Standard Practice for
Dimensioning Drawings
Introduction to
Mechanical Engineering
Fall 2004
Created by:
P.M. Larochelle
Dimensions
 Dimensions

are used to describe the sizes
and relationships between features in your
drawing.
 Dimensions a...
Dimensions
 Drawings

with dimensions and notes often
serve as manufacturing or construction
documents and legal contract...
Dimensions
 Definition:

Dimensions are the distances,
angles, and notes that define the geometry
and manufacturing of th...
Dimensioning
Good Dimensioning
 The
–
–
–
–

keys to good dimensioning are:

Choice of dimensions
Placement of dimensions
Technique of...
Choice of Dimensions


The dimensions you specify define how the object is
manufactured:
–



Dimension first for functi...
Placement of Dimensions
 Follow

accepted standards so that
dimensions are legible, easy to find, and
easy to interpret.
...
Placement of Dimensions
 Do’s
–
–
–
–

& Don’t’s

Avoid dimensions on the object itself
Avoid dimensioning to hidden line...
Placement of Dimensions


Follow closely
the rules for
placement of
dimension and
extension
lines in
section 9.14
on pg. ...
Technique of Dimensioning
 Follow

accepted standards & practices for
the appearance of lines, spacing of
dimension lines...
Lines Used in Dimensioning
A

dimension line
is a thin, dark,
solid line
terminated by
arrowheads that
indicate the
direc...
Lines Used in Dimensioning
 An

extension line is a thin, dark, solid line that
extends from a point on the drawing to it...
Lines Used in Dimensioning
A

center line is a thin, dark, solid line that
alternates long and short dashes to locate hol...
Lines Used in Dimensioning
 Arrowheads

are used to indicate the extent of a
dimension. They should be uniform in size &
...
Lines Used in Dimensioning


An leader is a thin, solid line directing attention to a note
or dimension. A leader starts ...
Dimension Tolerances


A tolerance is required for every dimension on a drawing.
Definition: a tolerance is the total amo...
Dimension Tolerances: Examples
Dimension Tolerances
 The
–
–
–

purpose of dimension tolerances:

Allows a range of acceptable variability on the
dimens...
Dimension Tolerances
 Tolerance

stacking is to be avoided by
dimensioning with respect to a datum.
Do’s & Don’ts of Dimensioning




Do not trust the automatic creation & placement of
dimensions done for you by CAD soft...
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: Examples
Dimensioning: A real drawing
Dimensioning: Homework


Do Figure #9.71 on page 328 of the text.
Create a sketch with metric dimensions on
green enginee...
References
 Chapters

9 of Modern Graphics
Communication by Giesecke, Mitchell,
Spencer, Hill, Dygdon, Novak, and Lockhar...
Upcoming SlideShare
Loading in …5
×

Dimensioning 1

1,863 views

Published on

Published in: Design, Technology, Business
  • Suresh Kothandaraman, Thank you very much for sharing to us this very informative and useful presentation. Emong (Philippines)
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here

Dimensioning 1

  1. 1. Standard Practice for Dimensioning Drawings Introduction to Mechanical Engineering Fall 2004 Created by: P.M. Larochelle
  2. 2. Dimensions  Dimensions are used to describe the sizes and relationships between features in your drawing.  Dimensions are used to manufacture parts and to inspect the the resulting parts to determine if they meet the drawing’s specifications.
  3. 3. Dimensions  Drawings with dimensions and notes often serve as manufacturing or construction documents and legal contracts.  ASME Y14.5 is the current geometric dimensioning and tolerancing standard.
  4. 4. Dimensions  Definition: Dimensions are the distances, angles, and notes that define the geometry and manufacturing of the object.  Do not give superfluous dimensions – – Only those dimensions that are needed to manufacture and inspect the object are to be included on the drawing Do not include dimensions just because they are needed to produce the drawing
  5. 5. Dimensioning
  6. 6. Good Dimensioning  The – – – – keys to good dimensioning are: Choice of dimensions Placement of dimensions Technique of dimensioning Specifying dimension tolerances
  7. 7. Choice of Dimensions  The dimensions you specify define how the object is manufactured: –  Dimension first for function and then review seeking improvements for production/manufacturing purposes such as manufacturability, inspection, etc. Do not give superfluous dimensions – – Only those dimensions that are needed to manufacture and inspect the object are to be included on the drawing Each dimension should appear only once; do not repeat dimensions in different views.
  8. 8. Placement of Dimensions  Follow accepted standards so that dimensions are legible, easy to find, and easy to interpret.  The spacing of dimensions lines must be uniform throughout the drawing.
  9. 9. Placement of Dimensions  Do’s – – – – & Don’t’s Avoid dimensions on the object itself Avoid dimensioning to hidden lines Don’t float dimensions Do group dimensions around a central view
  10. 10. Placement of Dimensions  Follow closely the rules for placement of dimension and extension lines in section 9.14 on pg. 291 of the text.
  11. 11. Technique of Dimensioning  Follow accepted standards & practices for the appearance of lines, spacing of dimension lines, size of arrowheads, etc. so that others may correctly interpret your drawing.
  12. 12. Lines Used in Dimensioning A dimension line is a thin, dark, solid line terminated by arrowheads that indicate the direction and extent of a dimension.
  13. 13. Lines Used in Dimensioning  An extension line is a thin, dark, solid line that extends from a point on the drawing to its associated dimension line. – A gap of ~1.5 mm should be left between the extension line and the point on the part.
  14. 14. Lines Used in Dimensioning A center line is a thin, dark, solid line that alternates long and short dashes to locate holes and other symmetrical features.
  15. 15. Lines Used in Dimensioning  Arrowheads are used to indicate the extent of a dimension. They should be uniform in size & style throughout the drawing.
  16. 16. Lines Used in Dimensioning  An leader is a thin, solid line directing attention to a note or dimension. A leader starts with an arrow or dot: – – Use an arrow when the leader can point to a specific line in the drawing such as the edge of a surface Use a dot when the leader is locating a feature within the outline of the part
  17. 17. Dimension Tolerances  A tolerance is required for every dimension on a drawing. Definition: a tolerance is the total amount that the feature on the actual part is allowed to vary from what is specified by the dimension. – A general tolerance applicable to most dimensions can be specified in the title block.  – Example: “All tolerances +/- 0.01 inches unless otherwise noted”. A tolerance for a particular dimension may be specified by limit dimensions or plus and minus dimensions.  Example: “1.500 +/-.003” or “1.252/1.248”
  18. 18. Dimension Tolerances: Examples
  19. 19. Dimension Tolerances  The – – – purpose of dimension tolerances: Allows a range of acceptable variability on the dimensions of a part Assures that parts interchanged between assemblies will fit properly Allowing parts be manufactured to prescribed tolerances rather than exact dimensions permits efficient and economical manufacturing. In general: high precision means high cost!
  20. 20. Dimension Tolerances  Tolerance stacking is to be avoided by dimensioning with respect to a datum.
  21. 21. Do’s & Don’ts of Dimensioning   Do not trust the automatic creation & placement of dimensions done for you by CAD software. Review & use the list in section 9.43 pg. 318 of the text for every dimensioned drawing you create: 1. 2. 3. 4. Each dimension should be given clearly so that it can be interpreted only one way Dimensions should not be duplicated Dimensions should be given so that the machinist will not have to calculate, scale, or assume any dimensions. The list goes on to #57!
  22. 22. Dimensioning: Examples
  23. 23. Dimensioning: Examples
  24. 24. Dimensioning: Examples
  25. 25. Dimensioning: Examples
  26. 26. Dimensioning: Examples
  27. 27. Dimensioning: Examples
  28. 28. Dimensioning: Examples
  29. 29. Dimensioning: Examples
  30. 30. Dimensioning: Examples
  31. 31. Dimensioning: Examples
  32. 32. Dimensioning: A real drawing
  33. 33. Dimensioning: Homework  Do Figure #9.71 on page 328 of the text. Create a sketch with metric dimensions on green engineering paper. Due before lecture begins on Wednesday October 20th.
  34. 34. References  Chapters 9 of Modern Graphics Communication by Giesecke, Mitchell, Spencer, Hill, Dygdon, Novak, and Lockhard, 3rd edition. Prentice-Hall, 2004.  Technical Drawing by Giesecke, Mitchell, Spencer, Hill, Dygdon, and Novak, 9th edition. Macmillan, 1991.

×