Precision Pipe Bending

I am looking at having to form two bends in a number of lengths of stainless tube, 10mm dia by 2mm wall. One or two is fine and easy using a pipe bender, but I have to produce 10+ all exactly the same. Any ideas on how I could do this? Some sort of jig?

Carl.

Not difficult to do, but without knowing what bender you are using, what angle the bend (or bends) are to be, how far the bends are from each other (and whether they are in the same plane it not possible to say how to do it. How much 'precision' does your application need?

If it was something simple like a 90 degree bend just creating an 'L' shape then put the bend anywhere and trim the two legs to length.

Ian P

You make the first bend and then place this against some form of a STOP before you make the second bend. If the second bend is not in the same plane as the first, then you may have to make a jig to hold the tube. You can't rely on pencil marks in my experience.
BobH

Difficult to say but I think that the bends will need to be within 0.5 - 1 degree of each other. Both bends in the same plane. One of 30 degrees and then 35-40mm along second bend in opposite direction to the first, 15 degrees.

Carl

What type of bender are you using?

Ian P

It is a Ridgid 400 series level instrument tube bender. Fairly bog standard tool in hydraulics work.

What I've been thinking is to set the bender up on the mill table, then have a series of stops to locate the length of tube. Further stops to indicate when the bends are complete.

Carl,

I confess that I have no experience to offer ... but the question is interesting; so I went digging, and found this video which might help.

MichaelG.

Hello Michael,

Thank you for researching on my behalf. I'm familiar with laying out and bending tube as shown in this video. What I've never done (it has just never occurred in my experience before) is to produce a series of tubes that have to all be ostensibly exactly the same. I do not know and indeed have never had cause to wonder exactly how repeatable bending tube is using the time honoured method. I guess it is only as repeatable as my measuring...but there are other factors to consider here.

I'm hoping to come up with a simple way to ensure the bends all turn out the same within the limits of measurement. I thought it worth posting here as there is such a wealth of experience that I thought someone might provide me with food for thought, if nothing else.

I think the next edition of the SMEE journal is going to have something on pipe bending in it, hopefully I'll have got there before that comes out.

I've done thousands of bends in stainless tube (Mostly 1/4" to 1/2" using a similar (but not as good) bender. Most of the time I mounted the bender in the bench vise because apart from it being more controllable, 3/8" tube with 1/16" wall needs quite a lot of effort. Plumbing was for gas analysis equipment so generally thinner wall than your hydraulic stuff but only accurate pipework was acceptable so hand tweaking of runs to get tubes to line up with fittings was very rarely done.

Can you cheat by mounting the fitting and whatever it is going into, 'after' you have bent the tube?

Actually I think you might struggle with that bender on 2mm wall tube although if its within Ridgid's rating it must be doable.

Ian P

Hello Ian,

Thanks for your post. Like you I've also done a lot of tube bending in 1/4, 3/8 and 1/2 stainless. I usually put one half of the bender in the vice too, for anything over 1/4. I actually think my bender will struggle with the 2mm wall too, but we shall see.

Fortunately there will not be any fittings on the end of these tubes, they are going to be welded or brazed up into a sort of heat exchanger.

Well, the pipe bender was easily able to bend the 10x2mm tube. Here is a rough example of what I'm going to do. Only another 30 or so to go...

Carl

I presume that the most critical/precision aspect of the part that you have to get right is the is the angle between the entry and exit straight sections? with the centre section length and its two angles only having to be visually similar.

I have not handled that particular bender but it looks to be robust and well engineered and (in your hands) produces a nice result.

Ian P

There must be some "wiggle" room on the final assembly to ensure the tube ends are in the correct position to each other for welding / brazing to the component(s) it attaches so it may be that the bend centres to each other are important and that in one plane, the pipe is flat (You already told us that)

Instead of allowing the bender to "Float" it is after all a "Site" type bender (Two handles), fasten the side with the circular former down onto some for of fixed plate (Mill table is brutal to the mill) and after effecting first bend, turn pipe end for end to a fixed stop and clamp pipe to stop lateral rotation after ensuring the bend is flat and bend the second angle.

DON'T try to bend it in your hand, fixing the bender down is the clue.

Bet you only manage to waste ONE as a pattern. Don't get complacent when you're shelling them like peas.

Regards Ian..

EDIT. Forgot to mention, However many you have to bend, put one bend in the whole batch FIRST, then go for the second one rather than complete each one individually (Sorry if it's sucking eggs)

Edited By Circlip on 13/12/2014 18:01:16

Thanks Ian and Circlip for taking the time out to post. As I mentioned I always clamp one side of the tube bender in the vice. I can manage three shredded wheat, but I can't bend 10x2mm 316 tube freehand without a series of jerky movements, which are not conducive to neat, repeatable work!

A good idea to do the first bend in the whole batch, then the second. Mill table would indeed be brutal; I have a table that I can mount stops etc on that I usually use for TIG welding.

Thanks again,

Carl.

Thanks Jason for taking the time out to post. I don't recall stating that the part between the bends was the critical length. What is obvious to one may not be to others. So always worth stating.

My current thinking follows yours closely, to use extra length as required for ease of use of stops etc. Thanks again for the interest.

Carl.

And the important aspects are the similarity of the two angles and the distance between them.