How to Measure, Cut and Thread Pipe for Plumbing Repairs in Your Home

Because iron pipe is so inflexible, precise measuring is essential to a neat and efficient job. If you plan to let someone at the hardware store cut your pipe for you, it's even more critical in order to save running back and forth to the store and avoid buying a lot of extra pipe.

First sketch out the installation you are planning. It can be quite rough, just clear enough for you to follow. Mark on the sketch the fittings you'll need. Will you need a union? A tee? How many ells? In order to get accurate measurements, it would be a good idea to go buy at least one of each of the fittings you'll need and to use them to precisely determine their dimensions and that of the pipe.

For instance, if the new pipe must go from a mainline pipe to a wall and then turn and follow the wall, you will need to know how much distance will be taken up by the tee you'll put in the main line and the elbow at the wall. When measuring the length of pipe, hold the fitting in place and mark the position of the face of the fitting. Measure the distance between the faces of the fittings and then add the length of the threads that will be inside each fitting. The thread inside the fitting will be almost exactly ½ inch if you are using ½ or ¾ inch pipe.

You can cut and thread iron pipe at home very easily. You will have to buy a pipe cutter, a reamer, and a set of dies with a holder, also called a stock, with pipe handles to hold and turn the dies. A pipe vise is also a good idea if you are going to do very much cutting. If you are only going to cut and thread a few pieces of pipe, you can usually rent the cutter, reamer, threader, and vise. You can also modify a machinist's vise to hold the pipe. If you have one or two pieces of pipe to cut and thread, let your local hardware store or pipe supply shop do it for you. As long as your measurements are accurate, this will cost the least in both time and money.

The dies for threading pipe are made of hardened steel teeth that cut the threads into the relatively soft steel of the pipe. Most die sets have cutters for pipe of 3/8, ½, ¾, and 1-inch diameters, which are the sizes you'll need to work on any water or gas supply pipes in your house. Make sure the piece of pipe you are going to cut is long enough. Check both ends to be sure the threads are not damaged.

To cut the pipe, put it in your vise with your mark about 6 to 8 inches from the vise. Open the cutter wide enough to clear the diameter of the pipe. Set it on the pipe with the cutting wheel on the mark. Apply cutting oil to the cutting wheel and rollers of your pipe cutter to make the cutting easier and to prolong the life of the wheel. Turn the handle so the wheel bites into the metal just a little bit. Rotate the cutter a full turn around the pipe to make a very shallow cut. Then turn the handle a little more and rotate the cutter. Then do it again. You will soon get the knack of how deep to set the cutting wheel each time. Turning the handle too much can break cutting wheel or spring the frame of the cutter. Once the pipe is cut off, wipe the end with a rag.