PROE-ch03
description
Transcript of PROE-ch03
3Datums
Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.
• Explain the purpose of datums.• Define common terms related to datum
features.• Interpret information provided by datum feature
symbols.• Describe methods for representing datum
surfaces on drawings.• Explain how to establish datum reference
frames.
L earning Objectives
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• Identify the degrees of freedom of a part.• Explain how to establish datum targets.• Identify datum target points, areas, and lines.• Describe methods for representing datum axes
on drawings.• Describe methods for representing datum
center planes on drawings.
L earning Objectives
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Datums
• Represent true geometric counterpart of a datum feature
• Reference features of an object• Establish location and size dimensions
Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.
Datum Feature Simulator
• Opposite shape of datum feature• Two types:
– Theoretical datum feature simulator– Physical datum feature simulator
• Manufacturing examples:– Machine tables– Surface plates– Gauge surfaces– Surface tables– Specially designed rotation devices
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Datum Feature Symbol
• Do not apply to centerlines, center planes, or axes
• Draw using thin lines• Use any letter to identify a datum feature
except I, O, or Q• Use double letters when number of datums
exceeds number of letters in alphabet
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Datum Feature Symbol
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Datum Feature
Datum plane
Simulated datum plane
Datum feature
Part
Physical datum feature simulator
Surface of manufacturing or verification equipment
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Datum Feature Terms
• Actual mating envelope• Simulated datum• Tangent plane
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Datum Feature Symbol Placement for Surfaces
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Datum Surface
• Can be controlled by geometric tolerance • Datum plane measurements do not take
variations in datum surface from datum plane into account
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Geometric Control of Datum Surface
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Datum Reference Frame (DRF) Concept
• Select three perpendicular datum features based on their importance to part design
• Assign precedence and datum reference order– Primary datum– Secondary datum– Tertiary datum
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Datum Reference Frame Concept
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Datum Reference Frame Concept: Inspecting the Part
• All parts have six degrees of freedom– Three degrees of translation– Three degrees of rotation
• Movement is either translational or rotational
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Degrees of Freedom
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Establishing Multiple Datum Reference Frames
• Datums X, Y, and Z establish one datum reference frame
• Datums L and M establish second datum reference frame
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Datum Features Specified Individually
• Place a note next to datum feature symbols indicating how many datum features to consider separately
• Place the note “2X INDIVIDUALLY” next to datum feature symbols of two separate datum features identified by same letter
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Datum Target Symbols
• Identify datum targets• Useful on parts with surface or contour
irregularities• Connect to datum target point, line, or area
with a leader
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Datum Target Symbols
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Datum Target Points
• Establish primary datum plane by locating at least three points on primary datum surface
• Establish secondary datum plane by locating at least two points on related secondary datum surface
• Establish tertiary datum plane by locating at least one point on related tertiary datum surface
• Dimension using baseline or chain dimensioning
• Location dimensions originate from datums
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Datum Target Points
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Datum Target Points
• Datum plane established by locating pins at datum target points
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Datum Target Areas
• Used to establish datums using areas of contact
• Locating pins are flat end tooling pins with pin diameter equal to specified size of target area
• Top half of the datum target symbol identifies size of target area
• Use datum target point at center location when area is too small to accurately or clearly display on drawing
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Datum Target Areas
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Datum Target Lines
• Indicated by a target point on edge view of surface and a phantom line on surface view
• Locating pins are cylindrical or knife-edged with datum target line along tangency where pins meet the part
• Surface is often placed 90 to the pin to create datum reference frame
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Datum Target Lines
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Partial Datum Surface
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Coplanar Surface Datums
• Used to establish coplanar surfaces as one datum plane
• Specify number of surfaces with a note such as: "2 SURFACES" below related feature control frame
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Coplanar Surface Datums
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Datum Axis
• Represents two theoretical planes intersecting at 90
• Represented in drawings with centerlines• Pitch cylinder for screw threads establishes
datum axis unless otherwise specified– When not using pitch cylinder for screw threads,
place note such as "MAJOR DIA" or "MINOR DIA" next to datum feature symbol
• Simulated datum axis established by inspection equipment
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Datum Axis
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Datum Feature Symbol Placement for a Datum Axis
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Coaxial Datum Features
• Separate datum reference letters by a dash in one compartment of the feature control frame
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Datum Axis Established with Datum Target Symbols
• Primary datum axis established by two sets of three equally spaced targets
• Identify datum target points in correlation to adjacent cylindrical datum feature when two cylindrical features of different diameters establish a datum axis
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Datum Axis Established with Datum Target Symbols
• Cylindrical datum target areas and circular datum target lines can be used to establish datum axis– Target area represented by two phantom lines
with section lines between– Datum target line represented by phantom line
all around part
• Establish secondary datum axis by placing three equally spaced targets on cylindrical surface
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Movable Datum Target Symbols and Datum Target Points
• When datum targets establish a center point, axis, or center plane on a RMB basis, datum feature simulator movement is normal to true profile
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Movable Datum Target Symbols and Datum Target Spheres
• Circular phantom line represents spherical datum feature simulator to establish datum axis
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Datum Center Plane
• Axis and center plane datum feature symbols align with/replace dimension line arrowhead or appear on feature, leader shoulder, dimension line, or feature control frame
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Datum Center Plane
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Translation Modifier
• Added to feature control frame following datum feature reference and any other applicable modifiers
• Specifies that basic location of datum feature simulator is unlocked and free to translate within specified geometric tolerance
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Translation Modifier
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Using Contoured Surface as Datum Feature
• 3D mathematical coordinate system defines compound surface feature on a part
• Datum simulator results from mathematical data• Common when design copies contour of an
actual object that has few or no flat surfaces to use as datums
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Identify the datum feature, part, simulated datum plane, physical datum feature simulator, and datum plane.
A. Datum feature
B. Datum plane
C. Part
D. Simulated datum plane
E. Physical datum feature simulator
R eview
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Identify Parts A and B.
A. Datum feature symbol
B. Feature control frame
R eview
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Identify parts A and D and provide dimensions for B, C, and D.
A. Datum plane A
B. 12.2 minimum
C. 12.8 minimum
D. 0.1 geometric tolerance
R eview
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Identify items A–G.
A. Basic dimension
B. Datum feature symbol
C. Target point
D. Datum target symbol
E. Datum reference
F. Target number
G. Datum target line
R eview
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Identify items A–C.
A. Datum target area
B. Datum target symbol
C. Target area size
R eview
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Identify whether the datum reference symbol represents a datum surface, datum axis, or datum center plane in items A–C.A. Datum surfaceB. Datum center planeC. Datum axis
R eview