DIMENSIONINGby Mr. Curtis Marcelle and Mrs. Kya Morris

OBJECTIVES

At the end of this lesson, students will be able to:

Define the term dimensioning

Recognize the rules for proper dimensioning

Explain the different types of dimensioning techniques

Illustrate the different dimensioning techniques

Dimension any plane and irregular figure

Value the purpose of dimensioning

WHAT IS A DIMENSION?

In Technical Drawing, dimensions are: a numeric value expressed in measureable units

such as, mm, cm, inches, etc. that define the size, location, or orientation of a geometrical part or object.

A method of communication for persons in the industries.

WHAT IS THE PURPOSE OF DIMENSIONING?

The purpose of dimensions is to provide a clear and complete description or measurement of an object or part.

To communicate numeric values for a particular geometrical part or object.

WHEN DO WE USE DIMENSION?

We use dimensions when details of a particular geometrical part or object is needed.

Dimensions should be done on all drawings that will be interpreted later on.

HOW DO WE DIMENSION?

In Technical Drawing, we must dimension with: Accuracy - correct values must be given. Clearness - dimensions must be placed in

appropriate positions. Completeness - nothing should be left out, and

nothing duplicated. Readability - the appropriate line quality must be

used for legibility.

PARTS OF A DIMENSION

BASIC TYPES OF DIMENSIONING

Linear/Chain Radius/Diameter Aligned Parallel Angular Combined

LINEAR/CHAIN A type of dimension that measures in a straight line

(either horizontal or perpendicular).

ALIGNED This type of dimension measures a line that

is at an angle. This dimension is parallel to the angled line.

ANGULAR A type of dimension that measures the angle

between two lines.

PARALLEL All dimensions are parallel to each other and

originates from the same line.

COMBINED A combination of two or more types of

dimensioning

RADIUS/DIAMETER

A type of dimension that measures the radius or diameter of a circle or arc.

RULES FOR DIMENSIONING

RULES FOR DIMENSIONING Dimension lines must be kept at least 5mm from the

object, and at least 10mm from each other.

RULES FOR DIMENSIONING

Dimensions that are not needed should not be given.

When the overall dimension is given, one of the smaller ones should be eliminated.

RULES FOR DIMENSIONING

On a part with a circular end, dimension to the centerline.

Always give the diameter of a circle, not the radius. Use symbol Ø.

RULES FOR DIMENSIONING Always give the radius of an

arc, with the abbreviation ‘R’ given before dimension text.

Do not use a centerline or a part of an object as a dimension line.

RULES FOR DIMENSIONING Do not use an object line

as an extension line. Do not cross dimension

lines.

CONCLUSION

We learned: What was a dimension The purpose of dimensions When to use dimensions How to use dimensions Types of dimensioning

QUESTIONS?