KELIBRON 3 guides
Plate inspection & GD&T
The surface plate as the bench reference: plates, height gauges and accessories, datums and datum systems, and form-error checks such as flatness and straightness on the plate.
- 4 min readParallelism and perpendicularityParallelism and perpendicularity are orientation tolerances, so the datum comes first.
- 5 min readRoundness and cylindricityRoundness controls one complete cross-section; cylindricity controls the whole cylindrical surface, and neither uses a datum.
- 4 min readAngle measurement with a protractor and sine barUse a universal bevel protractor for a direct contact reading; use a sine bar when the angle can be built from gauge-block height.
Browse by topic
Measurement basics
What a measurement is and what makes it count: units and traceability, terms, methods, drawings, conditions and how to record a reading.
Reading instruments
How to read vernier, dial and digital calipers, outside micrometers, dial and lever indicators, and comparison against gauge blocks: which scale gives which digit, how to correct a zero error, worked examples and the school physics practical. Start here if you are new.
- How to read and use a caliper
- How to read a vernier caliper
- How to read an inch vernier caliper
- How to read a dial caliper
- How to use a digital caliper
- How to read a micrometer
- Micrometer zero check and zero error correction
- How to use a micrometer: ratchet and thin parts
- Types of micrometer
- Dial indicators
- Lever test indicators and cosine error
- Comparative measurement with a dial indicator
- Physics practical: length measurement
- Least count of a vernier caliper
- Screw gauge: least count and reading
- Vernier caliper exercises with worked answers
Measuring methods
Measuring outside diameters, bores (including with a dial bore gauge), depths, steps, centre distances and runout on real parts, planning the measurement, first-article inspection records, and the caliper and micrometer mistakes that spoil a reading.
- Finding the inspection characteristics on a drawing
- How to measure a machined part
- Measuring common parts
- Inspecting prismatic parts: block and box check
- How to measure a bore
- Measuring a bore with a dial bore gauge
- Steps, hole-to-edge and centre distance
- Radial and axial runout with a dial indicator
- First article inspection and inspection record
- Inspection records and reports
- Caliper measurement errors and how to avoid them
- Common micrometer mistakes
Tolerances and decisions
Limits and fits, choosing an instrument for the tolerance, how uncertainty affects pass or fail, and gauge R&R studies.
- Tolerances and fits basics
- Looking up IT grades and fundamental deviations
- General tolerances for untoleranced sizes
- Acceptance limits and the safety margin A
- Go no go gauges: how a plain limit gauge judges a size
- Caliper or micrometer? Choosing the instrument
- Repeated measurements: mean and standard deviation
- Measurement uncertainty basics
- An uncertainty budget for a caliper measurement
- Decision rules and guard bands
- Gauge R&R and measurement system analysis (MSA)
Instrument care
Choosing a caliper, daily checks, calibration with gauge blocks, registers, labels and records.
Teaching and certification
Using the lab in class and in company training, what practical assessments check, and the terms in English and Chinese.