Module 4: Assessment Quiz

Module: U8M4 - Precision Measurement & Safety Duration: 20-30 minutes Passing Score: 70%

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What is the resolution (smallest graduation) of a standard outside micrometer?

0.01"

0.001" (with vernier scale: 0.0001")

0.1"

0.00001"

Submit

Explanation: A standard outside micrometer reads to 0.001" on the thimble scale. Most quality micrometers include a vernier scale on the sleeve that provides an additional digit, reading to 0.0001". Digital micrometers display 0.00005" or 0.001mm resolution.

What measuring instrument is best for checking the inside diameter of a bored hole to ±0.0005" accuracy?

Steel rule

Telescoping gauge measured with an outside micrometer, or a bore gauge

Digital calipers

Depth micrometer

Submit

Explanation: Telescoping gauges are inserted into the bore, locked at the diameter, then measured with an outside micrometer. Bore gauges (also called bore micrometers or dial bore gauges) directly measure internal diameters. Both achieve ±0.0005" or better. Calipers lack the precision needed for this tolerance.

What is the purpose of a dial indicator in machining?

To measure workpiece weight

To set spindle speed

To measure small deviations in position, alignment, or runout with high precision (typically 0.001" or 0.0005" per division)

To determine material hardness

Submit

Explanation: Dial indicators (also called dial gauges) measure linear displacement. They are used for checking runout (TIR), aligning vises and fixtures, centering workpieces in four-jaw chucks, checking flatness, and verifying parallelism. They do not measure absolute dimensions—they measure deviations from a reference.

How should a micrometer be handled to maintain its accuracy?

Spin the thimble rapidly for fast measurement

Use the ratchet stop or friction thimble for consistent pressure, handle by the frame (not the anvil or spindle), and store in a protective case

Apply heavy clamping pressure for firm readings

Store it on the machine tool surface

Submit

Explanation: The ratchet stop ensures consistent measuring pressure (typically 2-5 lbs). Handling by the frame prevents body heat from affecting the anvil/spindle. Heavy pressure distorts readings. Storing in a case prevents damage to the precision ground surfaces.

What is the difference between accuracy and precision in measurement?

They mean the same thing

Accuracy is how close a measurement is to the true value; precision is how repeatable the measurements are

Accuracy is for small parts, precision is for large parts

Precision is always better than accuracy

Submit

Explanation: A measurement system can be precise (giving very consistent readings) but inaccurate (consistently wrong). Or it can be accurate on average but imprecise (widely scattered readings). Good metrology requires both accuracy and precision. Calibration addresses accuracy; technique addresses precision.

What is GD&T (Geometric Dimensioning and Tolerancing)?

A software program for CAD design

A brand of measuring instruments

A standardized system of symbols and rules for defining and communicating engineering tolerances on technical drawings

A type of cutting tool specification

Submit

Explanation: GD&T (per ASME Y14.5) uses symbols on engineering drawings to communicate geometric requirements—flatness, parallelism, perpendicularity, position, runout, etc. It provides a more precise and unambiguous way to define tolerances than simple ± dimensions, especially for features like hole positions and surface relationships.

At what frequency should precision measuring instruments be calibrated?

Never—factory calibration lasts forever

Only when they break

At regular intervals (typically annually or semi-annually) and whenever they are dropped, damaged, or give suspicious readings

Every day before use

Submit

Explanation: Precision instruments drift over time due to wear, thermal cycling, and mechanical stress. Regular calibration against traceable standards ensures measurements remain accurate. Most shops calibrate annually, with more frequent checks for heavily used or critical instruments. Any physical impact warrants immediate re-calibration.

What is the proper way to read a vernier caliper at 1.573"?

Read only the main scale

Read the main scale (1.5"), the sliding jaw scale (0.07"), then find the vernier line that aligns with a main scale line (0.003")

Estimate between the two nearest lines

Use a calculator to determine the reading

Submit

Explanation: Vernier calipers use three readings: (1) the main scale gives the integer and first decimal (1.5"), (2) the sliding scale gives the next digit (0.07"), (3) the vernier scale identifies which vernier line aligns perfectly with any main scale line, giving the thousandths digit (0.003"). Total: 1.573".

What is a gauge block (Jo block) used for?

To cut precise slots

To hold workpieces for machining

As a dimensional reference standard for calibrating measuring instruments and setting up precision measurements

To check surface finish

Submit

Explanation: Gauge blocks are hardened steel, ceramic, or carbide blocks ground to extremely precise dimensions (±0.000002" or better for Grade 0). They can be wrung together (adhered by molecular attraction) to create any dimension needed. They serve as the primary calibration reference for micrometers, calipers, indicators, and other instruments.

What safety practice is most important when using compressed air to clean chips from a machined part?

Wear gloves to protect hands

Never point compressed air at yourself or others; use a safety nozzle with a maximum 30 PSI rating; always wear safety glasses

Use maximum pressure for fastest cleaning

Compressed air is always safe to use

Submit

Explanation: Compressed air propels metal chips at high velocity—effectively creating shrapnel. OSHA requires air guns used for cleaning to be below 30 PSI at the nozzle (with chip guards). Never direct compressed air at skin (can cause air embolism), eyes, or other people. Always wear safety glasses when using compressed air.

What should you do if you discover a measuring instrument gives readings that differ from a known standard?

Continue using it and compensate mentally

Discard it and buy a new one

Remove it from service, tag it as "out of calibration," and have it professionally calibrated or replaced

Adjust it yourself

Submit

Explanation: An out-of-calibration instrument can produce parts that appear to be in tolerance but are actually out of spec. It must be removed from use immediately, tagged so no one else uses it, and sent for professional calibration. Any parts measured with the suspect instrument since its last known-good calibration should be re-inspected.