SMALL RADIUS BENDS IN COPPER TUBE

[CHARLES lipscombeParticipant @charleslipscombe16059]

As part of a motorcycle-based project I need to bend annealed 1/4 inch OD copper tube with an I.D. of approx 4 mms (sorry for the mixed units!) into a 90-degree bend with a radius of 1/4-inch.

Can anyone suggest a suitable technique or bending tool for this?

Is a 1/4-inch radius bend in 1/4-inch tube what is known as a 1:1 bend?

Chas

[CHARLES lipscombeParticipant @charleslipscombe16059]

[EmgeeParticipant @emgee]

Hi Charles

Not likely that you can bend such a tight radius, you should be able to machine from solid but perhaps having to accept a restricted bore.

Emgee

[Brian Sweeting 2Participant @briansweeting2]

One suggestion I've seen is to crimp one end and then fill the tube with a low temperature filler such as cerro alloy or even plumbers solder.

Form your bend and then melt the filler out of the tube.

[Nick HulmeParticipant @nickhulme30114]

As Brian suggests fill a length with low a melting point alloy.

You could make your own pipe bender with the correct mandrel and roller sizes, if the copper doesn't tear on the outside of the bend you're golden.

If you shared with the class the reason for and reasoning behind the design you might get some more constructive answers

[Chris TriceParticipant @christrice43267]

Prepare yourself for the possibility that I don't think it's possible, not with that radius. How cosmetic has it got to be? A cast elbow silver soldered in is the obvious choice but without knowing what the pipe is intended to do, it's hard to comment on a "safe" solution.

[Simon CollierParticipant @simoncollier74340]

I don't think it is possible. Consider cutting through the tube at 45 degrees and silver soldering back together in a 90 degree bend with zero radius. It is quite easy. To get tight bends, I part a deep groove in a bit of bar wide enough such that the tube barely can be pushed into the groove and bent around whatever radius the i.d. of the groove is. The tight fit prevents the tube from flattening and kinking.

[Jeff DaymanParticipant @jeffdayman43397]

+1 for not easy if not impossible, even if the 1/4" bend rad is the inside rad.

A better design to turn the fluid 90 deg in shortest distance would be a banjo joint or a cone and seat type bolted joint with clamp as used in hydraulics. Chances are things can be rearranged to permit bends of normal good practice radii, or banjos or bolted joints can be used.

If doing a new motorcycle design you would be wise to design out this sort of tight bend.

If restoring something ancient the original fitting may have been a casting soldered to a pipe, and the whole assy probably with some common sense should not have been done that way, but history is history.

[CHARLES lipscombeParticipant @charleslipscombe16059]

Thanks to all that have replied.

Yes it is possible. I was trying to make my request as short as I could hence gave little detail. I am reproducing petrol filler caps for vintage racing motorcycles. The original items were made by the firm of Best & Lloyd of Birmingham who made many brass items for the motor trade in the 1920's as well as high quality light fittings. Their racing filler cap incorporates a breather tube with the dimensions I quoted.I have no idea how Best & Lloyd managed this feat 80 years ago!

My present method which works after a fashion is to pack the I.D. of the tube with the steel spiral "tube"that surrounds the inner cable of push bike brakes. However this method is very slow and removal of the spiral inner from the finished job is very difficult.

I thought that bending small size tubing would be more or less a routine job for railway engine enthusiasts?

Chas

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

When i bend the pipe who has small radius, i used the jig for exact length and radius . The pipe was filled with sand and use torch lamp to heat up pipe while the pipe was bending on the jig.

 

Edited By Jens Eirik Skogstad on 03/12/2017 05:27:08

[john carruthersParticipant @johncarruthers46255]

Try cupro brake pipe, you can get formers and flaring tools to suit.
Surprising how tight a radius you can get it.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by CHARLES lipscombe on 03/12/2017 05:18:00:

… I am reproducing petrol filler caps for vintage racing motorcycles. The original items were made by the firm of Best & Lloyd of Birmingham who made many brass items for the motor trade in the 1920's as well as high quality light fittings. Their racing filler cap incorporates a breather tube with the dimensions I quoted.I have no idea how Best & Lloyd managed this feat 80 years ago!

.

It may be worth asking them, Charles

**LINK**

http://bestandlloyd.com/history/

They clearly have at least some of the old drawings on file:

**LINK**

http://bestandlloyd.com/wp-content/uploads/2015/09/BestLloyd_Heritage.pdf

MichaelG.

[Sam Longley 1Participant @samlongley1]

There was a thread on this forum a short while ago entitled " bending small bore copper pipe"

I picked up a link there & made my own bender but I could have bought a brake pipe bender quite cheaply. Not sure if one could be adapted to bend as tight as you want though. More fun making my own & I now can bend wire & tube in small sizes

This is similar to what i made:-

lhttp://www.modelengineeringwebsite.com/bender.html

But the thread has another design

 

 

Edited By Sam Longley 1 on 03/12/2017 09:39:34

[Geoff GParticipant @geoffg]

I'm with Simon Collier – fabricate the bend. I have done it by cutting the parts at 22.5 deg, holding them in a jig (rough!) and silver soldering. The application of a little time and an assortment of files should produce a visually passable result. This method should suit any size, in any material. In view of the use of butt joints, I guess that working pressure sould be limited. A couple of pics to show the idea:

[Neil WyattModerator @neilwyatt]

I understand that the minimum bend radius for ductile tubes is equal to the diameter, so yes it is possible

The best way is a bender that has a 'bullet ended' rod that supports the tube at the bending point.

[Michael GilliganParticipant @michaelgilligan61133]

Presumably the required bend is similar to that illustrated on the "Benton & Stone" advertisement, here:

**LINK**

Fuel taps and accessories

MichaelG.

[JasonBModerator @jasonb]

This shows how a bullet will improve the bend.

As it is only a vent and quite short pipe length I would anneal then cerrobond it and bend in a two part former

[not done it yetParticipant @notdoneityet]

It is a 'breather' so no real need for 4mm ID, I would suggest.

[Russell EberhardtParticipant @russelleberhardt48058]

Here's a very simple design of bender that you could adapt: **LINK**

DIY tube-bending tool

Russell

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 03/12/2017 10:31:53:

It is a 'breather' so no real need for 4mm ID, I would suggest.

.

A good point ^^^

Reducing the bore would give more wall-thickness and significantly stabilise the bend against wrinkling.

MichaelG.

[vintagengineerParticipant @vintagengineer]

A way to get kinks from a pipe is to use balls the same size as the bore. After bending fill the tube with balls and keep forcing the balls through the tube until the kink is removed.

[mechman48Participant @mechman48]

I made a small tube bender that would cope with 1/8" & 1/4" copper tubing…

George.

[Michael GilliganParticipant @michaelgilligan61133]

A useful range of wall thicknesses available here: **LINK**

http://www.holmedodsworth.com/materials/copper/copper-tube

… and a handy SWG converter here: **LINK**

https://www.rapidtables.com/calc/wire/swg-to-mm.html

MichaelG.

[Tim StevensParticipant @timstevens64731]

I presume that the handle and small roller assembly is spring loaded, or is it enough to keep pressure on the bigger roller manually? And the collets of various sizes are held somewhere out of sight behind the rest of the device?

And I agree with the comments that a breather does not need such a big bore (or a big tube). The main reason I suspect for adding a tube, instead of the usual hole, was to stop fuel from squirting upwards when the rider went over eg Ballaugh Bridge.

Cheers, Tim

[CHARLES lipscombeParticipant @charleslipscombe16059]

My thanks to all the people who have replied with help to my posting

Yes Tim,

That is exactly the purpose of the bent breather. With no special precautions and a full fuel tank, under heavy braking the fuel would surge to the front of the tank and exit via the breather hole in the fuel cap, straight into the riders face – not an ideal racing situation. The B&L design had this right-angle bend on the vent and the rider was meant to attach a piece of rubber tube to this and lead the spray down below the tank where it would cause no harm to the rider.

I guess that the largish bore size was either what was readily available or perhaps thought necessary for alcohol fuels.

Whatever method B&L used it must have been quick and easy because this was a routine production item.

My next step is a thorough study of everyone's posting and with special thanks to Michael Gilligan, Jason B and Mechman48

Chas

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