Overview
This lecture explains the structure, function, and reading method of the universal bevel protractor, a precision instrument used for measuring angles with high accuracy.
Parts of the Universal Bevel Protractor
- The base serves as the reference surface and attachment point for acute angle tools.
- The blade fits through a groove in the base and rotates to measure various angles.
- A lock nut secures the blade after adjustment.
- The fine adjusting wheel allows precise positioning of the blade.
Scales and Measurement Features
- The main scale is divided into four 90-degree quadrants for a total range of 360 degrees.
- The vernier scale, located under a magnifying glass, breaks each degree into twelve parts (5 minutes per division).
- The vernier scale provides an accuracy of 5 minutes (1/12 of a degree).
- There are two sets of vernier scale markings: one for clockwise and one for counterclockwise readings.
- The acute angle attachment is added to measure angles less than 90 degrees.
How to Read the Universal Bevel Protractor
- Align the zero mark on the vernier scale with the main scale to begin measurement.
- Read the main scale (in full degrees) up to the position just before the zero of the vernier scale passes the next degree mark.
- Determine the direction (clockwise or counterclockwise) and continue on the corresponding vernier scale.
- Move along the vernier scale to find the line that aligns exactly with a line on the main scale; multiply its position by 5 minutes to get the additional minutes.
- The final angle is the sum of the main scale degrees and the vernier scale minutes (e.g., 45° 45').
- Always read both scales in the same direction to avoid errors.
Key Terms & Definitions
- Base — The flat reference part from which all angles are measured.
- Blade — The movable arm that aligns with the object being measured.
- Main Scale — The graduated scale marked in degrees.
- Vernier Scale — A fine scale providing reading precision to 5 minutes of a degree.
- Lock Nut — Secures the blade during measurement.
- Acute Angle Attachment — An accessory for measuring angles under 90 degrees.
Action Items / Next Steps
- Practice taking readings in both clockwise and counterclockwise directions.
- Review how to properly align and read both the main and vernier scales.
- Study the purpose and use of the acute angle attachment.