Machine Drafting Chapter 8 Dimension Ing

8/2/2019 Machine Drafting Chapter 8 Dimension Ing

1/31

4/20/2012 1

Basic Dimensioning

Dimensioning Standards

ANSI: American National Standards Institute

ASME: American Society of MechanicalEngineers.

MIL-STD: Military Standards

ISO: International Standards Organization


2/31

4/20/2012 2

Basic Dimensioning

Location Dimensions


3/31

4/20/2012 3

Basic Dimensioning

Size Dimensions


4/31

4/20/2012 4

Basic Dimensioning

Complete dimensions


5/31

4/20/2012 5

Basic Dimensioning

Dimensioning Types

Unidirectional: Dimensions that are orientatedto read from the bottom of the drawing.


6/31

4/20/2012 6

Basic Dimensioning

Aligned: Dimensions that are orientated toread from the bottom and the right of thedrawings. (Parallel to the dimension line).


7/31

4/20/2012 7

Basic DimensioningDimensioning Types

Base Line/Datum: Dimension which specifythe location of features from a fixed referenceor datumline .


8/31

4/20/2012 8

Basic DimensioningDimensioning Types

Chain or Continuous: Dimensions that locatevarious features of an object with respect toeach other.


9/31

4/20/2012 9

Basic Dimensioning

Chain or Continuous: Tolerance accumulationproblems.


10/31

4/20/2012 10

Basic DimensioningTolerance Accumulation

100mm + 0.1mm = 100.1mm total length.

45.1 + 30.1 + 25.1 = 100.3mm total length.


11/31

4/20/2012 11

Basic DimensioningTolerance Accumulation

Solution: Eliminate one dimension in thechain.


12/31

4/20/2012 12

Basic Dimensioning

Dimensioning Terms

Detail Drawing: The drawing of a single part

completely specified for manufacture.

Specifications: Notes, material call-out,hardness amount, heat treatment, surfacequality, plating, testing, etc.

Dimensions: Values placed on a drawing toindicate location and size of geometry.


13/31

4/20/2012 13

Basic Dimensioning

Dimensioning Terms

Size Dimensions: Indicate the physical size of

a feature. Location Dimensions: Show the location of

features relative to a datum.

Dimension Lines: Drawn between extensionlines, contain the dimension value, and areterminated with arrowheads.


14/31

4/20/2012 14

Basic Dimensioning

Dimensioning Terms

Arrowheads: Placed on the ends of the

dimension line. Are drawn to a 3:1 ratio. Mayvary with the type of drafting.

Extension Lines: Extend from the featurebeing dimensioned with a gap of about 2 mm.

Leaders: Lines inclined 20 to 70 fromhorizontal. They point to some feature on thedrawings.


15/31

4/20/2012 15

Basic Dimensioning

Dimensioning Terms

Datums: Planes, points, or lines used as a

reference for dimensions. General Notes: Place general notes on a

drawing to indicate operations orspecifications that apply to the entire drawing.

(ie. ALL FILLETS AND ROUNDS R3 UNLESSSPECIFIED).

Local Notes: Provide information or sizevalues for a specific feature of a part.


16/31

4/20/2012 16

Basic Dimensioning

Contour Rule for Dimensioning

The contour view is the one that will show a

characteristic shape more clearly than any ofthe other views. Will show the true shapeofthe feature being dimensioned.


17/31

4/20/2012 17

Basic Dimensioning

Fundamental Rules

Organize dimensions: The first dimension line

is placed approximately 9mm /.38 from theobject with additional dimension lines spacedabout 6mm/.25 from each other.

Be specific: Each dimension can only be

interpreted one way.

Repetition: Do not repeat dimensions.


18/31

4/20/2012 18

Basic Dimensioning

Fundamental Rules

Placement: Dimension to visible lines, not

hidden lines. Dimension to true shapeviews,not oblique views. Place dimensions outsideof the part unless it cant be avoided.

Size: Each dimension must be to actual size

with no scaling allowed. If this is not possiblea line must appear under the dimension toindicate that it is not to scale.


19/31

4/20/2012 19

Basic Dimensioning

Fundamental Rules

Manufacturing Operations: Generally, do not

place manufacturing operations ondimensions. (i.e. .75 DRILL or 1.252 REAM)

Do not cross dimension lines.

Place dimensions between views whenpossible.

Sub-Dimensions first followed by overalldimensions.


20/31

4/20/2012 20

Basic Dimensioning

Fundamental Rules

Dimensions should be 3mm (1/8) in height.

Titles can be 6mm (1/4) high.

Centerlines can be used as extension linesfrom round features.

Dimension to the longitudinal view of apositive cylinder.


21/31

4/20/2012 21

Basic Dimensioning

Fundamental Rules

Dimensions to the circular view of a negative

cylinder.

Omit one dimension in a chain or continuousset of dimensions to prevent tolerancebuildup.

Dimension full circles using the Diameteroption and arcs using the Radius option inCAD.


22/31

4/20/2012 22

Basic Dimensioning

Fundamental Rules

Dimension holes and other symmetricalobjects to their centerlines.


23/31

4/20/2012 23

Dimension to the longitudinal view of positive cylinders. Use lineardimensions and add the prefix %%c to get the diameter symbol.


24/31

4/20/2012 24

Dimension to the circular view of negative cylinders. Use the diameterdimension tool and add the suffix x to get the depth symbol. (GDT font

using the lowercase x.)


25/31

4/20/2012 25

Dimensioning a slot.


26/31

4/20/2012 26

Dimensioning a slot.


27/31

4/20/2012 27

Dimensioning Locate the slot and give the size


28/31

4/20/2012 28

Dimensioning Locate notch.


29/31

4/20/2012 29

Dimensioning Show thickness


30/31

4/20/2012 30

Dimensioning Add overall dimensions


31/31

4/20/2012 31

Dimensioning Completed

Documents

Machine Drafting Chapter 8 Dimension Ing