The Architect’s Metric Scale Rule

In architectural drawings, it is not always possible to represent objects at their actual size. Therefore, drawings must be made showing the objects greatly reduced or magnified in size.

In order that such a geometrical representation shall be of use, it is necessary that every part of the drawing shall bear the same ratio of proportion to the original object. Such a drawing is said to be drawn to scale.

The scale, being the ratio of proportion, is one in which the graphical representation bears the original object e.g. 1cm=1m. The instrument on which the scale is marked is called The Scale Rule

Function: The scale rule enables dimensions to be read, transferred or converted from or between drawings

Materials: They are made from plastic, ivory or wood.

Shapes: Standard shapes of the scale rule on section are

-          Bevel

-          Oval

-          Triangle

The shape of the scale suggests the usage.

For the oval shape, its edge can be brought so close to the paper for marking off or measuring distances. For the triangular section, it is the most comprehensive scale containing up to 12 scales on its six faces.

Length: Standard lengths are

-          300 mm

-          150 mm

The longer the scale, the more convenient it is to use.

Graduations and Divisions: The architect’s metric scale rule is either open or fully developed. In fully developed, each main unit is fully sub-divided throughout the scale. In open divided, the main units of the scale are graduated with a fully sub-divided extra unit at each end.

The fully divided scale is easier to use.

Standard metric scales are

-          1:5, 1:50, 1:500, 1:5000 and multiples

-          1:10, 1:100, 1:1000, 1:10000 and multiples

-          1:2, 1:20, 1:200, 1:2000 and multiples

-          1:125, 1:1250, 1:12500 and multiples

Qualities

A good scale rule should

1.       Have precision

2.       Be calibrated

3.       Graduated

4.       Engraved marking

5.       Warp resistance

Those with engraved calibrations are best because their figured divisions cannot wear off and being colour-coded, are always visible.

Usage: The architect’s scale is only as accurate as its user and as the sharpness of his/her pencil. In drawing to scale, it is significant to think of, and to speak of each dimension in its size, and in its reduced size shown on paper. In using the scale, it is advisable to always layout the overall dimensions first. It is not good practice to use the pair of dividers to pick a dimension of a scale and transfer to a drawing for the dividers may shift accidentally and mistakes in dimension may result.

Also, when a scale is chosen in a drawing, that scale MUST NOT be changed in that drawing.

The student must learn to use the scale and take off dimensions from the scale indicated on the drawing as this is fundamental to architectural graphics.

Care of the Scale Rule

-          Scale should not be used for ruling lines or other purposes which they are not intended for.

-          Edges should be protected from clipping off or being broken.