Transcript Geometric Dimensioning and Tolerancing

Geometric Dimensioning and
Tolerancing
Unit 6 – Datums
GDT
1. Establish a reference coordinate system.
2. Tell me where ‘perfect’ is.
3. Tell me how far off from ‘perfect’ is allowed.
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Department of Mechanical and Aerospace Engineering
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Introduction
• Datums are nothing more and nothing less than the
physical features of parts from which to make repeatable
measurements.
• These features are considered theoretically exact.
• Datums define a coordinate system from which to
measure everything.
• Datums are usually a plane, a line, or a point.
• We will need to label the datums on our drawing so that
the part inspector will know from where to measure.
EML 2023
Department of Mechanical and Aerospace Engineering
3
Datum Feature Symbol
• Datum Feature Symbol
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Department of Mechanical and Aerospace Engineering
4
Three-Plane Concept
•
define primary, secondary,
and tertiary datum planes
•
the primary datum is the
one that functionally is
usually the most critical
feature or surface of the
part
•
the primary datum feature
of the part will make
contact with the theoretical
datum plane in a minimum
of three points
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Department of Mechanical and Aerospace Engineering
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Three-Plane Concept
•
the secondary datum plane
is  to the primary datum
•
secondary datum feature is
the one that functionally is
the 2nd most critical feature
or surface of the part
•
2 point minimum contact
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Department of Mechanical and Aerospace Engineering
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Three-Plane Concept
•
the tertiary datum plane is
 to the primary & sec.
datums
•
1 point minimum contact
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Department of Mechanical and Aerospace Engineering
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Three-Plane Concept - Circular
• circular parts also require a three-plane concept for
repeatable orientation
• the primary datum is usually one flat surface of the part,
•
defines a datum axis along the center of cylinder
should be
a construction line
(or omitted)
should have
a center line
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Department of Mechanical and Aerospace Engineering
8
Features with
and without
Size
1.9
Establishing Datums
from Primary
Plane Surfaces
15.9 ±0.2
5H7(5/5.012)
0.2
25±0.3
LL
M-10x1.25
12.7±0.1
25 ±0.3 H
2X 6±0.25
Theory
Datum features H and L are mated with a
theoretical perfect plane contacting the
high points of the datum feature.
Physical
Datum features H and L are mated on the high points
of the manufacturing or inspection equipment
6.15
Datum Features
without Size
P
L
5H7(5/5.012)
15.9 ±0.2
0.2
25±0.3
M-10x1.25
N
M
K 2 SURFACES
12.7±0.1
H
2X 6±0.25
25 ±0.3
S 17±0.02
Datum planes established from planar datum features
Datum feature N establishes a plane on the high
points of the left surface.
Datum feature L establishes a plane on the high
points of the rear surface.
Datum feature H establishes a plane on the high
points of the bottom
surface.
Datum feature M establishes a plane on the high
points of the left side of the
slot.
Datum feature K
establishes a plane on
the high points of two
surfaces.
6.16
Datum Features
without Size
P
L
5H7(5/5.012)
15.9 ±0.2
0.2
25±0.3
M-10x1.25
N
M
K 2 SURFACES
12.7±0.1
H
2X 6±0.25
25 ±0.3
S 17±0.02
Datum planes established from planar datum features
Datum feature N establishes a plane on the high
points of the left surface.
Datum feature L establishes a plane on the high
points of the rear surface.
Datum feature H establishes a plane on the high
points of the bottom
surface.
Datum feature M establishes a plane on the high
points of the left side of the
slot.
Datum feature K
establishes a plane on
the high points of two
surfaces.
6.16
Datum Features
without Size
P
L
5H7(5/5.012)
15.9 ±0.2
0.2
25±0.3
M-10x1.25
N
M
K 2 SURFACES
12.7±0.1
H
2X 6±0.25
25 ±0.3
S 17±0.02
Datum planes established from planar datum features
Datum feature N establishes a plane on the high
points of the left surface.
Datum feature L establishes a plane on the high
points of the rear surface.
Datum feature H establishes a plane on the high
points of the bottom
surface.
Datum feature M establishes a plane on the high
points of the left side of the
slot.
Datum feature K
establishes a plane on
the high points of two
surfaces.
6.16
Datum Features
without Size
P
L
5H7(5/5.012)
15.9 ±0.2
0.2
25±0.3
M-10x1.25
N
M
K 2 SURFACES
12.7±0.1
H
2X 6±0.25
25 ±0.3
S 17±0.02
Datum planes established from planar datum features
Datum feature N establishes a plane on the high
points of the left surface.
Datum feature L establishes a plane on the high
points of the rear surface.
Datum feature H establishes a plane on the high
points of the bottom
surface.
Datum feature M establishes a plane on the high
points of the left side of the
slot.
Datum feature K
establishes a plane on
the high points of two
surfaces.
6.16
Datum Features
without Size
P
L
5H7(5/5.012)
15.9 ±0.2
0.2
25±0.3
M-10x1.25
N
M
K 2 SURFACES
12.7±0.1
H
2X 6±0.25
25 ±0.3
S 17±0.02
Datum planes established from planar datum features
Datum feature N establishes a plane on the high
points of the left surface.
Datum feature L establishes a plane on the high
points of the rear surface.
Datum feature H establishes a plane on the high
points of the bottom
surface.
Datum feature M establishes a plane on the high
points of the left side of the
slot.
Datum feature K
establishes a plane on
the high points of two
surfaces.
6.16
Datum Features
of Size
C
R
15.9 ±0.2
5H7(5/5.012)
25±0.1
M10x1.25
E
F
B
12.7 ±0.1
A
25±0.1
2X 6±0.25
0.2 M
SR 8.5
0.4
D
G
Theory
Datum axis E is the axis of the
theoretical datum feature simulator
6.18
Physical
Simulated datum axis E is the axis
of a collet, chuck, CMM etc.
Datum Features
of Size
C
R
15.9 ±0.2
5H7(5/5.012)
25±0.1
M10x1.25
E
F
B
12.7 ±0.1
A
25±0.1
2X 6±0.25
0.2 M
SR 8.5
0.4
D
G
6.19
Datum Features
of Size
C
R
15.9 ±0.2
5H7(5/5.012)
25±0.1
M10x1.25
E
F
B
12.7 ±0.1
A
25±0.1
2X 6±0.25
0.2 M
SR 8.5
0.4
D
G
Physical
Theory
6.19
Datum center plane B is
the center plane of the
datum feature simulator.
Sim ulated datum center plane B is
the center plane of the gage block.
Datum Features
of Size
C
R
15.9 ±0.2
5H7(5/5.012)
25±0.1
M10x1.25
E
F
B
12.7 ±0.1
A
25±0.1
2X 6±0.25
0.2 M
SR 8.5
0.4
D
G
Theory
6.20
Datum axis C is the axis of the
datum feature simulator
Physical
Simulated datum axis C is
the axis of the gage pin
Datum Features
of Size
C
R
15.9 ±0.2
5H7(5/5.012)
25±0.1
M10x1.25
E
F
B
12.7 ±0.1
A
25±0.1
2X 6±0.25
0.2 M
SR 8.5
0.4
D
G
Theory
Physical
Datum D axis and two planes are
established from a pattern of two
holes
6.20
Simulated datum feature D axis
and two intersecting planes
established from gage
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25
Datum Feature Symbol Placement is Important
Datum feature symbol R in
line with the dimension line,
establishes center plane of
the width.
R
K
5H7(5/5.012)
15.9±0.2
25±0.2
Datum feature
symbol K on the
extension line,
establishes a
plane from the
high points on
the surface.
M10x1.25
Datum feature symbol
M on the extension line
establishes a plane from
the high points on the
surface.
Datum feature symbol B
in line with the dimension
line establishes the center
plane of the slot.
M
B
12.7±0.1
S
17±0.2
25±0.2
6.21
2X
6±0.25