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.

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.

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.