Here are common tools for measuring angles on metal parts, categorized by type and precision:
Protractors:
Basic Protractor: Simple semicircular tool with a degree scale (typically 180°). Used for rough measurements.
Universal Bevel Protractor / Vernier Protractor: Combines a protractor head with a vernier scale and an adjustable blade (stock). Allows measurements typically to an accuracy of 5 arcminutes (0.083°) or 0.1°. The most common precision hand tool for angles.
Digital Protractor: Electronic version with a digital display. Offers easier reading and often higher resolution (e.g., 0.05° or 0.01°), but accuracy depends on quality.
Angle Gauges:
Precision Angle Gauges (e.g., Sine Bars): Use trigonometric principles (sine function) with gauge blocks to set or measure angles very accurately (down to arcseconds). Essential for high-precision setups in toolrooms and metrology labs.
Angle Gauge Blocks: Sets of precisely ground blocks with specific angles (e.g., 1°, 3°, 9°, 27°, 41°) that can be wrung together to build compound angles.
Squares & Levels:
Combination Square: Features a ruler head with a 90° and 45° reference, often including a protractor head and center finder. Versatile for layout and basic angle checks.
Precision Squares (e.g., Engineer’s Squares, Try Squares): Primarily for checking 90° angles with high accuracy. Master squares are used for calibration.
Bevel Gauge (Angle Finder): Adjustable tool with two blades locked by a knob. Used to copy or transfer an angle from a part to a protractor or vice-versa.
Spirit Level (Inclinometer): Measures angles relative to horizontal (level) or vertical (plumb). Digital versions provide precise angle readouts.
Optical Tools:
Optical Comparator / Projector: Magnifies a part’s profile shadow onto a screen with a rotatable protractor graticule. Measures angles on complex 2D profiles.
Autocollimator: Highly accurate optical instrument that measures small angular deviations (down to fractions of an arcsecond) by reflecting a beam of light off a mirror attached to the part. Used for alignment and ultra-precision metrology.
Electronic/Digital Tools:
Digital Inclinometer: Electronic sensor providing digital angle readout relative to gravity. Often used on machinery or large structures.
Electronic Level: Similar to a digital inclinometer, often with multiple axes and data output capabilities.
Laser Tracker: High-end portable coordinate measuring machine (CMM) that uses laser interferometry to measure 3D points. Calculates angles between measured points or surfaces with very high accuracy over large distances.
Articulating Arm CMM: Portable CMM with rotary encoders in its joints. Measures 3D points and calculates angles between features.
Specialized Fixtures & Gauges:
Angle Plates: Precision-ground blocks with accurate 90° faces used to hold parts perpendicular for measurement or machining. Can have other angles.
Sine Plates / Sine Tables: Similar principle to sine bars but provide a flat, tiltable surface for holding parts. Used with gauge blocks to set precise angles for inspection or grinding.
Roller Type Angle Gauges: Use precision rollers and distance measurements to calculate angles.
Key Selection Factors:
Required Accuracy: Ranges from rough estimates (±1°) to ultra-precision (±0.1 arcsecond).
Part Size: Small parts suit protractors, gauges, optical comparators; large parts suit inclinometers, laser trackers.
Environment: Workshop, toolroom, metrology lab, or production floor.
Features: Simple angle, compound angle, angle between features, relative to datum.
Portability: Hand tools vs. fixed machines.
Cost: Varies significantly from basic protractors to high-end CMMs.
The choice depends heavily on the specific application’s precision requirements, part characteristics, and available resources. Universal bevel protractors and digital protractors are the most common general-purpose tools, while sine bars, autocollimators, and CMMs are used for high-precision applications.
