dimensioning technique

DIMENSIONING

Prashant AmbadekarDIMENSIONINGDimensioningBIS (Bureau of Indian Standards SP 46: 2003) defines dimension as a numerical value expressed in appropriate units of measurement and indicated graphically on technical drawings with lines, symbols and notes.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULTerms used in dimensioning

Dimension : Numerical value assigned to shape, size or location of the feature being described.

Dimension line : Thin continuous line terminated by arrowheads touching the extension lines.

Extension line : Extension of an outline or centerline.

SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULTerms used in dimensioning

Arrowhead : It is placed at each end of dimension line.Its pointed end should touch the extension line.It should be closed and filled.Length of arrowhead should be about three times its width.The size of all arrowhead in the entire view should be same.

SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULSystems of Dimensioning

Aligned SystemDimensions are aligned with the entity being measured. They are placed perpendicular to the dimension line such that they may be read from the bottom or right-hand side of the drawing. Dimensions are placed at the middle and on top of the dimension lines.

SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULSystems of Dimensioning

Unidirectional SystemIn the unidirectional system, dimensions are placed in such a way that they can be read from the bottom edge of the drawing sheet. Dimensions are inserted by breaking the dimension lines at the middle.

SIES GRADUATE SCHOOL OF TECHNOLOGY, NERUL

Methods of dimensioning

Parallel (progressive) dimensioning

All the dimensions are shown from a common reference line. All these dimensions share a common extension line. This method is adopted when dimensions have to be established from a particular datum surface.

SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULMethods of dimensioning

Chain (continuous) dimensioning

All the dimensions are aligned in such a way that an arrowhead of one dimension touches tip-to-tip the arrowhead of the adjacent dimension.

SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULMethods of dimensioning

Combined dimensioningWhen both the methods, i.e., chain dimensioning and parallel dimensioning are used on the same drawing, the method of dimensioning is called combined dimensioning


Guidelines for dimensioning

Dimension line is a thin line. After dimensioning of views, there should be no need to calculate or assume any dimension. A dimension should be given to such an entity that the best feature is dimensioned.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULGuidelines for dimensioning

Dimension line should always be parallel to the outline that is to be dimensioned.

Dimension lines should be drawn at least 10 mm away from the outlines and from each other.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERUL


Dimension must not be repeated.

Dimension line should be perpendicular to the extension lines.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULGuidelines for dimensioning

Extension lines are thin lines and should extend beyond the dimension lines for about 3 mm.

Extension lines may cross each other or outline of the object. Dimension lines should not cross each other or any other line in the view.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULGuidelines for dimensioning

The outline of view should not be used for dimensioning.

Only extension lines should be used for dimensioning.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULGuidelines for dimensioning

The centre lines should not be used for dimensioning.

In case a centre line is to be used for dimensioning, use it properly as extension line.



The dotted lines should not be used for dimensioning. As far as possible dimension should not be given inside the view.

But in some cases where more clarity and readability is required, one can also dimension inside the view.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERUL


Smaller dimensions should be placed nearer to the view and larger further away so that extension lines do not cross the dimension lines.

SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULGuidelines for dimensioning

Dimension of circular part or arc should be preferably given in the view where it is seen as a circle or an arc.

The leader line should be used for dimensioning the circles or for introducing a note.

A leader line is an inclined line followed by a short horizontal line. The angle of inclination should be 45 30 or 60 in the given order as the space is available.

Dimension should be written above the horizontal dimension line and never be written below the line.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERULGuidelines for dimensioning

Dimension should be written to the left of vertical dimension line and should be readable from the left side of the drawing.

All the dimensions on a drawing must be shown using either Aligned System or Unidirectional System. The two systems should not be mixed on the same drawing.

The unit should not be written after each dimension, but a note mentioning the unit should be placed below the drawing.SIES GRADUATE SCHOOL OF TECHNOLOGY, NERUL19

dimensioning technique

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