310101f Precision Measurement

Precision Measurement ILM 310101f

Objectives

  • Understand precision measurement in dimensional measurement.

  • Identify measuring instruments used for precision measurement.

Measurement & Layout Techniques

1. Direct Measurement (Eye)

  • Utilize a rule and protractor against the workpiece.

  • Directly read measurements from the tool.

  • Accuracy is up to 1/64” with a rule.

2. Surface Contact Measurement

  • Provides better accuracy than visual measurement.

  • Measures workpiece dimensions using jaws or points.

  • Common tools include:

    • Calipers

    • Micrometers

    • Vernier Calipers

3. Optical Measurement

  • Used for highest accuracy requirements.

  • Involves optical magnifying lenses and specialized equipment.

Measuring Instruments

Steel Rule

  • Most commonly used measuring tool.

  • Can read fractions of inches or millimeters.

  • Flexible versions available to wrap around curves.

Measuring Tape

  • Features a true zero end hook for inside and outside measurements.

  • Free-play design compensates for measurement discrepancies.

Hook Rule

  • Measures from edge or shoulder of workpiece.

  • Useful for flanges and circular pieces.

  • Sets caliper sizes effectively.

Short Length Rules

  • Designed for measurements in tight spaces.

  • Interchangeable rules, sizes can range from ¼” to 1”.

  • Metric options are available.

Depth Rule

  • Specifically made to measure holes and depressions not achievable with standard rules.

Thickness Gauges

  • Known as feeler gauges.

  • Capable of measuring gaps as small as 0.0002" (two tenths of one thousandth of an inch).

Calipers

  • Instruments for internal and external measurements.

  • Spring joint ensures measurement accuracy; use additional tools for optimal results.

Vernier Caliper

  • Accurate measuring device for inside and outside measurements.

  • Measures to an accuracy of thousandths of an inch.

  • Size variations from 6" to 24".

    • Outside Jaws: External measurements.

    • Inside Jaws: Internal measurements.

    • Depth Probe: Measures object depth.

    • Includes scales in cm and inches.

Vernier Scale

  • Invented by Pierre Vernier for precise interpolation on a fine scale.

Reading the Vernier Caliper

How to Read Metric Vernier Caliper

  • Locate the centimetre mark on the fixed scale to the left of the Vernier scale's 0-mark (example: 10mm).

Reading in Millimetres

  • Find the millimetre mark to the left of the 0-mark on the Vernier scale (example: 6mm).

Precision Measurements

  • Align the marks on the Vernier and fixed scales for measurement accuracy (example: 0.25mm).

  • Add readings to get the final measurement; e.g., 10 + 6 + 0.25 = 16.25mm.

Micrometers

General Information

  • Highly precise measurement tools.

  • Common readings: 1/1000" = 0.001" (thousandths of an inch).

  • Some models include a vernier scale up to 1/10,000" = 0.0001".

Size Variations

  • Ranges from 1" to 60" commonly.

  • An example: a 20” micrometer reads between 19” & 20”.

Gauge Blocks (Joe Blocks)

  • Precision ground metal or ceramic blocks for standardized lengths.

  • Main means of length standardization in the industry.