To evaluate a material’s resistance to scratching or shearing, various tools are available for use with the Shear / Scratch Tester:

• Conical Diamond tools (Models 139-55 and 139-56) are used for scratching materials of ordinary hardness.  These tools are precision lapped to a 90° angle, and are available with a radius point of 3 mil (Model 139-55) or 3.5 mil (Model 139-56).
• Diamond Scratch tool (Model 139-58) is used for scratch testing unusually hard materials. This tool is the converging point from three sides and edges of a perfect cube.
• 1.0mm Hemispherical Scratch tip is ideal for materials that are fragile or when a sharp cutting tool is too aggressive.  Intended for use with model 550 or 551, this tool has a modified post and requires the Scale Beam Height Extension Kit.
• Carbide Scratch tip satisfies EN 14565 for resilient floor coverings.  This tip includes a 45° angle and 0.25mm radius point.
• S-20 Tungsten Carbide Contour Shear Tool is used for shearing tests.  Precision ground, this tool features a cutting edge lapped to a 25mm diameter with a 30° clearance. The edge is set at a 22° shear angle in relation to the rotation of the table and is designed to shear a groove between 50 to 100 mils in width.
• Other shear tools include Model S-20-3 ‘Honda’ Tungsten Carbide Tool (similar to S-20, but no radius) and S-20-4 Tungsten Carbide Tool (similar to S-20, but R2.6mm).

Over time, the scratch / shear tools will wear out.  Due to material differences in the test specimen, there is no way to predict how long the tool will last.  A Diamond Standardization Plate is also available to perform the standardization procedure referenced in test method ISO 4586-2.  These plates are manufactured from a high molecular weight polymethyl methacrylate (PMMA) cast sheet, and provide an inexpensive method to determine if the diamond tool is worn.  Sold in packages of two, each plate is 4 inches square with a 1/4″ center hole and is pre-dried and vacuum sealed.

Taber recommends that an extra tool is kept on hand for standardization purposes.  If you have access to optical measurement equipment that offers an accuracies of ±0.01mm and ±1°, you can monitor the wear on your scratch tools.  Inspect the tool at set intervals (e.g. every 250 or 500 tests), if any flatness or other kind of damage is found the scratching tool should be rejected and replaced with a new one.

For best results, conduct three to four tests on the specimen surface.  Each test should be approximately 90° from each other (e.g. in the 12, 3, 6 and 9 o’clock positions) and at least 6mm in length.  A 10x Measuring Magnifier is included with each Shear / Scratch Tester. This allows you to visually measure the width of a scratch to the nearest thousandth of an inch.  For more precise measurements, TABER recommends an Optical Micrometer.

Diamond Scratch Test

The standard criterion for scratch resistance is the minimum load required to penetrate the surface of the testing material with the diamond tool.  Alternatively an average scratch width can be calculated using a specified load, and results compared.

Shear Tests

The standard criterion for shear resistance is the minimum load necessary to shear the surface of the testing material with the contour shear tool with a width ranging between 1mm to 2.5mm.  Due to the difficulty in cutting grooves of identical width, minor deviations can be compensated for by averaging the measurements.

Adhesion of Coatings

Using the TABER Shear / Scratch tester, adhesion of coatings can be rated.  This is determined by recording when the tool breaks through the junction of the topcoat and the undercoat.  See graphic for suggested ratings.

NOTE: An irregular or ‘jumpy’ cut not caused by careless test procedures may indicate lack of uniform composition or surface irregularities.

The following link provides a listing of test methods the Taber Shear/Scratch Tester satisfies.  Please note, additional accessories may be required.