Soldering/forming guidance for copper pipe?

[Papa Bear]

OK, I could use advice from those of you who know something about joining and forming metal, since my usual local source of advice is unavailable for a while and I need to make some progress...

I'm attempting to create a series of angles in a section of 1/2" copper pipe. The goal here isn't to bend the pipe into an actual curve, but rather to create short sections that butt up against one another at angles. The eventual goal is a dragonfly tail (two of them, actually), as in this image:



(Those are technically damselflies, but you get the idea.)

My initial thought was to cut the pipe at an angle at each section (using half the angle I need), rotate one piece 180 degrees so that the oval ends line back up at the full angle, and then solder them back together. The first part of that was easy, but joining them back up is proving to be challenging - I've managed to dribble a lot of solder onto the firebrick, but haven't been able to get the pieces to stick.

Any suggestions? I'm not sure whether I just need more soldering practice/better technique, or whether I'm barking up the wrong tree with my whole approach. I did consider using sweat fittings, but I need some angles other than 45 and 90 degrees.

I don't actually care if the join seams are visible - I can incorporate that into the visual design. Nor do I need a great deal of structural integrity beyond the simple ability to hold its own weight when suspended from a string. The wings will be made of wire, so there shouldn't be a huge amount wind stress to worry about.

[TT120]

Look up "sweat welding" for copper pipes. That will show you the proper way to solder copper pipes together. The key is lots of flux and getting both sections heated up enough to flow the solder. There wont be much structural integrity if you just butt the 2 ends together and solder them together however.

[Token]

Sweat solder relies on capillary forces to draw the molten tin into the tightly fit overlapped pipe ends.

I.e. You slide the fitting which is snug and it creates a big surface area where capillary action can happen.

You are trying to do this with tiny surface area and no snug fit. There will be no capillary action at all.

Two ways to do this:

1. Don't fully cut the pipe. Use a Dremmel and cut out a wedge on the concave side and leave some intact pipe on the convex. Bend the pipe then tack it with solder or a tig stick (yes, you can use a welder on copper.

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2. Make the full cut. Pre-tin the ends you will join by liberal dip in flux, then get the tin on. Must heat the pipe real good for the tin to stick. Heat pipe above tin area to keep tin on pipe and not scattered by the flame jet. Once the ends are good and tinned, use several vice to position the pieces such that you have maximum surface contact and heat both pipes without torching the tin area, or you will just splatter away the tin. Once the tin flows, remove flame and spritz with water from a spray bottle.

Now, the problem with 2 is you want to string a bunch of these together, and that all must be done in the same firing. That means allot of prep to line up the many parts and keep them locked in place

Go with 1 is my advice or switch to tack welding.

[Papa Bear]

Thanks, Token - I think that's exactly what I needed to know. "Splattering away the tin" is a pretty good description of my most recent attempt at this - and now that you've described how to do that right, it does sound pretty daunting to get it all lined up properly. Some of these pieces are no more than an inch long, which doesn't leave much room for a vise.

I'll give #1 a try. I was under the impression that copper melted too easily for a welder, but then, I've never used a TIG. Fortunately, I do have access to a decent one and have someone here who can show me the ropes on that.

[Papa Bear]

Hmm... actually, "or switch to tack welding". Are you suggesting I could also just tack the pieces I've already cut together, or is that just asking for more trouble?

[EGAZ]

Token has the idea. He beat me to it. Cut a wedge.

The key is to clean the shit out to the pipe before cutting. (makes it easier to clean then after the cut) Sand it shiny, make the cut, leave any burrs as it gives the solder something to grab onto. Then apply flux. You torch flame needs to be low and 'wafty' Not sharp and blue tipped for welding and brazing. But not so low it leaves soot, just above that. A hand held propane torch would be fine for this. Personally I would skip the tinning step, but maybe try it both ways.

Slowly heat the crotch portion of the pipe. (the parts that are pushed together after the wedge cut) slowly touch the solder right on the same point while heating. As it heats the solder will just start to melt. Pull the torch away while keeping the solder in place. trying to keep the copper temp just at solder melt temp. If you have done any gas welding with filler rod, this is what we are doing but not melting the material. This is were practice and skill come in as you want to leave a 'fillet' of solder like welding. The tipping point temp of when the solder softens and fills, to flows everywhere is small so some practice is required. Larger dia solder will help.

Slowly apply heat, while 'laying' the solder down the seem to the heel of the bend. Easy peezy!

To hold the short pieces use some needle nose vise grips to hold the piece, vise grips in the vise.

But if you have a TIG, that might be the way to go too. I really want a tig. I have no need but I have always wanted one,

[Papa Bear]

Token has the idea. He beat me to it. Cut a wedge.

That was actually my initial plan. Then I realized I could make more accurate angles on each end if I cut all the way through using a metal-cutting horizontal bandsaw and then just rotated one piece. Didn't adequately plan for the back end of that particular optimization, though.

You torch flame needs to be low and 'wafty' Not sharp and blue tipped for welding and brazing.

Probably my other error. It's been a while since I've done any soldering.

I really want a tig. I have no need but I have always wanted one,

This is what my local makerspace is for. I couldn't justify a TIG, laser cutter, 3D printer, glassworking bench, CNC mill, or a host of other things for myself, but being a member means I get all sorts of opportunity to use them anyway.

[Popeye]

The low temperature solder used in plumbing connections- both the older lead solder and the newer silver bearing solders- will not hold a butt connection under any kind of stress. You will need to use a brazed joint or have a coupling/sleeve or swaged connection or braze the joint. For 1/2" copper a brazed connection can be made with propane or MAPP. A swirl tip torch will help. Clean your connection with emery paper or open weave plumbing cloth, use flux unless using sil-fos http://www.silfos.com/products/catalog/ ... p-150.html which I reccomend you try. A little pricy but looks like you only have 8 joints. You don't have a lot of surface area to connect so the joint will be weak. Experiment a little, you may end up putting a short copper strap across the joint to add strength. If using SilFos you can cool with a wet rag at once. The most often problem is getting the joint too hot. Clean your joint.
You will want to have exactly flush surfaces to make this work. More like jewelers techniques than a plumbers. A jeweler will tell you he is "soldering" but their connections are generally a braze due to the temperatures involved. Semantics. After you cut, line the two pieces up the way you want them and clamp, then use a fine tooth FLAT souble sided file to dress the ends. There should be no air gap anywhere around the joint.
If you end up doing a lot of joints Rio Grande has a roll of copper solder (actually braze) that is fairly inexpensive their number 132198. Made for color matching jewelry. I have used it twice and it seems to be ok. You will need to use a flux with this I found Ultra Flux II to work ok but Borax may work also.
If all this is to much work have you considered soft copper and bending around a form? This might be kind of saggy but filling with urethane spray insulation might make it rigid enough. Copper work hardens so tapping with a hammer while it is in the form might help. Copper also softens/anneals when heat is applied. Wrap both sides of the joint with a wet rag to minimize this.
This looks like a really nice project. Looking forward to seeing it on the playa. If I lived in Colorado I'd try to give you a hand.

[ygmir]

there are several angles of copper fittings available....thought it'd leave a bump at each one.
Or, leave a tab/make a strap/fishplate from copper and bridge the seam in a spot or two. Especially if you don't cut all the way through.
Third would be get copper stranded welding cable, or whatever stranded copper you can find, feed it tightly inside both sides of the joint, and solder, letting the solder run into the stranded wire and permeate it, as well as sticking to the inside of the pipe. When the stranded copper is infused with solder and dries, it'll become stiff, and stuck inside.
As will all advise for soldering, clean the crap out of all surfaces and used flux.

[Token]

Hmm... actually, "or switch to tack welding". Are you suggesting I could also just tack the pieces I've already cut together, or is that just asking for more trouble?

Yes you can. Tack 3 spots each join.

There is another trick you can do with pre tinned pipe and solder.

Get some steel cable, 1/16 or 1/8.

Attach a blocking washer on one end using a u-bolt

String your pre-tinned pieces like a necklace so they form the shape you want, then tighten the cable. I would drill a hole on a board, run the loose end of the cable through, then stack a 10 pound weight on it to hold steady tension on the parts. Maybe have a ceramic spacer between the board and copper tube to prevent scorching.

Now you can heat up the whole string in one shot.

[Papa Bear]

there are several angles of copper fittings available....thought it'd leave a bump at each one.

Hmm... that was one of the first things I thought of, but for the life of me, I've been unable to find anything other than 45 and 90 degree fittings online or in stores. Do you know of a place that carries a larger variety?

[Papa Bear]

String your pre-tinned pieces like a necklace so they form the shape you want, then tighten the cable. I would drill a hole on a board, run the loose end of the cable through, then stack a 10 pound weight on it to hold steady tension on the parts. Maybe have a ceramic spacer between the board and copper tube to prevent scorching.

I'm having a little trouble envisioning this. I can see how tightening the cable would work if I was working with a single piece with wedges cut out (rather than separate pieces cut all the way through), but it's not clear how it would help line up 10 separate pieces.

Spent some time learning the TIG welder at the local makerspace yesterday. Copper's definitely a challenge to get right - it's a good thing I have another 5 feet of copper pipe to cut up and practice on before I think about trying it on the angled pieces.

I really appreciate all of the suggestions. I'm definitely going to experiment with a few approaches - not just to figure out the one that feels right, but also because they feel like useful skills to have in their own right.

[EGAZ]

.....like useful skills to have in their own right.

TIG is the winner here.

[Token]

Yeah, the whole string of pearls is hard to explain.

Think of a standard tent pole. It has the rubber-band like string in the core and the sections can pop out and the pole can be folded up.

Similar concept.

Either way, the TIG experience is solid gold!

[ygmir]

there are several angles of copper fittings available....thought it'd leave a bump at each one.

Hmm... that was one of the first things I thought of, but for the life of me, I've been unable to find anything other than 45 and 90 degree fittings online or in stores. Do you know of a place that carries a larger variety?

seems bigger plumbing houses should have 22.5 deg. bends...the other thing you can do is combine two 45's, with a very short nipple piece, and twist them to create any angle between 0 and 90 deg. then solder. Though, that will create and offset of sorts.

one questions I have is why specifically must you use copper pipe?

[Papa Bear]

one questions I have is why specifically must you use copper pipe?

I don't have to. Mine is just one of thirty different interpretations that will be suspended from the art installation (The Dragonfly Mating Ritual), and the individuals working on them are using a variety of materials. Some are building from laser-cut wood, others are using foam and fabric, another is being done in stainless steel wire, and at least one is literally being knitted from thread stretched over a rigid wire frame.

My reason for attempting this in copper, aside from a bit of uniqueness, is simply that copper patinas nicely in a variety of colors. So the next step, should I actually be successful creating the bodies, is to etch and patina the two dragonflies in contrasting colors before tying them together into a single piece.

If I can't make it work, I'll figure something else out - and if I succeed and have enough time, then I'll contribute a second pair in some other media. Though having that much time is unlikely, since I'm also doing the LED animation programming for the blossom at the top of the installation.