Post on 14-Oct-2015
description
Data Analysis Lab
ME 288
L7 abc
GD & T
Is a method (systems of symbols) for defining a parts geometry it goes beyond the form description
based simply on tolerance dimensions
as directed under rule #1
A basic dimension is a theoretical
perfect size, location
or orientation dimension.12
Varies
Basic Dimension
2h
These symbols are used when dimensioning.
1.5h
12
Varies
Basic Dimension
Diameter
1.5h
0.3h
0.3 h
2h
( )(
ST
R SR S CR
X
2h
h h
90
h
h
0.6h60
h 2h
0.5h0.5h
30
h
h
h
15
2.5h
1.5h0.8h
60
Counterbore Countersink Depth (or deep)
Dimension Origin Conical Taper Square
Arc Length Reference Slope
Radius
Places or By
Statistical Tolerance(dimensional)
SphericalRadius
SphericalDiameter
ControlledRadius
These symbols are used when dimensioning.
2h
h h
90
h
h
0.6h 60
h 2h
0.5h0.5h
30
h
h
Counterbore Countersink Depth (or deep)
Dimension Origin Conical Taper Square
h = height of lettering
These symbols are used when dimensioning
1.5h
12
Varies
Basic Dimension
Diameter
1.5h
.3h
1.6
2h
( )(
ST
R SR S CR
X
h
15
2.5h
1.5h0.8h
60
Arc Length Reference Slope
Radius
Places or By
Statistical Tolerance
(dimensional)
Spherical
Radius
Spherical
Diameter
Controlled
Radius
A feature control frame (the backbone of GD & T) modifies a parts geometry.
0.2 A B C
Modifier
Numeric tolerance(feature tolerance)
Geometric tolerance(characteristic)symbol (position)
Tertiary datum
Secondary datum with modifier
Primary datum
2h
Diameter symbol
Two additional examples of feature control frames modifying a parts geometry.
0.08 0.05 A
Geometric tolerance(flatness)
Numeric tolerance
Geometric tolerance(perpendicularity)
Diameter symbol
Numeric tolerance
ModifierDatum
(A) (B)
Geometric characteristic(tolerance) symbols are categorized in two ways.
**
Perpendicularity
Angularity
Runout Circular
Runout Total
Profile surface
Profile line
Symmetry
Cylindricity
Position
Concentricity
Circularity
Straightness
Parallelism
Flatness
Either filled or unfilled
Symbol Description
Form
Pro
file
Ori
enta
tio
nLo
cati
on
Ru
no
ut
Type oftolerance
Individualfeatures
Individual orrelated features
Relatedfeatures
Geometric Characteristic Symbols
*
No datum or datums needed
A datum or datumsare required
Depending on the situation
GD&T geometric characteristic symbols illustrated.
1.5h M1.5h h 0.8h
2h1.5h
0.6h
h
1.5h
Concentricity Circularity Modifier
Straightness Parallelism Flatness
1.5h
1.5hh
2h
h h
60
1.5h
h
h2h
2h1.2h
0.5hCylindricity Position
All round Profilesurface
Profile
line
Symmetry
GD&T geometric characteristic symbols illustrated.
GD&T geometric characteristic symbols illustrated.
h0.8h
0.8h3h
0.6h
1.5h
2h 1.5h
30
45
0.6h
1.5h
1.1h
**
Perpendicularity Angularity
Runout Circular Runout Total
Between
*
Filled or unfilled*
Table lists GD&T geometric characteristic symbol modifiers.
M
L
P
F
T
Maximum Material Condition
Least Material Condition
Projected Tolerance Zone
Free State Variation
Tangent Plane
Modifiers
ST Statistical Tolerance (geometric)
Between
Maximum Material Condition
Least Material Condition
Projected Tolerance Zone
Free State Variation
Tangent Plane
Modifiers
Between
Maximum Material Condition
Least Material Condition
Projected Tolerance Zone
Free State Variation
Tangent Plane
Modifiers
*Between
*Filled or unfilled
Modifiers
Maximum material condition, MMC(M)
It should be taken literally.
The geometric feature or size is as large as it can be.
In the case of a hole, as small as it can be.
Least material condition, LMC(L)
It should be taken literally.
The geometric feature or size is as small as it can be.
In the case of a hole, as large as it can be.
7B
Rule #1:Where only a tolerance of size is
specified, the limits of size of an
individual feature prescribe the extent of
which variations in its geometric form, as
well as size, are allowed.ANSI Y14.5 1994
When only size tolerance is specified the objects form can vary within the stated size limits.
11.8
(B)
(C)
12.2
11.8
12.2
11.8
12.2
11.8
12.2
11.8 for entire length 11.8 for entire length
External dowel plug Internal hole
(A)
at 12.2 MMC must be perfect form
at 11.8 MMC must be perfect form
12.2
11.8
12.211.8
A cylinder can have a variety of shapes yet stay within the limits of size.
(A) (B) (C)
Min Min Min
Max Max Max
The rectangular prism can vary in shape as long as it stays inside the volume of the limits of size.
1614
119
97
2220
8
7(A) (B)
1816
16.015.8
8.0 MMC
7.8 LMC alongentire lengthof dowel
6.8MMC
7.0LMC
7.06.8
8.07.8
Ring gage
Plug gage
(A) Checking geometric form with ring gage
(B) Checking geometric form with plug gage
Checking the size limits envelope:
A ring gage and plug gage are used to check the geometric form of a pin and hole.
Standard Stock Item
Items whose geometry are already controlled by established industrial or government standards
bars, sheet stock, tubing or structural shapes
Datums
A datum is an exact surface, line, point ,axis or cylinder from which measurements are taken.
Ex. A surface plate or a polished slab of granite (simulated datum).
3 points define a plane.
Datum feature is the surface of the part in contact with the simulated datum.
A height gage measures the height of an object from the simulated datum surface of a surface plate.
Datumfeature
Simulateddatum(surface plate)
Measuredheight
Dial face
ProbeUp
Down
Note: the datum feature rests on the simulated datum.the height is measured from the simulated datum and not from the datum feature.
Degrees of freedom (12) allow movement in two directions along each axis and rotation about each axis (clockwise and counterclockwise).
+Y
-X
+Z
-Y
+X
-ZIn order to measure geometric features part motion must be restricted.
A datum reference frame consists of three intersecting planes at 90 to each other.
The part can still move in the positive X, Y and Z directionspart motion must be restricted
What if we temporarily clamped the part? Measurements can be taken from the simulated datums.
Datum surfaces must be indicated on the drawing
2H for single lettering4H for double lettering
A2H H
H
60
16
G
H
E
F
Filled orunfilled
(A) H = height of lettering
(B) Applications
Varies
7C
The datum symbol is applied to solid cylinders.
KJ
J
148
14
J
-or-
F G H0.1
12
N
P
RM
6
12
6
M
The datum symbol is applied to holes.
Note: letters I, O and Q are not used to indicate datums because they may be confused with numbers one(1) and zero(0).
Double letters can be used e.g. AA, BB etc.
Order of Datums:Primary datum S has 3 pts of contact, secondary datum T has 2 pts and tertiary datum U 1pt of contact.
(A)This drawing
symbology
(B) Means this
SU
T
3 pts of contact1 pt of contact
2 pts of contact
S T U0.1
TS12
2X 6 0.2
6
M
8
U
10
The order of the datums is critical!
(1 pt)
(2 pts)
(3 pts)
V W X0.1
2X 6 0.08
M
X
W
V
(1 pt) (3pts)
(2 pts)
Trueheight
VX
W
Correct inspection procedure
True width(1 pt)
(3 pts)(2pts)
VX
W
Falseheight
Incorrect inspection procedure
Falsewidth
The datum axis is formed by two intersecting planes.
GH
(A) This drawing
8
8
8 8
24
0.5 G H4X 40.5 Intersecting planes
perpendicular to G
Primarydatum G
Datum axis
(B) Means this
The plug gage establishes the datum axis.
(A) This drawing
(B) Means this
C
10.80.1
Simulated datumcylinder C - largest that fits into hole
Datum axis
Datum feature C
Plug gage
The smallest circumscribed cylinder establishes the simulated datum and the datum axis.
(A) This drawing
(B) Means this
D
Datum feature DSimulated datum D
Datum axis
190.5
The simulated central datum plane is established by the center plane of
the largest block that fits into the groove.
B) Means this
A) This drawing 24.223.8
12.211.8
0.4 Y Z
Z
Y
Central datum plane
Simulateddatums atmaximumseparation
Datum features
The simulated central datum plane is established by the center plane located by the two blocks at minimum separation.
B) Means this
A) This drawing
18.2
Simulated datumplanes at minimumseparation
Central datum plane
0.6 A B
B
A
17.8