Knowledge of Different Types of Scale
In the ITI Draughtsman Civil trade, the concept of scale is very important in technical drawing. Since it is not possible to draw large objects like buildings, roads, and structures in their actual size on paper, scales are used to reduce or enlarge the dimensions proportionally. A scale represents the ratio between the actual size of an object and its size on the drawing.
Proper knowledge of different types of scales helps draughtsmen prepare accurate drawings that can be easily interpreted by engineers and construction workers.
Definition of Scale
A scale is defined as the ratio of a linear dimension on a drawing to the corresponding actual dimension of the object. It is usually expressed in the form of a ratio such as 1:50, 1:100, etc.
- Representative Fraction (RF): Ratio of drawing size to actual size.
- Example: In a scale of 1:100, 1 unit on the drawing represents 100 units in actual size.
Types of Scales
There are different types of scales used in engineering drawing depending on the requirement. These are mainly classified as follows:
1. Plain Scale
A plain scale is used to measure lengths in two units or a unit and its subunit. It is simple to construct and commonly used in basic drawings.
- Represents units like meters and decimeters
- Easy to read and use
- Used in general engineering drawings
2. Diagonal Scale
A diagonal scale is used when more accuracy is required. It can measure up to three units or provide finer subdivisions.
- Provides precise measurements
- Uses diagonal lines for subdivision
- Used in detailed engineering work
3. Vernier Scale
A vernier scale is used for very precise measurements. It consists of a main scale and a sliding vernier scale.
- High accuracy and precision
- Commonly used in instruments like vernier calipers
- Suitable for advanced applications
4. Comparative Scale
A comparative scale is used to compare measurements in different units, such as kilometers and miles.
- Shows two different units on the same scale
- Useful in map reading and conversion
5. Scale of Chords
This type of scale is used to measure angles. It is based on the properties of a circle.
- Used in angular measurements
- Helpful in geometrical constructions
Types of Scales Based on Size
Scales can also be classified based on whether the drawing is reduced, enlarged, or of the same size:
- Reducing Scale: When the drawing is smaller than the actual object (e.g., 1:100).
- Enlarging Scale: When the drawing is larger than the actual object (e.g., 2:1).
- Full Scale: When the drawing is of the same size as the object (1:1).
Uses of Scales in Draughting
Scales are widely used in civil engineering drawings for various purposes:
- Preparing building plans and layouts
- Drawing maps and site plans
- Representing structural details
- Measuring distances accurately
Without proper use of scales, it would be difficult to represent large structures on paper.
Common Scales Used in Civil Drawing
In the Draughtsman Civil trade, certain scales are commonly used:
- 1:50 – Detailed building drawings
- 1:100 – General building plans
- 1:200 – Site plans
- 1:500 or 1:1000 – Layout plans
The choice of scale depends on the level of detail required in the drawing.
Importance of Using Correct Scale
Using the correct scale is essential for accuracy and clarity in drawings:
- Ensures proper representation of objects
- Helps in accurate measurement and construction
- Improves readability of drawings
- Reduces chances of errors
Incorrect use of scale can lead to serious mistakes in construction work.
Precautions While Using Scale
Students should follow certain precautions while using scales:
- Always check the scale before starting the drawing
- Use proper instruments for measurement
- Avoid mixing different scales in one drawing
- Clearly mention the scale on the drawing sheet
These precautions help in maintaining accuracy and consistency.
Conclusion
Knowledge of different types of scales is essential for students of the ITI Draughtsman Civil trade. Scales help in representing large objects in a manageable size while maintaining accuracy.
By understanding and applying various types of scales, students can prepare precise and professional drawings. This knowledge is fundamental for successful work in civil engineering and construction fields.