bending 4mm copper tubing

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi again Clive ,

There is one more way of doing it that I have also used successfully .

Make the section that is to be the bend as a solid block with connecting right angle drillings inside and silver solder to two pieces of tube . Hand file outsides of block to exactly match tube . Works best if block covers not just the bend but a little bit of straight where the plain tubes join . May need a very simple jig for the silver soldering but no problem to do otherwise .

For interest only :

Ratio of wall thickness to od of tube greatly affects the minimum bend radius achievable . It may seem paradoxical but the thicker the wall is the tighter the bends that are possible . This is because a very thin wall tube behaves like a toilet roll tube and collapses before it can even start to bend properly . A thick wall tube on the other hand behaves much better and bends more like a solid bar .

Anyone that remembers the old type small diameter copper alloy hydraulic pipes with the tiny hole down the middle will know that these could be bent nearly square in a bench vice without too much dificulty .

Regards ,

Michael Williams .

[ChrisParticipant @chris16039]

Hi Clive,

John Barrett did an improved little bender in issue 4345 which was one of my first projects. It has proved very useful and just an evenungs work for someone like yourself. I should still have the mag if you need a copy.

Chris

[SteambuffParticipant @steambuff]

Chris,

Its 4346 page 284/5 ( Feb 27 2009) … Its in the Digital Archive.

Dave

[DustyParticipant @dusty]

Clive

What is going through this pipe? If it is in any way abrasive i.e. Steam, then I would be very wary of creating such a sharp bend. In any bend there are two main forces acting, the inside of the bend is being compressed and the outside is being stretched. This stretching will cause thinning of the tube on the outside of the bend, the sharper the bend the more pronounced this effect is. I like Michael Williams idea, if the bend must be that sharp, if not a comprimise of increasing the radius of the bend is a better option. I am sure that someone on this forum will have the mathematical skills to work out how much the tube will thin, I am afraid, I do not posses the knowledge to do it.

[Clive HartlandParticipant @clivehartland94829]

Dusty , its just a small 2 cyl. steam engine of 13mm bore and I doubt I will run on steam. I will use air for a trial run.

I thought that the annealed copper tube would bend nicely but it will not and hardens very quickly maybe due to the pressure exerted in pipe bending tool.

Other commitments at the moment have meant putting it to one side and I see it everytime I walk in. I want to get the pipe run true and parallel to the engine base but at the moment the bend being a larger radii than needed puts it all out of shape as it goes imto the flanges.

I will shortly start on it again and show howe far I have got. Look in 'My pics. for the engine.

Thank you ockl 1 the drawings came through fine and I will examine them today sometime.

Clive

[Sub MandrelParticipant @submandrel]

Clive,

Are you using 4mm copper brake pipe? I find it very easy to bend.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Clive,

Another thought … with the important caveat that I have NO experience

Why not try electro-forming ?

You could make the armature [if that's the right word] from either Wax (with Graphite powder coating), or Woods Metal. ElectroPlate a thick layer of Copper, then melt out the armature.

May be a lot of faffing-about, but could do the trick.

MichaelG.

[Ed DuffnerParticipant @edduffner79357]

Hi Clive,

 

A couple of thoughts I had about this being an ex electrician. The spring benders we used to use for PVC conduit were flat-ground on the outer diameter, which helped prevent kinks, so not sure if you have access to this type of spring at that size.

My old boss used to have a block of wood about 4"x2"x36" with a hole through one end the same size as steel conduit OD. On one side of the wood the hole was carved/routed to the shape of the bend radius. The conduit was inserted through the hole and then bent into the curve and along the face of the wood.

Here's a crude cross-section image. Maybe this could work with 4mm copper.

 

Regards,
Ed.

Edited By Ed Duffner on 06/11/2012 00:04:34

[TerrydParticipant @terryd72465]

Hi Ed,

You've just raised an old memory for me, we used this type of wood block bender when I worked with the electricians as an apprentice. To use the 'bender' one end of it was rested on the ground and the conduit pushed through the hole and the 'bender' held at an angle to the ground . The conduit would then be pulled down just a little against the angled block putting a small part of the bend into the conduit. The conduit would be pushed further through a fraction and bent a little more. This was repeated until the required bend was acheived.  For reverse bends the tube woud then be rotated by the correct angle and the process repeated.

I much preferred using this method than the bending machine (we called it a cripple for some reason) as I had better control of the bend, especially when complex bends or joggles were needed. It took a bit of planning for the complex stuff though. The other end of the hole would also be carved, but in a 'trumpet' shape this was to allow areverse or complex bends or when such shapes as joggles were needed.

Happy memories,

Hi Clive,

In my experience a 1:1 bend is impossibe to achieve except by the cut and shut method, which Michael suggested, or other methods of fabrication.  We produced some very nice tight bends on work in this way on thin walled steel tube around 25mm diameter, and as Eric Morecambe used to say, "you can't see the join"

Best regards,

Terry

Edited By Terryd on 06/11/2012 06:44:10

[Bill DawesParticipant @billdawes]

Hi Clive, noticed you first posted some time ago so you may be sorted now but I recently bought a bender from RS components, model 2166. Designed for various sizes of small tube.

Not used it in anger yet but a quick trial seemed ok.

Bill D.

[Clive HartlandParticipant @clivehartland94829]

Thank you all for your helpful comments and I have now been thinking over the procedure that I used on the pipe bender that I made and realize that I should have anchored the end of the pipe so that as the lever went round the form it did not pull the tube through as it has been doing and so making the radius bigger than I wanted.

I will go back to it and design a form of anchor for the tube and let you know how I get on.

Thanks Clive

Edited By Clive Hartland on 06/11/2012 21:12:49

[TerrydParticipant @terryd72465]

Hi Clive,

This may help,

Best regards

Terry

[Clive HartlandParticipant @clivehartland94829]

Just now Ive been in the workshop and succesfully carried out the bends I wanted, it all came down to clamping the tube so that it could not pull through the rollers. I have achieved the radius I wanted and the tubes cut to length are symmetrical with the outline of the engine.

There is a slight compression of the inside of the bend but I expected this and am quite satisfied with it.

I ran out of 4mm copper and had some 4mm Brass tube which I tried and it bends just the same as the copper. When its all finished and attached I will post another pic. in my photos.

I now need to find some 2mm hex. nuts for the flange bolts.

Clive

[TerrydParticipant @terryd72465]

Hi Clive,

well done, but could I ask where you are measuring the bend radius from, i.e. is it the outside radius, inside radius or the centre line of the tube radius?

Best regards

Terry

[Clive HartlandParticipant @clivehartland94829]

Hi Terry, the spec for the tube bend was 8mm dia, When I made the mandrel/rollor I turned the base of the groove to 8mm. So its the inside radius.

On the original drawing the rollor was was stated as any dia. you needed, so I went ahead for what I wanted but as I mentioned my first draws were very poor and were well over the size of radius I was looking for because the tube was being drawn through the bend as it went around and became larger. After much thought I realized that the tube had to be anchored to stop this, so this evening I just clamped the tube against the body with a piar of pliers as a stop and the bends came true.

As I said, what surprised me was that the brass tube rolled as well as the copper, though it was slightly thinner wall thickness.

I have now trimmed to size and length and now have to solder the tubes into the flanges, but first have to bolt the flanges in place to ensure alignment.

Found the nuts and some M2 washers at:- pts-uk.com who have a comprehensive listing of smaller screws washer and sundry items, mostly in Stainless steel, worth a look through but dont be surprised at the prices! Needs must so I pay up.

Clive

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