Tooke® Paint Inspection Gauges

1. Open the carrying case and remove the instrument.
2. Check the positioning of the cutting tips. Ensure that the curved cut-out on the side of each cutting tip, the relief cut, is oriented toward the guide studs. This relief cut allows the coating(s) being incised to curl up and away from your incision, making for a cleaner incision. For field use, secure the safety lanyard to the wrist to prevent accidental dropping. As originally supplied, the tip positions will be from top to bottom 1X, 2X, and 10X. The numerals 1, 2, and 10 are engraved in the body alongside each tip respectively. The 1X and 10X tips will be bottomed in the slot, and the operable tip should be extended and secured so the narrow face of the gauge will be parallel to the surface to be incised. In general, this is the correct configuration for making an initial measurement on a film.
3. An indelible marker is included in the Tooke Gage kit. Marking the top before incising in not required; however it may help determine where to stop counting hashmarks. If you can easily differentiate between the “slope” formed by the incision and the edge marking the top of the coating, marking may not be helpful and can be skipped. Depending, too, on the coating color, other markers may be useful: Wite-Out® for dark colors or a silver- or gold-Sharpie® marker rather than the black one provided, may provided a clearer differentiation. Make a small mark with the marker, if used, at the desired measurement location on the coated surface.
4. Grasp the instrument with the cutting tip down.
5. Place the cutter tip and guide studs in firm contact with the surface with the tip slightly above the mark and aligned to scribe across the mark.
6. Align the forearm with the intended cutting direction to assure a straight cut.
7. Draw the cutter tip straight across the mark, applying just sufficient pressure for the tip to cleanly penetrate through the film into the substrate. In this operation, the cutter trails midway between the two guide studs, and continuous 3-point surface contact should be maintained to ensure precise vertical alignment of the groove. Excessive pressure on the guide studs should be avoided. The incision does not need to cut deeply into the substrate; merely ensure the substrate is incised along your entire cut.
8. Turn on the microscope lamp with the slide switch on top of the case next to the eyepiece.
9. Center the foot of the microscope on the scribed line with the mark about one-quarter inch from the foot directly under the microscope objective.
10. Check the microscope for focus. If the image is not clear, it may be brought into sharp focus by turning the focusing screw in the body below the microscope. This may be quickly accomplished by using the supplied hex key wrench to loosen the tip set screws. Allow all three tips to bottom in their slots, then pull the selected tip out to the correct height, matching the height of the guide studs and retighten all tips with moderate finger pressure.
11. With focusing accomplished, view the intersection of the mark and the cut. Note how 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 gage slightly. Nor does it need to be lined up; any hashmark will do.)
12. The universal scope is no longer available: all Tooke Gages now come with the Dual-Measure scope. However, since the cutting tip angle determines your calculations, using the view through the universal gauge in Fig. 4a shows the same process as through a Dual-Measure scope. "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.
13. Count the hashmark spaces for each layer of coating. (For instance the top coat, B-to-C, in Fig. 4a is 5 hash wide.) Important: The type of microscope your Tooke Gage is fitted with makes an absolute difference in calculating your measurement.
    • Using the mils-scale on the new Dual-Measure reticle, you divide the number of hashmark spaces by the number designation of the cutting tip. So, if you used the 2X tip to draw your incision, you would divide the 5 hash by 2, which gives your your coating depth in mils (2.5mils). If you used the 1X tip (45-degree face), the ratio is 1:1, so the coating depth would be 5 mils.
    • Using the micron scale on the new Dual-Measure reticle, you use the same division (1x tip = 1:1; 2x tip = 1/2 the counted hash; 10X tip = 1/10 the counted hash) but multiply your calculated count by 20 microns to get your coating depth.
    • Using the older "universal" scope, with its reticle marked in 50microns per hash, you use the same division (1x tip = 1:1; 2x tip = 1/2 the counted hash; 10X tip = 1/10 the counted hash) but multiply your calculated count by 50 microns to get your coating depth.
    • 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.
    • Measurement Principle with a Tooke Gage is a function of the cutting tip and NOT of the microscope. The easiest example to follow in understanding the principle is demonstrated using the 1X cutting tip. In essence, you are incising a triangle into your coating by cutting the hypotenuse of a right-angle triangle. With the 45° 1X tip, you’re drawing an equi-lateral triangle. That is, the side of the triangle (/ the bottom of your view), which you are measuring by counting the harshmarks across the ‘cut-width,’ equals the triangle-side that is your coating depth. A 1 : 1 ratio with the 1X tip. With the 10X tip, you’re drawing a right-angle triangle, and one-tenth (1/10) the number of hashmarks across the cut-width is your coating depth.

Suggestions to Users

• On wood or other directional material, make incisions in the grain or “machine” direction to avoid ragged cuts.
• Soft or elastic materials can sometimes be cooled or frozen with ice or dry ice to obtain good cutting characteristics. An accessory device, the MG402 Microgroover with a precision positioning block that provides an abrasion readable using the Tooke Gage is available. Contact Gardco for details.
• Dyes or indicator solutions such as phenolphthalein are sometimes helpful to develop appearance contrast between metals (iron-galvanizing) or paint coats.
• With some coatings, improved cuts can be achieved by wetting the surface, or by speeding or slowing the cutting rate.
• Coatings with poor adhesion will exhibit a ragged line at the substrate interface. Read thickness from the left incision edge in the SUBSTRATE in these cases. (Note Reference on "Coatings Adherence Measurement")