MECHANICAL
ENGINEERING
WORKSHOP
GROUP - 2
TOPIC-
FITTING
INTRODUCTION
Machine tools are capable of producing work at a faster
rate, but there are occasions when components are
processed at the bench. Sometimes it becomes
necessary to replace or repair a component, which must
fit accurately with another component on re-assembly.
This involves a certain amount of hand fitting. The
assembly of machine tools, jigs, gauges, etc., involves
certain amount of bench work. The accuracy of work
done depends upon the experience and skill of the fitter.
The term bench work refers to the production of
components by hand on the bench, whereas fitting deals
with the assembly of mating parts, through removal of
metal, to obtain the required fit.
APPLICATION AND
IMPORTANCE
In engineering, particularly in heavy and medium engineering, even to-day,
with the use of automatic machines, bench work and fitting have important
roles to play to complete and finish a job to the desired accuracy.
The assembly of machine tools, jigs, gauges, etc., involves certain amount of
bench work. The accuracy of work done depends upon the experience and
skill of the fitter
FITTING TOOLS
All types of work require the use of large number
of tools involving a number of operations such as
filing, chipping, scraping, sawing, tapping, etc. to
finish the work to the desired shape and size.
Different types of tools
used in Fitting

Holding Tools – Bench wise, V-Block with clamp.

Marking and Measuring Tools – Scriber,
Vernier Caliper, Divider, Punches, etc.

Cutting Tools – Files, Chipping, Hack-Saw, Taps, twist-Drills, Dies, etc.

Striking tools / Hammers – Ball peen hammer, Cross peen hammer, etc.

Finishing tools – Hand File, Square File, Round File, etc.

Supporting tools – Anvil.

Miscellaneous tools – Number punch, Letter punch.
HOLDING TOOLS
A holding tool is a tool that firmly holds any material together.
Each holding tool is different but the common principles between them
is that they all secure a piece of material when your working with it. Not
every holding tool can be used for every material, this can be a common
misconception and if you make this mistake then your work could
become damaged - especially if you have applied a finish to the material.
Different Holding Tools
BENCH VICE: The bench vice is a work-holding device. It is the most commonly
used vice in a fitting shop. It is fixed to the bench with bolts and nuts. The vice
body consists of two main parts, fixed jaw and a movable jaws. Jaws are made
of hardened steel. The size of the vice is specified by the length of the jaws.
The vice body is made of cast iron which is strong in compression.
V-BLOCK WITH CLAMP: The V-block is a rectangular or square block with a Vgroove on one or both sides, opposite to each other The angle of the 'V is
usually 90°. V-block with a clamp is used to hold cylindrical work.
MARKING AND
MEASURING TOOLS
These are the tools used for marking out and measuring that you need
to know about: rules punches squares templates gauges micrometers
scribers.
Without these tools, it is not easy to measure the accurate values of the
given components.
Different Marking and Measuring Tools
STEEL RULE: It is stiff, straight steel strip having all the faces machined
true. On one of the flat faces, graduations are marked in inches and
centimeters. The least count is1mm. It is used to set out dimensions.
SCRIBER: A scriber is a slender steel tool, used to scribe or mark lines on
metal work pieces . It is made of hardened and tempered high carbon
steel.
SURFACE PLATE: The surface plate is machined to fine limits and is used for
testing the flatness of the work piece. It is also used for marking out small works
and is more precise than the marking table. The surface plate is made of cast
iron, hardened steel or granite stone. It is specified by length ' width ' height'
and grade.
ANGLE PLATE: The angle plate is made of cast iron. It has two surfaces,
machined at right angle to each other. Plates and components, which are to be
marked out, may be held against the upright face of the angle plate, to facilitate
the marking. Slots are provided on the angle plate to clamp the work in position.
UNIVERSAL SCRIBING BLOCK: This is used for scribing lines for layout work and
checking parallel surfaces. It may be noted that its spindle can be quickly
adjusted to any angle, by an adjusting screw.
DIVIDER: It has two straight legs sharpened at one end,
hinged at other end. This is used for marking circles, arcs,
laying out perpendicular lines, bisecting lines, etc.
CALIPER: A caliper is used to transfer and compare
dimensions from one object to another or from a part to a
scale
INSIDE CALIPER: These are also of two types ordinary,
spring type. It has two steel legs, which are bent outward.
These are used to set internal dimensions, to transfer them
to work.
OUTSIDE CALIPER: These are also of two types ordinary,
spring type. It has two steel legs that are bent inward. These
are used to measure the out side dimensions of round
objects.
ODD-LEG CALIPER (HERMAPHRODITE): It is made of
steel tapered strip, which is hinged between washers
at one end, one leg is bent at the tip inwardly and the
other has a straight pointed end. It is used to find the
center of a bar. It is extremely used for scribing lines
parallel to edge of work.
TRY SQUARE: Try square is used for making and
testing angles of 90degree. It consists of a steel blade,
riveted into a hard wood stock which has a protective
brass plate on the working surface. Another type is
the all-metal square, with steel blade and cast iron
stock. Sizes vary from 150 to 300mm,according to the
length of the blade.
VERNIER CALIPERS: These are used for measuring outside as well as inside
dimensions accurately. It may also be used as a depth gauge. It has two jaws.
One jaw is formed at one end of its main scale and the other jaw is made part of
a Vernier scale. 49 main scale divisions are divided into 50 equal parts in the
Vernier scale. Hence, one division of Vernier scale is 1/50 mm less than 1mm.
This gives a least count of .02mm. Vernier caliper is generally made of nickelchromium steel. Its size is specified by the maximum length that can be
measured by it.
VERNIER HEIGHT GAUGE: The Vernier height gauge, clamped
with a scriber. It is used for layout work. An off-set scriber is used
when it is required to take measurements from the surface, on
which the gauge is standing. The accuracy is same as Vernier
calipers. Its size is specified by the maximum height that can be
measured by it. It is made of nickel-chromium steel.
VERNIER DEPTH GAUGE: It is used for precision measurement of
blind holes, slots, grooves, etc. The working principle of this
instrument is the same as that of the Vernier caliper. It is made of
nickel-chromium steel. Its size is specified by the maximum depth
that can be measured by it.
PUNCHES: These are used for making indentations on the scribed lines, to make
them visible clearly. These are made of high carbon steel. A punch is specified by
its length and diameter. Punches and drifts of various types of extensively used
in the mechanical engineering workshop and here we will discuss about a few
basic types of punches which are commonly including center punch, dot punch,
prick punch and so forth.
DOT PUNCH: This is used to lightly indent along the layout lines, to locate center
of holes and to provide a small center mark for divider point, etc. For this
purpose, the punch is ground to a conical point having 60 degrees included
angle.
CENTRE PUNCH: This is similar to the dot punch, except that it is ground to a
conical point having 90 degrees included angle. It is used to mark the location of
the holes to be drilled.
PRICK PUNCH: It is sharply pointed tool. The tapered point of punch has an
angle of usually 400. it is used to make small punch marks on layout lines.
CUTTING TOOLS
Cutting Tools are used to cut the given specimen(plate) w.r.t the given
dimensions.
There are different types of cutting tools which are used for cutting or
removing the excess parts of different types of specimen.
DIFFERENT CUTTING TOOLS
CHISELS: Chisels are used for removing surplus metal or for cutting thin sheets.
These tools are made from carbon steel of octagonal or hexagonal section.
Chisels are annealed, hardened and tempered to produce a tough shank and a
hard cutting edge. The cutting angle of the chisel for general purpose is about
60°
HACKSAW: The hacksaw is used for cutting metal by hand. It consists of a frame,
which holds a thin blade, firmly in position. Hacksaw blade is specified by the
number of teeth per centimeter. Hacksaw blades have a number of teeth ranging
from 5 to 15 per centimeter (cm). Blades having lesser number of teeth per cm
are used for cutting soft materials like aluminum, brass and bronze. Blades having
larger number of teeth per centimeter are used for cutting hard materials like
steel and cast iron.
FILE CARD: It is a metal brush, used for cleaning the files, to free them from
filings, clogged in- between the teeth.
CHIPPING: Removing the metal with a chisel is called chipping and is normally
used where machining is not possible .While chipping, safety goggles must be put
on, to protect eyes from the flying chips.
TWIST DRILL: Twist drills are used for making holes. These are made of high
speed steel. Both straight and taper shank twist drills are used. Cutting angle of
the twist drill is 118°.
TAPS AND TAP WRENCHES: A tap is a hardened steel tool, used for cutting
internal threads in a drilled hole. Hand taps are usually supplied in sets of
three for each diameter and thread size. Each set consists of a taper tap,
intermediate tap and plug or bottoming tap. Taps are made of high carbon
steel or high speed steel.
First tap, or rougher - to start threading.
Second tap or intermediate - to cut the
thread.
Bottoming tap or finisher - to finish the
thread.
BENCH DRILLING MACHINE: Holes are drilled for fastening parts with rivets, bolts
or for producing internal threads. Bench drilling machine is the most versatile
machine used in a fitting shop for the purpose. Twist drills, made of tool or high
speed steel are used with the drilling machine for drilling holes.
DIES: Dies are used to cut external threads on round rods. A die is a round block of
hardened steel with a hole having internal threads and flutes across the threads.
The die is fitted inside a die holder called die stock.
STRIKING TOOLS
These tools are used to strike or hit the workpiece by the application of
external force.
A striking tool is a very basic hand tool consisting of a weighted head
attached to a handle.
DIFFERENT STRIKING TOOLS
BALL-PEEN HAMMER: Hammers are named, depending upon their shape and
material and specified by their weight. A ball-peen hammer has a flat face,
which is used for general work and a ball end, particularly used for riveting.
CROSS-PEEN HAMMER: It is similar to ball peen hammer, except the shape of
the peen. This is used for chipping, riveting, bending and stretching metals and
hammering inside the curves and shoulders.
STRAIGHT- PEEN HAMMER: This is similar to cross-peen hammer, but its peen is
in-line with the hammer handle. It is used for swaging, riveting in restricted
places and stretching metals.
SPANNERS: A spanner or wrench is a tool for gripping nuts and bolts. It is usually
made of forged steel. There are many kinds of spanners. They are named
according to the application. The size of the spanner denotes the size of the bolt
on which it can work.
FINISHING TOOLS
They are used to remove the material from the surface of the workpiece
in order to get a high surface finish. The Finishing tools are also called as
Files.
Files are multi-point cutting tools. They are used to remove the material
by rubbing on the metals(workpieces) to get a good surface finish.
DIFFERENT FINISHING TOOLS
FILES: A file is a hardened piece of steel containing a percentage of carbon or
tungsten. Fine teeth are cut on the surface of the teeth in slanting rows. Files
are classified according to the following factors: (i) The cut, (ii) The shape,
(iii) The length.
SINGLE CUT FILE: A single cut file will be having parallel teeth at 60 degree
inclination to the center line.
DOUBLE CUT FILE: Double cut files have two times cut-teeth; one as 60 degree
and the other cut is 80 degree.
HAND FILE: Rectangular in section, tapered in thickness but parallel in width.
The faces have double cut teeth and one of the edges, single cut. It is used for
filing a surface, at right angles to an already finished surface.
FLAT FILE: Rectangular in section and tapered for 1/3rd length in width and
thickness. The faces have double cut teeth and edges single cut. Used for
general purpose filing.
SQUARE FILE: The square file is square in its cross section. It is used for filing
square holes, internal square corners, rectangular openings, keyways and
splines.
ROUND FILE: A round file is circular in its cross section. It is used for enlarging
the circular holes and filing profiles with fillets.
HALF ROUND FILE: A half round file is in the shape of a segment of a circle. It is
used for filing internal curved surfaces.
KNIFE EDGE FILE: A knife edge file has the cross section of a sharp triangles. It is
used for filing narrow grooves and angles above 10 degree. The above files have
one third of their lengths tapered. They are available both single and double
cuts.
TRIANGULAR FILE: A triangular file is of a triangular cross section. It is used for
filing corners and angles which are more than 60 degree. Square, round, halfround and triangular files are available in lengths of 100, 150, 200, 250, 300 and
400mm. These files are made in bastard, second cut and smooth grades.