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LIMITS FITS AND TOLERANCE

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gives a study of limits fits And tolerances

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									LIMITS FITS AND TOLERANCE


It has been practically observed that all items can’t be produced to their exact size due to various reasons. They are of
two types
     1) Assignable causes

          -Material of all items may not be the same
          -Cutting tool may have worn out
          -Measuring tool have lost their accuracy
          -Machine and equipments have become loose and have developed error

          2) Random causes

          -Operator picks up quarrel with his supervisor, so he spoils few pieces
          -Power goes suddenly, so piece and machine is spoiled
          -There is inspection and operation is duly tensed and hence result is variation

          Now, consider the example of manufacturing of axles of 520mm. when these axles are inspected the data
          observed as follows.


              Diameter          19.6 19.7 19.8 19.9 20 20.1 20.2            20.3   20.4
              Frequency         5     4    8   10 30 20     11               9      3
          We find that only 30 out of 100 axles are as per drawing requirements. The rest 70 are not can we afford to
          reject all these 70 axles? No, because cost of 30 axles will be as high that we can’t sell them to customers. On
          the otherside customer objects to accept all 100 axles, saying variation is too much. So, limit is fixed with in
          which he will accept. Thus an element of flexibility is introduced. The flexibility helps in the following

          -In reducing rejection and hence rate of effective production.
          -In reducing cost of production.
          -In making the items available to the customer in time.
          -In fixing the limits and tolerance and thus helps in quality control.

          Related Terms

                  1)   Basic Size : This is the theoretical, ideal and absolute dimension of an item without any
                       consideration of limits and tolerances
                  2)   Nominal Size: This is the size by which a dimension is called or in reference to eg:- 20± 0.01mm
                       20mm nominal size.
                  3)   Actual Size: This is the actually measured dimension of an item


            LIMITS

            These are prescribed dimensions within which an item is acceptable on manufacturing. There are two
            limits
            Max limit:-This is the upper limit or the max dimension on item should have

            Min limit: - This is the lower limit or the min dimension on item should have

            Eg:- ф20 ± 0.01mm
            0.02mm

            Max limit = 20 + 0.01 = 20.01mm
            Min limit = 20 - 0.02 = 19.98mm
              TOLERANCE

              This is the error or deviation which is tolerable when accepting an item at the time of inspection it is of two
              types

                1)     Unilateral: It is only given in one direction of the basic size
     .
                       Eg:- In ф 20 + 0.01mm, here the tolerance is + 0.01mm unilateral tolerance is usually kept
                       positive.

                2)     Bilateral: It is given in both directions

     Eg: In ф 20 ± 0.01mm
                                       0.02mm

     Here the tolerance is + 0.01mm and -0.02mm



     FITS

     By fit, we mean mating of two parts (male and female) of an assembly in such a way that they can work together
     and fulfill the function for which they are made and designed.

          Types of fit


                1)     Clearance fit

                In this fit there is a clearance between hub and shaft. So that the outer one can freely move over the
                inner one when in use. It is subdivided into

                - Loose fit

                - Tree fit

                - Medium fit


          Transition Fit
          This fit lies between clearance and interference fit and hence called as transition fit.

          _Conning fit

          _Tight fit


3) Interference fit

          In this fit, there is a negative allowance, and when shaft moves into the hole, it experiences interference and
          hence a force is needed.

          -     Medium force fit

          -     Heavy force fit

          Allowance: It is the difference which is allowed between size of two mating parts of an assembly i.e. male
          and female.
          Degree of accuracy and measurement

          The degree to which a measurement can be made or should be made will depend upon a number of factors.

          -    Type or work
          -    Skill, type and condition of plant available
          -    Measuring method.
          -    Job specific requirements.



          Measuring equipments

               1.   Calipers
               2.   Micrometers
               3.   Height gauges
               4.   Gauges
               5.   Combination Set
               6.   Universal level protractor




          MILLING MACHINE

          It is a versatile machine making use of a multi point revolving cutting tool known as milling cutter. It can
          also hold one more no: of cutters at a time. This is superior to other machine as regards to accuracy and better
          surface finish and is designed for machining a variety of tool work.


          WORKING PRINCIPLE

          A milling machine works using a milling cutter which gets a rotary motion from the machine spindle while
          the work piece is fed under the moving cutters. The cutter has got many cutting edges while two come in
          contract at a time, and hence there is no use of a cutting fluid except air.


          Method of milling

          Convectional or up milling
          Down milling
Up milling: It is used in most of the case and hence it is called convectional method. It is the process of removing
metal by a cutter which is rotated against the direction of travel of work piece.

Down milling: In this, cutter is rotated in same direction of travel of work piece.


TYPES OF MILLING MACHINE

               1.   Horizontal milling machine / column knee type

          -    Head milling machine.
-    Plain milling machine.
          -    Universal milling machine.
          -    Omniversal milling machine


               2.   Vertical milling machine
               3.   Fixed bed milling machine
               4.   Plano- miller or planer milling machine.
HORIZONTAL MILLING MACHINE

For general shop work, the mostly commonly used is the column and knee type where the table is mounted on the knee
casting which in turn is mounted on vertical slides of main column, so that the table can be moved up and down to
accommodate work of various method of supplying powers to the table, different movements of table and different axis
of rotation of main spindle.


VERTICAL MILLING MACHINE

It can be distinguished from a horizontal milling machine by the position of its spindle which is vertical or
perpendicular to work table. The spindle head which is clamped to the vertical column may be switched at an angle,
permitting the milling cutter mounted on the spindle to walk on angular surface. In some machines the spindle can be
adjusted up or down relative to the work. The machine is adapted for machining grooves, slots and flat surfaces. The
end mills and face milling cutters use the usual tools mounted on the spindle.


PRINCIPLE PARTS

The base, column, knee, saddle, table, over hanging arm, front brake, spindle


MILLING CUTTERS

They are revolving tools having one or several cutting edges of identical form equally spaced on the circumference of
the cutters. The cutting elements are called teeth which intermittently engage the work piece and remove metal by
relative movements of the work piece and cutter. The cutter may be classified as
      1) According to the constructional features of cutter a) Solid cutter, b) Step solid cutter, c) Inserted tip cutter
      2) According to the relief characteristics of cutter teeth a) profile relieved cutter b) form relieved cutter
      3) According to methods of mounting cutter a) Arbor type b) Shank type c) falling type.
      4) According to direction of rotation of cutter a) Right hand rotational b) Left hand rotational
      5) According to direction of helix of cutter teeth a) Parallel or straight b) Right hand c) Left hand d) Alternative
      6) According to use of cutter a) Standard milling cutter b) Special milling cutter


STANDARD MILLING CUTTER

   There are many different types standard milling cutters they are:-

            1.   Plain milling cutters
            2.   Side milling cutters
            3.   Metal slotting saw
            4.   Angle milling cutter
            5.   End mill
            6.   T- Slot milling cutter
            7.   Formed cutter


       ELEMENTS OF PLAIN –MILLING CUTTER

       BODY OF CUTTER: The part of cutter left after the exclusion of teeth and portion to which the teeth are
       attached.

       CUTTING EDGE: The edge formed by the intersection of the face and the circular land or the surface let by
       provision of primary clearance.

       FACE: The portion of cutter adjacent to the cutting edge on which the pitch impinges as it to cut from the work.

       HEAD: The axial advance of the helix of the cutting edge in one complete revolution of cutter.

       OUTSIDE DIAMETER: The diameter of the circle passing through peripheral cutting edge.
ROOT DIAMETER: The diameter of the circle passing through the bottom of the fillet.

DIVIDING OR INDEXING HEAD:

Indexing is the operation of dividing the periphery of a piece of work into any number of equal parts. In cutting
spur gears equal spacing of teeth on the gear block is performed by indexing. This operation can also be adopted
for producing hexagonal and square headed slots, cutting on shafts, fluting of drills, taps, reamers and many
other jobs all requiring periphery of the work piece to be divided equally and accurately. It is accomplished by a
special attachment known as dividing head. They are of three types,

      1.   Plane or Simple
      2.   Universal
      3.   Optical


 UNIVERSAL DIVIDING HEAD

 It is the most common type of indexing arrangements used in shops. It can be used to execute all terms of
 indexing. This is used for following purposes

 a) For sending the work in vertical, horizontal or inclined position relative to table surfaces.
 b) For turning the work pieces periodically through a given angle to impart indexing movements.
 c) For imparting a continuous rotary motion to the work piece for milling helical grooves.

 The main spindle housed on two accurate bearings carries a worm fear which is keyed on it. The worm which
 meshes with worm gear is mounted on the shaft at the other end of which crank is fitted. The worm gear has 40
 teeth and the worm is singled threaded. The 40 turns of the crank will rotate the spindle through one complete
 revolution or one turn of the crank will cause the spindle to be rotated by 1/40 of a revolution. In order to turn
 the crank a fraction of a revolution, an index plate is used. An index plate is a circular disc having a number of
 equally spaced holes arranged in concentric circles. The index plate is reserved on a sleeve which is loosely
 mounted on worm shaft. Normally the index plate remains stationary by a lock pin connected with a frame. A
 spring loaded pin fixed to the crank fits to the holes in the index plate. If the pin is moved from one hole to next
 in an 18 hole circle of index plate. The sector arms are used to eliminate the necessity of counting holes. If the
 pin is moved from one hole to next in a whole circle of the plate, the spindle will revolve

 1/40 ×1/18 = 1/720 of a turn.




 INDEXING METHODS


 Simple or plain indexing

 It is more accurate and suitable for numbers beyond range of rapid indexing. Hence the dividing head spindle is
 moved by the crank has a single threaded worm which mates with worm gear having 40 teeth, 40 turns of the
 crank are necessary to rotate the index crank spindle through one revolution. To facilitate indexing to fraction
 of a turn index plates are used to corner practically all numbers.

 Plate no: 1   15, 16, 17, 18, 19, 20

 Plate no: 2   21, 23, 27, 29, 31, 33

 Plate no: 3   37, 39, 41, 43, 47, & 49
In Batli machine

Inside 24, 25, 28, 30, 34, 37, 38, 39, 41, 42, and 43
Second side 46, 47, 49, 51, 53, 54, 57, 58, 59, 62, 66


Compound indexing

The name is due to the separate movements of the index crank in two different hole circles of one index plate to obtain
a crank movement not obtained by plane indexing.


Differential indexing

The name is due to required division is obtained by a combination of two movements.

Angular indexing

It is the process of dividing the periphery of a crank in angular movements and not by number of divisions. There are
360˚ in a circle and index crank is rotated by 40 no: of revolution. The spindle rotates through one complete rotation or
by 360˚. Therefore, one complete turn of crank will cause the spindle and work to rotate through 360/40 = 9˚.


SHAPING MACHINE

The shaping machine is one of the basic machine tool. It is used for machining jobs and giving them flat surfaces. In
horizontal, vertical or inclined plane shaping machine is frequently used in tool room and production shop. In general
shaper can be used to produce any surface composed of straight line elements. Modern shapers can generate continued
surface.

Working principle

Shaper makes use of ram which imparts reciprocating motion to cutting tool. The cutting tool removes the material
from job mounted on shaper tabled during its cutting stroke, while the job is given indexed feed during the return
strokes of cutting tool.


Classification

       1)     According to type of mechanism which is used for giving reciprocating motion to ram

            -Crank type
            -Gear type
            -Hydraulic type

       2)     According to position and travel of ram.

-Horizontal
-Vertical
-Traveling head

       3)  According to type of design of table
         -Standard shaper
         -Universal shaper
4) According to type of cutting stroke
-Push type
-Draw type
  PRINCIPLE PARTS

  1. Base: - It is the necessary bed or support required for all machine tools. The base is rigidly bolted to floor or shop.
  It is so designed that it can take up entire load of machine and the force set up by the cutting tool over the tank. It is
  made up of cast iron to resist vibrations and take up high compressive loads.

2. Column: - It is a box like casing mounted upon the base. It encloses the ram driving mechanism. Two accurately
       machine guide ways are provided on the top of the column on which ram reciprocates. The front vertical phase of
       the column which serves as the guide ways for the cross rail is also accurately machined.


  3. Cross rail: - The cross rail is mounted on the front vertical guide ways of the column. It has two parallel guide ways
  on its top in the vertical plane. The table may be raised or lowered to accommodate different sizes of job by rotating an
  elevating screw which crosses the cross-rail to slide up and down of the vertical phase of column. A horizontal cross-
  feed screw which is fitted with cross-rail and parallel to the top guide ways of rail activates the table to move in cross
  wise direction
                   .
  4. Saddle: - It is mounted on the cross-rail which holds the table firmly on its top. Cross wise movement of the saddle
  by rotating the cross feed given by hand or power the table to move sideways
           .
  5. Tables: - It is bolted to saddle, receives cross wise and vertical movements from saddle and cross-rail. It is a box type
  casting having T-slots both on top and sides for clamping work.

  6. Ram: - It is the reciprocating member shape. It is hemi- cylindrical in form and heavily ribbed inside to make it rigid.
  It slides on the accurately machined dove tail guide ways on the top of the column and is connected to the reciprocating
  mechanism contained with in column.

  7. Tool head: - It holds the tool rigidly provides vertical and angular feed movement of the tool and allows the tool to
  have automatic relief during its return stroke.
       .

    SHAPER MECHANISM
            .

    In a shaper rotary movement of the driver is converted into the reciprocating movement by the mechanism contained
    with in the column of machine.

    Crank and slotted link mechanism

    The motion or the power is transmitted to bull gear through a pinion which receives its motion from an individual
    motor or overhead shaft through speed on to mechanism. The speed of bull gear may be changed by different
    combination of gearing or simply shifting belt on the step-cone pulley. Bull gear is a large gear mounted with in the
    column. Bolted to the centre of bull gear in a radial slide which carries a sliding block into which the crank pin is
    fitted. Rotation of bull gear will cause the crank pin to revolve at a uniform speed. Sliding block which is mounted
    on the crank pin is fitted within slotted link. The slotted link also known as rocker ram pivoted at its bottom and
    attached to the frame of the column. The upper end of rocker arm is forked and connected to ram block by a pin. As
    the bull gear rotates causing the crank pin to rotate the sliding block . The sliding block is pushed to the crank pin
    will rotate on the crank pin circle and at the same time will move up and down. The slot in the slotted ring gives a
    rocking movement which is communicated to the ram. Then the rotating motion of bull gear is converted to
    reciprocating movement of ram.


    TOOL HEAD OF A SHAPER.

    Tool head of shaper holds the tool rigidly provides vertical and angular feed movement to tool and allow the tool to
    have an automatic relief driving its return stroke. The vertical slide of the tool head has a swivel base, which is held
    on a counter seat on the ram. The swivel base is graduated in degrees so that the vertical slide may be set
    perpendicular to the work surface on any desired angle. By rotating the hand feed angle the vertical slide carrying the
    tool gives down feed or angular feed movements while machining vertical or angular surfaces.

    The amount of feed or depth of cut may be adjusted by a micrometer drill on the top of the down feed screw. Apron
    consisting of clamping box, clamper block and tool post in clamped upon vertical slide wire screw. By releasing the
  clamping screw, the apron may be swiveled upon the apron either towards left or right. The arrangement is necessary
  to provide relief to the tool while making vertical or angular cuts. The two vertical walls on the apron called clapper
  box houses the clapper block which is connected to it by means of a hinge pin. The tool post is mounted upon the
  clapper block, on the forward cutting stroke. The clapper fits to the clapper box to make a rigid tool support. At the
  return stroke a slightly frictional drag of the tool on the work lifts the block out of clapper box, a sufficient amount
  preventing the tool cutting edge from dragging and consequent wear.


  AUTOMATIC FEED MECHANISM

  Down feed and cross feed can be given at the end of return stroke only by automatic feed mechanism. The rotating
  bull gear rotates driving disc. As the disc rotates through half of the revolution the top of the revolving arm now
  moves in anticlockwise direction and straight side of pawl engages with teeth of the socket wheel to move in
  anticlockwise direction only. As the driving disc is connected to bull gear the table feed movement is affected when
  the bull gear or the driving disc rotates through other half imparts no feed movement. To reverse the direction of
  rotation feed a knob at top of pawl is rotated through 180 degrees, after moving the pin. The amount of feed may be
  altered by increasing the eccentricity at the driving disc.


  SHAPER OPERATIONS


          -    Horizontal flat surface machining.
          -    Vertical surface machining
          -    Machining angular surface
          -    Cutting slots and keyways
          -    Irregular surface machining
          -    Machining pliers or cutting gears



SLOTING MACHINES

It is a machine tool used only in production shop, because in tool rooms and training centers slotted work is done either
by slotter or milling machines. It falls under the category of reciprocating types of machine tool. It operates on the
principles as that of shaper. The major differences are that in slotter, the ram holding work piece rotate in horizontal
axis. It is also known as vertical shaper. The ram can be swiveled not more than 5˚ to vertical. It is used for cutting
grooves, keyways and slots.

TYPES - Puncher slotter
Precision slotter


SLOTTING MACHINE PARTS

Base: - The base is rigidly built to take up all the cutting forces and entire load of the machine. The top of the bed is
accurately machined to provide guide ways on which saddle is mounted. The guide ways used are perpendicular to the
column wall.

Column: - It is the vertical member which is integrate with base and houses the driving mechanism of ram and feeding
mechanism. The front vertical face of the column is accurately finished for providing ways on which ram reciprocates.

Saddle:- It is mounted upon the guide ways and may be moved towards or away from the column either by power or
manual control to supply longitudinal feed to work. The top face is accurately finished to provide guide ways for cross-
slide.

Cross slide:- It is mounted upon guide ways of the saddle and may be more parallel to the base of the column. The
movement may be controlled by hand or by power supply control feeds.

ROTATING TABLE: - It is a circular table mounted on top of cross slide. It may be rotated by rotating a worm which
meshes with a worm gear, connected to side of table Ram and tool head assembly. It is the reciprocating member of the
machine on the guide ways of column. It supports the tool at its bottom and as tool head.
WHIT WORTH QUICK RETURN MECHANISM

The bull gear located at the back of the machine receives its motion from the pinion, which is driven by an electrical
motor. The gear is mounted on a fixed pin or hub attached to top machine frame. The driving plate is mounted on the
shaft. The shaft is placed eccentrically with respect to the bull gear rotates the crank pin and sliding block rotates in a
circular path, but owing to the eccentricity of the bull gear the driving plate. The block rotates and slides with in the slot
of the driving plate imparting it and the shaft rotating movement. The rotation of driving plate is transmitted to the disc
which is attached to the end of shaft. A radical T- slot is cut on the face of the disc. The position of pin fitted within the
T- slot may be altered with respect to centre of disc and then clamped to one end of the connecting rod, it is attached to
ram by clamping the bolt. The rotation of disc is converted to reciprocating movement of the ram by connecting rod
and pin eccentrically mounted on the disc.


SLOTTER OPERATIONS

The operations performed in a slotter are:
    1. Machining flat surface
    2. Machining cylindrical surface
    3. Machining irregular surface and cam machining
    4. Machining slots, keyways and grooves.

Machining flat surface: - The external and internal flat surface may be generated on a work piece easily in slotting
machines. The work to be machined is supported on parallel strips so that the tool will have clearance with the table
when it is at the extreme downward position of the stroke. The work is then clamped properly on the table and the
position and the length of stroke is adjusted. A clearance of 20 to 25mm is left before the beginning of cutting stroke,
so that the feeding movement may take place during this idle part of the stroke. The table is clamped to prevent any
longitudinal or rotary travel and the cut is started from one end of the work. The cross feed is supplied at the beginning
of each cutting stroke and the work is completed by using a roughing and a finishing tool. While machining an internal
surface, a hole is drilled in the work piece through which the slotting tool may pass during the first cutting stroke. A
second surface parallel to the first machined surface can be completed without distributing the setting by simply
rotating the table through 180˚ and adjusting the position of the saddle. A surface perpendicular to the first machined
surface may be completed by rotating the table by 90˚ and adjusting the position of the saddle and cross slide.

Machining circular surface:- The external and internal surface of a cylindrical can also be machined in a slotting
machine. The work is placed centrally on the rotary table and packing piece and clamps are used to hold the work
securely on the table. The tool is set radially on the work and necessary adjustments of the machine and the tool are
made. The saddle is clamped in its position and the machine is started. While machining the feeding is done by the
rotary table feed screw while rotates the table through a small arc at the beginning of each cutting stroke.


Machining irregular surface or cams: - The work is set on the table and necessary adjustments of the tool and the
machine are made as detailed in other operations. By combining cross, longitudinal and rotary feed movements of the
table any contoured surface can be machined on a work piece.

Machining grooves or keyways:- Internal and external grooves are cut very conveniently on a slotting machine. A
slotter is specially intended for cutting internal for cutting internal grooves which are difficult to produce in other
machines. External or internal gear teeth can also be machined in a slotter by cutting equally spaced grooves on the
periphery of the work. The indexing or dividing the periphery of the work is done by the graduations on the rotary
tables.


SLOTTER TOOLS

A Slotting machine tool differs widely from a shaper or a planner tool as the tool in a slotter removes metal during its
vertically cutting strokes. This changed during continuous presets a lot of difference in the tool shape. In a lathe, shaper
or a planer tool the cutting pressure acts perpendicular to the tool length, where as in a slotter the pressure acts along
the length of the tool. The rake and the clearance angle of a slotter tool apparently look different from a lathe or a
shaper tool as these angles are determined with respect to vertical plane lather than the horizontal. Slotter tools are
provided with top rake, front clearance and side clearance, but no side rake is given. The nose of the tool projects
slightly beyond the shank to provide clearance. The amount of rake angle given is similar to that of a shaper tool.
CUTTING SPEED, FEED AND DEPTH OF CUT

Similar to shaper, the cutting speed of a slotter is defined by the rate with which the metal is removed during downward
cutting stroke and is expressed in meters per minute.
Feed is the movement of the work per double stroke expressed in mm.
Depth of cut is the perpendicular distance measured between the machined surface and unmachined surface expressed
in mm.

SHAPER TOOLS

The cutting tool used in a shaper is a single point cutting tool having rake, clearance and other tool angles similar to a
lathe tool. It differs from a lathe tool in tool angles. Shaper tools are much more rigid and heavier to withstand shock
experienced by the cutting tool at the commencement of each cutting stroke. In a lathe tool the effective angle of rake
and clearance may be varied by rising or lowering the point of the tool in relation to the centre of the work but in a
shaper the tool angles cannot be changed as the tool is always clamped perpendicular to the surface of the work. When
it becomes necessary to change the tool angles. It can only be done by grinding. In a lathe tool sufficient amount of side
clearance angle must be provided as the tool is continually fed sideways tracing a helical path, but in a shaper tool as
the feed is given at the end of cutting stroke, a very small clearance angle is necessary to give relief to the side cutting
edge. In a shaper tool the amount of side clearance angle is only 20 to 30 and the front clearance angle is 40 for cast iron
and steel. Small clearance angle adds strength to the cutting edge. The most common cutting tools are
                                            1) A left hand roughing tool for planning.
                                            2) A left hand finishing tool for planning.
                                            3) A left hand side facing tool for vertical shaping and for shaping sharp
                                                  corners.
                                            4) A left hand side facing tool.
                                            5) A left hand dovetail cutting tool (roughing).
                                            6) A left hand dovetail cutting tool (finishing).
                                            7) A parting or slotting tool.


CUTTING SPEED, FEED AND DEPTH OF CUT

Cutting speed: - in a shaper the cutting speed is the rate at which the metal is removed by the cutting tool. This is
expressed in meters per minutes. In a lathe as the cutting action is continuous the cutting speed is expressed by the
peripheral speed of the work. But in a shaper the cutting action is considered only during the forward cutting strokes.

Cutting speed = length of the cutting stroke            .
Time required by the cutting strokes

Feed: - feed is the relative movement of the tool or work in a direction perpendicular to the axis of reciprocating of the
ram per double stroke and expressed in mm. the feed is always given at the end of return stroke. When the tool is not
cutting the metal the selection of feed is dependent upon the kind of metal type of job etc.

Depth of cut: - Depth of cut is the thickness of metal is removed in one cut. It is the perpendicular distance measured
between machined surface and non machined surface of the work piece.

MILLING CUTTERS

PLAIN MILLING CUTTERS

The plain milling cutters are cylindrical in shape and have teeth on the circumferential surface only. The cutters are
intended for the production of flat surfaces parallel to the axis of rotation of the spindle. The cutter teeth may be
straight or helical according to the size of the cutter.

a) Straight teeth plain milling cutter

Very wide plain milling cutters are termed as stabbing cutters. These cutters have nicked teeth. The nicks are uniformly
distributed on the entire periphery of the cutter. The object of the nicks is to break up the chips and enable the cutter to
take a coarse feed. The plain milling cutters are available in diameters from 16 to 160mm and the width of the cutter
range from 20 to 160mm.
b) Helical plain milling cutter

The helical plain milling cutters have further coarse pitch and the helix angle of the teeth ranges from 45˚ to 60˚. The
cutter is useful in profile milling work due to its smooth cutting action and is adapted for taking light cuts on soft steel
or brass and where wide surface are to be machined.


SIDE MILLING CUTTER

The side milling cutters have teeth on its periphery and also on one or both of its sides. The side milling cutters are
intended for removing metals from the side of a work. The side milling cutters are available from 50 to 200mm in
diameter and the width of the cutter range from 5 to 32mm.

a) Straggled teeth

The straggled teeth side milling cutters have alternate teeth with opposite helix angle. This design of the cutter teeth
increases the chip space to a great extent. The cutter is suitable for milling deep narrow slots or key ways on work
pieces.

b) Interlocked teeth

The interlocking slide milling cutters are formed out of two half side milling cutters or two staggered teeth side milling
cutters which are made to interlock to form one unit. The teeth of the two cutters may be plain or of alternate helix. The
path of the teeth overlaps when the cutters are assembled. The cutters are used for milling wider slots of accurate width.
The width of the cutter may be varied by inserting spacers of suitable thickness between the two halves of the cutter.
The width of the cutters ranges from 10 to 32mm and diameter ranging from 50 to 200mm.

METAL SLITTING SAW

The metal slitting saws resemble a plain milling or a side milling cutters in appearance but they are of very small width.
The cutters are used for parting- off operation or for slotting.

a) Plain metal slitting saw

The plain metal slitting saw are thinner in construction and the width of the cutter is limited to 5mm. The side of the
cutter is relieved in order that the side faces may not rich against the work.
b) Staggered teeth metal slitting saw
The staggered teeth metal slitting saws resemble a staggered teeth side milling cutter, but the width of the cutter is
limited to 6.5 to 7mm.

ANGLE MILLING CUTTER

The angle milling cutters are made as single or double angle cutters and are used to machine angle other than 90˚. The
cutting edges are formed at the conical surface around the periphery as the cutter.

     a)   Single angle milling cutter

          The single angle milling cutters have teeth on the conical or angular face of the cutter and also on the large
          flat side. The angle of the cutter is designated by the included angle between the conical face and the large
          flat face of the cutter. The cutter having different included angles of 30˚, 45˚, 60˚, 65˚, 70˚, 75˚, 80˚ & 85˚are
          available with diameter of 50mm and width of 12mm. There are another set of cutter having the same range
          of included angle. But the diameter of the cutters is 63mm and width 28mm

     b)   Double angle milling cutter

The double angle milling cutters have V-shaped teeth with both conical surfaces at an angle to their end faces. The
angle of teeth with conical surface at an angle to their end faces. The angle of teeth may not be symmetrical with
respect to a plane at right angles to the cutter axis. The unsymmetrical double angle cutters are available in diameters of
50, 63, 80, & 100mm and their width of varies from 12 to 36mm. the cutters are available in different included angles
of 55˚,60˚, 65˚,70˚ , 75˚ , 80˚, 90˚ ,& 100 ˚degrees. The equal angle cutters are available in diameter from 56 to
100mm having width ranging from 10 to 28mm.
END MILL

The end mills have cutting teeth on the end as well as on the periphery of the cutter. The peripheral teeth may be
straight or helical and the helix may be right hand or left hand. The end mills are used for light milling operations like
cutting slots, machining accurate and for profile milling operation.

     a)   Taper shank end mill

          The taper shank end mills have a tapered shank or extensions on one end for mounting and driving the
          cutters. The cutter may be double fluted or multiple fluted. The taper shank end mills are available from 10
          to 63mm in diameter and may have tanged end or tapped end for mounting on the arbor.

     b)   Straight shank end mill

The straight shank end mills have round shanks for mounting and driving the cutters. The cutter teeth may be straight
or helical. The diameter of the cutter ranges from 2 to 63mm.


     c)   Shell end mill

The shell end mill is larger and heavier than end mills provided with a central hole for mounting the cutter on a short
arbor. This design of the cutter gives economy in tool material as the cutters having different diameters may be
interchanged on a single shank. The cutting edges are provided at the end and around the periphery of the cutter the
teeth may be straight or helical and may be left or right handed. The diameters of cutters range from 40 to 160mm and
width from 32 to 63mm. the bore diameter of cutters ranges from 16 to 50mm.


T-SLOT MILLING CUTTER

The T-slot milling cutters are special form of end mills for producing T-slots. The teeth are provided on the periphery
as well as on both sides of the cutter.


FORMED CUTTER

The formed cutters have irregular profiles on the cutting edges in order to generate an irregular outline of work.

a) Convex milling cutter

     The convex milling cutters have teeth curved outwards on the circumferential surface to form the contour of a
     semicircle. The cutter produces concave semicircular surfaces on a work piece. The diameter of the cutter ranges
     from 50 to 125mm and the radius of the semicircular varies from 1.6 to 20mm.

     b) Concave milling cutter

          The concave milling cutters have teeth curved inwards on the circumferential surface to form the contour of a
          semicircle. The concave milling cutters produce a convex semicircular surface on a work piece. The diameter
          of the cutter ranges from 56 to 110mm.

c) Gear cutter

The gear cutters have formed cutting edges which reproduce the shape of the cutter teeth on the gear blank. The shape
of the cutter teeth may be involutes or cycloid according to the gear tooth profile. The cutter tooth profile should be
differently shaped for each pitch of the gear and also for each change in number of teeth on the gear which it is going to
cut. But in practice a compromise is affected by using one cutter to cover a range of gear sizes.


SPINDLE DRIVE

1)   Belt drive :- Belt drive is one of the most common and affective devices of transmitting motion and power from
     one shaft to the other by means of a thin inextensible band running over two pulleys. This is largely used for
     general purposes in mills and factories especially when the distance between the shafts is not very great. Belt can
     transmit however up to a distance of about 10m with a maximum surface speed of 1400m per min when flat belts
     are used. While a maximum surface speed of 1500m per min can be used with V-belts. In a belt drive
     arrangement, one of the pulleys called driver is mounted on the driving shaft while the other, which is mounted on
     the shaft is which power is to be transmitted is called the driven pulley or follower.

2)   Chain drive: - Chains are used for high transmission number (up to 15) and can impart as much as 5000 HP. They
     are mostly used when the distance between centers is short. But they are also employed when the centre distance
     is as much 8m. They are now in general use for the transmission as power in cycles, motor vehicles, agricultural
     machinery, road rollers etc and for gearing in workshops and factories and are continuously being installed to
     displace belt or rope drive and wheel gearing. Well conceived chain drives are highly effective are positive in
     motion I e permit no slip, and may be used where an exact averages velocity ratio is essential. A chain drive takes
     up less space than a belt drive and has no initial tension for belt or rope drives a certain minimum distances
     between the shaft is necessary unless jockers pulleys are to be used. This prevents the use of belts on ropes for
     connections directly two shafts which are close together.

3)   Rope drive: - Rope drive is used to transmit power over a moderately long distance. The horizontal distance apart
     of the shape centers in a rope drive should not be less than 9 or 12m, but may be made as much as 24 or 30m. the
     working stress on the rope is usually taken 14 kg per sq cm of section and their can impart as much as 2000 h.p
     one big advantage of rope drives is that a number of separate drives may be taken from one as the driving pulleys,
     rope for transmitting power are made of cotton, manila or hemp, cotton ropes being usually considered the best on
     account of their greater driving power and fit into circumferential grooves on the pulleys which they connect, and
     are from 35 to 50mm in diameter.

4)   Clutches: - A clutch is a form of connection between a driving and a driven member on the same axis. It is so
     designed that the two members may be engaged or disengaged at will either by a hand-operated devices or
     automatically by the action of some power- driven device. The common types of clutches may be divided into
     positive clutch and the friction clutch.

5)   Friction drive: - Friction drive is used for light load transmission between parallel shafts or between shafts with
     intersecting axes. In friction drive one wheel drives another with which it is in contact by reason of the friction
     between their surfaces provided the surfaces of the two wheels are sufficiently rough. If the cylindrical friction
     wheels are assumed to operate without slip, the surface speed of both the wheels must be equal. The velocity ratio
     of a pair as wheels is therefore, inversely proportional to their diameters that is d1 /d2 =n2 /n1

      As in a belt drive slipping may occur if the power to be transmitted is too great for the frictional grip
      between the surfaces and friction wheels do not give a positive drive.

6)   Gear drive: - it is possible to drive shafts that are parallel intersecting or neither parallel nor intersecting by the use
     of toothed gears. Toothed gearing is after used in preference to belting, friction drives or chain drives where
     moderate or large amounts of power must be transmitted at a constant velocity ratio. Many different forms of
     gears are used and the most commonly used are
1. Spur gear
2. Helical gear
3. Spiral gear
4. Bevel gear
5. Worm and Worm wheel
6. Rack and Pinion

								
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