Lesson 6: Scaling
Scale
in Engineer's languagemeans the proportion or ratio between the dimensions adopted for the drawing and the corresponding dimensions of the object. It is the proportion by which we either reduce or increase the actual size of the object on a drawing. It is not possible always to make drawings of an object to its actual size as the extent of drawing paper is limited and also sometimes the objects are too small to make it clearly understandable by drawing its actual size in drawing paper. Scale is the technique by which one can represent an object comfortably as well as precisely within the extent of drawing paper. Numerically scales indicate the relation between the dimensions on drawing and actual dimensions of the objects.
USES OF SCALE
To prepare reduced or enlarged size drawings. To set off dimensions. To measure distances directly.
Chord Scale
The scale which is used to make or to measure angles of any magnitude is known as chord scale. This scale is usually marked on a rectangular protractor.
Vernier Scale
It is device for measuring fractional parts of the smallest division of the main scale. It consists of a fixed main scale and a movable vernier scale. The vernier part is graduated in "n" number of divisions in such a way that it coincides with "n-1" number of smallest divisions of main scale.
R.F. or S.F.
The ratio of the distance on drawing paper of an object to the corresponding actual distance of the object is known as the ________.
Plain Scale
The scale that can measure one main unit and one sub-unit of the main unit or up to a fraction of 1st decimal point of the main unit is known to be a plain scale. It is simply a line divided into a number of equal parts and the 1st part is further sub-divided into small parts. Kilometers and Hectometers, Meters and Decimeters, Meters and 1/10th of Meters etc. can be measured using plain scales.
Diagonal Scale
The scale that can measure one main unit and two sub-units of the main unit or up to a fraction of 2nd decimal point of the main unit is known to be a diagonal scale. It is so named because the 2nd sub-unit or 2nd decimal of main unit is obtained by the principle of diagonal division. Kilometers-Hectometers-Decameters, Decameters- Meters-Decimeters, Meters-1/10th of Meters- 1/100th of Meters etc. can be measured using diagonal scales.
Enlarging Scale
Thescaleinwhichtheactualmeasurementsoftheobjectareincreased to some proportion is known as reducing scale. The standard formats of enlarging proportions are:
Comparative Scale
When the given scale of a plan reads a certain measure and it is required to construct a new scale for the same plan to read in some other measures, the new scale is called comparative scale or corresponding scale. For example let us consider a plan drawn in inch units and scale provided with drawing can measure in feet and inch. If we draw another scale taking same R.F. that can measure in feet, inch and 1/8th of inch it will be a comparative scale. Also if we draw another scale that can measure in cm and mm with same R.F. it will also be a comparative scale.
Full size scale
The scale in which the actual measurements of the object are drawn to the same size on the drawing is known as full size scale. It is represented as 1:1 scale. If possible, drawing should be done in full scale
Reducing scale
The scale in which the actual measurements of the object are reduced to some proportion is known as reducing scale. The standard formats of reducing proportions are: