Tooke Paint Inspection Gage IV
The Tooke Paint Inspection Gage IV is a precision tool for inspection and dry-film 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 Gage uses an illuminated 50-power microscope equipped with a “universal scope” with a measuring reticle that accommodates measurement in mils, microns, and millimeters. This gauge mounts tungsten carbide cutting tips for precise incision of the work surface. Standard cutting tips are 1X, 2X, and 10X. An optional 5X 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 dry-film coating thickness and thickness of individual coats of paint is a unique capability of the Tooke Paint Inspection Gage. Thus, in addition to routine use, it often serves as a “referee” instrument to calibrate indirect or non-destructive thickness measuring instruments.
(Note: Each universal microscope is validated before sale against a certified gage block traceable to the National Institute of Standards & Technology (NIST). An OEM calibration certificate is available for an additional fee.)
The Tooke Gage 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.
Other uses include assessment of substrate conditions and coating adhesion, and observation of microscopic cracking, tendency for brittleness, cratering, or other microscopic film symptoms.
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.
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.
The gauge in standard configuration mounts 1X, 2X, and 10X cutting tips. (An optional 5X tip is available.) The gauge can be ordered in any desired configuration, such as with three tips of the same size. You may also order (for a lower price) a gauge with only a single cutting tip and two blank tips (spacers).
Cutting tip ratios: A to A′
|1X||45° 0'||A : A′ = 1 : 1|
|2X||26° 34'||A : A′ = 1 : 0.5|
|5X||11° 18'||A : A′ = 1 : 0.2|
|10X||5° 42'||A : A′ = 1 : 0.1|
Principle: using the universal microscope
The incised V-groove is observed vertically through an illuminated microscope bearing a measuring reticle (scale). The OG202 is equipped with a “universal scope” that has a reticle that accommodates measurement in mils, microns, and millimeters. (The universal scale is metric, so conversion is necessary for English units.)
Reading the universal microscope
Note that in the photo below, the zero-line of the reticle is not lined up for the actual measurement (nor does it need to be; any hashmark will do). The gray/silver-colored “line” is the metal substrate; the white “line” is the (inside of the) green coating, which is what is measured visually through the scope. (See below for a different annotated version.) The cutting tip “draws” the (specifically-angled, depending on the chosen tip face) incision, which allows for calculation of the coating thickness. In this photo, the black marker has not been used to make the edge (top) of the green coating more easily seen.
In the next photo, the “zero-line” of the reticle is not lined up with the edge of the primer coating (the white line to the left of the zero-line); it is approximately centered in the substrate (gray/silver line). (This was not intentional; lining up the camera moved the gauge slightly.) “Line A” is on the edge between the substrate and the beginning of the primer-coating: begin your measurement there. “Line B” marks the top of the primer coating/beginning of the top coating (light blue). “Line C” is the incision into the top coating, made easier to see by using the black marker provided with the Tooke Gage.
Thus, in this photo and using a “universal” scope
(0.05mm hashmark space),
the thickness measured for each tip equals:
1 X tip
- “white primer” = 2 reticle/hashmark spaces = 100 µm
- “blue topcoat” = 5 reticle/hashmark spaces = 250 µm
- “white primer” = 2 reticle/hashmark spaces = 50 µm
- “blue topcoat” = 5 reticle/hashmark spaces = 125 µm
- “white primer” = 2 reticle/hashmark spaces = 10 µm
- “blue topcoat” = 5 reticle/hashmark spaces = 25 µm
(If you have an older gauge, with an English-only or metric-only reticle, please see this page for the measurements that would apply to this incision. These old-style scopes have a green-anodized barrel, which is visible at the top of the gauge.)
Universal reticle specifications
|1X tip||2X tip||10X tip|
|* 1.0 mil = 0.001" = one thousandth of an inch
**micron = micrometer (µm) = 1,000,000th of a meter
The geometry of the Tooke Gage incision
Measurements made using the Tooke Gage are a function of the cutting tip geometry (and not of the microscope). A detailed explanation of the geometry of the Tooke Gage called “Measuring: the Geometry of the Tooke Gage” is available.
The injection-molded high-impact polycarbonate plastic Tooke Gage comes ready for use in a polycarbonate plastic carry 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 1X, 2X, and 10X.
- An optional 5X cutting tip is available.
- Any configuration of tips may be requested (for example, three 10X tips; or a 1X, 2X, and 5X).
- You may also order (for a lower price) a gauge with only a single cutting tip and two blank tips (spacers).
|Material||Polycarbonate plastic body|
|Overall dimensions||4.5" x 3.5" x 1"|
11.4cm x 8.9cm x 2.5cm
|Microscope||50-power, 45-degree, illuminated|
|Power||Two 15V AA drycells, plus two spares|
|Lamp||LED 222 bulb plus spare|
|Cutting tips||Precision-ground tungsten-carbide: |
usually 1X, 2X, and 10X; or as desired
|Shipping Weight||1.75 pounds (0.8kg)|
A detailed explanation of the geometry of the Tooke Gage called “Measuring: the Geometry of the Tooke Gage” is available.
Website design and management provided by SnowTao Editing Services.
A (slightly pained) comment (by a technical editor) on spelling: In the coatings industry, the word gauge is often spelled gage. Because the Tooke Paint Inspection Gage is – and always has been – known by this spelling, I have used that spelling in the proper name of the gauge, but not elsewhere.