ME2103 Engineering Visualization & Modeling Limits, Fits...

ME2103 Engineering Visualization & Modeling Limits, Fits & Geometrical Tolerances

A/P Lee Kim Seng

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Limits, Fits & G. Tolerances Limits, Fits & Geometrical Tolerances are used to ensure that component parts fit together predictably so that the whole assembly functions correctly.

Approximation relationship between production cost and manufacturing tolerance

UN

ITS

OF

CO

ST

0.1 0.2 0.3 0.4 0.5 TOLERANCE (mm)

20

40

60

80

100

Limits

Tolerances

60.05 60.00

60 +0.05 -0

50 ± 0.3

49.97 50.03

Limit Tolerances Limit Tolerance is the permissible deviation on a dimension.

41±0.2

Limit of size Range

41.2 40.8

Limit Tolerances Limit Tolerances can be referred to the tables on Limits and Fits. (SS ISO 406:1987 & ISO 286-1&2:1988)

Ø25g6

Limits

Ø25g6 = Ø24.980 - Ø24.993

Limit Tolerances

Basic Size: ø40

Limit Tolerances

Shaft

Hole H7

Shaft g6

Shaft p6

Limit Tolerances

H7

(H7/g6) (H7/p6)

Limit Tolerances

Fundamental Deviation & International Tolerance Grade

Basic size FD

FD

IT Grade

International Tolerance Grade

1. International tolerance grade establishes the magnitude of the tolerance zone or amount of size variation allowed. (number; smaller number grade provides smaller tolerances zone)

5 6 8 7 9 10 11

IT Grade

Limits & Fits IT Grades

4 5 6 7 8 9 10 11

Lapping and Honing

Cylindrical Grinding

Surface Grinding

Diamond Turning

Diamond Boring

Broaching

Reaming

Powder Metal - Sizes

Turning

Powder Metal - Sintered

Boring

Milling

Planing and Shaping

Drilling

Punching

Die Casting

Fundamental Deviation 2. Fundamental Deviation establishes the position of the tolerance zone with respect to the basic size.

(Capital letter for internal

dimensions i.e. Hole

Common hole tolerance: H7, H8,

H9, H11

Small letter for external

dimensions i.e. Shaft)

Common shaft tolerance: c11, d9,

e8, f7, g6, h6, k6, n6, p6, s6, u6 c

d e f

g h

k n p s u

Shafts

Basic size

FD

Posi

tive

devi

atio

ns

Neg

ativ

e de

viat

ions

FD

FD

H F

D

C

K P

U

Holes

Basic size

Neg

ativ

e de

viat

ions

Po

sitiv

e de

viat

ions

FD

G

E

N S

Deviation closest to the basic size. Designated by letter (e.g. H, g…)

Illustration

f = fundamental deviation

f f

*

*

* = Int tolerance grade

BS 4500 ‘ISO Limits & Fits’

For Hole Basic size ø90 For Shaft

90H7 90g6

90.035 90.000

First Choice 89.988 89.966

90 90 +0.035 -0

-0.012 -0.034

Fundamental Deviation f = -0.012

Illustration

f f

*

*

For shaft: 90g6

Max shaft dia = 89.988 mm

Min shaft dia = 89.966 mm

f = 0.012 mm (-ve)

For hole: 90H7

Max hole dia = 90.035 mm

Min hole dia = 90.000 mm

f = 0 0

0.03

5

0.01

2 0.

034

89.9

88

89.9

66

90.0

00

90.0

35

∅90

0.

035

0.02

2

Engineering Fits between Two Mating Parts Can be divided into 3 types:- Clearance fit: Interference fit:

Transition fit:

Engineering Fits between Two Mating Parts Clearance fit: Relation between assembled parts when clearance occurs under all tolerance conditions

Tolerances

Basic size

Minimum clearance Maximum

clearance

Tolerances – Hole Basis

f7 h6

e8

d9 c11

H7 H8 H9 H9

H11

FD

Basic size

Example of Clearance Fits

Disc Couplings

Elastomer Couplings

Engineering Fits between Two Mating Parts Transition fit: Relation between assembled parts when either a clearance or interference fit can result depending on the tolerance conditions of the mating parts

Example – Transition Fit

Engineering Fits between Two Mating Parts Interference fit: Relation between assembled parts when interference occurs under all tolerance conditions

Example of Interference Fits Bearing and Shaft

Limits & Fits - Hole Basis Constant hole basic diameter

Shaft size varies according to type of fit

Recommend for general applications

Gives greater economy of production

This chart is to scale for basic size above 30mm up to 40mm

Holes

Shafts

Limits & Fits - Hole Basis

Shaft Basis Constant shaft basic diameter

Hole size varies according to type of fit

Costly

Shaft Basis

Preferred Fits

FIT ISO SYMBOL

Descriptions Hole Base Shaft Base

H11/c11 H9/d9 H8/f7 H7/g6 H7/h6

C11/h11 D9/h9 F8/h7 G7/h6 H7/h6

Loose running fit Free running fit Close running fit Sliding fit Locational clearance fit

H7/k6 H7/n6

K7/h6 N7/h6

Locational Transition fit Locational Transition fit

H7/p6 H7/s6 H7/u6

P7/h6 S7/h6 U7/h6

Locational Interference fit Medium Drive fit Force fit

Tran

s fit

C

lear

ance

fit

In

terf

eren

ce

fit

Example

H9/d9

H7/g6

Ø12 H9/d9 (f = -0.050) Hole Ø H9 d9 Shaft Ø 12.043 43 -50 11.950 12.000 0 -93 11.907

Ø25 H7/g6 (f = -0.007) Hole Ø H7 g6 Shaft Ø 25.021 21 -7 24.993 25.000 0 -20 24.980

Ø12 H9/d9 (f = ) Hole Ø H9 d9 Shaft Ø

Ø25 H7/g6 (f = ) Hole Ø H7 g6 Shaft Ø

Example

Given diameter as 30mm

IT Grade 10-3 mm

6

7

8

9

11

5 6 8 7 9 10 11

IT Grade

13

21

33

52

130

Example

Given Shaft diameter as 30mm F. Deviation 10-3 mm

c d f g h k n p s u

c

d e f

g h

k n p s u

Shafts

Basic size

FD

Posi

tive

devi

atio

ns

Neg

ativ

e de

viat

ions

FD

FD

H F

D

C

K P

U

Holes

Basic size

Neg

ativ

e de

viat

ions

Po

sitiv

e de

viat

ions

FD

G

E

N S

-110

-7

0 +2

+15 +22

+35 +48

-65 -20

For Hole Basis:

Example

Given Shaft diameter as 30mm

Next

For Hole Basis:

IT6 = 13

IT7 = 21

SD g = -0.007 30.000

30.021

29.987

30.000

30.021

29.993

29.980

f f

* *

Limits & Fits - Hole Basis

Methods of Tolerance

Permissible deviation for basic

size range

Tolerance class Description (Designation)

Over (mm)

Up to (mm)

Fine (f)

Medium (m)

Coarse (c)

Very coarse (v)

0.5

3

±0.05

±0.1

±0.2

3

6

±0.05

±0.1

±0.3

±0.5

6

30

±0.1

±0.2

±0.5

±1

30

120

±0.15

±0.3

±0.8

±1.5

120

400

±0.2

±0.5

±1.2

±2.5

400

1000

±0.3

±0.8

±2

±4

1000

2000

±0.5

±1.2

±3

±6

Permissible deviations for linear dimensions (ISO 2768-1) General Tolerances

Limit Dimension Tolerances

H11/c11

Unilateral Tolerances Variation is permitted only in one direction from specified dimension

57.15 +0.00 -0.13

16.51 +0.08 -0.00 16.51 – 16.59

57.02 – 57.15

Variation is permitted in both directions from specified dimension

Bilateral Tolerances

57.2 ±1.5

57.2 +0.8 - 1.5 55.7 – 58.0

55.7 – 58.7

CumulativeTolerances

Ordinate Dimensioning Cumulative Tolerances

Poor

Ordinate Dimensioning

29.95 30.00

10.00 9.95

10.00 9.95

10.00 9.95

Cumulative Tolerances

10.00 9.95

29.95 30.00

20.00 19.95

Dimensioning of Screw Threads Threads are shown conventionally on drawings, hence need to be designated by dimensions or notes.

For metric thread: example

M16 x 1.5 – 6H (internal thread)

M6 x 0.75 – 6g (external thread)

M – Thread system symbol for metric thread 16, 6 – Nominal diameter in mm 1.5 & 0.75 – Pitch in mm 6H, 6g – Thread tolerance class symbol

Dimensioning of Screw Threads

Note: 1. If no pitch is shown in dimension,

coarse thread is implied. (fine threads are used mainly in special applications, not common)

2. Thread tolerance provide 3 classes of fit:

a) Free – (7H/8g) for application requiring quick & easy assembly

b) Medium – (6H/6g) suitable for most general applications

c) Close – (5H/4h) commonly used


3. If thread is left hand, abbreviation LH should be used.

No indication of hand is required if thread is right-handed.


Acetylene Oxygen

Geometrical Tolerances

Geometrical Tolerances Very often, specifying the limit tolerances on the parts may not be sufficient, as they do not consider the tolerances due to the geometrical shape or form of the parts such as straightness and cylindricity etc.

In today’s industry where mass production and interchangeability of parts are a norm, the control of both limit tolerances and geometrical tolerances are essential.

Geometrical Tolerances

Linear Tolerances

Inspecting Tolerances

Specifying Tolerances

30° ± 0.1

40 ± 0.1

100 ± 0.1

50 ±

0.1

Specifying Tolerances

30° ± 0.1

40 ± 0.1

100 ± 0.1

50 ±

0.1

30° ± 0.1

40 ± 0.1

100 ± 0.1

50 ±

0.1

Drawing Tolerances

Drawing G.Tolerances

Drawing Tolerances

Specifying Tolerances Designed part Fabricated part

Geometric Dimensioning & Tolerancing

Geometric Tolerancing Symbols Feature Tolerance Characteristic Symbol

Individual features

Form

Profile

Straightness

Flatness Circularity (Roundness) Cylindricity

Individual or related features

Profile of any line Profile of any surface

Related features

Orientation

Parallelism Perpendicularity Angularity

Location

Position Concentricity Symmetry

Run-out Circular Run-out Total Run-out

Incorporating Datum References

On extension line On outline of the part

On centre line

Ø24.80


Application of Symbols to Position and Form Tolerance Dimensions

Application of Symbols to Position and Form Tolerance Dimensions

WSS competition 2004

Maximum Material Condition (MMC) applied to tolerance of position

Pin ø6.35

Drawing G.Tolerances

Specifying Position Tolerances

544_20a

The actual point of intersection must be within a circle of ∅0.1 mm, the center of which is the theoretical exact position of the considered point.

Position

Specifying straightness of Surface Elements Form Tolerances

Symbol

Indication

Definition

Illustration

544_01a

Straightness is a condition where an element of an axis is a straight line. The tolerance zone of which when projected in a plane must be within 2 parallel straight lines a distance 0.1 mm apart.

Specifying straightness of Surface Elements

Straightness

Specifying flatness

The tolerance zone must be between two parallel planes 0.05 mm.

Form Tolerances

Flatness

Specifying roundness for a cylinder or cone

Form Tolerances

The tolerance zone at a given plane must be within two concentric circles of 0.01 mm.

Circularity

Specifying cylindricity Form Tolerances

The tolerance zone must be within two coaxial cylinder of 0.01 mm.

Cylindricity

Specifying concentricity 544_23a

The tolerance zone of the shaft must be within a cylinder ∅0.1 mm, which is coaxial with datum axis A.

544_24a

The tolerance zone of the shaft must be within a cylinder ∅0.1 mm, which is coaxial with datum axis B-C.

Concentricity

Specifying parallelism for a plane surface

Orientation Tolerances

544_12a

The tolerance surface must be within 2 parallel planes 0.3 mm apart, and parallel to the datum surface D.

Parallelism

Specifying perpendicularity for a plane surface

544_16a

The tolerance surface must be within 2 parallel planes 0.1 mm apart, and perpendicular to the datum surface D.

Perpendicularity

Specifying angularity for a plane surface 544_17a

The tolerance zone must be within two parallel planes 0.2 mm apart, which are inclined at 30° to the datum face A.

Angularity

Specifying Circular and Total Runout 544_26a

The run-out at a given plane must be less than 0.08 mm during one revolution about datum axis C-D.

544_27a

The total run-out on the specified surface must be less than 0.1 mm during several revolutions about datum axis C-D.

Circular Runout

Total Runout

Surface Texture & Roughness

Surface Texture

Surface Roughness Measurement

Typical cut-off length: 0.25, 0.8 and 2.5mm Instrument : Taylar-Hobson Talysurf Note that for a purely triangular profile, the surface roughness, Ra = Rt ÷ 4

Texture symbol and its interpretation

Surface texture symbol

Applications of surface texture symbol Symbols Interpretation

Indicates machining is necessary to obtain the desire surface

texture Indicates material removal is NOT permitted

Indicates a particular machining process (turning) and the roughness value

The maximum and minimum limits of surface roughness obtained by any machining process

The maximum and minimum limits of surface roughness obtained without machining

Surface Roughness values Roughness value (Ra) Roughness grade

number (N series) µm µin

0.025 1 N1

0.05 2 N2

0.1 4 N3

0.2 8 N4

0.4 16 N5

0.8 32 N6

1.6 63 N7

3.2 125 N8

6.3 250 N9

12.5 500 N10

25 1000 N11

50 2000 N12

Process Roughness value Ra (µm) 25 12.5 6.3 3.2 1.6 0.8 0.4 0.2 0.1 0.05 0.025

Sand casting

Forging

Die casting (Pressure)

Cold rolling, drawing

Flame cutting

Sawing

Planing, shaping

Drilling

EDM

Milling

Broaching

Reaming

Laser

Boring

Turning

Grinding

Honing

Polishing

Lapping

Tumbling

Super-finishing

Thank You

A/P Lee Kim Seng

ME2103 Engineering Visualization & Modeling Limits, Fits...

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