1. PART DESIGN SPECIFICATION
Spring 2011
Dr. R. A. Wysk

2. Agenda Go over engineering specifications Functional requirements
Form, fit and function
Dimensioning
Tolerancing
Engineering drawings
datum

3. Materials
Read Chapter 2 and 3 from Computer Aided manufacturing (3rd Edition)
Overview of engineering design
Mechanical design representations
Engineering drawing
Geometric dimensioning and tolerancing
AMSE Y14.5

4. THE DESIGN PROCESS Product Engineering
Off-road bicycle that ...
1. Conceptualization
2. Synthesis
3. Analysis
4. Evaluation
5. Representation
Design Process
How can this be accomplished?
1. Clarification of the task
2. Conceptual design
3. Embodiment design
4. Detailed design
Functional requirement -> Design
Steps 1 & 2 Select material and properties, begin geometric
modeling (needs creativity, sketch is sufficient)
mathematical, engineering analysis
simulation, cost, physical model
formal drawing or modeling

5. DESIGN REPRESENTATION
Engineering
Representation
Manufac-
turing
• Verbal
• Sketch
• Multi-view orthographic drawing (drafting)
• CAD drafting
• CAD 3D & surface model
• Solid model
• Feature based design
Requirement of the representation method
• precisely convey the design concept
• easy to use

6. A FREE-HAND SKETCH Orthographic Projection

7. A FORMAL 3-VIEW DRAWING 0.9444" A 4 holes 1/4" dia
around 2" dia , first
hole at 45°
2.000
0.001 A

8. DESIGN DRAFTING Third angle projection Drafting in the third angle Y Pz o n t a l Z I X I I V F r o n t a l p l a n e
Third angle projection
Drafting in the third angle

9. INTERPRETING A DRAWING

10. DESIGN DRAFTING Partial view Cut off view and auxiliary view2 . 1
Partial view A - A
Cut off view and auxiliary view
Provide more local details

11. DIMENSIONING Requirements 1. Unambiguous 2. Completeness
3. No redundancy
Incomplete
dimensioning
0.98 '
1.22 '
1.72 '
0.83 '
3.03 '
Redundant dimensioning
0.86 '
1.22 '
0.83 '
3.03 '
Adequate dimensioning

12. TOLERANCE Dimensional tolerance - conventional
Geometric tolerance - modern
nominal dimension + -
means a range
tolerance
+ 0.10
- 0.00
+ 0.00
- 0.10
unilateral
bilateral
0.95
1.05 + -

13. TOLERANCE STACKING
1. Check that the tolerance & dimension specifications are
reasonable - for assembly.
2. Check there is no over or under specification.
"TOLERANCE IS ALWAYS ADDITIVE" why?
1.20 '
±0.01
0.80 '
±0.01
1.00 '
±0.01 ?
What is the expected dimension and tolerances?
d = = 3.00
t = ± ( ) = ± 0.03

14. TOLERANCE STACKING (ii)?
0.80 '
±0.01
1.20 '
±0.01
3.00 '
±0.01
What is the expected dimension and tolerances?
d = = 1.00
t = ± ( ) = ± 0.03

15. TOLERANCE STACKING (iii)x
1.20 '
±0.01 ?
0.80 '
±0.01
3.00 '
±0.01
Maximum x length = = 1.03
Minimum x length = = 0.97
Therefore x = ± 0.03

16. TOLERANCE GRAPH A B C D E G(N,d,t)
N: a set of reference lines, sequenced nodes
d: a set of dimensions, arcs
t: a set of tolerances, arcs
d : dimension between references i & j
t : tolerance between references i & j ij ij
Reference i is in front of reference j in the sequence.

17. EXAMPLE TOLERANCE GRAPH
d,t
d,t
d,t
A B C D E
d,t
different properties
between d & t

18. OVER SPECIFICATION
If one or more cycles can be detected in the graph, we say that the dimension and tolerance are over specified. d1 d2
A B C
d1,t1
d2,t2 d3
Redundant dimension
d3,t3 A B C t1 t2
A B C t3
Over constraining tolerance
(impossible to satisfy) why?

19. UNDER SPECIFICATION
When one or more nodes are disconnected from the graph, the
dimension or tolerance is under specified. d1 d2
A B C D E d3 A B C D E
C D
is disconnected from the
rest of the graph.
No way to find

20. PROPERLY TOLERANCED A B C D E
d,t
d,t
d,t
A B C D E
d,t

21. TOLERANCE ANALYSIS For two or three dimensional tolerance analysis:
i. Only dimensional tolerance
Do one dimension at a time.
Decompose into X,Y,Z, three one dimensional problems.
ii. with geometric tolerance
? Don't have a good solution yet. Use simulation? d i a m e t e r
& t o l e r a n c e
A circular tolerance zone, the size is influenced
by the diameter of the hole. The shape of the
hole is also defined by a geometric tolerance. t r u e p o s i t i o n

22. 3-D GEOMETRIC TOLERANCE PROBLEMS
datum surface
datum
surface
± t
Reference
frame
perpendicularity

23. TOLERANCE ASSIGNMENT Tolerance is money
• Specify as large a tolerance as possible as long as functional and assembly requirements can be satisfied.
(ref. Tuguchi, ElSayed, Hsiang, Quality Engineering in Production Systems, McGraw Hill, 1989.) Q u a l i t y
function C o s t
cost + t - t d ( n o m i n a l d i m e n s i o n )
Tolerance value
Quality cost

24. REASON OF HAVING TOLERANCE
• No manufacturing process is perfect.
• Nominal dimension (the "d" value) can not be achieved exactly.
• Without tolerance we lose the control and as a consequence cause functional or assembly failure.

25. EFFECTS OF TOLERANCE (I)
1. Functional constraints
e.g.
flow rate
d ± t
Diameter of the tube affects the flow. What is the allowed
flow rate variation (tolerance)?

26. EFFECTS OF TOLERANCE (II)
2. Assembly constraints
e.g. peg-in-a-hole dp
How to maintain the clearance? dh
Compound fitting
The dimension of each segment affects others.

27. RELATION BETWEEN PRODUCT & PROCESS TOLERANCES
Machine uses the locators as the reference. The distances from the machine coordinate system to the locators are known.
The machining tolerance is measured from the locators.
• In order to achieve the 0.01 tolerances, the process tolerance must be or better.
• When multiple setups are used, the setup error need to be taken into consideration. A . 1 t o l e r a n c e s
Design specifications S e t u p l o c a t o r s . 5 . 5 . 5
Process tolerance

28. TOLERANCE CHARTING
A method to allocate process tolerance and verify that the process sequence and machine selection can satisfy the design tolerance.
Not shown are
process tolerance
assignment and
balance
blue print
Operation
sequence
produced tolerances:
process tol of 10 + process tol of 12
process tol of 20 + process tol 22
process tol of 22 + setup tol

29. SURFACE FINISH w a v i n e s s r o u g h n e s s r o u g h n e s s w id t h w a v i n e s s w i d t h
Usually
simplified:
waviness height
waviness width 63
roughness
height
(m inch) 63
0.010
0.005
roughness width cutoff
default is 0.03" (ANSI Y )
roughness width
Lay
(inch)

30. PROBLEMS WITH DIMENSIONAL TOLERANCE ALONE
As designed: 1 . . 1 6 . . 1
As manufactured: 1 . 1
Will you accept the part
at right?
Problem is the control of
straightness.
How to eliminate the
ambiguity? 1 . 1 1 . 1 6 .

31. GEOMETRIC TOLERANCES
ANSI Y14.5M-1977 GD&T (ISO 1101, geometric tolerancing;
ISO positional tolerancing; ISO 5459 datums;
and others), ASME Y
FORM
straightness
flatness
Circularity
cylindricity
ORIENTATION
perpendicularity
angularity
parallelism
Squareness
roundness
LOCATION
concentricity
true position
symmetry
RUNOUT
circular runout
total runout
PROFILE
profile
profile of a line

32. DATUM & FEATURE CONTROL FRAME
Datum: a reference plane, point, line, axis where usually a plane where you can base your measurement.
Symbol:
Even a hole pattern can be used as datum.
Feature: specific component portions of a part and may include one or more surfaces such as holes, faces, screw threads, profiles, or slots.
Feature Control Frame: A
datum
// M A
modifier
symbol
tolerance value

33. MODIFIERS Maximum material condition MMC assembly
Regardless of feature size RFS (implied unless specified)
Least material condition LMC less frequently used
Projected tolerance zone
Diametrical tolerance zone
T Tangent plane
F Free state
maintain critical wall thickness or critical location of features.
MMC, RFS, LMC
MMC, RFS
RFS

34. SOME TERMS MMC : Maximum Material Condition
Smallest hole or largest peg (more material left on the part)
LMC : Least Material Condition
Largest hole or smallest peg (less material left on the part)
Virtual condition:
Collective effect of all tolerances specified on a feature.
Datum target points:
Specify on the drawing exactly where the datum contact points should be located. Three for primary datum, two for secondary datum and one or tertiary datum.

35. DATUM REFERENCE FRAME .
Three perfect planes used to locate the imperfect part.
a. Three point contact on the primary plane
b. two point contact on the secondary plane
c. one point contact on the tertiary plane P r i m a r y T e r t i a r y S e c o n d a r y
Secondary
O M A B C
primary
Tertiary C B A

36. STRAIGHTNESS Tolerance zone between two straightness lines.. 1
Value must be smaller than the size tolerance.
1.000 '
±0.002 M e a s u r e d e r r o r Š . 1 . 1
1.000 '
±0.002 . 1
Design
Meaning

38. FLATNESS Tolerance zone defined by two parallel planes. . 1 1.000 '. 1
1.000 '
±0.002 p a r a l l e l p l a n e s . 1

39. CIRCULARITY (ROUNDNESS)
a. Circle as a result of the intersection by any plane perpendicular to
a common axis.
b. On a sphere, any plane passes through a common center.
Tolerance zone bounded by two concentric circles. . 1
1.00 '
±0.05 . 1 T o l e r a n c e z o n e
At any section along the cylinder

40. CYLINDRICITY
Tolerance zone bounded by two concentric cylinders within which the cylinder must lie. . 1
1.00 '
±0.05
Rotate in a V . 1
Rotate between points

41. PERPENDICULARITY
A surface, median plane, or axis at a right angle to the datum plane
or axis. . 2 T A . 2 A . 2
1.000 '
±0.005 t o l e r a n c e z o n e p e r p e n d i c u l a r t o t h e d a t u m p l a n e
0.500 '
±0.005 A
2.000 '
±0.005 A . 2 d i a m e t e r t o l z o n e i s p e r p e n d i c u l a r O 1 . . 1 t o t h e d a t u m p l a n e . 2 A

42. ANGULARITY
A surface or axis at a specified angle (orther than 90°) from a datum
plane or axis. Can have more than one datum. . 5 A 1 . 5 . 5 4
3.500 '
±0.005 A

43. PARALLELISM
The condition of a surface equidistant at all points from a datum plane,
or an axis equidistant along its length to a datum axis. . 1 A
1.000 "
±0.005
2.000 "
±0.005 A . 1

44. PROFILE A uniform boundary along the true profile within whcih
the elements of the surface must lie. . 5 A B B A . 1

45. RUNOUT
A composite tolerance used to control the functional relationship
of one or more features of a part to a datum axis. Circular runout
controls the circular elements of a surface. As the part rotates
360° about the datum axis, the error must be within the tolerance
limit.
1.500 "
±0.005 A
0.361 "
±0.002 . 5 A D e v i a t i o n o n e a c h c i r c u l a r c h e c k r i n g i s l e s s t h a n t h e D a t u m t o l e r a n c e . a x i s

46. TOTAL RUNOUT 1.500 " ±0.005 A 0.361 " ±0.002 . 5 A D e v i a t i o n o. 5 A D e v i a t i o n o n t h e t o t a l s w e p t w h e n t h e p a r t i s r o t a t i n g D a t u m i s l e s s t h a n t h e a x i s t o l e r a n c e .

47. TRUE POSITION Dimensional tolerance Hole center tolerance zone. 2 2 1 . . 1 1 . 2 . 1 O . 8 . 2
Hole center tolerance zone O . 1 M A B
True position
tolerance T o l e r a n c e z o n e . 1 d i a 1 . B A 1 . 2

48. HOLE TOLERANCE ZONE Tolerance zone for dimensional toleranced
hole is not a circle. This causes some assembly
problems.
For a hole using true position tolerance
the tolerance zone is a circular zone.

49. TOLERANCE VALUE MODIFICATION1 . . 2 O . 1 M A B
Produced True Pos tol
hole size
out of diametric tolerance
out of diametric tolerance 1 .
M L S B 1 . 2
MMC
LMC A
The default modifier for
true position is MMC.
For M the allowable tolerance = specified tolerance + (produced hole
size - MMC hole size)

50. MMC HOLE ,
Given the same peg (MMC peg), when the produced hole size is greater than the MMC hole, the hole axis true position tolerance zone can be enlarged by the amount of difference between the produced hole size and the MMC hole size.

51. PROJECTED TOLERANCE ZONE
Applied for threaded holes or press fit holes to ensure interchangeability
between parts. The height of the projected tolerance zone is the thickness
of the mating part. . 3 7 5 - 1 6 U N C - 2 B O . 1 M A B C . 2 5 p

52. SOME NUMBERS
Krulikowski, A., GD&T Challenges the Fast Draw, MFG ENG, Feb 1994.
GD&T drawings are more expansive to make, however, saves revision cost.
Drawing revision costs $500 - $2000 on the paper work
How much does it cost to “put a part number” onto a part? Estimates range from $1,000 -$10,000.