PIPE THREADING
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.
THREADS.--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
--------+----------------+-------------------+----------------
3/8 | 9/16 | 18 | 10.825
1/2 | 3/4 | 14 | 10.500
3/4 | 3/4 | 14 | 10.500
1 | 15/16 | 11-1/2 | 10.800
1-1/4 | 1 | 11-1/2 | 11.500
1-1/2 | 1 | 11-1/2 | 11.500
2 | 1-1/8 | 11-1/2 | 12.930
--------+----------------+-------------------+----------------
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.
[Illustration: FIG. 67.]
MATERIALS NECESSARY.--Six feet of 1-inch black pipe; four 1-inch
black ells; two 1-inch tee; one 1-inch right and left coupling;
oil.
TOOLS NECESSARY.--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.
DIES.--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.
STOCK.--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.
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.
CUTTING AND THREADING NIPPLES.--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.
[Illustration: FIG. 68.--Nipple chuck and nipples.]
NIPPLE HOLDERS.--Take a piece of 1-inch pipe about 12 inches long
and on one end cut a thread that is 2 inches long. Take a 1-inch
coupling and screw it on this end until the end of the pipe is
almost through the end of the coupling. At least four threads
should be allowed at this end of the coupling. Now we have a piece
of pipe 12 inches long having a thread 2 inches long on one end
with a coupling on the thread. This is called a nipple holder. Now,
to cut a nipple, cut a thread on a piece of pipe and cut the pipe
off at any desired length, say 2 inches. Put the nipple holder in
the vise with the coupling out from the vise about 8 inches. Take
the 2-inch piece of pipe with a thread on one end, screw this
thread into the coupling until it touches the pipe that has been
screwed through from the other end. Now the stocks having the 1
dies and the follower in are put on the pipe. The follower will not
go over the coupling, therefore take the follower out of the
stock. Now the stock will slip over the coupling and the thread can
be cut. With this procedure a nipple of any length can be cut.
There are a number of patented nipple chucks on the market, but as
they are not always at hand the above method is resorted to and
serves every purpose.
LONG SCREWS.--To cut a long screw which comes in use frequently on
vent pipe work, a piece of pipe 12 inches long is taken and a
regular length thread is cut on one end, and a thread 4 inches long
is cut on the other end. Then a coupling is cut while screwed on a
pipe, so that a lock nut about 1/2 inch wide is made. The
description and use of these long screws will come under screw pipe
venting.
Now that the proper use of the tools has been explained, we will
proceed with the exercise according to the sketch. With a length of
pipe in the vise and the 1-inch dies in the stock, run over the
thread on the pipe. Note that all the measurements are center to
center. Screw an elbow on the pipe and measure off the first
length, which we will take as 12 inches center to center. Place the
rule on the pipe with one end of it at the center of the opening of
the elbow just screwed on. Mark 12 inches off on the pipe. This
mark represents the center of another ell. Now take another ell and
hold the center of one outlet on this mark. It will readily be seen
that to have the measurement come right, the pipe must be cut off
at a point where it will make up tight when screwed into the ell.
Therefore, about 1 inch will have to be cut off, making the pipe 1
inch shorter than where it was first marked. Cut the pipe, and
before taking it out of the vise make a thread on the pipe still in
the vise. After the thread is cut, take the reamer and ream out the
burr that is on the inside of the pipe caused by the pipe cutter.
An elbow can be screwed on this pipe. The next measurement is
marked off as explained, the pipe cut, then the piece in the vise
threaded and reamed. The measurements must be accurate and the
dies should be adjusted to cut all threads the same depth. When the
measurements are all out, there should be seven pieces of pipe,
each piece having one thread. Now the threads on the other end can
be cut except the 12 inch piece that screws into the right and left
coupling. This thread is a left-handed thread and must be cut with
the left dies. Change the dies now to the 1-inch left dies; turn
the stock in the opposite direction of the right-hand thread, and
the dies will cut the left thread. The pipe and the fittings can
easily be put together as shown in the sketch by following the
center to center measurements. The right and left coupling is the
only fitting that will cause the beginner trouble. A right and left
coupling can be used only when there is sufficient _give_ to the
pipe, that is, the two ends of the pipe to be coupled together are
only 1/2 inch apart. To get the coupling in place to start the
threads, the pipe must spread apart at least 2 inches. If the pipe
cannot be spread that much, a right and left coupling cannot be
used. The proper way to make up a right and left coupling is as
follows:
[Illustration: FIG. 69.--_F_ reads center of ell to end, _C_ reads
center of ell to center of valve, _D_ reads center of valve to
center of T, _E_ reads center of T to center of ell.]
Screw home the coupling on the right thread. Mark with a piece of
chalk on the coupling and the pipe showing a point on each where
the coupling makes tight. Take off the coupling and count the turns
and make note of the number. Now do the same on the left thread
and make a note of the number of threads. If the left thread has
six turns and the right has four and one-half, then to insure that
the left thread will be tight when the right thread is, the
coupling must be put on the left thread one and one-half turns
before it is started on the right thread. Now with four and
one-half turns, the right and the left threads will both be tight.
A little thought and practice will make this connection clear. If
all the measurements in this exercise are not cut accurately, the
right and left coupling will not go together.