Dr. Soleh 013515104X_pp9a dimensioning 23.9.13.

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Dimensioning

Chapter 9


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Modern Graphics Communications 4 th EditionGiesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart

2010 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Objectives

Use conventional dimensioningtechniques to describe size and shapeaccurately on an engineering drawing

Create and read a drawing at aspecified scale

Correctly place dimension lines,extension lines, angles, and notes


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Aspects of Good Dimensioning

Dimensions are given in the form of distances, angles, and notes regardless

of the dimensioning units being used The ability to create good dimensions

requires:

Technique of dimensioning Placement of dimensions Choice of dimensions


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Lines Used in Dimensioning

Dimension line a thin, dark, solid lineterminated by arrowheads, indicatingthe direction and extent of a dimension


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Extension line a thin, dark, solid linethat extends from a point on thedrawing to which a dimension refers


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Centerline athin, dark line

alternating longand short dashescommonly used inlocating holes andother symmetricalfeatures


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Using Dimension and

Extension Lines


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Using Dimension and

Extension Lines Dimensions should be lined up and

grouped together as much as possible


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Arrowheads

Arrowheads indicate the extent of dimensions

They should be uniform in size andstyle throughout the drawing


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Leaders

A leader is a thin solid line directingattention to a note or dimension andstarting with an arrowhead or dot


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Dimension Units

Dimension values are shown using themetric system or decimal inch values

It is standard practice to omit millimeterdesignations and inch marks ondrawings and note the units in the titleblock except when there is a possibilityof misunderstanding


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Placing Dimensions

Never letter a dimension value over anyline on the drawing

In a group of parallel dimension lines,the dimension values should bestaggered

Do not crowd dimension figures intolimited spaces making them illegible


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Placing Dimensions

Place dimensions between views whenpossible, but only attached to a singleview

Dimensions should not be placed on aview unless doing so promotes theclarity of the drawing


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Placing Dimensions

When a dimension must be placed in ahatched area or on the view, leave anopening in the hatching or a break inthe lines for the dimension value


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Placing Dimensions

Avoid dimensioning to hidden lines Do not attach dimensions to visible lines

where the meaning is not clear Notes for holes are usually placed

where you see the circular shape of the

hole An external cylindrical shape is

dimensioned where it appears rectangular


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Placing Dimensions

Give dimensions where the contours of the object are defined


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Superfluous Dimensions

All necessary dimensions must beshown but avoid giving unnecessarydimensions

Do not repeat dimensions on the sameview or on different views, or give the

same information two different ways


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Dimensioning Angles

You should dimension angles byspecifying the angle in degrees and alinear dimension


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Dimensioning Arcs

A circular arc is dimensioned in the viewwhere you see its true shape by givingthe value for its radius preceded by theabbreviation R


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Fillets and Rounds

Individual fillets and rounds aredimensioned like other arcs

If there are only a few and they areobviously the same size, giving one typicalradius is preferred

Fillets radii can also be given in a generalnote


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Size Dimensions: Cylinders


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Size Dimensions: Holes


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Dimensioning Various Shapes


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Dimensioning Curves


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Dimensioning Curved Surfaces


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Dimensioning Rounded-end

Shapes


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Dimensioning Threads


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Dimensioning Tapers


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Dimensioning Chamfers


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Shaft Centers


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Finish Marks

A finish mark is used to indicate that asurface is to be machined


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Surface Roughness


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Location Dimensions


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Location Dimensions


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Location Dimensions


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Modern Graphics Communications 4 th Edition 2010 Pearson Education Upper Saddle River NJ 07458

Location Dimensions

Dr. Soleh 013515104X_pp9a dimensioning 23.9.13.

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