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Introduction
Types of surfacesNomenclature of surface texture
Surface roughness value
Machining symbolsRoughness grades and symbols
Surface roughness indication
Direction of lay
Roughness symbol on drawing
Surface roughness for various
machining processes
SURFACE QUALITY & MACHINIG SYMBOLS
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Engineering components are manufactured by
casting, forging, welding etc These components are then subjected to various
machining operations for getting required
geometrical surfaces
It is not practically possible to produce a
component having a geometrically ideal surface
The surface finish after machining depends upon
the material, vibration, deflection, speed, feed
and other working conditions
The surface finish requirements depend upon the
functional requirements of the components to be
assembled
INTRODUCTION
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For high class of accuracy, surface finish
requirements are high and hence it is moreexpensive
Surface quality or surface texture or surface
finish is the amount of geometric irregularity
produced on the surface
Surface texture notes on a drawing refer the
required finish that must be machined on any
particular surface
INTRODUCTION
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Surface of a body is its boundary which
separates it from another body.
Surface may be;
(i) Normal surface (ii) Rough surface
(iii) Wavy surface and
(iv) Wavy surface roughness superimposed
TYPES OF SUFRACES
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(1) Profile: It is the contour of a surface in a plane
which is perpendicular to the surface itself.
(2) Surface roughness: It is the micro irregularities
in a surface resulting from the action of
production process. It is also called primary
texture roughness.
NOMENCLATURE OF SURFACE TEXTURE
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(3)Roughness height: It is the arithmetic average
of the roughness deviation and is measured in
micrometers
(4)Roughness width: It is the distance parallel to
nominal surface between the adjacent peaks or
ridges which constitute the predominant pattern
of the roughness
NOMENCLATURE OF SURFACE TEXTURE
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(5)Roughness-width cut off: It is a particular length of
the profile decided to evaluate the arithmetic
average deviation. It is also calledsampling length
It is the greatest spacing of repetitive surface
irregularities to be included in the measurement of
average roughness height It must be greater than roughness width
It may be taken as 0.8mm if not specified
NOMENCLATURE OF SURFACE TEXTURE
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(6) Waviness: It is the irregularities in a surface
having wider spacing than the roughness-width
cut off resulting from machine deflection,
vibrations, heat treatment, warping etc
(7) Waviness height: It is the distance from the
peak to the valley of the wave and is measured
in millimetres
NOMENCLATURE OF SURFACE TEXTURE
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(8)Waviness width: It is the distance between the
adjacent peak or valley of the wave and is
measured in milimetres.
(9) Lay: It is the predominant direction of tool that
makes the surface pattern on the machined
surface.
NOMENCLATURE OF SURFACE TEXTURE
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(10) Flaw: It is an irregularity that occurs in a
surface due to cracks, blow holes, ridges,
scratches etc
There are no finish symbols for flaws
Special note should be included on the drawing
where no flaw is permitted
NOMENCLATURE OF SURFACE TEXTURE
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SURFACE ROUGHNESS VALUE
Figure shows hypothetical profile of a surface
Centre line is a line about which the roughness
is measured
The roughness may be calculated by;
(1) Centre Line Average (C.L.A.) method and
(2) Root Mean Square (R.M.S.) method
In both methods, surface roughness is measured
as average deviation from the nominal surface
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SURFACE ROUGHNESS VALUE
In Centre Line Average (C.L.A.) method;
Centre Line Averagey1+y2+y3+.+yn
n= In Root Mean Square(R.M.S.) method;
Root Mean Square =n
y
2
n
2
3
2
2
2
As per BIS, the surface roughness is assessed interms of C.L.A. value and is denoted by Ra
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The quality of surface texture is indicated by
certain symbols on technical drawings
The basic symbol consists of two unequal legs at
600 included angle to the line representing the
surface under consideration with vertex touching
as shown in figure. Here,
MACHINIG SYMBOLS
a = Surface may be produced by any method
b = Removal of material is not permitted
c = Removal of material by machining
d = If special surface characteristic is to be indicated
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The principal criterion of surface roughness, Ra
may be indicated by the corresponding
roughness grade number, as shown in Table
ROUGHNESS GRADES & SYMBOLS
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The value or values defining the principal
criterion of roughness are added to the symbol as
shown in figure
SURFACE ROUGHNESS INDICATION
a = Roughness value, Rain micrometres
b = Production method/ treatment of coatingc = Sampling length
d = Direction of lay
a
b
de
(f)
e = Machining allowance and
f = Other roughness values
= Roughness limits or grade numbers N1to N12
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DIRECTION OF LAYThe direction of lay is the direction of the
predominant surface pattern ordinarily determined
by the production method and is shown in table.
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DIRECTION OF LAY
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INDICATION OF ROUGHNESS SYMBOLSON DRAWING
The symbols should be oriented such that they
may be read from the bottom or the right handside of drawing Figure (a)
If it is not practicable to adopt this general rule,
the symbol may be drawn in any position provided
that it does not carry any indications of special
surface texture characteristics as in Figure (b).
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INDICATION OF ROUGHNESS SYMBOLSON DRAWING
The symbol may be connected to the surface by a
leader line, terminating in an arrow.The symbol or the arrow should point from outside
the material of the piece, either to the line
representing the surface, or to an extension of it
as shown in Figure (a)
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INDICATION OF ROUGHNESS SYMBOLSON DRAWING
In accordance with the general principles of
dimensioning, the symbol is only used once for agiven surface and, if possible, on the view which
carries the dimension, defining the size or position
of the surface.
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INDICATION OF ROUGHNESS SYMBOLSON DRAWING
If the same surface roughness is required on majority
of the surfaces of a part, it is specified with the
addition of the notation, except where otherwise stated
(Figure a), or a basic symbol (in brackets) without any
other indication (Figure b), or the symbol or symbols
(in brackets) of the special surface roughness or
roughnesses (Figure c).
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INDICATION OF ROUGHNESS SYMBOLSON DRAWING
To avoid the necessity of repeating a complicated
specification a number of times, or where space is
limited, a simplified specification may be used on the
surface, provided that its meaning is explained near
the drawing of the part, near the title block or in the
space devoted to general notes.
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SURFACE ROUGHNESS FOR VARIOUSMACHINING PROCESSES
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SURFACE ROUGHNESS FOR VARIOUSMACHINING PROCESSES
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SURFACE ROUGHNESS FOR VARIOUSMACHINING PROCESSES
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SURFACE QUALITY
MACHINING SYMBOLS
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