Height gauges

A height gauge locates a contact vertically relative to a reference. The surface plate, support and probe geometry contribute to the result.

Idealized geometry example, not an instrument operating recipe: suppose a 5.000 mm ball measures a horizontal internal opening with actual lower/upper surfaces at 20.000 and 30.000 mm. At lower contact the ball centre is at 22.500 mm; at upper contact it is at 27.500 mm. Centre travel is only 5.000 mm, while opening size is 5.000 + 5.000 = 10.000 mm. The feature centre is 25.000 mm. A correctly compensated feature mode handles the effective contact offset; manually adding the ball diameter to an already compensated result would count it twice. Real probing also includes deflection and alignment effects.

Instrument and feature selection

Conventional vernier, dial and electronic gauges commonly use a scriber or indicator. More capable instruments add controlled-force probing, diameter compensation, extremum capture and feature calculations. Mitutoyo describes height gauges as nominally single-axis instruments and explains that some advanced models obtain two-dimensional feature information by rotating the workpiece. A digital display alone does not establish those capabilities. Mitutoyo, Ins and Outs of Height Gages, undated technical article

Treat the last three rows as functions requiring validation, rather than consequences of owning a height gauge. A few sampled contacts do not automatically establish a complete surface profile or a drawing's geometric acceptance requirement.

The surface plate is part of the measurement

The gauge base and supported workpiece must share a controlled reference arrangement. A zero on the plate establishes an origin; it does not prove the plate is flat throughout the measurement path. Starrett's May 2, 2023 guidance distinguishes regular checks for local wear from calibration of overall flatness. It also emphasizes using the plate's intended support system: its published examples include different support arrangements for different plate sizes. Follow the supplied plate instructions rather than adopting a universal support count. Starrett, Gaging is Baseless Without Standards

Clean the plate, base and workpiece bearing surfaces. Ensure the part does not rock, and define any fixture or parallel included beneath it. Keep the part's datum realization consistent between readings; re-seating a part can change the measurement even when the display reference remains unchanged.

Excessive downward force on the slider can lift the base during setting. Mitutoyo's quick guide also warns that locking can slightly change the setting and that scriber mounting and measuring-face alignment matter. Keep the contact secure and the working offset controlled; verify the setting after clamping when relevant. View mechanical graduations straight on to avoid parallax. Mitutoyo, Quick Guide to Precision Measuring Instruments, E11003(2), height-gauge section, undated edition

Scriber faces, balls and probe constants

A scriber presents a measuring face with its own relationship to the base. A ball probe contacts opposite faces at opposite sides of the ball. Consequently, a single-direction zero does not by itself establish the compensation needed for upward/downward measurements. Mitutoyo explains why ball compensation and feature calculations extend measurement to underside surfaces and centre distances. Mitutoyo, height-gauge measurement methods

For a concrete procedure, Sylvac Z5 manual version 1.4 defines the probe constant as compensation for both insert dimension and deflection during opposite-direction probing. It requires checking and storing the constant again after changing the insert, its position in the holder, measuring force or floating-suspension adjustment. Its internal-diameter routine finds reversal points by moving the instrument or part laterally at each opposing profile. These instructions apply to the Z5; use the matching procedure for another model. The manual identifies its version but no calendar publication date. Sylvac Z5 user manual, sections 4.1 and 5.3

Specifications and uncertainty

Mitutoyo's LH-600F/FG catalogue E12012(5) separates selectable resolution from accuracy. It lists 0.0001 mm as the finest resolution and indication accuracy at 20 °C as ±(1.1 + 0.6L/600) µm, with L the measured length in millimetres. At 600 mm that expression gives ±1.7 µm, compared with a 0.1 µm display increment. Neither number alone represents uncertainty for an arbitrary part, probe or shop environment. The catalogue's printed production code is 2303(5). Its perpendicularity/straightness specifications require the specified Lever Head 519-521 and Mu-Checker 519-561; they are not unconditional properties of every probe setup. Mitutoyo LH-600F/FG catalogue

Distinguish the manufacturer's permissible indication error or accuracy specification, repeatability and measurement uncertainty. Evaluate the reference artefact, plate/reference geometry, repeated positioning, contact response, probe configuration, alignment and temperature for the task. NPL explains these distinctions and uncertainty contributions; repeatedly obtaining the same value does not exclude a systematic offset. NPL, Fundamental Good Practice in Dimensional Metrology, GPG80, July 2005; corrected reprint October 2012

Setting, calibration and reporting

Zeroing and probe qualification prepare the measurement configuration. Calibration must examine relevant performance over the working range. For example, Sylvac's SYL 810, dated 07.04.2014 in the document, covers Hi_Gage ONE 400/600 mm instruments. It checks functions, contact parallelism, indication errors at distributed step-gauge heights and repeatability. Its preparation specifies 20 °C reference conditions and at least six hours for the instrument and masters under calibration conditions. That is a model-specific calibration instruction, not a universal shop-floor waiting time. Sylvac SYL 810 calibration standard

Record instrument/probe identification, reference artefacts, origin and compensation state, part support, contact directions and locations, individual values and environmental conditions. State corrections, uncertainty and the acceptance rule when reporting conformance. Investigate reference drift, poor repeatability or changes after re-seating before treating the result as a part defect.

Related reference

Inspection and quality documents