it cools so as to grip the inside of the tubing and is malleable enough to bend without breaking.  This is what you want to make a smooth bend.  You must also be sure the tube is full of Cerrobend with no air pockets.

Do not try bending with Cerrosafe as it shrinks initially and then expands back to original size after a 1/2 hour or so, but never firmly grips the tube ID.  It is also brittle and will snap and slide inside the tube as you try to bend it making a mess out of the bend. 

WOB


----------



## makila (Oct 8, 2015)

I just had a look at the Cerro-bend web site (something I should have done earlier!) and they recommend coating the ID with a lubricant prior to bending. They also say that once the tube is filled and still hot (warm?) rapid cooling is required to crystalise the material. Not sure what effect that would have but will follow this instruction on one more bend to see if it works.

The tool I am using is correctly made, there is no gap between the wheels but I checked it all the same to ensure this was okay, it is also concentric and holds the tube tight.

I have also made a system to melt lead and have a small pouring ladle, this will be used should the Cerro-bend fail. If that does not work, then I think a new tool will have to be made, designed similar to the tool shown earlier.  I have tried stainless and aluminium tube and both of these work well using the bending tool but the wall thickness is too thick giving a ID that is too small, possibly having an effect on performance. The Brass tube has a thin wall but this means work hardening issues when cold forming. I hope to have some good news in a week or so when I get my new tube stock, so hoping for some success.


----------



## 10K Pete (Oct 8, 2015)

Good luck and post back with results and pictures!th_wwp

Pete


----------



## dnalot (Oct 8, 2015)

I have had very good luck with filling a tube with very fine "olivine sand". start by crimping one end and then fill with sand. It is so fine that a few taps and its packed. I then crimp the open end.  The sand can be found at pottery supply type business. I got Mine from Seattle pottery supply. It is also the best sand for making "cores" for creating hollows in a casting.

Mark


----------



## ICEpeter (Oct 9, 2015)

Under post #8 I am showing a pipe bender that I built for bending thin wall 0.014" brass tubing of dia. 3/16 / 7/32 and dia. 3/8 stainless tubing. The inspiration to built the bender for my personal needs was based on a youtube video posted by a British company that can be found at following internet address:
http://shop.useful-tools.co.uk/mandrel-tube-bender-2-p.asp

I modified the bender design to suit my application and pipe bending needs but the approach is similar. You may find watching the video interesting.


Peter J.


----------



## makila (Oct 10, 2015)

Hi Peter,
Just watched the video and I am impressed. I think that it might be necessary to build something similar to yours as the tool from Useful tools is quite an expensive investment especially with the ID mandrel. A quick question, did you make the internal ID mandrel, is it necessary for thin material and if so what would the bullet tip be formed to? Is the the side profile of the tip round or does it follow the ID's outside radius - e.g. bullet shaped?
Many thanks.
Steve


----------



## Swifty (Oct 10, 2015)

That is an impressive bender, looks like the next quick project to make.

Paul.


----------



## MachineTom (Oct 11, 2015)

A point not mentioned is lubing the outside diameter, before bending. I had been at a plant that bent exhaust tubing for HD trucks, 4" 5" steel tube. The outside of the  tubes was coated with a soap lube, as was the inside mandrel. That mandrel was a cable with steel disks that were shaped like donuts, hydraulics kept a constant pressure of the inside mandrel, as the dies were sung to the needed angle. Interesting t watch.


----------



## ICEpeter (Oct 11, 2015)

Hello Makila / Steve,
I did make a provision in my design and built of the pipe bender for the use of a mandrel if the bending of the brass tubing without mandrel had failed. As it turned out, I could bend the brass tubing as well as the stainless tubing without the use of a mandrel. Hence, I did not develop a suitable mandrel or a particular mandrel shape.

If I remember correctly, in the video there is a very brief showing of a picture of the mandrel they were using and it looks like a bullet shape. In the video, there was a brief verbal reference to the position of the mandrel related to the forming tool location and its relation to each other during the bending process. 

Also, they stated lubricating the inside of the tubing when using the mandrel. I id not see or hear a reference to lubricating the outside of the tubing because the shown bending process does not involve sliding the outside of the tubing over a surface or a forming tool over the tubing, instead when bending, the tubing is pulled over the forming tool without sliding and the straight half round tube support moves with the tubing in a straight line as it is pulled over the forming tool.

I believe my successful bending of the 0.014" wall brass tubing without a mandrel was the result of two main factors:

- The tubing being held firmly in the grove of the forming tool and the sliding tubing support. When I milled the two grooves in the two pieces, I made sure the depth of the groves were a few thou (~ 5 thou I believe) less than half the OD of the tubing. When clamping the tubing with the hand wheel, the tubing is forced into the shape of the grooves very tightly and can not move anywhere when bending, thus maintaining a decent cross sectional shape all along during bending.
- The second factor is to use annealed tubing in the semi / half hard stage. I was not successful bending tubing that was harder than semi hard. The tubing collapsed and broke in the process. Have not experimented with soft or fully annealed tubing and don't know how they would preform.

Peter J.


----------



## makila (Nov 7, 2015)

Tube bending tool shootout!

Since my last post, I did not have a tube bending tool that was worthy of neatly bending thin wall 5/16" brass tube, see previous picture. The tool was not capable of bending brass tubing at a tight radius of about 2-1/2 times the OD hence my posting here.

One of the reasons for coming to this site is the great help that is offered and I was kindly supplied a drawing from Ice Peter of a tube bending tool that he had developed for bending tight radius's in small tubing. I had started to build the GBritnell tube bender, drawings supplied on this site, which I decided to complete and is an excellent tool. I then constructed the bending tool that Ice Peter had drawn up as this supports the development of a internal sliding mandrel which does not require ID support material. A great time saver!

I will not be using Cerro-Bend as a ID filling material as it is too brittle and cracks during tight radius forming giving a staggered out side bend surface, I will either use lead or make a forming bullet if I have time.

I have tried a piece of 5/16" stainless tube without any ID supporting material and it gives a perfect 90 degree bend, the brass will need ID support material as it will certainly deform. Once I figure out what I will use as a ID support, I will post the results with some pictures. I feel a bit more confident of success but still a bit apprehensive with brass, if brass fails, then I will go straight over to stainless tube, it is much easier to work with. The only issue is, if I use stainless, the whole engine will look silver, brass was a nice contrast.

Once again, thanks for the help received, especially from Ice Peter who send lots of photos. This tool is heavy, lots of mild steel had to be cleaned, milled and cut, the mill is covered in metal chips from the all the cutting!

Here are some pictures of what I have, just about ready to go and bend some tubes. Note the stainless tube - perfectly bent at 2-1/2 times radius with no internal support.


----------



## ICEpeter (Nov 7, 2015)

Hello Makila,
Looks familiar and good to my eyes. You got it done in no time, great! Glad it worked for you with stainless in your first try. I wouldn't hesitate to try a couple of bends using the 5/16" brass. You may be pleasantly surprised with the results. Have you considered using a mandrel if the brass bending without internal support fails?

Peter J.


----------



## makila (Nov 7, 2015)

Hi Peter,

The issue with brass is it work hardens when its being formed and will most likely collapse, I will give it try without internal support once some stock arrives. 

I will certainly be making the internal sliding mandrel, if it works then finding a filler will be a thing of the past. 70% of the time is used filling tubes so we will be onto something if the internal mandrel works with small diameter tubes.


----------



## xpylonracer (Nov 7, 2015)

Hi IcePeter

Is your drawing for the small radius bending tool available to download ?

Emgee


----------



## ICEpeter (Nov 7, 2015)

Emgee,
I sent you a private message.

Peter J.


----------



## makila (Nov 18, 2015)

Tubes complete!
Just to round off this thread, I have completed the inlet/exhaust tubes that was giving me an issue with the thin wall brass tubes. All 9 exhaust assemblies were completed using the Ice Peter bending tool that worked very well. Nevertheless, I had to use a tube filler that prevented the collapse of the brass tube, stainless tube with .035" wall thickness did not need a filler during experimentation with the bending tool. 
My process was to heat the tube to bright orange to anneal it then fill with a material called Polybend. This material has similar application properties as Cerrobend but is not brittle causing steps in the bend due to cracking.
I noted that after annealing the tube, it had a forming life of about a day, beyond this time, the tube returned to its former hard properties and was difficult to bend. Therefore annealing through to bending has to be done within a few hours. I have posted a picture of the results.

Many thanks for all the help given on this thread, the job turned out to be a success.

Steve


----------



## ICEpeter (Nov 19, 2015)

Hello Makila,
That looks like a well done job. Congratulation on the final success. Waiting to see your radial getting done!

Peter J.


----------



## Wizard69 (Nov 23, 2015)

Has anyone considered fine dry sand and heated tubing.   I'm not sure if it would work with brass but for difficult hydraulic pipe bending it is an approach we took at work sometime ago.   You need to pack the tube and put vented plugs in each end of the tube.   

Obviously brass tubing is a different beast than steel hydraulic tubing but I'd thought I'd throw this out for comments. 

To emphasis what was said above the sand must be dry.  You don't want massive steam formation once you start heating the tubing.


----------

