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Off-The-Shelf Hacker: How to Solder Tubing with a Propane Torch

11 May 2019 5:00am, by

Because we’ve been on the subject of soldering in recent articles, I felt like it would be a good time to go back and add a nice copper tubing base to my steampunk monitor project. Dark composite wood flooring formed the original base and it worked pretty well. I need a place to mount the battery and a handle, so copper tubing will work much better than the wood. Today, we’ll discuss the basic process of soldering a piece of tubing to an elbow. I’ll show you the finished base, battery mount and handle in a future article.

Cutting the Tubing

The base will be made by cutting two long and short pieces of 1/2-inch copper tubing, that I purchased at Lowes. The cost was a little under $10 for a 10-foot length. There are several different grades of copper tubing available, although I couldn’t tell the difference between the $10 stick and the $15 one.

I use a standard cheapo tubing cutter. Here’s a similar one from Amazon. These cut just as well as the $40 name-brand industrial-strength models.

Measure and mark the location of the cut with a pencil or pen. Unscrew the tubing cutter so that it fits with the two parallel rollers firmly lined up on the pipe. Position the cutter wheel squarely over the cut line and gently tighten the screw, just enough to hold it on the pipe. Give it another quarter twist to seat the cutting wheel.

Next, without further twisting the screw spin the cutter around the pipe one turn. Give the screw a half tightening twist and rotate the cutter around the pipe again. Repeat this process, tightening the screw slightly each time until the pipe separates. I usually hold the long length of tubing with my left hand and operate the cutter with my right. After a couple of cuts, you’ll get the hang of it. You can also clamp the pipe or hold put it in a vise.

Be careful to tighten the cutter squarely over the cut line or it will “settle” a little bit to one side or the other, changing the length of the cut by a fraction of an inch. This may not be a problem with 1/2-inch tubing. On smaller 3/16-inch brass tubing, I sometimes have to touch the end with a Dremel and small grinding wheel to get exact matching lengths. Matching lengths promote square frames.

Once cut, it’s time to prep the end of the tubing for soldering.

Soldering with a Propane Torch

For a high-quality joint between the elbow and copper tubing, it is important to clean the metal before soldering. I use a little fine sandpaper to brighten the outside of the end of the tubing and the inside of the elbow. You can also use a sanding sponge or a Scotchbright pad. Finish up by wiping the ends with a clean rag. We don’t want any oil, grease, dirt or dust that may contaminate the soldering process.

Next, lightly clamp the elbow in the vise so that an end is facing up. I like to solder tubing into elbows vertically so gravity helps pull the solder into the joint. Capillary action does the same thing. Some elbows have printing or a logo on one side, so temporarily assemble them flat on a workbench, to get the orientation right before soldering.

Swab a little flux around the end of the tubing and inside the ends of the elbows and then push the joint together.

I used a common everyday, readily available propane torch to solder the copper tubing together. You can get a cylinder of propane and the torch at any big box home improvement or hardware store. I picked up a kit that also has solder, flux and a little flux brush for around $20. Here’s one from Home Depot. Notice that this one an integrated trigger ignition feature that might be handy. I just use either a welders striker or a candle lighter to fire off the torch.

Gently open the propane valve and hold the striker over the end of the torch. Squeeze the device to generate some sparks and ignite the propane. You may have to open the valve a little to get a nice flame. In bright daylight, the flame is light blue and sometimes hard to see. The flame is HOT, so be careful where you point the end of the nozzle. Once you have a flame, adjust the valve to the inner blue cone is about 3/4-inch long.

Make sure there are no combustibles in the area and evenly heat the elbow/copper tubing joint with the flame. You should direct the flame all around the joint. Occasionally move the flame off of the joint and touch the end of your solder to the intersection of the elbow and the tubing. If the solder doesn’t melt into the joint, continue to heat it up a little more. When the joint is hot enough, the solder will be drawn into the joint. Don’t run the flame over the solder because it will just melt and drip on the floor. The following clip shows heating and applying the solder to the joint.

In this clip, I lightly sanded the end of the tubing. I used rosin core solder so in this case flux was optional and I chose to skip that step.

The joint should have a smooth thin silver ribbon of solder all around the joint. You can always reheat the joint and add a little more solder if needed.

One trick I use is to keep a clean damp rag handy and run it around the joint immediately after soldering. This removes any leftover flux and makes the joint clean and smooth. Be careful because the copper is very hot and will painfully burn unprotected skin.

Also, be aware of where you set the torch. I usually do one joint, then turn the torch off, set up the next joint, restart the torch, solder and repeat. It’s a little tedious, but I feel I always know where the flame is pointed, that way. Needless to say, keep fire extinguishing equipment handy, just in case.

Next Steps

One good thing about soldering copper tubing, elbows, t-joints and so on is that they are reusable. If you don’t like a joint, heat it up, pull it apart and use the individual parts in a different project. Gadget isn’t interesting anymore? Take it apart, clean up the ends and store them for a new future project.

Off-the-shelf hackers use a variety of skills. Learning to solder connectors to wires, small brass tubing to brackets and copper elbows for monitor frames is a valuable skill that will serve you well as you make your future a reality.

Catch Dr. Torq’s Off-The-Shelf Hacker column, each Saturday, only on The New Stack! Engage him directly or leave him a message for consulting, speaking appearances and commissioned projects at doc@drtorq.com or 407-718-3274.

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