Stuart Triple/Bending Copper Tubing/How to do it??

[atomarcParticipant @atomarc]

Any suggestions on the best ‘kink-free’ method to achieve accurate bends in copper tubing for the Stuart triple expansion engine. I think I’m going to forego the hard tubing sent with the kit and utilize soft copper tubing as it’s easier to bend in the tight 5/16″ radius called out on the print.

 

I’ve seen pictures of completed triples, and the two sections of tubing are flawless, straight and fit perfectly. I would like to achieve that same look.

Thanks,

Stuart

Eureka, CAL  USA

[noel shelleyParticipant @noelshelley55608]

I don’t have details of the diameters needed ? But fill with woods alloy, bend, then melt out the woods alloy with boiling water ! Melts at about 90*c That’s one way ! Noel.

[JAParticipant @ja]

Stuart

I am making the smaller Stuart two cylinder marine compound engine as a one day a week project (my major project takes up the other six). I am looking forward to tackling the steam transfer manifold, the copper pipe.

First the copper must be annealed, that is softened. The short length supplied can quickly be annealed. Second, the tube MUST be straight. Third, use a tube bender that supports the side of the bend. These are easy to make and there are some fine designs on the internet. Use Woods Metal if you want (I have only ever used packed sand on larger bore copper tubing). Re-anneal if you think necessary as you do the work. I think the most difficult part will be straightening the tube in the first place.

Like most things it is just trial and error. Do not expect a good job after one or two attempts.

All the best with the engine (and please post some pictures).

JA

[atomarcParticipant @atomarc]

Gentlemen,

 

Thank you both for your suggestions. I do have some Cerrobend  if I choose the ‘fill-em’ route. The supplied pieces of copper tube are dead straight, but are very stiff, and I wasn’t sure about annealing them, but it would seem the only way to get that tight bend radius called out in the prints

I’ll try to post some pictures of the whole project so far, and hopefully some of the finished piping, if it turns OK.

I started this project in 1981, so it’s been a challenge to get back in the groove again.

Thanks again,

Stuart Miller

[duncan webster 1Participant @duncanwebster1]

The way I straighten copper tube is to first anneal it, then roll it between 2 breadboard. Only works for shortish lengths, 300mm say.

For really tight bends, cheat and use end feed plumbing fittings. You can get long radius ones if you search hard enough

[Nigel Graham 2Participant @nigelgraham2]

The minimum bend radius is 3X tube diameter – don’t expect to make plumbing-style elbows.

Yes, there are plenty of designs to make tube-benders about but frankly this is one case where buying a tube-bender from our or another of our suppliers is better – they are not expensive and you save materials, time and electricity.

I did this and was very pleased I did so.

[JasonBModerator @jasonb]

Commercial benders give too big a radius for a job like this and you would end up with a “U” shaped pipe. Filling and bending round a tighter former means it gets bent more like solid bar than tube. Solder and lead are other options for filling the tube.

Unless you are into bling and brightly polished copper pipe with no visible joints then fabrication is a good option and will also help get the bends exactly where needed.

This one used a couple of commercial “crossover” fittings that had the sockets cut off and some internal spigots added for strength.

Another option is to use a ball nose cutter to drill two holes at 90deg to each other in a block of metal, solder in the pipe and then shape the outside

It’s the grey exhaust pipe

Same method here for the exhaust

Only difference between that and the previous is I shaped the outside on the CNC rather than filing the first to shape

For really tight bends you can take a compression elbow

Chop and file it a bit

Add soem flanges and solder together

Paint or lag and who knows what it was made from

[JasonBModerator @jasonb]

This shows the  1D bend radii required on the drawings

 

[JasonBModerator @jasonb]

Another method I have used which is good where you have two bends close together which can make it hard to get the bending formers into position is to make a series of cuts with a piercing saw that go almost through the pipe. You van then bend it which closes up the keft and finally silver solder it all back together, the thin piercing saw kerf fills easily with solder don’t use a jnr hack saw.

[atomarcParticipant @atomarc]

Jason,

 

Thanks for the ideas, great picture examples and for the look at some beautiful machine work on those engines.

 

Stuart Miller

[atomarcParticipant @atomarc]

I read all the above posts, built a small bender specific to the radius called out in the Stuart print and started messing around. After several attempts, this was the end result, which I’m fairly happy with. The long tube was bent after being filled with Cerrobend 158F to prevent distortion, and the short tube, although not quite perfect, was filled with sand out of my blast cabinet. Several tries were required to achieve a accurate center to center distance on the bends. There is no gasket between the LP steam chest and cylinder casting at present, and as this engine will only be run occasionally on air,  I intend on using a thin smear of some silicone or similar material which won’t alter the center distance of the long tube.

I’m happy with the results, they’re better than I anticipated..and that part of the model is DONE, yahoo!

Stuart Miller

Eureka, CA USA

[Andrew TinsleyParticipant @andrewtinsley63637]

My Wood’s metal has gone walkabout. I have had it for many years, so don’t have a clue as to modern day suppliers.

I suspect that it will be quite expensive!

Andrew.

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