The Microgroover is the major accessory tool for creating coating incisions for film thickness measurements with the Tooke® Paint Inspection Gage. This tool greatly extends the range of the measuring technique to include almost any coating on any substrate. The Microgroover adaptation utilizes drill-like grinder tips for groove cutting operations (cylindrical face cutting).
The Microgroover is especially effective on hard and brittle (concrete) materials, as well as soft or elastomeric (rubber) substances. In addition, fibrous composites are incised easily and cleanly. Aside from film thickness measurements, small-scale operations of cutting, grinding, sawing, and polishing can be performed with this useful cordless power tool.
Setting up the Microgroover
The Microgroover is a high-speed rotary tool for creating the small, almost microscopic, incisions required for measurements with the Tooke Paint Inspection Gage. This technique completely eliminates the deformations of coating and substrate which may occur when conventional gage cutting tips are used.
The high-speed cutter, usually with either tungsten carbide or diamond-studded surfaces, “erodes” away surface material in a precise pattern, leaving adjacent and underlying areas totally undisturbed. Hard, brittle, tough, fibrous, tender, or elastomeric materials exhibit clean, non-tearing, controlled disintegration under the rotary cutter.
For precise and rapid measurements, a “drum mode” of cutting was developed. In this mode the grinder is fitted with the No. 9902 tungsten carbide cutter (or equivalent) installed in a precise position. With the round rim (“flange”) of the Microgroover in continuous contact with the work surface or positioning block, the unit is pivoted until the tip contacts the surface. A light touch with the rotating tip creates the required incision.
The cutting angles (slopes) of 1X, 2X and 4X are accomplished by using the positioning block to elevate the contact shoulder of the Microgroover as required. The required shoulder elevations are as follows:
|1X||0.97" (block resting on narrow face)|
|2X||0.41" (block resting on wide face)|
|4X||0.00" (block not used)|
Principle: reading the incision
When the incision is examined with the Tooke Paint Inspection Gage microscope, it will appear as a partial cylindrical cavity, with the cavity wall angling gradually upward to the paint surface. Where the wall of the cut penetrates the substrate surface, the paint film above it describes a crescent shape, see the drawing below. The thickness is correctly read axially across the thickest part of this shape.
The correct observed thickness for the 1X, 2X, or 4X position of the grinder will be the number of hashmarks observed divided by 1, 2, or 4 respectively.
A measuring demonstration
(Important note: the calculated size of the hashmark space is different depending on which scope is used for reading the incision: the current universal metric scope, the old-style English-unit or metric reticle, or coming soon: the new enhanced dual-measure reticle scope.)
|50 microns||1/10th mil||20 microns|
Count the number of graduations of the microscope reticle (one hashmark space for the primer and almost five hashmarks for the finish coat in the detail photo above); the correct observed thickness for the 1X, 2X, or 4X position of the grinder will be the number of hashmarks observed divided by 1, 2, or 4 respectively.
So, in the detail photo above, the incision was abraded with the positioning block in 1X position. The primer coat measures 1 hashmark space; and it's a universal scope, so the actual measurement of the hashmark space is 50 microns (or 2 mils / 1.97mils). Using the 1X block position, you divide the number of spaces by 1 – so the primer is 50 microns (or ~2 mils) thick.
The 5 hashmark spaces for the top coat, divided by 1 (for the 1X block position) is 5 times the measurement unit of the universal scope, so 5 times 50 microns = 250 microns. (Quick conversion: 9.8 mils.)
If you had used the 4X block position to make the abrasion, you would divide the number of hashmark spaces (1) by 4. So the primer would be 0.25 times (the universal scope's) 50 microns = 12.5 microns. And the 5 hashmark spaces counted for the top coat divided by 4 is 1.25, times the 50 microns = 62.5 microns for the top coat.
(The actual number of hashmark spaces appears to be closer to 4.5 than 5. The same math applies. It is also much easier to see the hashmark lines with the human eye; the photos are mediocre at best. Please note that until the Tooke Gage camera adapter is designed, manufactured, and made available, these pictures are taken holding an instamatic-type camera over the scope; so the quality … just isn't.)
Which Tooke Gage reticle am I using?
The grinder unit is the Dremel Minimite® Model 7300 Cordless Rotary Tool. It comes in a polypropylene plastic carry case, complete with two batteries, a charger, and a technical data sheet; and with special accessories for grooving operations (attached positioning block and MG402-02 grinding tip). An optional conical grinding tip (MG402-09) is available. The grinder is powered by rechargeable Ni-Cad batteries in a removable battery pack. A full charge should suffice for 100 or more measurements. The charger will completely recharge in three hours.
|Grinder Unit||Dremel 7300 MiniMite® Cordless Tool|
|Motor||4.8 volt DC; 5/10 thousand RPM|
|Carry case||Polypropylene plastic, 5" x 12" x 3" |
(137mm x 308mm x 76mm)
|Supplied tip||MG402-02 cylindical grinding tip|
|Battery Pack||Plugs into bottom of grinder or charger|
|Charger||Plugs into 110 volt AC outlet|
|Accessories||Various bits and positioning block|
|Shipping Weight||~2 pounds (77kg)|