# Tube bending radius



## Reed (Mar 1, 2010)

I built a bending jig, inspired by the Frank Ford wire bending jig. I went overboard but that is another story. 

In building a Maytag 1/2 scale engine, it calls for a part that is from 1/4" brass tubing bent at a 51 degree angle. I look at the wire bending jig and realize it will work if I revamped it to use a bar to bend with and make the pressure plate and holding parts. So I do.

A web search indicates 2.5 times the diameter of the tube is the minimum bending radius. Another site indicated this with a 35 thou thick wall. So I make the form with a 1" diameter and proceed with the bend. I get some ovality but not enough to make another form. My tube is brass with a 18 thou thick wall.

I would like to find a chart similar to the one at:
http://www.wintonmachine.com/details.php?prod_id=44
for model tubing such as the brass tubing I used. Actually any charts for any small tubing would be useful for the future projects.

Thanks, - Reed


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## JaguarB (Mar 6, 2010)

Hello Reed
I am jumping on your band wagon as you have asked a question that I would like to know the answer to.

I like the look of the bender you have designed and would like to help get a set of sizes for the tooling that will work with the brass tube that you describe. Could you let me have a sketch and some dimentions for what you have made so far

I am making a 12th scale extrusion press and there are going to be lots of small pipes to bend see http://www.boscott.co.uk


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## gbritnell (Mar 6, 2010)

Hi Reed, I don't know of any charts pertinent to tubing bending but in the past year I have had occasion to bend tubing numerous times. I built a small tubing bender that will handle up to .312 diameter tube and have posted the drawing in the files section. I also just built another bender because I had to bend .375 stainless tubing for my V-twin exhaust system, there's a thread on it. The biggest improvement I have found in bending nice smooth curves is by pouring Cerro alloy into the tube prior to bending. I got minimal distortion by doing this.
gbritnell


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## ironman (Mar 6, 2010)

gbritnell, Where is the drawing for your bender that you are talking about? I looked in the downloads. Where is the files section?. Thanks, ironman


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## gbritnell (Mar 6, 2010)

Here's a copy of it.
gbritnell 

View attachment TUBING BENDER rev1.pdf


View attachment TUBING BENDER rev1clarification.pdf


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## ToniTD1490 (Mar 7, 2010)

Hi gbritnell, could you tell me what cerro alloy have you used? Pb-Sn? for bending tubes? and how did you introduce the alloy into the tube? Do you put solid alloy tube and melt it?
Thanks, 

ToniTD1490


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## gbritnell (Mar 7, 2010)

Hi Tony, I put the chunk of alloy into an old tin can and put that into a pot of boiling water. I bent the edge of the tin can to form a funnel. I then put another small pot of water on to boil next to the one I was melting the alloy in. The purpose of the second pot was to hold the tubing in with pliers and keep it hot. Any alloy that spilled over into the water was just cooled and put back into the tin can. 
 Here's a link to the Ebay seller that I bought the Cerro from. It gives the specs.
gbritnell
http://cgi.ebay.com/Low-Temp-Alloy-...emQQptZLH_DefaultDomain_0?hash=item4ced3df13a


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## Reed (Mar 8, 2010)

Paul et al,

I did a sketch in visio simply to eliminate obvious dimensional mistakes. Pls bear in mind this was an evolution of making a simple bending jig to to then bend the thinwall brass pipe for the Maytag engine. ;D Seem there was a set of plans for a really nice pipe bender in Projects in Metal, ME, Modeltech, or one of the other mags.

From what I have been able to find, .014" in 1/4" tubing at .375" radius is much to thin to bend without some amount of oval in the bend. I understand I'd need to do the filler method as noted in gbritnell's post, increase the radius, or get thicker walled pipe. In any event, I soldered the pipe to the carb and called it good. I highly suspect the prototype engine also has some ovalness in its intake pipe.   ;D 

Anyway, here is the sketch including the rough coordinates for drilling the holes. 

- Reed



View attachment BendingPlate-rev1.pdf


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## capjak (Mar 8, 2010)

Hi Reed,

I had to bend 1/8" brass pipe for my last engine. I used the pipe that is sold at a local hobby shop. I annealed it first and then bent it ninety degrees using a mandrel that I made out of some scrap wood. I heated the metal to a dull red, let it cool to grey and then quenched it. It bent with very little ovalling. I don't know how much tighter a radius I could achieve with some type of filler in the pipe. I am going to get some Cerrobend and give it a try.

Jack


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## JaguarB (Mar 9, 2010)

Hello Reed

Thank you for the most detailed sketch I will make this up 6 inch version and let you know the results

I will be an ideal warm up project as I am waiting on some more detail before I can finish the drawing for the press.


yours Paul


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