The proper cutting of threads on pipe is overlooked by some mechanics. There are many different kinds of dies and different kinds of pipe to contend with. Steel pipe threads very hard and the adjustable dies should be used on it. These dies cut more easily and leave a cleaner thread than other dies when used on steel pipe. When threads are cut on wrought-iron pipe the adjustable dies should be used as they cut a better and cleaner thread than other dies. To preserve the life of the dies and the quality of the thread, oil is used freely while the dies are cutting.
The standard thread on pipe and fittings is a right-handed thread. Left threads can be cut on the pipe and the fitting can be tapped with a left thread. When a fitting is tapped with a left thread it is marked so. The following table gives the standard number of threads that a die will or should be allowed to cut on the pipe:
|Size||Length, inches||Threads per inch||Threads per end|
To acquaint the beginner with iron pipe work, the following exercise is given. In it there are a great many of the actual problems that come up when the pipe is put in on a job. This is the last exercise that is required in this book. The sketch shows clearly just what the job is and below I have gone over each operation that is necessary to complete the job.
Six feet of 1-inch black pipe; four 1-inch black ells; two 1-inch tee; one 1-inch right and left coupling; oil.
Two 14-inch pipe wrenches, vise, pipe cutters, stock and 1-inch follower right and left die and reamer.
The vise is made secure on a bench or post, care being taken before it is put in place to provide room enough to swing the stocks. A length of 1-inch pipe is put into the vise and the vise clamped around it. The end of the pipe that is to be threaded should stick out through the vise about 9 inches. If there is a thread on this end, the dies should be run over it to make sure that it is a standard thread and to clean the threads. Before proceeding further with this exercise the dies and stocks will be described and their use shown.
A full set of dies is taken. The full set of stocks and dies is composed of right and left dies from 1⁄8 inch up to 1 inch, with a guide for each size, also a small wrench with which to turn the set screws. The dies come in sets, two in a set. These are the Armstrong patent that I am describing. Take the stock and the handles, and a set of 1-inch right dies with the guides out of the box. The dies will have marked on them 1" R (if 1-inch left were wanted, the mark would be 1" L). The set screws are taken out of the stock and the dies inserted in their proper place. There is a deep mark on the edge of each die and under it a letter S. This letter means "standard." This mark on the die is set even with a similar mark on the stock and when the set screws are in place and tightened, a standard thread will be cut. There is an adjusting screw on the stock to make the proper adjustment on the dies.
The stock is taken and the handles are put into it. There are two sets of set screws on the stock, one set for holding the dies in place and the other set for adjusting the dies. On the stock there is a deep mark to correspond with the standard thread mark on the dies. On the opposite side of the stock there is a place for the follower and a set screw to hold it in place. After the stocks have been looked over and examined thoroughly, the 1-inch right dies are taken and inserted. Then the 1-inch follower is put in place. The tool is now ready to cut a 1-inch thread. Now take a piece of 1-inch pipe at least 15 inches long and put it in the vise, letting it extend out from the vise about 9 inches. The stock is now taken and the follower end is put on the pipe first and the dies brought up in place to cut. The end of the pipe is allowed to enter in between the two dies so that the teeth of each die rest on the pipe. Now, holding the handles of the stock about 6 inches from the body of the stock and standing directly in front of the pipe, push and turn to the right at the same time and the dies will be started. Now put some oil on the dies and turn the stock, taking hold of the ends of the handles and standing at one side. The dies are run up on the pipe until the pipe extends through the face of the dies one thread. Oil is put on the pipe and the dies at least twice during the cutting. When the thread is long enough the stock is turned back a little and then forward a little and the loose chips are blown out from between the dies and pipe. If the dies are set right, a good clean standard thread will have been cut. This thread can now be cut off with the pipe cutters.
To cut pipe with a one-wheel pipe cutter is a simple matter. I will not dwell at length on the cutter itself. There are one-wheel and three-wheel cutters. We will use a one-wheel cutter tool. This cutter is forced into the surface of the pipe with a set screw having a long tee handle. The pressure that is brought to bear on the pipe while being cut is sufficient to cause a large burr to form on the inside of the pipe. Sometimes the pipe is completely crushed and rendered unfit for use. Therefore the user of these cutters should exercise care when cutting pipe. The pipe is put in the vise and the cutters are so put on the pipe that the pipe will be between the two rollers and the cutter wheel, the cutter resting on the mark that indicates the point at which the pipe is to be cut. The handle is screwed down and the cutters turned around the pipe; each time the cutters make a complete turn the handle is screwed down more. This procedure is continued until the furrow has been cut clear through the pipe.
Nipples are short pieces of pipe threaded on each end. Pieces of pipe longer than 6 inches are not called nipples. When a nipple is so short that the threads cut on each end meet in the center of the piece, the nipple is called a "close nipple." When there is a space of about 1⁄4 inch between the threads, it is called a "space or shoulder" nipple. To cut and thread these nipples a nipple chuck or nipple holder is necessary.
Fig. 68. - Nipple chuck and nipples.