Pipes are required to be cut in
suitable lengths and sizes as demanded in a layout of piping. We always get the
pipes in standard lengths only from the market. Hence they need be cut to suit
our requirements.
Pipes can be cut either by
using hacksaws or standard pipe cutting tools. Smaller diameter and gauge pipes
can be easily cut by using hacksaws, but for larger diameters it requires
longer time to cut. Moreover, square face cutting of pipe is difficult as it is
a hand operation. It is important to get the cut surface a square to be length
of pipe when threaded ends are desirable for fitment.
Pipe Cutting Tools
There tools are either ‘solid
hook type’ or ‘chain type’. They are commercially known as pipe cutters.
A ‘hook type cutter’ consists
of a forged hook shaped frame carrying a handle at its one end. The hook frame
carries three wheels which are very hard and have sharp cutting edges along
their periphery. Out of these three wheels, two are mounted permanently on the
rigid frame in bush bearings, and the third one is mounted on the projected
part of the adjustable handle. All the three wheels revolve freely on their
supporting spindles.
The pipe to be cut is held
firmly in a gripping device such as pipe vice and the cutter is inserted round
the pipe. By moving handle, all the three cutting wheels are adjusted to touch
the periphery of pipe with some pressure. For cutting action to start the
cutter is revolved round the pipe and moving the adjustable cutting wheel
forwards a little distance every time, till it covers complete thickness of
pipe. This type of cutter is available in different sizes to suit cutting of
various sizes of pipes.
Fig.
Hook type Cutter
A ‘chain cutter’ is very widely
used for cutting cast iron pipes. It consists of a handle and a flexible chain.
At every link joint of the chain a cutter wheel, similar to that described
above, is provided. One end of the chain is hinged on the handle and the other
end can be fitted into it as desired when the pipe is to be cut the chain is
wrapped round the pipe and its free end is fixed in the handle. The grip is
adjusted by means of the screw provided for this purpose and then the tool
revolved round the pipe in the same manner as with the hook type cutter.
Pipe holding devices or Grips
·
Pipe vice
When it
is necessary to hold a piece of pipe rigidly for cutting or screwing it is
fixed in a vice. The vice is of two types, the pipe vice and the square jaw
vice.
The
pipe vice is usually bolted down firmly on to a bench. For light work, it may
be mounted on a portable frame. Common types of pipe vices are 1) Fixed type
and 2) open type
In each
case, the height of the opening of the jaws is called the nominal size and
common sizes in which these are available are 80 mm, 105 mm, 130 mm and 170 mm.
Fig.
Fixed Type Pipe Vice
Open Type Pipe Vice
Pipe
vices consist of a cast iron or steel base and frame. The frame is made in two
parts; the top part being hinged to the bottom at one end. The bottom part of
the frame carries the base which has holes on the both sides to accommodate the
bolts when it is fixed to the work bench. Two jaws are provided for holding the
work. Both of these are made serrated or provided with Vee grooves, to ensure
positive gripping of pipe.
One of
these jaws is fitted to the frame at the bottom while the other to the screw in
the top frame. This jaw is movable and is guided in the frame with a guide
block.
After
resting pipe in the bottom jaw, the top frame is positioned by engaging quick
release clamping lever on the left side with the lug on the bottom frame. The
movable Vee jaw is then adjusted by rotating the tommy bar. The pressure of the
grip can easily be adjusted by tightening the screw by means of the tommy bar.
·
Pipe Wrench
A pipe
wrench is an indispensable tool in pipe work. They are used to grip pipes, nuts
and fitting firmly.
Pipe
wrenches are to three types
1.
Stilson type
2.
Foot-print type and
3.
Chain wrench
Fig.
Stilson Wrench
The
‘stilson wrench’ has a fixed bottom jaw attached to a lever handle. The top jaw
is movable and adjustable by means of a milled adjusting wheel. The inside of
which is so cut as to enable it to engage with teeth on the movable jaw.
This
pattern of wrench may be obtained in a variety of sizes.
Fig.
Fig.
Foot Print Wrench
‘Footprint’
wrenches consist of two movable cut jaws which hinge on a centre bolt. These
may be adjusted to fit various sizes of pipe and nuts by altering the position
of the centre securing bolt.
Fig.
Fig.
Chain Wrench
The
‘chain wrench’, a very efficient type consists of a gripping jaw fixed to a
lever handle. At one side of the jaw is attached a strong chain, which is
passed round the pipe, and secured by means of a catch at the other side of the
jaw. As tension is applied the cut jaw bites into the pipe and assures a good
grip as pressure increases.
Cutting Threads On Pipes:
Different lengths of pipes are
to be connected to each other according to the given pipe layout. This is done
by using different pipe fitting described earlier. The ends of such pipe
fittings are provided with threads, so that the pipe ends, after cutting into
suitable lengths, are also required to be threaded. These threads are cut by
hand using different kinds of dies of required size. The dies are held in a
holder called ‘die stocks’.
The ‘taps’ are used to prepare
threaded holes and are also available in different size ranges. To turn these
taps, tap wrenches are used.
Pipe threads cut are of two
types-
1. British
standard pipe threads (B.S.P.)
2. Metric
Pipe threads (I.S.P. – International standard pipe threads).
The difference between standard
B.S. and Metric threads and the pipe threads is that the pipe threads have
little finer pitches and thus the depth of threads is lesser. This is because
the pipe threads do not require as much strength as in the other applications.
I.S.P.
Threads
Thread Angle = 550 Depth of thread = 0.6403 X pitch
|
|||
Designation, Inches
|
Pitch, mm
|
Minor dia. mm
|
Minor dia. mm
|
FP 1/4
|
1.34
|
11.45
|
13.16
|
FP 1/2
|
1.81
|
18.63
|
20.96
|
FP 3/4
|
1.81
|
24.12
|
26.44
|
FP 1
|
2.31
|
30.29
|
32.25
|
FP 1/2
|
2.31
|
44.85
|
49.80
|
FP 2
|
2.31
|
56.66
|
59.61
|
BSP
Threads
Thread Angle = 550 Depth of thread =
0.6403 X pitch
|
|||
Nominal size, Inches
|
Threads per Inch
|
Minor dia. mm
|
Minor dia. mm
|
1/8
|
28
|
0.337
|
0.383
|
1/4
|
19
|
0.451
|
0.518
|
3/8
|
19
|
0.589
|
0.656
|
1/2
|
14
|
0.734
|
0.825
|
3/4
|
14
|
0.950
|
1.041
|
1
|
11
|
1.193
|
1.309
|
1 1/2
|
11
|
1.766
|
1.882
|
2
|
11
|
2.231
|
2.347
|
Note –
Table 1 and 2 shows only some of the sizes. For complete range to threads refer
any standard data book.
Type Of Dies:
A die is a metal piece with
internal threads used for cutting an outside thread on a cylindrical work such
as pins, shafts, pipes etc.
The dies may be made from high
carbon steel or alloy steel material commonly known as die steel. They are
hardened and tempered suitably to give good cutting abilities and adequate wear
life.
Dies are available in different
forms, namely,
1. Circular
split die
2. Two
piece die
3. Die
plate
4. Die
nuts
Circular die
Fig.
Circular Split Die
This
die has one cut on the radial line for spring action. The die can be expanded
with the help of a screw on the holder. When the first cut is taken the die is
expanded and for the finish cut, the die is adjusted to the normal position.
This die is used for cutting small diameter screws.
Two piece die
Fig.
Two Piece Die With Die Stick
The two
piece die with its holding arrangement in a die stock. There two pieces of die
are the matched pairs and are numbered properly to avoid confusion. Die pieces
are available in standard size range. The depth of cut is adjusted with the
help of set screws provided in the holder. This die is used for large screws
and pipes. Lubricating oil is used while cutting threads.
Die
plate
Where
threads have to be cut on rods of 3 mm (1/8 “) diameter and under, it is common
to use a screw plate of the type. This is hardened steel plate with a series of
holes tapped for various sized threads. Usually there are three holes for each
size of screw so that the thread is cut gradually by running the plate down,
using the holes in turn. The third hole cuts the thread to the correct depth.
These holes are slightly enlarged on one side of the plate, and care must be
taken to see that the screw thread is always started from this side.
Die
nuts
Fig.
Die Nut
A die
nut is similar in shape to an ordinary square or hexagonal nut, and may be
obtained in all sizes of standard threads. Its main use is for running down an
existing thread that has become burred or damaged. It may be turned with an
ordinary spanner or a box-spanner, and is particularly useful for restoring
bruised threads on studs such as those of cylinder covers or valve chests,
where ordinary die stocks and dies cannot be used.
Steps in cutting threads by
hand
- Chamfer the end of the blank which is to be threaded. This helps the die to start easily.
- Fix the blank in the bench vice or chuck of the lathe.
- Fix the die in the die stock keeping the marked side on the top. The threads on the bottom side are tapered which helps in biting the blank easily.
- Adjust the die with set screws. First adjust the set screws for a free fit of die on the blank and then a cut.
- Place the die on the blank. Keep your hand over the die, apply pressure and turn as the die cuts the threads.
- Apply a cutting a coolant.
- Keep the die stock perpendicular to the blank. Turn it clockwise and then anticlockwise till the required length is reached.
