Pipe Threading
A pipe thread is cut with stock and dies. Adjustable dies are used in pipe threading because of slight variations in fittings, especially cast- iron fittings. Figure 8-21 illustrates an adjustable pipe stock and dies for double-ended dies. As shown, each pair of dies has one size thread at one end and another size at the other end. Thus, the two dies in the stock are in position for cutting 1⁄2-inch thread, and by reversing them they will cut 3⁄4-inch thread. The cut shows plainly the reference marks, which must register with each other in adjusting the dies by means of the end setscrews to standard size.
A vise is used in conjunction with the pipe stock and dies when threading a pipe. After securing the pipe in the vise, use plenty of oil in starting and cutting the thread. In starting, press the dies firmly against the pipe until they take hold. After a few turns, blow out the chips and apply more oil. This should be done several times before completing the cut. When complete, blow out the chips as cleanly as possible and back off the dies. When drawing in your breath preliminary to blowing out the chips, turn your head away from the die to avoid drawing the chips into your lungs.
A nipple is short piece of pipe 12 inches in length or less and threaded at both ends. Nipples are properly cut by using a nipple holder designed for use with hand stock and dies. The holder is double ended and holds two sizes of nipples, one being for 1⁄2-inch nipples and the other for 3⁄4-inch nipples. In construction, there is a
pin inside the holder having a fluted end that digs into the nipple end when pressed forward by driving down the wedge. In opera- tion, the nipple is screwed by hand into the holder as far as it will go, and then the wedge is driven down sufficiently to firmly secure the nipple. The holder is arranged in such a way that when the thread is cut, the nipple can be removed by simply starting back the wedge, which loosens the inner part of the holder and allows the nipple to be easily unscrewed by hand. The holder can be used for making either right or both right and left nipples.