Micro-Metrics Company

OG204
Tooke Paint Inspection Gauge

The Tooke Paint Inspection Gauge (Plastic) is a precision tool for inspection and thickness measurement (in accordance with ASTM D4138) of single or multiple coats on any substrate, and for microscopic observation and measurement of substrate and film defects. The Tooke Gauge uses an illuminated 50-power microscope equipped with a “universal scope” with a measuring reticle that accommodates measurement in mils, microns, and millimeters. (Note: Each universal microscope is validated before sale against a certified gage block traceable to the National Institute of Standards & Technology (NIST).) This gauge mounts tungsten carbide cutting tips for precise incision of the work surface. Standard cutting tips are 1×, 2×, and 10×. An optional 5× tip is available. Also, a gauge can be ordered with three tips of the same size, or with a single precision-ground tip and two blanks.

Direct measurement of total coating thickness and thickness of individual coats of paint is a unique capability of the Tooke Paint Inspection Gauge. Thus, in addition to routine use, it often serves as a “referee” instrument to calibrate indirect or non-destructive thickness measuring instruments.

Other uses include assessment of substrate conditions and coating adhesion, and observation of microscopic cracking, tendency for brittleness, cratering, or other microscopic film symptoms.

Construction

The OG204 Paint Inspection Gauge shown with the new
"universal" microscope, with a reticle selected for accommodation of
measurement in terms of mils, microns, and millimeters.

The gauge body is a injection-molded high-impact polycarbonate plastic. It contains the microscope and lamp batteries and the groove-cutting tungsten-carbide cutting tips mounted on the narrow side. Two adjustable threaded guide studs project from the body on the same side as the cutting tips. The tripod thus formed by the three legs (guide studs and cutting tip) provides precise alignment of the tool with the surface to be grooved. A lanyard with keeper looped through the body secures the instrument to the inspector’s wrist. The entire unit is designed for convenience and completeness in field inspection tasks.

Operation

A special cutting tool (the “cutting tip”) that is integral to the gauge is used to incise a small precision V-groove through the paint film and into the substrate.

Incising the V-groove with the OG204 Tooke Gauge

Micro-Metrics Company cutting tips are precision-ground by hand from tungsten-carbide blanks in a multiple-step process that includes a final inspection by microscope for accuracy of angle, fineness of finish, and lack of chips and damage.

1×, 2×, and 10× cutting tips

The gauge in standard configuration mounts 1×, 2×, and 10× cutting tips. An optional 5× tip is available. The gauge can also be ordered with three tips of the same size or in any desired configuration (including a single cutting tip with two non-functioning blanks).

The tip slot is marked for the standard tip arrangement

Close-up of a standard arrangement of tips,
showing 2× tip extended for use

Principle: using the new universal microscope

The incised V-groove is observed vertically through an illuminated microscope bearing a measuring reticle (scale). The OG204 is equipped with a “universal scope” with a reticle that accommodates measurement in mils, microns, and millimeters.

Reading the universal microscope

(We’re very sorry, but we do not yet have a professionally done photograph through the new miscrope reticle; we hope to have one soon. This was taken by Elenor. A larger version is also posted.)

Not yet lined up for an actual measurement.

The geometry of the Tooke gauge incision

Principle: using the old-style microscope

The incised V-groove is observed vertically through an illuminated microscope bearing a measuring reticle (scale). Both the “English” (Imperial) version with the reticle marked in mils and the metric version with the reticle marked in microns, are no longer available. Micro-Metrics is attempting to have these scopes custom made.

The view through the (English) microscope

English Reticle Specifications

An enlargment of the (English) reticle view showing the divisions

Metric Reticle Specifications

An enlargment of the (metric) reticle
view showing the divisions

The geometry of the Tooke Gauge incision

Special applications

The Tooke Gauge has been used to assess sandblast cleaning work, to measure plating and paint thickness on ceramics, metal, wood, and concrete, and even to measure protective backing thickness on mirrors. It is virtually the only tool for measuring paint on plastics. The quality of the incision in the film discloses much about the characteristics of the brittleness and adhesion of the material.

Shipping Specifications

The injection-molded high-impact polycarbonate plastic Tooke Gauge comes in a polycarbonate plastic case with two spare batteries, a spare LED bulb, a marking pen, a hex wrench, and a technical data sheet. Standard cutting tip configuration is 1×, 2×, and 10×. An optional 5× cutting tip is also available. Any configuration of tips may also be requested (for example, three 10× tips; or a 1×, 2×, and 5×).