Precision surface finishing techniques

ABSTRACT
Lapping is low pressure, low speed abrading operation for refining
surface finish within the high dimensional and geometrical accuracies.
Lapping is generally used for flat, regular surfaces, gauges, piston
rings, pins. valves, roller bearings, crank shaft, cylindrical surfaces etc.
centreless lapping machine is generally used for super finishing operations
on cylindrical surfaces and this machine gives super finish in microns.

CONTENTS
1. INTRODUCTION
2. TYPES OF SURFACE FINISH
2.1 HONING
2.2 SUPERFINISHING
2.3 ROLLER BURNISHING
2.4 LAPPING
3. TYPES OF LAPPING
3.1 HAND LAPPING
3.1.1 LAPPING FLAT SURFACES
3.1.2 LAPPING OF INTERNAL CYLINDRICAL SURFACES
3.2 MACHINE LAPPING
3.2.1 VERTICAL LAPPING M/C WITH TWO CIRCULAR PLAT
3.2.2 MACHINE WITH SINGLE ROTATING CIRCULAR PLATE LAP
3.2.3 CENTRELESS ROLL LAPPING MACHINE
3.2.4 CENTRELESS LAPPING MACHINE
3.2.5 LAPPING MACHINES FOR INTRENAL CYLINDRICAL
SURFACES
4. LAPPING OF SLIP GAUGES
5. LAPPING FINISHES AND ACCURACIES

6. LAP MATERIALS
7. LAPPING MEDIUM
7.1 SILICON CARBIDE
7.2 ALUMINIUM OXIDE
7.3 BORONCARB1DE
7.4 DIAMOND
8. VEHICLES
9. LAPPING SPEEDS AND PRESSURES
10. ALLOWANCES FOR LAPPING
11. DESIGN
11.1 MOTOR SPECIFICATION
11.2 PULLIES SELECTION
11.3 CALCULATION FOR LENGTH OF BELT
11.3.1 FOR LAPPING WHEEL
11.3.2 FOR REGULATING WHEEL
11.4 CALCULATION FOR BELT TENSION
11.4.1 FOR LAPPING WHEEL
11.4.2 FOR REGULATING WHEEL
11.5 SHAFT DESIGN
11.5.1 1NTERMIDIATE SHAFT

11.5.2 SHAFT DESIGN FOR LAPPING WHEEL
11.5.3 SHAFT DESIGN FOR REGULATING WHEEL
11.6 BEARING SELECTION
12 PROCESS CHARTS
12.1 LAPPING WHEEL SHAFT
12.2 REGULATING WHEEL SHAFT
12.3 INTERMIDIATE SHAFT
12.4 BEARING HOLDRE
12.5 LAPPING WHEEL
12.6 REGULATING WHEEL
13. COST SHEET
14. CONCLUSION
15. REFERENCES

LIST OF FIGURE
TITLE
LAP FOR EXTERNAL THREADS.
LAPPING MANDREL.
VERTICAL LAPPING M/CWITII UONDLD AIJKAC'IVI-S LAPS
CENTRELESS ROLL LAPPING M/C
SPHERICAL LAPPING
DIAGRAMS FOR DESIGNS
DIAGRAMS FOR PROCESS CHARTS
LIST OF TABLES
TAB.NO. TITLE
LAPPING ACCURACY AND FINISH
RECOMMENDED LAPPING ALLOWANCES

LIST OF PROCESS CHART
CHART NO. TITLE
01 LAPPING WHEEL SHAFT
02 REGULATING WHEEL SHAFT
03 INTERMIDIATE SHAFT
04 BEARING HOLDER
05 LAPPING WHEEL
06 REGULATING WHEEL

1. INTRODUCTION
The dimensional and geometrical accuracy obtained by normal
method of machining, like turning, milling, etc. are limited. The geometrical
error includes circularity, cylindrical, flatness and parallelism of functional
surfaces. Also, the surface finish has vital influence on most important
functional properties such as wear resistant, fatigue strength, corrosion
resistance and power losses due to friction. Poor surface finish will lead to
rupture of oils films on the picks of micro irregularities, which lead to state
approaching dry friction, and results in excessive wear of rubbing surfaces.
Therefore, fine finishing processes are employed in machining the surfaces
of many critical components to obtained very high surface finish or high
dimensional and geometrical accuracies. Such processes include honing,
super finishing, burnishing and lapping.

2. TYPES OF SURFACE FINISH
There are four types of surface finishing methods, they are as follows.
1. Honing.
2. Super finishing.
3. Roller burnishing.
4. Lapping.
2.1 HONING
Honing is low velocity abrading process in which the stock is removed from
metallic or non-metallic surfaces by bonded abrasive sticks. It is a finishing
operation employed not only to produce high surface finish, but also to
correct out-of-roundness, taper and axial distortion in work pieces.
In honing, since a simultaneous rotating and reciprocating motion is given to
stick, the surface produce will have a characteristic crosshatch lay pattern.
Honing is employed very frequently for finishing of bores, but there arc
numerous external surfaces, which are honed to obtain required properties.
Some examples are gear teeth, valves setting, race of ball and roller bearing.
Moreover, bores of any size can be honed whether long, short, blind,
tandem, or with keyways. It is effective on almost any ferrous or non-ferrous
material in a hardened or soft conditioned.

2.2 SUPERFINISHING
Super finishing is an abrasive process utilizing either a bonded abrasive
stone for cylindrical surfaces or a cup wheel for flat and spherical surfaces.
It is, in a way, a fine honing operation. By this process it is possible to
achieve higher surface finish on components. In addition, Super finishing
removes chatter marks, feed spirals, grindings commas and other
imperfection left by the previous grinding operation.
Stock removal in the Super finishing process is of the order of 0.005 to
0.025 mm on diameter. The surface produce will have a mirror like finish,
and surface finish obtained is of order of 0.05 to 0.2 micrometers.
In super finishing, the stones makes contact with the work piece over a large
area. The stone is given an oscillating motion in the axial direction and
simultaneously the job is given a rotary motion about the axis. As feed
movement could also be given, if necessary. The contact pressure exerted by
the stone on the work piece is very low, and it normally depends on material
being machined. Some time a light pressure is used in the beginning and
when the operation near completion, the pressure is increased to about 3
Kg/cm". The low operating pressure does not cause any appreciable
temperature rise and has a tendency to improve (he geometrical shape of the
part.

2.3 ROLLER BURNISHING
Roller burnishing is cold working process, by which improvement in surface
finish; dimensional accuracy and work hardening can be effected, without
the removing metal. It is finishing operation, and normally done on parts
which arc turned, bored, reamed, or ground. Any ductile or malleable
material with hardness less than 40 HRC can be successfully burnished.
Surfaces that could be burnished include external and internal cylindrical
surfaces, external and internal tapered surfaces, spherical surfaces and
circular flat surfaces. Machines normally used for burnishing operations can
be drill presses, lathe, boring machine, automatic bar chucking machines,
multispindles machines, or even special purpose transfer machines.
Instead of reaming, roller burnishing is some time used for finishing, but it is
most often used to supplement reaming or boring. Since roller burnishing
improves the surface hardness, metals that work hardens rapidly must be at
lower hardness before roller burnishing is done. The depth of surface
hardness obtained by roller burnishing varies from 0.1 to 0.7 mm.

2.4 LAPPING
Lapping is a low pressure abrading process, which is employed as precision
finishing operation to:
 Improve geometrical accuracy
 Achieve high dimensional accuracy
 Refine surface finish
 Ensure close fit between mating parts
Lapping is perform manually or by machine by charging a lap made of
material softer than the works piece with abrasive particles and rubbing with
over the work piece surface with slight pressure. Special lubricating and
bonding agent, known as vehicles, are used during the process
Hand lapping is done with abrasive powder as the lapping medium, where as
machine lapping is done either with abrasive powder, or with bonded
abrasive wheels. In both manual and machine lapping operations, the quality
of surface finish and the extent of dimensional accuracy that can be achieved
mainly depend on-
1] The type of lap material. 2] Type of lapping medium. 3] Speed of lapping
motion and pressure applied. 4] Material to be lapped.
Various lapping methods are divided in two main groups.

3. Types of lapping
1] Hand lapping. 2] Machine lapping.
3.1HAND LAPPING
3.1.1 LAPPING FLAT SURFACES
Hand lapping of flat pieces is perform by rubbing the parts over the
accurately finish flat surface of a master lap, accomplishing the abrading
action by a very fine abrasive powder mixed with vehicle. The work is
moved relative to master lap, along an ever changing path to ensure uniform
abrasive of both work and lap, and to eliminate, as far as possible, parallel
grain marks. A suitable abrasive should be selected for the works and it must
used sparingly as its excessive used will increase the wear op lap.
In lapping flat surfaces, fairly thick lapping blocks made of soft close-grain
cast iron, are used as a lap. For rough works, lap works better if it surface is
serrated. The lapping compounds collects in the grooves and continuously
rolls in and out as the work is moved, getting between the plate and work,
and it is crush into the cast iron, thus charging it toughly in short time. Cast
iron Laps, with plane flat surfaces, are used for work pieces, which have
been ground on a surface grinder.
Manual lapping of flat surfaces demands high operating skill since the
proper lapping speed and pressure depend upon his feel and judgment. Ring

lapping is simplest method of lapping external cylindrical surfaces. Ring
Laps are generally made of close grain cast iron.
Ring lap should always be shorter than the work piece and if the size
permits, it should have adjustable slots. The bore of ring lap should be very
close to size of work. Precision adjustments are normally made with the
used of closing and expanding screws provide on the lap. In some design, to
cover a range of diameters, a single holder with a set of interchangeable
bushes is employed. The work to be lapped is held in the chuck of lathe and
rotated, while the split ring lap held over the cylindrical surface is
reciprocated. The abrasive and vehicle are fed through the slots in the ring
lap and, when reciprocated, the lap should overrun the work by about one
third of its length.
Ring lapping recommended for plug gauges made in small quantities and for
precision machine spindle where great roundness accuracy is required.
External threads can also be lapped by this method. The laps [fig 01] are the
once which have an interchangeable threaded bush corresponding to the
external thread to lapped, with provision for precise adjustment.

Ring lapping when performed by a skill operator, offers two advantages over
machine lapping:
1} The out-of-roundness error can be corrected to higher degree than in
machine lapping.
2] The parts can be produced to extremely close tolerances.
Since ring lapping is tedious and calls for higher skills of the operator, it
should be considered only when:
1] There is too much of out of roundness in the work piece
2] The lot size is small

3] The works piece has key way or flats or similar interruptions on the
surface
4] The work piece has two or more different diameters to be lapped.
3.1.2 LAPPING; OF INTERNAL CYLINDRICAL SURFACES
Holes or bores are lapped using solid or adjustable laps. Rolling the laps on honing
machines, lathes or polishing heads, while the works piece is reciprocated over it does
the tapping operation.
Solid lap for larger sizes are generally made of cast iron, For the smaller sizes, steel or
hard brass is used. The laps are ground straight and round. Helical grooves cut on the
surface provide clearance for feeding abrasive and vehicles.
Adjustable laps are suitable for all plasters of hole lapping. Design of adjustable laps
for hole lapping include laps with partial split sleeves with screws expansion devices,
and laps with replaceable copper sleeves on taper mandrels for expansion of sleeves
(tig.02). Ring gauges arc examples of apart that are hip to extremely accurate
dimension with adjustable lap.

To obtain good results with lapping holes, the length of the lap should longer than the
work. The lap makes contact with the full length of the hole, thus preventing the
tendency to follow any already existing curvature. In internal cylindrical lapping,
virtually no material is removed, as the ease in honing. Sometimes, lapping follows
honing has touch up operation. The widest application of internal lapping is in match
lapping. In this, the male or female parts are hipped together to obtain the matched
pairs.

3.2 LAPPING MACHINES AND MACHINE LAPPING
Lapping machine has facilitated the machining of economic batch quantity. On
lapping machine, three types of lapping media arc used. Machines using metal laps
and abrasive powder mixed with suitable vehicle are employed where extreme
accuracy is required. Machines using bonded abrasive wheels are suitable for
commercial production. More recently, machines which employ abrasive paper or
cloth as lapping medium have also been developed.
Lapping machines can be mainly classified in to three types:-
 Machine using cast iron or bonded abrasive circular plates as laps for lapping
cylindrical and Hat work pieces.
 Machines using cast iron or bonded abrasive wheels as laps working on centre less
lapping principle for lapping cylindrical work pieces.
 Machines similar to honing machine used for lapping internal cylindrical surfaces.
3.2.1 VERTICLE LAPPING MACHINE WITH TWO CIRCULER
PLATES
This type of lapping machine consists of two opposed, heavy east iron or bonded
abrasive circular plates held in vertical spindles (12.17). When cast iron laps are used,
the lower lap drive the work pieces when the former is rotated at a speed of not more
than 100m/min. the upper lap is held stationary but is free to float in the vertical
direction . It rest upon the work during the lapping operation, thus applying the
constant pressure.

The work pieces are retained between these laps in slotted plates and made to rotate
and slide. The lower lap regulates the speed of rotation. The abrasive is used with a
paste type vehicle and is applied on the lap before the cycle is started. Oil or kerosene
is added during the cycle to prevent drying of vehicle.
Very fine finish of the order of 0.02micrometcr and tolerance of 0.5 micrometer are
feasible when cast iron laps are used. When bonded abrasive laps are used, both laps
are rotated. The laps are rigidly supported on the spindles and separately driven at
speed higher than that used for cast iron laps. Kerosene or similar lubricant is used as
coolant as well as to Hush the chips. Lapping takes place al a faster rate and
consequently, the machine does not produce extreme accuracy possible with
machines using cast iron laps. Since bonded abrasive laps must be dressed with
diamond tools, it is not possible le to make them as flat as cast iron laps on which the
machine generates flatness. Both cylindrical and flat lapping operation can be done on
this type of machine with the same arrangement of lapping plates.

Machine lapping between plates is an economical finishing method for parts like plug
gauges, piston pins, small valve piston, roller bearing, diesel injection valve, plungers
etc. a work piece with a diameter greater than its length is difficult or impossible to
lap between plates.
3.2.2 MACHINE WITH SINGLE ROTATING CIRCULAR PLATE LAP
Machines using single rotating cast iron lap are used for lapping. Work pieces placed
in carrier rings are given in a cycloid motion to distribute the wear evenly on the lap.
Pressure plates with or without air cylinders arc used to apply pressure, particularly
for light work pieces. The lap for single plates machines is usually made of cast iron,
For lapping with diamond powder, copper or other non-ferrous metals are preferred
because these metals readily become charge with abrasive,
The pressure plate and lap must be lapped together if work pieces are to be held to
close tolerance of thickness, flatness or parallelism,
Machine of this type, on which feeding, discharging and gauging of work piece is
performed in an automatic cycle, have been developed for production work. Such
machines have an automatic control of facility for the flow of lapping compound, and
they can also be equipped with pneumatic cylinder lifts for raising and lowering the
carrier rings and pressure plates. This speeds up loading and unloading of work piece.

3.2.3 CENTRELESS ROLL LAPPING MACHINE
A centre less roll lapping machine is designed for processing a single piece at time, and it
is used for lapping plug gauges, measuring wires, and similar straight or taper cylindrical
objects.
The machine [fig,04] consists of two cast iron rolls and a reciprocating device for holding
down the work piece and controlling the size. The diameter of larger roller, known as
lapping roller, is twice that of regulating roller. In opera I ion abrasive compound is
applied to the rolls and both the rolls are rotated in the same direction. Because of its
increased surface speed over that of the work, the lapping roller creates a lapping action.
The work piece feeds across the rolls at very slow rates as the 1200
V-Notched fiber stick
is uniformly reciprocated over (lie entire surface. This machine needs less time to be
setup and is suitable for lapping small quantities of jobs.
Workpiece

3.2.4 CENTRELESS LAPPING MACHINE
A center less lapping machine works on same principle as that of center less grinding
machine. But the lapping machine is constructed to produce very high roundness
accuracy and fine surface finish. The bonded abrasive lapping and regulating wheels
are much wider than those used for centerless grinding to allow the work to remain
longer in abrading contact and to receive final finish. The lapping wheels speed vary
from 175m/min to650m/min, depending upon the surface finish and production
requirement, where as the regulating wheels speed range between 70m/minto
175m/min.
The axis of regulating wheels and lapping wheel are not parallel normally, the axis of
regulating wheel is adjusted to an angle of 1 to 3° in the vertical plane depending
upon production and finish requirement and lapping wheel is generally adjusted to an
angle of 4° in the opposite direction. When the wheels are trued, they form a slight
hourglass shape, which causes a wrapper- round effect on the work pieces as it passes
between them. Also, wheels come in contact with the work piece at an angle to their
axes, which are different from axial line of contact of grinding wheel. This
arrangement eliminates lapping marks.
To obtain the fine finish of the order of 0.05 micrometer by centreless lapping,
the work piece requires three passes each with progressively finer lapping wheels.
Clean flow of coolant should be ensured through the operation.
During the first operation, a vitrified bond wheel of a 200P grad is used to
remove a maximum of 0.012mm of stock and surface finish of the order of 0.1 to 0.15

micrometer is obtained. For the second and third operations, the work piece is
supported on a rubber blade. During the second operation, to obtain a finish of 0.06 to
0.08 micrometer a maximum of 0.005 mm stock is removed, using resinoid bonded
wheel of C 320 T grade. For the third operation, resionoid bonded wheel of C 500 T
grade is used to remove less than 0.002 mm stock, which produces a finish of 0.05
micrometer.
3.2.5 LAPPING MACHINES FOR INTERNAL CYLINDRICAL
SURFACES
Lapping machine used for lapping internal cylindrical ssurfaces resemble honing
machines used for power stroking.
These machines reciprocate either the lap. Either solid or adjustable laps, in addition
to rotating the lap. Either the work piece or the lap, usually made of cast iron, is used.
Machines, which have one or two rotating spindles, such as drill presses or milling
machines, can be used for spindle against a stationary work piece. The work piece
axis. The lap itself must be heavy enough to provide the lapping pressure. When
machines with two spindles are used, the work piece is held in one spindle and
rotated, while the lap is held in the other spindle, which is free to rotate (fig. 05). The
spindle carrying the lap is including to the work spindle at a suitable angle. The axial
alignment must be accurate so as to generate a true radius. One of the spindles must
be so designed that it is free to slide to account for the wear of the lap and work piece,

and to apply the necessary pressure. The lap can be in the form of a ring with a
concave or convex rim.

4. LAPPING OF SLIP GAUGES
Lapping of slip gauges is carried out on special lapping machines after finish grinding the
gauge blocks to a reasonable accuracy in parallelism and thickness. with an allowance of
0.2 mm for lapping.
The lapping machine consists of two horizontal circular lapping plates of which the lower
one is fixed to the body of the machine whereas the upper one is supported freely from an
overhanging arm, which can be swung to one side so as to expose the gauge blocks.
When in use, the laps face each other and enclose between them a batch of 24 gauge
blocks, each resting freely en a circular hole in the steel plate, which acts as a guide. The
guide plate is toothed round its periphery and is driven by three pinions rigidly attached
to the ends of short cranks.
The lapping plates are held stationary while the gauges are carried round between them
by a rotary motion of the gauge plate. The guide plate is made to rotate about its axis,
while the gauges also move over a circular path. The ratio of the two circular motions is
such that the gauge blocks traverse different parts of the lapping plates at successive
revolutions distributing the wear uniformly.
The non magnetic cast iron plates with chequered working surfaces are machined and
scraped to a very high degree of flatness and then finished true by lapping together in sets
of three, taking them in consecutive pairs. During the truing operation they are charged
with a fine grade of emery, a small quantity of which is also added when lapping the
gauge blocks. Paraffin is used as lubricant.
In order to obtain a high degree of accuracy in parallelism and equality in thickness every
gauge block is transposed into a diametrically opposite position at integrals during the

lapping process. The lapping machine, which is driven electrically, can be set to perform
a given number of revolutions after which it stops automatically. A few gauge blocks arc
removed and measured and knowing the amount still to be removed, the machine is reset
to a further number of revolutions, after which the gauges are remeasured.

5. LAPPING FINISHES AND ACCURACIES:-
The dimensional accuracy, geometrical accuracy and finish that could be achieved by
various lapping process are given in table 01.
Property Dimensional Accuracy Geometrical accuracy Surface finish (CLA)
Method of
lapping
Very
fine
Fine Normal Very
fine
Fine Normal Very
fine
Nine Normal
External
cylindrical
IT I
To
IT3
To
IT5 0.05
To
0.1
To
0.6 To 0.025
To
0.05
To
O.I To
surface IT2 IT4 0.1 0.5 1.0 01 0.1 0.2
lapping.
Internal IT3 IT3 IT4 0.05 0.1 0.05 0.005 0.05 0.1
lapping. To To To To To To To
IT6 0.1 0.5 0.5 0.5 0.1 0.4
Flat IT1 IT3 IT4 0.03 0.05 0.6 0.005 0.05 0.1
Surface To To To To To To To To To
lapping. IT3 IT4 IT6 0.05 0.5 1.0 0.05 0.1 0.4
Table no. (01) Lapping accuracy and finish

6. LAP MATERIALS:-
The most efficient lap material for machine lapping is cast iron. Other materials, such
as soft steel, bronze, brass and lead are also used in manual lapping. Generally, the
material of the lap should be softer than the work piece material; so that the loose
abrasive material gets embedded in the lap until it is fractured from the pressure of the
lapping action.

7. LAPPING MEDIUM:-
Of the manufactured abrasives, silicon carbide and fused alumina are the most widely
used lapping media for the majority of lapping operations. Softer abrasives such as
emery, garnet, unfuscd alumina and chromium oxide are used for lapping soft metals
or for obtaining highly reflective surfaces without any significant material removal.
7.1 SILICON CARBIDE
Silicon carbide is extremely hard, being rated at 9.5 on the Moll's scale. Its grit is
sharp and brittle, making it idle as an abrasive for many lapping application. Because
it continuously breaks down and produces new cutting edges, silicon carbide is used
for lapping hardened steel or cast iron, particularly when an appreciable amount of
stock is to be removed.
7.2 ALUMINIUM OXIDE
Aluminum oxide rotted on the Moh's scale is sharp but it is tougher than silicon
carbide. Fused alumina is generally used to improve the finish in lapping soft still and
non-ferrous metals. Unfused alumina removes stock efficiently, but it is specially
suitable for obtaining extremely fine finishes.
7.3 BORON CARBIDE
Boron carbide is next to diamond in hardness (9.75 Moll's scale) and it an excellent
abrasive for lapping. However, it is used only in some specialized applications such
as lapping of dies, gauges, etc, owing to it's high cost.
7.4 DIAMOND
Diamond is hardest of all materials and it is used mainly for lapping tungsten carbide.

8 VEHICLES
Vehicles or binders used for loose abrasive include wide Varily of compound. The
commonly employed vehicles are water-soluble cutting oils, vegetable oils, mineral,
petroleum gully and grease. A good vehicle should have following properties:
 The abrasive particles should be held in uniform suspension during the operation.
 It should not evaporate easily.
 Temperature changes should not seriously affect the viscosity.
 It should be non-corrosive when in contact with any metal.
 The lapping compound made out of abrasive and vehicle must be capable of being
easily removed by normal cleaning method.
 It should be non-toxic.
Vehicles with an oils or grease based usually used for lapping ferrous metals. For
specific application, where oil or grease would be objectional, such as in copper based
alloys and other non-ferrous metals, water-soluble vehicles arc used. These vehicles,
which are readily removed with water, are low viscosity

9. LAPPING SPEEDS AND PRESSURES
The most efficient lapping speed range between 100 to 250 m/min. for fine lapping of
bores, with lapping allowances of 0,03 mm, a maximum lapping speed of 50 m/min is
recommended. With higher lapping allowances, higher lapping speed could be
employed. For lapping flat surfaces, the cutting speed can be as high as 250 m/min.
The amount of pressure applied depends upon the nature of abrasive used, the
material being lapped, and surface finish required. While lapping with loose
abrasives, the pressure ranges between 0.1 and 0.3 Kg/cm2
for soil materials including
not ferrous metals and alloys and upto 0.7 Kg/cm2
for hard materials. Excessive
pressures may cause scouring of workpiece surfaces. A uniform pressure during the
lapping operation provides the best result.

10. ALLOWANCES FOR LAPPING
Lapping allowances should not be high. The higher the allowances more will be time
for lapping. Lapping allowances are influenced by many factors, the most important
of them being the type of operation done on the part before lapping.
For example, if part has to be lapped after grinding normally 0.005 to 0.03 mm
allowance is left. Similarly, after milling, 0.1 to 0.2 mm and after broaching up to
0.03 mm allowances maintained.
Another factor to be taken into consideration is the hardness of the parts to be lapped.
Harder the material, lower should be lapping allowance.
Allowances recommended for different materials are given in table below.
Materrial Lapping allowance, mm
Cast iron 0.2
Aluminium alloy 0.1
Soft steel 0.01-0.02
Ductile steel 0.005-0.1
Hardened steel 0.005-0.02
Glass 0.03
Cemented carbide 0.03-0.05
Bronge 0.03
Table no. (02)
Recommended lapping allowance
11. Design
Power selection -
Lapping is low pressure abrading process which is material is employed as a precision
finish operation; rate of material removed from work piece is very minor (in microns). So
that power required for this operation is also low,

So we have selected here 1 H.P. motor.
11.1 Motor Specification-Three phase, induction type. Power-1 H.P.-746 W. R.P.M. -
1440 RPM.
11.2 Pullies Selection: -
In lapping machine the lapping will spits very from 175 m/min. to 650 m/min., where
as regulating wheel speed range between 70m/min to 175m/min. here motor rpm is
1440 reduction have been done to achieve required speed.
First step reduction we know
N1D1= N2D2
D1=Motor pulley, mm
= 3 inch = 76.2 mm
N1 = Motor rpm = 1440
1440x76.2=N2xl27

N2=864
N2 = Intermediate shaft speed
D2 = Intermediate shaft pulley mm
=5 inch = 127mm
Second step reduction
N2 = Intermediate Shaft speed
N2D2=N3D3 D2 = Intermediate Shaft pulley
864x76.2=N3xl52.4 = 3 inch = 76.2 mm.
N3=432
N3 = Lapping wheel &
regulating wheel space

Now check for speed ranges where
For lapping wheel V = Lapping wheel speed, in m/min
D = Diameter of Lapping wheel
V= πd n = 150 mm
= 0.15m
= π x 0.15x432
=- 203.5m/min n = Lapping wheel speed in rpm
= 432rpm
(Lapping wheel speed ranges from 175m/min to 650m/min)
For regulating wheel
V=πdn Where
= π x0.75x432 d = Diameter of regulating wheel
= 101.78m/min = 75mm=0.075m

11.3 Calculation for length of belt:-
First step:-
We know,
L=2C + (π/2) (D+d) + {(D-d)2
/4C}
Where
C= Centre distance = 250mm
D = Diameter of large pulley
= 5 inch = 127 mm
d = Diameter of small pulley
= 3 inch = 76.2 mm
L = Pitch length

Second step:-
1) Lapping wheel:-
L = 2C + {π/2} {D+d} + {(D-d)2
/ 4C}
= 3 x 345+(π/2) (152.4+76.2) + {(152.4-76.2)2
/4x345}
= 1053.29mm
= 1017.29 mm
= 40 inch.
So we have selected belt A40/1016

2) For regulating wheel:-
L = 2C + (π/2) (D+d) {(D-d)2
/4C}
= 3 x 345+(π/2) (152.4+76.2) + {(152.4-76.2)2
/4x345}
= 1053.29mm
= 1017.29 mm
= 40 inch.
So we have selected belt A40/1016
1.4 Calculation for belt tension:-
1) For first step:-

We know that for V belt
T1/T2=
еδα/sinθ/2
………………………………(A)
Where T1 = tension in tight side in N
T2 = tension in slack side N
δ = coefficient of friction = 0.3
α = Wedge angle = 400
α = 180 – 2 sin–1
{(D-d)/2C
= 180 – 2 sin-1
{(127-76.2)/2x265}
= 30
Putting this values in equation (A)
T1/T2 = е
(0.3X2.938)/sin (40/2)
T1/T2 = 13.893
T1 = 13.893 T2…………………………….(1)
Also
Power = (T1- t2) x V
Where
V = Linear speed, m/sec
= πdn/60 = (πx0.0762x1440)/60
= 5.745m/sec
373 = (T1-T2) x 5.745
T1 – T2 = 64.926 ……………………………..(2)

Solving equation (1) & (2) we get
T1 = 69.95 = 70N
T2 5.35 = 6n
2) For second step
For lapping wheel
For V belt
T1/T2 = еδα/sin(θ/2)
α = 180 – 2sin-1
{(D-d)/2C}
= 180 – 2 SIN-1
{(152.4-76.2)/2x345}
= 167.3190
= 2.92 rad.
T1/T2=е
(0.3x2.938)/sin(40/2)
T1=12.952…………………………….(1)

Also power = (T1-T2) x V
Where V = πd n/60 = 3.447m/sec
373 = (T1-T2) x 3.447
T1-T2 = 108.21 ……………………….(2)
Solving equations (1) & (2) we get
T1 = 117.26 =118N
T2 = 9.053 = 9n
For regulating wheel:-
For “V” belt
T1/T2 = еfα/sin(θ/2)
α = 180 – 2sin-1
{(D-d)/2C}
= 180 – 2 SIN-1
{(152.4-76.2)/2x345}
= 167.3190
= 2.92 rad.

T1/T2= е
(0.3x2.92)/0.342
T1 = 12.952 T2 …………………………..(1)
Also
Power = (T1-T2) x V (V=(πdn)/60) = 3.447
373 = (T1-T2) x 3.447
T1-T2 = 108.21 ……………………………..(2)
Solving equation (1) & (2) we get
T1 = 117.26 = 118 N
T2 = 9.053 = 9 N
11.5 Shaft design :-
11.5.1Intermediate shaft :-
Here shall goes into twisting and bending.

According to A.S.M,E code, The permissible shear stress for shaft with out key way
is taken as 30% of the yield strength in tension or 18% of the ultimate tensile strength
of material, which ever is minimum.
ζd=0.3Syt
ζd = 0.18 (whichever is minimum)
For twisting and bending
ζd = (16/7πd3
)/((Kbmb)2
+(Kt.mt)2
...............,...(A)
Where
Kb = combined shock and fatigue factor to bending moment =1.5
Kt = combined shock and fatigue factor to torsion moment = 1
Shaft made of plain carbon steel 55C8
(Sut = 720 N/mm2
and Syt - 460 N/mm2
)
ζd = 0.3xSyt
= 0.3 x460 -138 N/mm2
ζd = 0.18xSut
= 0.18 x 720
= 129.6 N/mm2
The lower of two is 129.6 N/mm2
Therefore
ζd = 129.6 N/mm2
Calculation for bending and torsional moment: -
a) Bending moment: -

Taking moment about A
174 RB- 76 x 227- 127x 53 - 127 x 98 = 0
RB = 209.362 N
ΣMB = 0
-127 x 272 - 127 x 227 - 174 x RA - 76 x 53 = 0
RB = 387.362 N
ΣMB = 127 x 45 = 5715 N mm
ΣMB = -127x98 -127x53
= 19177 N mm.
= - 76 x 53 - 4028 N mm.
Maximum bending moment occurs at A, that is 19177 N mm.
For torsional moment
Power = (2πNT)/60
373 = (2π x 864 x T)/60
T = 4.122Nm
T = 4122.55 N mm.
Putting all the values in the equation (A).
ζd = 16/(πd3
) / {(Kbmb)2
+ (Ktmt)2
}
129.6= 16/(πd3
) / {(1.5 x 19177)2
+ (1 x 4122.55)2
d= 10.45mm.
So we selected the diameter for intermediate shaft d - 16 mm.

11.5.2 Shaft design form lapping wheel:-
The procedure is same as we followed. Lapping wheel shaft is also made of plain carbon
55C8 (Sut = 760 N/mm2
& Syt = 460 N/mm2
).
Permissible shear stress (ζd) = 0.75 x 129.6
= 97.2 N/mm2
Calculation for bending moment and torsional moment:-
Bending moment:-

Taking moment about “A”.
127 x 98 + 224 x RB = 0
RB = -55.562 N.
Taking ∑MB = 0
127 x 322 – 224 x RA = 0
RA = 182.562 N.
Maximum bending moment occurs at “A”.
MA = 127 x 98 = 12446 N mm.
Torsional moment:-
Power P - (2πN T)/60
373 - (2π x 432 x T)/60
T = 8.245110 Nm.
T = 8245.11N mm.
Putting all these values I the equation given below.
ζd = 16/(πd3
) /{(Kbmb)2
+ (Ktmt)2
}
97.2 = (16/πd3
) x / {(1.5xl2446)2
+ (l x 8245.11)2
}
d = 10.22mm.
We have selected diameter for lapping wheel shaft is 16 mm.
11.5.3 Shaft design for regulating wheel shaft:-

Here shaft is made of 55C8.
Therefore ζd = 97.2 N/mm2
.

Calculation for bending moment and torsional moment:-
Bending moment: -
Taking ΣMA - 0
224 RB+ 127 x 53 = 0
RB = 30.044 N.
Taking ΣMB = 0
127x277.224 x RA -0
RA = 157.049 N.
Maximum bending moment occurs at "A" =127 x 53 = 6731 N mm.
Putting all these values in the equation given below.
ζd = 16/ (πd3
) /{(Kbmb)2
+ (Ktmt)2
97.2 = (16/πd3
) x /{(1.5 x 6331)2
+ (1 x 8245.11)2
}
d = 8.8mm.
We have selected diameter for regulating wheel shaft that is "d"= 18 mm.

Lapping Machine
11.6 Bearing selection: -
We know that L = (60 x n x Lh)/106
Where
L = bearing life in million revolution.
Lh = bearing life in hours = 15000.
N = revolution per minute.
L = (60x864xl5000)/106
L = 777.6 million revolution.
AlsoC-Lpl/3 .
Where
C = dynamic load capacity
C = 777.6 x 412.5l/3
C = 5788.47 N.
So we have selected bearing 6004. Dynamic load capacity is 7350 N.
Inner diameter = 20 mm.
Outer diameter = 42 mm.
B = 20.

12.1 Process chart
Part name: - Lapping wheel shaft. Material: - Plain carbon steel
Quantity: - 01 Raw material size:-φ25x325L
Sr. No. Operation Machined used Tool used Time
(Min)
01 Cutting to the length
(325 mm.).
Power hacksaw. — 15
02 Setting, facing & Centre
drilling. (Both side).
Lathe machine. Single point
cutting tool &
centre drill.
30
03 Holding the job between
centre & turning for φ23
mm &φ20 mm up to
length 4 mm & 1 6 mm
respectively, as per
Drawing (both side).
cutting tool.
40
04 Grooving. Lathe machine Parting tool. 20
05 Turning of φ18 & φ16
up to length 45 mm
respectively.
cutting tool.
25

2.2 Process chart
Part name: - Regulating wheel shaft Material: - Plain carbon steel
Quantity: - 01 raw material size:-φ25 X 285 L

Sr. No. Operation Machine used Tool used Time
(Min)
01 Cutting to the length 285
mm.
Power hacksaw. — 15
02 Setting, facing & centre
drilling (both side).
cutting tool.
30
03 Holding job between
centres & turning for φ23
& φ20 mm up to length 4
mm & 1 6 mm
respectively.
cutting tool.
40
04 Grooving for circle. Lathe machine. Parting tool. 20
05 Turning for φ1 8 up to
length 45 mm.
cutting tool
20

12.3 Process chart
Part name: -Intermediate shaft Material:- Plain carbon steel
Quantity:- 01 Raw material size:- 25x325L
Sr.No. Operation Machine used Tool Used Time
(Min)
01 Cutting to the length 325
mm.
Power hacksaw 15

02 Turning for 23 mm &
20 mm upto 4 mm &
16 mm respectively.
Lathe machine Single point
cutting tool.
30
03 Grooving for circle as
per drawing.
Lathe machine. Parting tool. 20
04 Turning for 1 8 mm
upto length 45 mm.
cutting tool.
15
05 Turning for 1 8 and
1 6 mm upto 45 mm
respectively.
cutting tool.
20

12.4 Process chart
Part name: - Bearing holder
Quantity: - 06
Material: - Mild steel.
Raw material size; - 20x50x70
(Min)
01 Cutting to the length
70mm
Power hacksaw — __
02 Marking for drilling
through out.
— Markers, scale,
punch &
hammer etc.
10
03 Drilling for 36 mm,
through out.
Lathe machine. Boring tool. 20
04 Boring of 42 mm & 
36 mm upto length 1 6
mm & 4 mm
respectively.
05 Chamfering. Lathe machine. Single point
cutting tool.
10

12.5 Process chart
Part name: - lapping wheel Quantity: - 01
material; - Mild steel niw material size: - φ153 x 200 mm (pipe)
(Min)
01 Cutting to the size 200
mm.
Gas cutting. 15
02 Setting, facing both
sides.
cutting tool.
20
03 Boring φ147 mm up to
length 6mm as per
drawing (both side).
04 Chamfering (3x3) both
sides.
cutting tool.
15

12.6 Process chart
Part name: - regulating wheel. Material: - mild steel
Quantity: - 01 raw material size: - φ88 x 180 (pipe)
Sr.No. Operation Machine used Tool used Time
(Min)
01 Cutting to the size 180
mm.
Gas cutting. 15
02 Setting, facing both sides. Lathe machine. Lathe machine. 25
03 Boring φ82 mm up to
length 5 mm both sides as
per drawing.
04 Chamfering (3x3) both
sides.
cutting tool.
15

13. COST SHEET
Sr. No. Name of
component
Material Quantit
y
Dimentions
(mm)
Weight (gm) Rate of raw
material
Machining cost Rs. Total cost Rs. Machine used
Lapping wheel C.1 01 φ153x200 3500 175 150 Lathe
02
A1
"*
Regulating
wheel
C.I 01 φ88x200
φ152.4
1900 95 140 Lathe
0.5 Pulley MS 06 φ127 ---- ---
φ76.2
φ30
04 Intermediate
shaft
Plain carbon 01 φ25x325L 2600 156 120 Lathe
steel

Sr.
No.
Name of
component
Material Quantity Dimentions (mm) Weight
(gm)
Rate of
raw
material
Machining
cost Rs.
Total Cost Rs. Machine used
04
05
Bearings
Bearing
holder
M.S
M.S
04
04
φ42 x 20
φ42
900
1100
56 240 ---- -----
Lathe
06
07
Frame
Belt
C.I
Rubb
er
01
03
500x400x850
40A 36A
8500 425 400 Welding m/c
08
09
Motor
Miscell
aneous
_____

14. CONCLUSION
A lathe machine alter turning a cylindrical purl finishes ihe job, hut this finish is not
super finish. So to obtain the super finish part Ihc lapping machine is introduced. This
lapping machine gives the superfmish in micro meter scale. The plug gauges, m in micro
meter scale. The plug gauges, measuring wires, various tools can also be superfmish with
the help of lapping machine.

TECHNICAL SPECIFICATIONS
ELECTRIC MOTOR:-
3-PHASE INDUCTION TYPE
POWER 1-H.P = 746 W
SPEED = 1440 R.P.M.

15. REFERENCES
 Production Technology By H.M.T.
 Production technology By R.K.Jain
 www.google.com
 www.howstuffworks.com

Precision surface finishing techniques

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