1. Dimensioning and Tolerancing
Chapter 17
Dimensioning and Tolerancing
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Homework Figure 17.88 Mounting Saddle

3. What three elements does this drawing have?
What are drawings?
Communication Tools
Graphics
Dimensions/ (Symbols)
Words (Notes)
Dimensioning-
process of adding size, location, and manufacturing information to a drawing (Find only in 1 place)
Current standard is ASME Y14.5M-2009

4. Reading Direction of Dimensions
Text is to read Unidirectional
What industry uses aligned?

5. Text and Arrow Standards
Inch- No 0 before decimal point
Metric- 0 precedes decimal point
Dimensions are always expressed to same number of decimal places as tolerance
What if dimension is only ½” but the tolerance is to the thousandths?

6. Rules to Dimension by: Dimension overall size first (H, W, D)
Dimension basic sizes and locations of features
Add notes describing details of construction for manufacture

7. Units of Measure:
America- all dimensions in inches unless otherwise noted
If parts are over 72” switch to feet and inches
Outside US- metric system or international system of measure (SI)
What is required to be on drawing if metric units are being used?
METRIC

8. Dimension Terminology
Who Can define each of these dimension elements?
Basic Dimensions- Numeric value defining theoretically exact size, location, profile, or orientation of a feature .
Reference Dimension- Numerical value in parenthesis , for information purposes only, not to be used to fabricate part

9. What is the most precise way to dimension a part?
Datum Dimensioning-
Theoretical exact surface used as a reference for dimensionS
Tape Measure Rule

10. Dimension in their most descriptive view
Contour Dimensioning
Dimension in their most descriptive view
Never to a hidden line

11. Angular Dimensions-
shown either in degree, decimal degree, or degree, minute, seconds
How many minutes are in a degree?
What would 45.5˚ be in degrees, minutes, seconds?
2 ways to dimension a chamfer

12. Dimension this part with a partner using methods we just discussed!

13. Size Location Machining Info How many views are needed?
What information is necessary to fabricate this block with a hole drilled through it?
How many views are needed?
Size
Height
Width
Depth
Location
X direction
Y direction
Machining Info
Hole thru unless noted

14. ___________ is the overall objective!
Standard Practices
Placement
Spacing
Not inside part
___________ is the overall objective!

15. Dimensioning Tricks Avoid over dimensioning
Dimension in most descriptive view
Avoid Chain line dimensioning
Staggering if dimensions are too close

16. Centerline and Extension line Practices
Why are center marks extended past largest concentric radius or circle?

17. Needing another process
Use of Chain Lines
Needing another process

18. Use multiples of occurrence in that view only
Repetitive Elements
Use multiples of occurrence in that view only
What is the centerline going through the center of all of the instances?
Leaders
Pass through center

19. Dimension this part with a partner using methods we just discussed!

20. Symbols for drilling operations
Symbol/ size/
Secondary operation symbol/ Symbol/ size
Depth Symbol/ size

21. Dimensioning Blind Holes and Slots
________hole is assumed if no depth is given.
What information is lacking to mill the slot?

22. Summary of current vs. previous standards
If we have had the new standard since 2009 why should we know these?

24. Dimensioning Threads & Grooves
Which groove method is easier to verify?
M8X2
M8X2

25. Homework Figure 17.88 Mounting Saddle

26. With a partner dimension a parts with 5 holes
With a partner dimension a parts with 5 holes. Use the two methods to dimension them 1” from each end and .50 apart with a tolerance of +/ Calculate how far off the last hole could potentially be from the left edge of the part.
Base line
Chain line

27. Why do we have Tolerencing?
Controlling the variation that exist on all manufactured parts (Total amount a dimension may vary)
System for two or more mating parts
Pen lids/ Markers

28. Functional Dimensioning
Dimension and Tolerance functional features first

29. Tolerances expressed in several ways:
Direct limits
Tolerance Values
Unilateral
Bi-lateral
Symmetric
Geometric Tolerances (GD&T)
General tolerance note or title block note

30. When does a part have MMC vs. LMC?
Tolerancing
When does a part have MMC vs. LMC?
Maximum Material Condition (MMC)- when it contains the most material (Weighs the most)
Least Material Condition (LMC)-
when it contains the least material (Weighs the least)

31. Important Tolerance Terms
Nominal size – General size ½”
Basic size- Theoretical size .500”
Actual size- measured size .498”
Limits- Max and Min shown in tolerance
Allowance- Min clearance or Max interference (Tightest fit)
Tolerance- allowable variance difference between upper and lower limits
Piece Tolerance- Difference between upper and lower limits of single part
System Tolerance- Sum of all piece tolerances

32. Dimension these two parts in groups of 2
How many views are needed for each part?
What is most important feature?
Assembled View

33. Tolerance Stack up: BAD GOOD Alternate method
Amount of Variation due to tolerances dimensioned from different sides or between multiple features
BAD
GOOD
Alternate method

34. Homework

35. Fit Types Clearance- a space when assembled
Interference- Interfere when assembled
Transition- Sometimes clearance and sometimes interference
What is the fit if the shaft is machined to its smallest diameter?
What is the fit if the shaft is machined to its largest diameter?

36. Standard Precision Fits for English Units
Running and Sliding Fits (RC)- Loosest Class where shaft must move freely
Clearance Locational Fit (LC)- Shaft and Hole may be same size (Line to Line fit)
Transition Locational Fit (LT)- Transition between LC & LN fits
Interference Locational Fits (LN)- Shaft larger than hole (Alignment dowel pins)
Force and Shrink Fits (FN)- Shaft is always bigger (Transmit torque)

37. Applying tolerances for Clearance basic hole system
Givens

38. Applying tolerances for Interference basic hole system
Givens

39. Higher the number=looser the fit
Metric Tolerancing
Use the tables
Higher the number=looser the fit

40. Surface Texture Symbols

41. Practice Exercise

42. Homework: Tolerance Handout
Use the tolerancing tables in appendixes 7 through 11 to calculate the limit dimensions between the shaft and hole for the given classes of fit

44. Homework