waste pipes. After the pipe is cut
this burr should be reamed out thoroughly. One of the strong points
of screw pipe is the strength of each joint. Care should therefore
be taken to see that perfect threads are cut on the pipe and that
the threads of the fittings are perfect. The dies should be set
right and not varied on each joint. There should be plenty of oil
used when threads are cut so that the thread will be clean and
sharp. The follower or guide on stocks should be the same size as
the pipe that is being threaded, otherwise a crooked thread will
result. If a pipe-threading machine is used, the pipe is set
squarely between the jaws of the vise that holds the pipe in place.
When cutting a thread on a long length of pipe, the end sticking
out from the machine must be supported firmly so that no strain
will come on the machine as the pipe turns. It is necessary to cut
crooked threads sometimes on the pipe to allow the pipe pitch for
drainage or to bring the pipe into alignment where fitting would
take up too much room. To cut a crooked thread on a piece of pipe,
simply leave the follower out of the stock or put in the size
larger. The dies not having a guide will cut a crooked thread.
Piping should be run with as few threads as possible. With a
thorough knowledge of and the intelligent use of fittings, a
minimum number of threads will result.

The pipes in a building are run in compact parallel lines in chases
designed especially for them. The tendency is to confine the pipes
to certain localities as much as possible. This makes a very neat
job and in case repairs are needed, the work and trouble incurred
will be confined to one section.

FITTINGS

The fittings used in screw pipe work are cast-iron recess type (see
Fig. 54). The fittings are so made that the inside bores of the
pipe and the fittings come in direct line with each other, thus
making a smooth inside surface at all bends. The fittings are all
heavily galvanized. All fittings should be examined on the inside
for any lumps of metal of sufficient size to catch solid waste
matter, and these must be removed or the fitting discarded. All 90 deg.
bends, whether Ts or elbows, are tapped to give the pipe that
connects with them a pitch of at least 1/4 inch to the foot.
Except where obligatory, 90 deg. fittings should not be used. To make a
bend of 90 deg. a Y-branch, a nipple and a 45 deg. bend should be used, or
two 45 deg. bends will make a long easy sw