BASIC DIMENSIONING RULES Dimension Terminology Extension line Arrowhead

BASIC DIMENSIONING RULES

Dimension Terminology Extension line Arrowhead Dimension number 59 Dimension line 2

Extension lines 40 Extension lines should extend 2 mm beyond the dimension line Extension lines should be offset from the part by 2 mm 3

Dimension Spacing The first row of dimensions will be 12 mm away from the part. 40 20 Any dimension beyond will be 8 mm apart. That is a reference for a 4 mm high text. Generally speaking, dimension numbers should be centred between arrowheads. 4

Arrowheads and numbers Should be 3 times longer than they are wide. Always dimension the actual size of the object, not the scaled size. For metric drawings, omit the use of the millimetre (mm) notation following the number, as millimetres are the default units. 5

Basic rules • Do not duplicate dimensions and avoid using unnecessary or superfluous dimensions. • Dimensions should be attached to the view that best shows the shape of the feature to be dimensioned. • All horizontal dimensions are read from the bottom edge of the paper and all vertical dimensions are read from the right-hand edge of the paper (aligned system). The number must be placed above the dimension line. 6

All horizontal dimensions are read from the bottom edge of the paper and all vertical dimensions are read from the right-hand edge of the paper (aligned system). The number must be placed above the dimension line. 50 110 40 70 70 40 7

Do NOT duplicate dimensions and avoid using unnecessary or superfluous dimensions. The same information should NOT be given in two different ways. The overall dimension should always be given. It should be placed outside of smaller dimensions and be the farthest dimension from the part. 8

The overall dimension should always be given. It should be placed outside of smaller dimensions and be the farthest dimension from the part. NEVER cross a dimension line and an extension line. 9

Avoid placing any dimension on the part (inside the view) unless there is no other option. 40 40 GOOD PRACTICE BAD PRACTICE 10

A dimension should be attached to only one view (i. e. , extension lines should not connect two views). 40 BAD PRACTICE 40 GOOD PRACTICE 11

Dimensions should be attached to the view that best shows the shape of the feature to be dimensioned. Avoid dimensioning to hidden features. 40 40 GOOD PRACTICE BAD PRACTICE 12

Extension lines may cross each other and over other lines on the part, but dimension lines should never be crossed (if possible). 13

Never Don’t. . . Never use draw aa line centre a dimension of the linepart or aas line a as of athe dimension continuation view as a dimension line. . . of a line, . . . of a view. . . … but centre lines can be used as extension lines 14

Circles and arcs Ø 25 45 65 • In general, a circle and an arc greater than 180º is dimensioned by its diametre. An arc less than 180º is dimensioned by its radius. • The dimension lines must be placed at different angles. • No more than two concentric circumferences can be dimensioned in the circular view. The other ones will be dimensioned in the rectangular view. • Dimension cylinders in their rectangular view with a diametre symbol (Ø). • DON’T PLACE THE SYMBOL IN THE CIRCULAR VIEW. 15

When If it isthere not enough is lack of room, space, thethe When there is no room for the dimension arrowheads number can becan placed be placed out of of thethe extension arrowheads lines, (to the right) arrowheads, they can be replaced by a point… pointing inwards. 45 156 35 50 16