How to Cut and Join Copper Pipe

By Murray Anderson

< Learn the Basics of Working with Copper Pipe

Cutting Copper Pipe

A pipe cutter makes cutting copper pipe easy. Simply hand tighten the pipe cutter onto the mark where you want to cut the pipe. Rotate the cutter around the pipe a couple of times to create a groove all around the pipe, and then each time you rotate the cutter, tighten the blade a little. Each rotation will cut a little deeper into the pipe and the cut will be straight. Don't tighten too much or you can bend the pipe out of round.

After cutting the pipe, remove any burrs inside the pipe with the burr removal tool built into regular pipe cutters (or you could use a round file). You want to remove all the burrs, because they will cause water passing through the pipe to swirl and make noise if you leave them there.

Joining Copper Pipe

There are three basic ways to join copper pipes to each other. Hard copper can be sweat soldered or joined using a compression coupler, while soft copper can be joined using compression couplers or a flare joint.

Sweat Soldering

The tools needed for sweat soldering: Propane torch, coil of solder, liquid flux (yellow bottle), steel wool, and sheet of metal to protect studs from the flame.

1. Cut the pipe to length and remove any burrs. Clean the end of the pipe that will be inserted into the fitting using a piece of emery cloth or some steel wool. Clean the inside and outside of the pipe and the inside of the fitting as well. You want the copper to be bright and shiny, so you know you've removed any oxidation, dirt or grease that might be on the surface.

2. Apply a light coating of soldering flux to the outside of the pipe and the inside of the fitting. Use a small brush or a cloth to spread the flux. (The flux prevents the copper from oxidizing when you apply heat.) Put the copper fitting in place on the pipe and rotate it a few times to make sure the flux is evenly spread.

3. Before you start to solder anything, unroll about 12 inches of solder off the roll and then make a right angle bend about 3 inches from the tip. This will make it easier to apply the solder to the hot fitting, particularly on the backside of the pipe.

4. Use a propane torch to heat the joint. Begin by playing the blue tip of the flame (the hottest part) over both the fitting and the pipe for a few seconds, and then concentrate the flame on the middle of the fitting. You can tell if the fitting is hot enough to solder by looking at the color of the flame on the side of the pipe away from the torch. If it looks green, the joint is hot enough to solder. Alternatively, you can just remove the flame and touch the solder to the pipe where it meets the fitting. If the joint is hot enough, the solder will melt and literally be sucked into the tiny seam.

5. If solder doesn't draw into the joint, remove the solder and keep heating the joint for a few a few more seconds and try again. Move the solder all around the joint. A joint is soldered when it appears silver all around. Finally wipe the joint with a damp cloth to remove any excess solder.

Compression Couplings

A compression fitting on a copper pipe, from right to left: compression nut, ferrule, and plumbing valve. The nut will slide down the pipe and thread onto the valve.

Compression fittings are a way of joining copper pipes or a copper pipe to a fixture where you can't solder or where you may have to take the joint apart in the future. Toilet supply line is a good example. A compression fitting consists of three parts - compression nut, compression ring (or ferrule - a metal or plastic washer that will be "compressed" against the fitting) and the compression seat.

When attaching a compression fitting, first get rid of any burrs from the inside or outside of cut pipes. Then slide the compression nut onto the end of the pipe (it'll be a tight fit), then the ferrule.

The compression fitting itself will have a threaded end. Slide the compression nut to the end of the pipe and screw it onto the compression fitting. Tightening the nut squeezes the compression ring/ferrule into the seat and against the copper pipe, making a watertight seal. Hand tightening may be enough, but if you get some drips you can tighten the joint using a wrench. Applying some Teflon® tape onto the threads of the compression fitting will also help prevent any small leaks.

Flare Fittings

Flare fittings are used with soft copper pipe. Similar to compression couplings, they are used to join pipes to each other or join pipes to fittings, but a flared coupling is different from a compression joint because there is no ferrule. A special fitting joint called a union is used to join the flared ends of two copper pipes together. The flared ends make a lip in the pipe that is squeezed between the nut and the body of the fitting.

Flaring the end of a pipe requires a special two piece tool called a flaring tool. One piece holds the end of the pipe in place. The other piece is essentially a rod, called a compression cone, that is slightly wider than the pipe. This cone is pushed into the open end of the pipe, forcing it back and forming the lip on the end of the pipe.

How to use a flared joint to attach a fixture:

First slide the nut onto the pipe, then clamp the end of the pipe into the flaring tool. Force the compression cone into the end of the tubing and slowly tighten it. As the cone forces its way into the pipe, it should widen the pipe and fold it backwards, making the lip. It's always as a good idea to flare the pipe end before cutting the pipe to length since pipes will sometimes crack when they are being flared and you need to start the process over. Put the flared end of the pipe into the seat of the fixture and tighten the nut.

There you have it, a quick primer on working with copper pipe. Since virtually anytime you need to work on plumbing you're going to bump into copper pipe, knowing something about it and understanding the techniques to work with it will make your plumbing projects much easier.

< Learn the Basics of Working with Copper Pipe