ENM202
ANADOLU U N I V E R S I T Y
Industrial Engineering Department
Lecture 3 – Dimensions, Tolerances and Surfaces
Spring 2007
Saleh AMAITIK
Manufacturing Processes
Affected Areas
Tolerance & Surfaces
Product Design
Quality Control
Manufacturing
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Manufacturing Processes
Dimensions, Tolerances and Surfaces
In addition to mechanical and physical properties, other
factors that determine the performance of a
manufactured product include:
Dimensions - linear or angular sizes of a component specified on
the part drawing.
Tolerances - allowable variations from the specified part
dimensions that are permitted in manufacturing.
Surfaces - surface finishes obtained by manufacturing process that
produce the shape
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Manufacturing Processes
Dimensions
A dimension is "a numerical value expressed in
appropriate units of measure and indicated on a
drawing and in other documents along with lines,
symbols, and notes to define the size or geometric
characteristic, or both, of a part or part feature"
Dimensions on part drawings represent nominal or
basic sizes of the part and its features.
The dimension indicates the part size desired by the
designer, if the part could be made with no errors or
variations in the manufacturing process
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Manufacturing Processes
Tolerances
A tolerance is "the total amount by which a specific
dimension is permitted to vary. The tolerance is the
difference between the maximum and minimum limits"
Variations occur in any manufacturing process, which
are manifested as variations in part size
Tolerances are used to define the limits of the allowed variation
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Manufacturing Processes
Why is tolerancing necessary?
It is impossible to manufacture a part to an exact size
or geometry
Assemblies: Parts will often not fit together if their
dimensions do not fall within a certain range of values
Tolerances are needed to control the dimensions of any
two mating parts so that any two parts may be
interchangeable.
Tolerances on parts contribute to the expense of a part,
The smaller the tolerance the more expensive the part
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Manufacturing Processes
Types of Tolerances
A Dimensional tolerance is the total amount a specific
dimension is permitted to vary, which is the difference
between maximum and minimum permitted limits of size.
A Geometric tolerance is the maximum or minimum
variation from true geometric form or position that may
be permitted in manufacture.
Geometric tolerance should be employed only for those
requirements of a part critical to its functioning or
interchangeability.
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Manufacturing Processes
How Is Tolerance Specified?
Tolerances can be expressed in Several ways:
General Tolerances
A note may be placed on the drawing which specifies the tolerance
for all dimensions except where individually specified
ALL DECIMAL DIMENSIONS TO BE HELD TO ±0.020
Specific Tolerances
The tolerance for a single dimension may be specified with the
dimension based on one of the following methods
• Limits
• Unilateral tolerance
• Bilateral tolerance
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Manufacturing Processes
Specific Tolerances
Limit Dimensions
Permissible variation in a part feature size, consisting of the
maximum and minimum dimensions allowed
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Specific Tolerances
Unilateral Tolerance
Variation from the specified dimension is permitted in only one direction,
either positive or negative, but not both.
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Specific Tolerances
Bilateral Tolerance
Variation is permitted in both positive and negative directions from
the nominal dimension.
It is possible for a bilateral tolerance to be unbalanced; for example,
2.500 +0.010, -0.005
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Manufacturing Processes
Dimensional Tolerances (Size)
Angular size dimension tolerance
It specifies the allowable variation on the
size or gap formed by two angular
elements of the shape.
Curved dimension tolerance
It is a tolerance on a dimension for a curved
feature element measured along the entire
path of the curve
Diameter dimension tolerance
It is the allowable variation of the size of a
hole in a feature.
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Manufacturing Processes
Dimensional Tolerances (Size)
Radial dimension tolerance
It is the allowable variation for the radial distance
from the center of a feature circular curve to a
point on the curve.
Location dimension tolerance
It is the allowable variation in locating one
feature of a point with respect to another.
Angular dimension tolerance
It defines the allowable variation in the angle
between two elements of a feature.
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Manufacturing Processes
Geometrical Tolerances (Form)
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Geometrical Tolerances (Form)
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Geometrical Tolerances (Form)
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Geometrical Tolerances (Form)
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Geometrical Tolerances (Location)
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Geometrical Tolerances (Location)
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Geometrical Tolerances (Orientation)
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Geometrical Tolerances (Orientation)
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Geometrical Tolerances (Orientation)
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Geometrical Tolerances (Orientation)
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Geometrical Tolerances (Orientation)
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Tolerance Grades
The tolerance of size is normally defined as the
difference between th upper and lower dimensions.
ISO 286 implements 20 grades of accuracy to satisfy the
requirements of different industries.
Production of gauges and instruments.
IT01, IT0, IT1, IT2, IT3, IT4, IT5, IT6.
Precision and general Industry.
IT 5, IT6, IT7, IT8, I9, IT10, IT11, IT12.
Semi finished products
IT11, IT14, IT15, IT16.
Structural Engineering
IT16, IT17, IT18 .
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Manufacturing Processes
ISO Tolerance Band "T "micrometres = (m-6) based on ISO 286 IT Grades 1 to 14
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Fits between Mating Parts
Fit is the general term used to signify the range of
Looseness and Tightness
of mating parts
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Important Terms
Nominal size: a dimension used to describe the general size.
Basic size: the theoretical size used as a starting point for the
application of tolerances.
Actual size: the measured size of the finished part after machining.
Limits: the maximum and minimum sizes shown by the toleranced
dimension
Allowances: the minimum clearance or maximum interference
between parts, or the tightest fit between two mating parts.
Tolerance (Tolerance zone): the total allowable variation in a
dimension; the difference between the upper and lower limits
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Manufacturing Processes
Tolerancing Holes and Shafts
Preferred fits: A specified system of fits for
holes and shafts for SI units
- Hole basis
•The minimum hole size equals
the basic hole size
• Uses the symbol “H” in the
tolerance specification
- Shaft basis
•The maximum shaft size equals
the basic shaft size
•Uses the symbol “h” in the
tolerance specification
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Manufacturing Processes
Fits Types
The most common types of fit found in industry
Clearance Fit occurs when two toleranced mating
parts will always leave a space or clearance when
assembled.
Interference Fit occurs when two toleranced mating
parts will always interfere when assembled.
Transition Fit occurs when two toleranced mating
parts are sometimes an interference fit and
sometimes a clearance fit when assembled.
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Manufacturing Processes
Clearance and Interference fits between two Shafts and a Hole
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Manufacturing Processes
Transition fit between a Shaft and a Hole
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Fit Type Determination
If feature A of one part is to be inserted into or mated with feature B
of another part, the type of fit can be determined by the following:
The
Loosest
difference
Fit
is
between
the
the
smallest feature A and the
largest feature B.
The
Tightest
difference
Fit
is
between
the
the
largest feature A and the
smallest feature B.
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Manufacturing Processes
ISO Tolerances for Holes (ISO 286-2)
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ISO Tolerances for Shafts (ISO 286-2)
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Recommended Fits
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Tolerances and Manufacturing Processes
Some manufacturing processes are more accurate than
others
Examples:
– Most machining processes are quite accurate,
capable of tolerances = 0.05 mm or better
– Sand castings are generally inaccurate, and tolerances
of 10 to 20 times those used for machined parts must
be specified
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Manufacturing Processes
Manufacturing Processes associated with ISO IT Tolerance Grade
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Manufacturing Processes
Metric Symbols of Fits
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Manufacturing Processes
Creating a Clearance Fit using The Basic Hole System
Given the following fit
Φ40 – H11/c11
From table for hole diameter = 40 and H11 we find
Upper deviation = +160 μm
&
Lower deviation = 0
From table for shaft diameter = 40 and c11 we find
Upper deviation = -120 μm & Lower deviation = -280 μm
Calculations of dimension limits for hole and shaft
- Maximum hole diameter = 40 + 0.16 = 40.16 mm
- Minimum hole diameter = 40 + 0 = 40 mm
- Maximum shaft diameter = 40 +(-120) = 39.88 mm
- Minimum shaft diameter = 40 + (-280) = 39.72 mm
Maximum clearance = Maximum hole diameter – Minimum shaft diameter
= 40.16 – 39.72 = 0.44 mm
Minimum clearance = Minimum hole diameter – Maximum shaft diameter
= 40 – 39.88 = 0.12 mm
Allowances = minimum clearance = 0.12 mm = 120 μm
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Manufacturing Processes
Creating an Interference Fit using The Basic Hole System
Given the following fit
Φ40 – H7/s6
From table for hole diameter = 40 and H7 we find
Upper deviation = +25 μm
&
Lower deviation = 0
From table for shaft diameter = 40 and s6 we find
Upper deviation = +59 μm
& Lower deviation = +43 μm
Calculations of dimension limits for hole and shaft
- Maximum hole diameter = 40 + 0.025 = 40.025 mm
- Minimum hole diameter = 40 + 0 = 40 mm
- Maximum shaft diameter = 40 + 0.059 = 40.059 mm
- Minimum shaft diameter = 40 + 0.043 = 40.043 mm
Maximum interference = Maximum shaft diameter – Minimum hole diameter
= 40.059 – 40 = 0.059 mm
Minimum interference = Minimum shaft diameter – Maximum hole diameter
= 40.043– 40.025 = 0.018 mm
Allowances = maximum interference = 0.059 mm = 59 μm
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Manufacturing Processes
Surfaces
Nominal surface - intended surface contour of
part, defined by lines in the engineering drawing
– The nominal surfaces appear as absolutely straight
lines, ideal circles, round holes, and other edges and
surfaces that are geometrically perfect
Actual surfaces of a part are determined by the
manufacturing processes used to make it
– The variety of manufacturing processes result in wide
variations in surface characteristics
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Manufacturing Processes
Why Surfaces are important
• Aesthetic reasons.
• Surfaces affect safety.
• Friction and wear depend on surface characteristics.
• Surfaces affect mechanical and physical properties.
• Assembly of parts is affected by their surfaces.
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Manufacturing Processes
Surface Technology
Concerned with:
– Defining the characteristics of a surface
– Surface texture
– Surface integrity
– Relationship between manufacturing
processes and characteristics of
resulting surface
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A magnified cross-section of a typical metallic part surface
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Manufacturing Processes
Surface Texture
The topography and geometric features of the surface
When highly magnified, the surface is anything but
straight and smooth. It has roughness, waviness, and
flaws
It also possesses a pattern and/or direction resulting
from the mechanical process that produced it
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Manufacturing Processes
Surface Integrity
Concerned with the definition, specification, and control of the
surface layers of a material (most commonly metals) in
manufacturing and subsequent performance in service.
Manufacturing processes involve energy which alters the part
surface.
The altered layer may result from work hardening (mechanical
energy), or heating (thermal energy), chemical treatment, or even
electrical energy
Surface integrity includes surface texture as well as the altered
layer beneath
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Manufacturing Processes
Four elements of surface texture
1. Roughness - small, finely-spaced deviations from nominal surface
determined by material characteristics and process that formed the
surface
2. Waviness - deviations of much larger spacing; they occur due to
work deflection, vibration, heat treatment, and similar factors
– Roughness is superimposed on waviness
3. Lay - predominant direction or
pattern of the surface texture
4. Flaws - irregularities that occur on
the surface
– Includes cracks, scratches,
inclusions, and similar defects in
the surface.
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Manufacturing Processes
Surface Roughness and Surface Finish
• Surface roughness - a measurable characteristic
based on roughness deviations
• Surface finish - a more subjective term denoting
smoothness and general quality of a surface
• In popular usage, surface finish is often used as a
synonym for surface roughness
• Both terms are within the scope of surface texture
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Manufacturing Processes
Surface Roughness
Average of vertical deviations from nominal surface over a specified
surface length
Surface roughness can be approximately calculated using the following equation
n y
i
Ra 
where
i 1 n
Ra = average roughness;

yi = vertical deviations (absolute value) identified by subscript i; and
n = number of deviations included in Lm
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Surface Integrity
• Surface texture alone does not completely describe a
surface
• There may be metallurgical changes in the altered
layer beneath the surface that can have a significant
effect on a material's mechanical properties
• Surface integrity is the study and control of this
subsurface layer and the changes in it that occur
during processing which may influence the
performance of the finished part or product
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Surface and Manufacturing Processes
• Some processes are inherently capable of
producing better surfaces than others
– In general, processing cost increases with
improvement in surface finish because
additional operations and more time are
usually required to obtain increasingly better
surfaces
– Processes noted for providing superior
finishes include honing, polishing, and
superfinishing
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Surface Roughness Produced by common Manufacturing Processes
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Surface Roughness and Production Cost
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Surface Roughness and Production Time
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Metrology
Science of physical measurement applied to variables
such as dimensions, surface finish, and mechanical and
physical properties.
Measurements require Precision and Accuracy.
Precision is the degree which the instrument gives
repeated measurements of the same standard.
Accuracy is the degree of agreement of the measured
dimension with its true magnitude.
Sensitivity is the smallest difference in dimensions
that the instrument can detect or distinguish.
Stability – The instrument’s capability to maintain its
calibration over a period of time
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