KELIBRON Instrument care
Gauge blocks
A gauge block is a block of steel, carbide or ceramic with two lapped, flat and parallel faces a known distance apart. Blocks wring together, so a small set builds a great many sizes: start from the last decimal place and use as few blocks as possible.
On this page
What they are
Gauge blocks carry length from the calibration laboratory to the workshop: instruments are checked and set on them, and comparative measurements use them as the reference. The idea of a small set combined into composite gauges goes back to C. E. Johansson in 1896 (NIST Monograph 180). The international standard is ISO 3650; the Chinese standard is GB/T 6093-2001.
Wringing
Two blocks with lapped faces slid together cling to each other. The film between them is of the order of 10 nm, usually within 25 nm, and it is defined as part of each block’s length, so a stack needs no correction for the number of wrings (NIST Monograph 180).
Clean the faces first, then slide the blocks together with light pressure.
Building a size
Use as few blocks as possible, usually no more than four, and remove the last decimal place first (textbook: 金莹, 公差配合与技术测量). With the 83-piece set in the textbook’s table, 33.625 mm is 1.005 + 1.02 + 1.6 + 30. Another example, 32.45 mm: 1.45 leaves 31, then 1 leaves 30, so 1.45 + 1 + 30 mm.
| Step | Block (mm) | Remaining (mm) |
|---|---|---|
| 1 | 1.45 | 31 |
| 2 | 1 | 30 |
| 3 | 30 | 0 |
By grade or by calibrated length
Blocks are made to accuracy grades (级), and calibrated blocks are assigned to classes (等) by verification. Used by grade, a block counts at its nominal length, which includes its manufacturing error. Used by class, it counts at its calibrated central length, which leaves only the smaller uncertainty of the calibration, so this use is more accurate (textbook: 金莹).
Handling
Hand heat lengthens blocks: handle them with insulated tongs or gloves where possible, and wash your hands when you cannot, to keep the faces from corroding (NIST Monograph 180). When blocks are not in daily use, coat them with a preservative recommended by the maker (NIST Monograph 180).
Planned for the lab
Gauge blocks are planned for KELIBRON (intake group G2), as the reference for comparative measurement with a dial indicator. Until then, practise the shared basics on a caliper.
References
- T. Doiron, J. Beers, The Gauge Block Handbook, NIST Monograph 180, 1995 · NIST
- 金莹 主编，《公差配合与技术测量》，清华大学出版社，2014（2024 年第 4 次印刷），ISBN 978-7-302-37145-8 (cited by number; no public page) · 清华大学出版社
- GB/T 6093-2001《几何量技术规范（GPS） 长度标准 量块》 · 国家质量监督检验检疫总局
- ISO 3650 — Geometrical Product Specifications (GPS) — Length standards — Gauge blocks (cited by number; no public page) · ISO
Practise the shared basics on a caliper
Questions
How many gauge blocks should a stack have?
As few as possible, usually no more than four: each block adds its own error.
What is the difference between using gauge blocks by grade and by class?
By grade, the block counts at its nominal length; by class, at its calibrated length, which is more accurate.
Practise the basics first
Cleaning, zero checks, square positioning, light even force and reading to the scale interval are the same on every instrument; practise them in a caliper scene.
Related guides
Measurement basicsLength units and traceabilityThe metre is defined by the speed of light: light in vacuum travels 299 792 458 m in one second.
Measurement basicsMeasuring methodsA direct measurement reads the wanted size straight off the instrument; an indirect one calculates it from other measured sizes; a comparative one measures only the difference from a standard of known size.- Reading calipersMicrometer zero check and zero error correctionCheck zero before every use: on a 0–25 mm micrometer close the clean faces gently with the ratchet; on 25–50 mm and larger close on the setting standard (25 mm, 50 mm, 75 mm).