1. Dimensioning
Review
Objectives:

2. Dimensioning
Orthographic and Isometric Views define the shape and general features of the object
Dimensioning adds information that specifies
Size of the object
Location of features (e.g. holes)
Characteristics of features (e.g. depth and diameter of hole)
Dimensions also communicate the tolerance (or accuracy) required
Why is Dimensioning important? Stress it is important that all persons realizing a drawing interpret it exactly the same way.
A well-dimensioned part or structure will communicate the size and location requirements for each feature. Communications is the fundamental purpose of dimensions.
This class will only touch on very basis of dimensioning practice. Much more is available ion other texts and through industry.
Tolerance will be addressed in upcoming sessions.

3. Some General Guidelines
Start by dimensioning basic outside dimensions of the object.
Add dimension for location and size of removed features
Add general and specific notes – such as tolerances
Tolerances not used now – will be handled in upcoming sessions – but point#3 needs to be reiterated when handled

4. Dimensioning Basic Shapes – Assumptions
Perpendicularity
Symmetry
Perpendicularity – Important point here is that lines that appear to be at 90 degrees are assumed to be, unless dimensioned something different. Really reduces the number of dimensions needed.
Symmetry – When parts are truly symmetric in all ways, this can reduce the number of dimensions needed. In this simple case, the center of the hole is located by one dimension from the base and the centerline.
The R dimension on the upper radius, starting from the line of symmetry and center of the hole, defines the width of the piece as 2R.
It also is part of defining the height of the piece as the 1.25 plus R .75 or 2. Note an overall dimension on height would be double dimensioning. We will discuss why this is not acceptable in more detail when we get into tolerancing.
Note: The lines leading out to the R and Diameter dimensions are called leader lines. It is important to note that if extended, they would always pass through the center of the circle the are dimensioning all or part of.

5. Dimensioning Shows: A) Size B) Location and Orientation
Basic dimensions give two things:
Size of feature or body: ht, wt, depth, diameter
Location or orientation: center of hole, start of angled plane, angle of plane
Emphasize that for full circles the Diameter is ALWAYS required, for arcs ALWAYS Radius.
The basic criterion for dimensioning is, “What information is necessary to manufacture or construct the object?”.
ALWAYS give DIAMETER
" " for full circles (360 degrees) and RADIUS "R" for arcs (less than 360 degrees)

6. Dimensioning – Terminology
Students need to be encouraged to spend some quality time making sure they have the terminology described in Chapter on Dimensioning in Textbook.
Note in particular:
Extension lines. (6) Thin solid line. (Thin does not mean light, it is just as dark as an object line, just narrower. Takes practice to do this. Traditionally different sizes of pencil leads might be used to help do this.) Note gap between extension and body (1/16”).
Dimension line (4) perpendicular to extension lines, will will use filled arrowheads as our convention on arrowheads.

7. Principles of Good Dimensioning
The overriding principle of dimensioning is CLARITY
Principles – not an infallible rule set, need to apply good judgment.
Encourage students to spend some time reviewing the Table 4.1 on pg125: Parts of a Dimension, Principles of Good Dimensioning
This will not fully make sense unless they have done the reading ahead of it. But is a good place to go back to to refresh the principles and guidelines.

8. Principles of Good Dimensioning
Each feature dimensioned once and only once
Dimensions should suit the function of the object
Instructor:
This may have been covered before but needs to be emphasized here. When you have an overall dimension and one feature dimensioned you can calculate the missing dimension. You do not want to ‘over’ dimension by providing both feature dimension and the overall dimensions.

9. Tolerance: Controlling of Variability
Objectives:

10. Objectives
Understand description and control of variability through tolerancing
Understand various classes of fits
Introduce multiple part tolerancing
*TWO PART LECTURE
Objectives:Tolerancing, Control of Variability - At the end of the session, students should be able to:
Define tolerance in engineering design
Recognize the different forms in which tolerances are expressed
Calculate tolerances for single parts
Identify types of fits and calculate tolerances/allowances in a multipart hole-shaft system
Allocate 30-minutes for Single Parts System and 10 minutes for More than Two Parts Systems
Note to all instructors:
It could be emphasized that tolerances apply to all engineering disciplines – not just dimensions of drawings; examples are tolerances in resistances.
This chapter is an introduction to tolerances in general with engineering drawings as examples; if you use examples of tolerances in other engineering disciplines, please notify the College of Eng, so that it could be incorporated for future classes

11. Tolerance
Tolerance is the total amount a dimension may vary. It is the difference between the maximum and minimum limits.
Ways to Express:
Direct limits or as tolerance limits applied to a dimension
Geometric tolerances
A general tolerance note in title block
Notes referring to specific conditions
A dimension is a single number. It is not possible to cut an object exactly the length specified in the dimension, and often, it is not necessary to be very precise in the cutting. Using precision equipment is very expensive, so if the cut does not have to be precise, the engineering should specify that. It will save time and money.
The person designing an object will indicate the upper and lower limits on each dimension so the machinist will know how precisely to cut the object. The tolerance is the upper limit minus the lower limit. The tolerance can be specified by giving two numbers, the upper limit and the lower limit, in the place where the dimension would normally be. It can be specified by writing, for example, /- .01. If the tolerance is the same for every dimension on the object, the tolerance can be specified in a note such as GEN. TOL.  Such a note often appears in the title block.

12. ANSI/ASME Standard ANSI/ASME Standard Y14.5
Tolerances
Introduction to Engineering Design TM
Unit 2 – Lesson 2.2 – Dimensions and Tolerances
ANSI/ASME Standard
ANSI/ASME Standard Y14.5
Each dimension shall have a tolerance, except those dimensions specifically identified as reference, maximum, minimum, or stock. The tolerance may be applied directly to the dimension or indicated by a general note located in the title block of the drawing.
ANSI is an acronym that stands for the American National Standards Institute.
ASME is an acronym that stands for the American Society of Mechanical Engineers.
Project Lead The Way, Inc.
Copyright 2007

13. Variation is Unavoidable
No two manufactured objects are identical in every way. Some degree of variation will exist.
Engineers apply tolerances to part dimensions to reduce the amount of variation that occurs.

15. Tolerances
Three basic tolerances that occur most often on working drawings are: limit dimensions, unilateral, and bilateral tolerances.

16. Tolerances
Three basic tolerances that occur most often on working drawings are: limit dimensions, unilateral, and bilateral tolerances.

17. Limit Dimensions
Limit dimensions are two dimensional values stacked on top of each other. The dimensions show the largest and smallest values allowed. Anything in between these values is acceptable.

18. Limit Dimensions These are limit dimensions, because the upper and
lower dimensional sizes are
stacked on top of each other.

19. Unilateral Tolerance
A unilateral tolerance exists when a target dimension is given along with a tolerance that allows variation to occur in only one direction.

20. deviate in one direction.
Unilateral Tolerance
This tolerance is
unilateral, because
the size may only
deviate in one direction.

21. Bilateral Tolerance
A bilateral tolerance exists if the variation from a target dimension is shown occurring in both the positive and negative directions.

22. 1. Direct Limits and Tolerance Values
Limits of a dimension or the tolerance values are specified directly with the dimension.

23. 1. Direct Limits and Tolerance Values – Plus and Minus Dimensions
Unilateral Dimensions vary only in one direction; Bilateral dimension vary in both dimensions

24. 2. Geometric Tolerance System
Feature Control Frame
Geometric Dimensioning and Tolerancing (GD&T) is a method of defining parts based on how they function, using standard ANSI symbols.
Concentricity Symbol
Geometric dimensioning and tolerancing (GD&T) is now used frequently in industry It is used to show how one part of an object is related to another. For example, in the figure on this slide, it is important that the cylinder with the small diameter be concentric with the cylinder with the large diameter. In other words, in order for this piece to fit properly into another piece, which perhaps is being made someplace else, the center of the small cylinder needs to be placed almost exactly in line with the center of the large cylinder. We need a way to indicate how much distance can be tolerated between the center of the large cylinder and the center of the small cylinder. This information is given in the feature control frame which has 3 boxes. The first box on the left indicates that the feature being controlled is concentricity. The middle box indicates how far apart the centers of the two circles can be – no more that The third box indicates that A is the reference.
AU 2008

25. 3. Tolerance Specifications in Title Block
General tolerance note specifies the tolerance for all unspecified toleranced dimensions.
Discuss the circled information with the students.
AU 2008

26. 4. Notes Referring to Specific Conditions
General Tolerances could be in the form of a note similar to the one shown below:
ALL DECIMAL DIMENSIONS TO BE HELD TO .002"
Means that a dimension such as .500 would be assigned a tolerance of 0.002, resulting in a upper limit of .502 and a lower limit of .498

27. Important Terms – Single Part
Nominal Size – general size, usually expressed in common fractions (1/2" for the slot)
Basic Size – theoretical size used as starting point (.500" for the slot)
Actual Size – measured size of the finished part (.501" for the slot)
Note these terms apply to a single part.

28. Important Terms – Single Part
Limits – maximum and minimum sizes shown by tolerances (.502 and .498 – larger value is the upper limit and the smaller value is the lower limit, for the slot)
Tolerance – total allowable variance in dimensions (upper limit – lower limit) – object dimension could be as big as the upper limit or as small as the lower limit or anywhere in between
Note these terms apply to a single part.

29. Important Terms – Multiple Parts
Allowance – the minimum clearance or maximum interference between parts
Fit – degree of tightness between two parts
Clearance Fit – tolerance of mating parts always leaves a space
Interference Fit – tolerance of mating parts always results in interference
Transition Fit – sometimes interferes, sometimes clears
Note these terms are used with multiple parts.

30. Fitting Multiple Parts
Part A
Tolerance of A
Part B
Tolerance of B
Fit Tolerance: Clearance or Interference
AU 2008

31. Fitting Multiple Parts
Relate the drawing here to the terms defined for multiple parts in slide 11

32. Shaft and Hole Fits Clearance Interference Instructor:
Here is another way to look at how parts fit together. In this illustration, the beige area represents the variation in size of one part and it is easy to see that on the left side we have a clearance fit where the smallest hole is larger than the largest shaft. This is called a clearance fit.
The opposite is true on the other end. This is a force fit, shrink fit or an interference fit.
Note the small print at the bottom: Allowance always equals the smallest hole minus the largest shaft. When you have an interference fit the allowance is negative.

33. Shaft and Hole Fits Transition CLEARANCE FIT + .003 Instructor:
This figure is slightly different than the previous one. Here they have put the smallest shaft on the left end and the largest shaft on the right side. The shaft on the left clears by .003 inch while the one on the right interferes by .002 inch.

34. Standard Precision Fits: English Units
Running and sliding fits (RC)
Clearance locational fits (LC)
Transition locational fits (LT)
Interference locational fits (LN)
Force and shrink fits (FN)
Instructor:
Here are the types of fits specified by ANSI. The tables are found in the Appendices in most graphics books.

35. Basic Hole System or Hole Basis
Definition of the "Basic Hole System":
The "minimum size" of the hole is equal to the "basic size" of the fit
Example: If the nominal size of a fit is 1/2", then the minimum size of the hole in the system will be 0.500"
Instructor:
There needs to be some order to doing tolerances and in this case the choice was to make the smallest hole the basic size. If the nominal size is given as a common fraction (1/2) then the basic size is .500 or depending on the type of fit.

36. Basic Hole System – G28-A Clearance = Hole – Shaft
SMAX
SMIN
HMAX
HMIN
Clearance = Hole – Shaft
Cmax = H____ – S____
Cmin = H____ – S____
Fill in the subscripts (min, max) in the equations above.
Most common system used in dimensioning is the Basic Hole system. These are important definitions, usually showing up on exams.
See generic definitions on slide. We will do a general example and then do 1) English unit example and then metric example.
Encourage students to reason their way through these two equations, individually or in pairs.

37. Basic Hole System Clearance = Hole – Shaft Cmax = Hmax – Smin
SMAX
SMIN
HMAX
HMIN
Clearance = Hole – Shaft
Cmax = Hmax – Smin
Cmin = Hmin – Smax
Both Cmax and Cmin <0 – _________ fit
Both Cmax and Cmin >0 – _________ fit
Cmax > 0; Cmin < 0 – ___________ fit
What types of fits are these?
Opportunity to review types of fits – interference, clearance, transition
AU 2008

38. Basic Hole System Clearance = Hole – Shaft Cmax = Hmax – Smin
SMAX
SMIN
HMAX
HMIN
Clearance = Hole – Shaft
Cmax = Hmax – Smin
Cmin = Hmin – Smax
Both Cmax and Cmin <0 – Interference fit
Both Cmax and Cmin >0 – Clearance fit
Cmax > 0; Cmin < 0 – Transition fit
System Tolerance = Cmax – Cmin
Allowance = Min. Clearance = Cmin
AU 2008

39. Basic Hole System Calculate Maximum and Minimum Clearance
.490
.485
.510
.505
Clearance = Hole – Shaft
Cmax = Hmax – Smin
Cmax = .510 – .485 = .025
Cmin = Hmin – Smax
Cmin = Hmin – Smax
Cmin = = .015
Type of Fit is Clearance
What is Cmax/ Cmin = 0??
Cmin = .505 – .490 = .015
What type of fit is this?
Cmax > Cmin > 0 Clearance

40. Metric Limits and Fits Based on Standard Basic Sizes – ISO Standard
Note that in the Metric system:
Nominal Size = Basic Size
Example: If the nominal size is 8, then the basic size is 8
Instructor:
In the metric system the nominal size is equal to the basic size given with the correct number of decimal places.

41. Metric Preferred Hole Basis System of Fits
Instructor:
When working in the metric system they use a series of letters and numbers where the capital letters represent the hole and the lower case letters represent the shaft sizes.
AU 2008

42. Metric Tolerance Homework – TOL-1
Free Running H9/d9
Basic Size: 10
(1) Nominal Size: 10
(1) Nominal Size: ?
9.960
9.924
????
(2) Shaft Limits:
(3) Shaft Tolerance: ????
(3) Shaft Tolerance:
(7) Minimum
Clearance: ????
(8) Maximum
(7) Minimum
Clearance:
(8) Maximum
Clearance:
10.036
10.000
????
(4) Hole Limits:
(5) Hole Tolerance:
(5) Hole Tolerance: ????
Instructor:
Here is an example done in the metric system.
This problem is now done in several steps. It might be a good idea to have students open their text to the appropriate page and supply the requested information. There are approximately 10 clicks to get through the slide.
(6) Ts:
(6) Ts: ????
CHECK: Ts = Cmax – Cmin?
CHECK: = – = 0.072

43. Today's Assignment
Tolerance Yellow Packet
All problems.
Due 4/16

44. Surface Control and Geometric Dimensioning and Tolerancing
Objectives:

45. Objectives Introduce Surface Control terms and symbols
Introduce Geometric Dimensioning and Tolerancing

46. Surface Control Why do we need to control surface characteristics?
Rough surfaces cause friction and wear
It is difficult to make accurate measurements from rough surfaces

47. Surface Characteristics
Roughness
Small hills and valleys found on a surface
Defined as the arithmetic average of the deviations above and below a mean height of a surface
Expressed in microinches or micrometers.

48. Surface Characteristics
Waviness
Surface irregularities greater than roughness
Expressed in inches or millimeters
See Figure 7.21 on page 7-14 of TG
Lay
Direction of tool marks on a machined surface.
See Figure 7.20 on page 7-13 of TG.

49. Surface Texture Symbols
.25 inches
.125 in
Surface Control Symbol
Material must be removed
Material must not be removed
Material removal not specified
Autumn 2009

50. Lay Symbols M C R P Parallel to line representing surface
Perpendicular to the line representing the surface
Both directions to the line representing the surface
Multidirectional marks
Circular
Radial
Lay particulate, non-directional, protuberant
Bar added M
Symbol
location C R P

51. Examples with Roughness and Lay24
Average roughness is inches, which is
often referred to as 24 microinches or µ inches.
Material must be removed. 28 14
Maximum average roughness is 28 microinches.
Minimum average roughness is 14 microinches.
Material must not be removed.
Average roughness is 45 microinches
Lines on the surface are radial with respect
to the center of the surface 45 R

52. Geometric Tolerancing
Geometric Tolerancing includes specifications of form, profile, orientation, location, and runout.

53. Geometric Tolerancing
What features of PART 1 need some constraints so that the assembly will work properly? Discuss with the people at your table.
Introduction of geometric tolerancing and an example of a situation where it might be needed.
Encourage students to talk about what needs to be constrained/toleranced.
Some students may talk about the diameter of the shafts and types of fits.
The goal is to have them come up with something like: “the shafts should be very close to parallel” or “the shafts should be close to perpendicular to the base”.
What happens if the two shafts are not parallel?

54. Geometric Tolerancing – Definitions
Basic Dimension – A numerical value for theoretical exact size or location
True Position – The theoretically exact location of a feature established by basic dimensions
Datum – A theoretically exact point, axis, or plane used as the origin from which location or geometric characteristics of features are located
Datum Target – A specified point, line, or area on a part used to establish a datum
Datum Feature – An actual feature of a part used to establish a datum

55. Geometric Tolerancing – Definitions
Maximum Material Condition (MMC) – The condition in which a feature of size contains the maximum amount of material with the stated limits of size. For example, minimum hole diameter and maximum shaft diameter
Least Material Condition (LMC) – Opposite of MMC, the feature contains the least material. For example, maximum hole diameter and minimum shaft diameter
Virtual Condition – The envelope or boundary that describes the collective effects of all tolerance requirements on a feature (See Figure 7-25 TG)
Autumn 2009

56. Virtual Condition Envelope All Required Tolerances
20.06" Maximum
Envelope
0.06"
Maximum
Allowable
Curvature
20.00"
Maximum
Allowable
Diameter

57. Basic Symbols for Geometric Characteristics
Individual Features Tolerance of Form Straightness
Flatness
Circularity (roundness)
Cylindricity
Individual or Related Tolerance of Profile Profile of a line
Profile of a surface
Related Features Tolerance of Orientation Angularity
Perpendicularity
Parallelism
Tolerance of Location Position
Concentricity
Tolerance of Runout Circular Runout
Total Runout

58. Modifying Symbols for Geometric Characteristics
At maximum material condition
At least material condition
Projected tolerance zone
Diameter
Spherical diameter
Radius
Spherical Radius
Reference
Arc length M L P S R SR
( )

59. Feature Control Frame .007 M B
Geometric
Characteristic
Symbol
Tolerance
Material condition
Datum
Reference
This feature must be parallel to Datum B within .007 at MMC (largest cylinder) as measured on the axis

60. Tolerance of Form – Straightness
This cylinder must be straight
within 0.03 mm.
0.03
19.89
19.86
What it means -
0.03 Tolerance Zone

61. Concentricity Tolerance Note
.007 A A XX YY
This cylinder (the right cylinder) must be concentric
within .007 with the Datum A (the left cylinder)
as measured on the axis

62. Concentricity Tolerance Note – What It Means
.007 Tolerance Zone