Double dimensioning is also not acceptable.

Spotface
Not to scale
Parallel Dimensioning

Simplified Parallel Dimensioning

Chain dimensioning
Staggered Dimensioning

Dimension lines Omitted

 Rule: British Standard 308

1. Dimension and projection lines are narrow continuous lines 0.35 mm thick, if
possible, clearly placed outside the outline of the drawing. NB: Outline is 0.7mm

2. The projection lines should not touch the drawing but a small gap should be left,
about 2 to 3 mm, depending on the size of the drawing.

3. Arrowheads should be approximately triangular, must be of uniform size and

shape and in every case touch the dimension line to which they refer.
Arrowheads drawn manually should be filled in. Arrowheads drawn by machine need
not be filled in.

4. adequate space must be left between rows of dimensions and a spacing of about
12 mm is recommended. (Bearing in mind the size of the actual dimensions and the
fact that there may be two numbers together where limits of size are quoted)
5. Centre lines must never be used as dimension lines but must be left clear and
distinct. They can be extended, however, when used in the role of projection lines.

6. Dimensions are quoted in millimeters to the minimum number of significant

figures. For example, 19 and not 19.0.

7. To enable dimensions to be read clearly, figures are placed so that they can be read
from the bottom of the drawing, or by turning the drawing in a clockwise direction, so
that they can be read from the right hand side.

8. Leader lines are used to indicate where specific indications apply. The leader line to
the hole is directed towards the centre point but terminates at the circumference in
an arrow. A leader line for a part number terminates in a dot within the outline of the
component
Dimensioning for manufacture
These symbols are used to communicate the surface
texture and manufacturing process to be used on the
part.

Only positions a, b, c, d and e should be

used. Position ‘a’ indicates one single surface texture
requirement. Positions ‘a’ and ‘b’ indicate two or more
surface texture requirements. Position ‘c’ indicates
manufacturing method, treatment, coating or other
process. Position ‘d’ indicates surface lay. Position ‘e’
shows machining allowance
When the same surface texture is required on
every surface around a work piece, then a small
circle is added to the symbol

Material shall be removed

Same surface
texture

Material shall not be

removed
• The R profile series relates to roughness parameters.
• The W profile series relates to waviness parameters.
• The P profile series relates to structure parameters
MACHINIG PROCESS AND THEIR Ra VALUES

Sl. Machining Process Ra

No. (in microns)
1 Drilling 6.3 – 25
2 Planing/ shaping 1.6 – 12.5
3 Turning 1.6 – 6.3
4 Boring 1.6 – 6.3
5 Reaming 0.8 – 6.
6 Cyclic grinding 0.4 – 3.2
7 Surface grinding 0.4 – 3.2
8 Lapping 0.05 – 0.4
What machining process should be adopted to each step of the
following components. Also give step drawing details ?

(a)
Tolerance, Limits and
Fits
 SYSTEM OF FITS AND TOLERANCES

The standard reference temperature is 20 C for industrial

measurements
and, consequently, for dimensions defined by the system.

Due to the inevitable inaccuracy of manufacturing methods, a part

cannot be made precisely to a given dimension, the difference
between maximum and minimum limits of size is the tolerance.

When two parts are to be assembled, the relation resulting from the
difference between their sizes before assembly is called a fit.
 SYSTEM OF FITS

HOLE BASIS SYSTEM: the hole is constant in diameter and various types
of fits are obtained by suitably varying the limits of the shaft.

SHAFT BASIS SYSTEM: the shaft is constant in diameter and various types
of fits are obtained by suitably varying the limits of the hole.
 LIMITS

Actual machine size - between the maximum and minimum limits

MAXIMUM LIMIT
Maximum permissible machine size corresponding to basic size.
Ø 30 mm is = Ø 30 + 0.035 = Ø 30. 035 mm.

Basic size Maximum limit

MINIMUM LIMIT

Minimum allowable machine size corresponding to basic size.

In Fig. 1.1, Ø 30 mm is = Ø 30 - 0.215 = Ø 29. 785 mm.

Minimum limit
Basic size
TOLERANCE

The difference between the maximum and minimum limits of a size is tolerance.

In Fig. 1.1 the tolerance is = Ø 30.035 - Ø 29.785 = 0.25m.

Max. limit Min. limit

Tolerance

DEVIATION

(Actual, or maximum, or minimum) – (Basic size).

UPPER DEVIATION - (Maximum limit) – (Basic size)

LOWER DEVIATION - (Minimum limit) – (Basic size)

ACTUAL DEVIATION - (Actual measured size) – (Basic size)

TOLERANCE ZONE
The zone bounded by the upper and lower limits of the basic
size.

ZERO LINE
 A straight line drawn for the basic size is called zero
line.

 Upper and lower deviation are referred to zero line.


 Zero line is drawn horizontally.

 Above zero line - positive deviations.
 Below zero line - negative deviations.
CLASSIFICATI
ON OF FITS
 Fit type
Determination
• The loosest fit is the
difference between the
smallest feature A and the
largest feature B.
• The tightest fit is the
difference between the largest
feature A and the smallest
feature B.
 Type 1: Clearance fit = Occurs when two toleranced mating parts
will always leave a space or clearance when assembled

 Type 2: Interference fit = Occurs when two toleranced mating

parts will always interfere when assembled
• Type 3: Transition fit = Occurs when two toleranced
mating parts are sometimes and interference fit and
sometimes clearance fit when assembled.
functional
dimensioning

When dimensioning a part,

identify the functional
features first. Functional
features are those that come
in contact with other parts,
especially moving parts.
Dimension and tolerance
these features first, then do
all the remaining features.
Tolerance Presentation
• Direct limits, or as tolerance values applied directly to a
dimension
• A general tolerance note in the title block

All decimal
dimensions to be held
to ±.002”

Note: A tolerance added to a dimension always

supersedes the general tolerance, even if the added
tolerance is larger than the general tolerance.
 TRANSITION FITS AND INTERFERENCE FITS
Combination
Quality of
of Hole and Typical uses
Fit
Shaft
H6 j5 fine
Clearance Very small clearance is obtained - used for fits where a
H7 j6 normal transition slight interference is permissible - coupling spigots
and recesses, gear rings clamped to steel hubs.
H8 j7 coarse

H6 k5 fine
True Fits averaging no clearance where slight interference
H7 k6 normal transition can be tolerated , with the object of eliminating
vibration - ball bearings races of light duty.
H8 k7 coarse

H6 m5 fine
Interference
H7 m6 normal Fits averaging slight interference - used for ball
transition
bearing races of medium duty.
H8 m7 coarse
Light press fit for nonferrous parts which can be
H6 p5 fine
Press fit dismantled when required-bearing bushes-press fit for
H7 p6 normal steel, cast iron or brass to steel assemblies- bush in a
gear.
H6 r5 fine
Drive fit Medium drive fit for ferrous parts and light drive fit for
H7 r6 normal non-ferrous parts that can be dismantled.
Permanent or semi permanent assemblies of steel and
H6 s5 fine
Drive fit cast iron with considerable gripping force- collars
H7 s6 normal pressed on to shafts, valve seatings etc. For light
alloys this gives a press fit.
H6 u5 fine High interference fit a thorough investigation into the
Force or
degree of grip and the stresses in the part must be
H7 u6 normal shrink fit
made.
 Geometric dimensioning and tolerancing
(GDT)
Size tolerances alone are sometimes not enough to
meet the design needs of a part. Relationships
between features may also need to be controlled.
In such cases, notes can be added to the drawing
defining these relationships. And these extra notes
can be placed by geometric dimensioning. The GDT
symbols specify concise requirements for features.
Feature control
box
Geometrical Tolerances
• Specify the maximum error of a component’s geometrical
characteristic, over its whole dimensioned length or surface.
• Applied over and above normal dimensional tolerances
when it is necessary to control more precisely the form or
shape of some feature of a manufactured part, because of
the particular duty that the part has to perform.
• Geometrical tolerances are used to convey in a brief and
precise manner complete geometrical requirements on
engineering drawings.
Types of Geometric
Tolerances
• Form: limit the amount of error in the shape of a feature.
Form tolerances are independent tolerances.
• Orientation: limit the direction, or orientation, of a feature
in relation to other features. Orientation tolerances are
related tolerances.
• Location: limit the location or placement of features.
Location tolerances are related tolerances
• Runout: A group of geometric tolerances that
simultaneously limit the form, location, and orientation of
cylindrical parts. Runout tolerances are related tolerances
requiring a datum axis.
(a) the characteristic symbol, for single or related features;

(b) the tolerance value

(i) preceded by Ø if the zone is circular or cylindrical,

(ii) preceded by SØ if the zone is spherical;

(c) Letter or letters identifying the datum or datum systems.

Maximum material and
Least material Principles

Maximum material condition (MMC): that condition of a part or

feature which contains the maximum amount of material, e.g.
minimum size hole, or a maximum size shaft.

Least material condition (LMC): that condition of a part or feature

which contains the minimum amount of material, e.g. maximum size
hole or a minimum size shaft.
Assignment 5
Fits and Limits Geometric Tolerances