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Activity 001: Precision Measurement Skills Lab

Activity ID: U8M4-ACT-001 Duration: 40 minutes Objective: Read micrometers and calipers accurately, measure machined parts, and compare results to drawing specifications.

Overview

Students practice reading and using precision measuring instruments on a set of machined sample parts. They record measurements, calculate deviations from nominal, and determine whether parts are within tolerance.

Materials & Equipment Needed

  • Outside micrometer set (0-1", 1-2")
  • Digital calipers (6")
  • Depth micrometer or depth gauge
  • Set of machined sample parts (5 parts with known dimensions and intentional tolerance variations)
  • Gauge block set (for micrometer zero check)
  • Part drawings with dimensions and tolerances
  • Measurement recording worksheet
  • Lint-free cloth for cleaning instruments
  • Safety glasses

Instructions & Procedure

Phase 1: Instrument Familiarization and Zero Check (8 minutes)

  1. Micrometer zero check: Close the micrometer gently using the ratchet stop. The reading should be exactly 0.000". If not, adjust using the zero-setting procedure (spanner wrench on the sleeve).
  2. Gauge block verification: Select a 0.500" gauge block. Measure it with the micrometer. Record the reading. It should read 0.5000" Β±0.0001".
  3. Caliper zero check: Close the caliper jaws fully. Press the zero button. Verify the display reads 0.000".
  4. Practice readings: The instructor calls out micrometer settings. Students set the micrometer to each dimension and verify against each other's readings.

Phase 2: Part Measurement (20 minutes)

For each of the 5 sample parts: 1. Read the part drawing. Identify all dimensioned features and their tolerances. 2. Measure each dimension using the appropriate instrument: - External diameters: outside micrometer - Lengths and widths: calipers for quick check, micrometer for critical dimensions - Depths: depth micrometer or depth gauge 3. Record each measurement on the worksheet. 4. Calculate the deviation from nominal: Measurement - Nominal = Deviation. 5. Determine Go/No-Go: Is the measurement within the stated tolerance? 6. Measure each critical dimension twice to verify repeatability.

Phase 3: Part Acceptance/Rejection (8 minutes)

  1. For each part, complete the acceptance criteria:
  2. All dimensions within tolerance β†’ ACCEPT
  3. Any dimension outside tolerance β†’ REJECT (note which dimension failed)
  4. Identify which rejected parts could be reworked (oversized parts can be re-machined; undersized parts are scrap).
  5. Complete the inspection report for all 5 parts.

Phase 4: Discussion (4 minutes)

  1. Compare your measurements with other students. How much variation exists between different operators?
  2. Which instrument did you find easiest/hardest to use consistently?
  3. Which parts were borderline (very close to the tolerance limit)?

Discussion Points

  • Why is measuring technique important for consistency between operators?
  • What is the cost of accepting an out-of-tolerance part?
  • How does the ratchet stop improve measurement consistency?
  • When would you use a micrometer vs. a caliper?

Expected Outcomes

  • Students read a micrometer correctly to 0.001" (with vernier to 0.0001")
  • Students read digital calipers correctly
  • Students make consistent measurements (Β±0.001" between repeated readings)
  • Students correctly accept/reject parts based on tolerance analysis

Assessment Rubric

Criteria Excellent (4) Proficient (3) Developing (2) Beginning (1)
Micrometer Reading All readings within Β±0.0005" of known values Within Β±0.001" Within Β±0.002" Cannot read micrometer
Caliper Reading All readings within Β±0.001" Within Β±0.002" Within Β±0.005" Cannot read calipers
Tolerance Analysis All accept/reject decisions correct 1 error 2-3 errors Cannot determine acceptance
Instrument Care Proper handling, zeroed, clean Minor lapse in care Left instrument unsecured Rough handling

Safety Considerations

  • Handle precision instruments with clean, dry hands
  • Never drop or impact measuring instruments
  • Do not leave instruments on the machine tool surface where they can fall
  • Safety glasses required in the shop area even for measurement activities
  • Gauge blocks have extremely sharp edgesβ€”handle carefully

Last Updated: 2026-03-19