Small pipe unions on a model

Whats the nornal way to connect up 1/8" OD copper steam pipes (actually compressed air in this case)? I have made a union and nut,
but I am not sure whether I should solder a ring onto the pipe, attempt a compression fitting, or make a nipple into which the 1/8" pipe can be soldered outside the nut. I am thinking the soldered brass ring, turned true, might be tidiest.
Steve
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Steve
It is usual to silver solder the nipple/olive onto the copper pipe (after putting the nut on first) Both the 'arrow' shaped nipples of the type sold by model suppliers and very small olive shapes work in my experience. You just have to be careful how much SS you use with the latter.
Steve (Sheffield)
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Steve wrote:

Presumably these arrow-shaped nipples are 1/8" ID and slip over the pipe. This will increase the hole size required in the union nut and decrease the shoulder for the union nut to work on. Also I am not sure it will look half as tidy to have an exposed soldered joint outside the union nut.
I am avoiding buying items like this as the main reason I am making this is to improve my skills with the lathe - and everything I make I learn something more.
Steve (Cheshire)
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[snip]

For compressed air, soft solder should be satisfactory and the solder should be inside the nipple and thus, all that ought to be visible will be a tiny fillet between the top of the nipple and the pipe. If you are unsure of your skills with a soldering iron, a small tub of solder paste is not cheap but in the quantities that you can expect to be using it will probably last a life-time.

Assuming that the required nut is 1/4" x 40 t.p.i it may be worth spending a couple of pounds on a small pack of commercial nipples and nuts. Attempting to replicate both nut and nipple may be much more difficult than you expect and hence be another new skill acquired.
--
Mike Hopkins
CSME <http://www.cheltsme.org.uk>
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Cheshire Steve wrote:

Do you want it to look scale? Does it have to be permanent?
Nick
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Nick Mueller wrote:

In this instance it doesn't have to be to scale, but for my next project it will, so if you can give me a pointer to something that looks like full scale practice that would be excellent. It will be semi-permanent, the other end of the pipe will have a connector for an air-hose at the edge of the plinth - which will also have a union. I have also to discover how much bend this pipe will take before it kinks - I dare say a search on this newgroup will reveal something on the topic.
Are you maybe going to suggest using a tiny silicone o-ring in place of an olive ? Do they come that small ?
Steve
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[snip]

First, anneal the region that you intend to bend. Heat to red heat, allow to cool (cooling rate does not seem to matter) then re-polish with fine steel wool.
There are relatively cheap bending tools on the market. But for really small radius bends that need to follow an accurate line you may well find that you need to make your own bending jig(s).
--
Mike Hopkins
CSME <http://www.cheltsme.org.uk>
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Cheshire Steve wrote:

Yes. O-ring rulez! :-)
+--------------HHHHH VVV----------+ | +-------------+ +--+ | | | | O | | | | <- Nut (bored through) +-------------+ | | +-----+ --SSS+ +----+SS+------------------- <-Tube | | ----+ +-------------------------
---- . --- . --- C.L.
Not to scale. :-))
VVV is a thread, of course the mating part has one too. O is the O-ring (bigger, just fits over the tube) SSS is silver solder. HHH is where the hex is.
Made something like this with a tube OD of 6mm.
With a 6mm tube, the O-ring might be a 6 x 1. So the sleeve soldered over the left tube will have an OD of 8mm. The bored nut will have an OD of 10mm. Thread will be M8 x 0.5.
It is wrong if the OD of the O-ring has contact with the thread. It wouldn't be compressed.
Example: <
http://www.motor-manufaktur.de/ellwe/pics/ellwe_2fb_m12.JPG
If you follow the tube coming up near the flywheel and going horizontally to the left and then making a 180° bend into a valve. The joint valve/tube is of that type. Has to hold 10 bar.
HTH, Nick
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Hi Nick,
Thanks for your advice, but I am curious to know what is 'classical' full scale practice, and could I follow it ? I think its covered in various ancient ME magazines I can spot in the index, but I don't have those issues.
Steve
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[snip]

A 3/16" pipe on my locomotive is equivalent to a 1" pipe full size. Little nuts and nipples on the model replicating and bigger nuts and nipples full size.
--
Mike Hopkins
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Smaller pipes tend to have a coned sleeve and larger ones a ring, though the practice varied from one railway to another. Remember that a most of the larger pipes would be flanged, except in the cab, where they mostly were not, except on the manifold where they often were. Don't ask me to explain why.
--
Charles Lamont

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[snip]

Yes
--
Mike Hopkins
CSME <http://www.cheltsme.org.uk>
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