The design of Taber's Multi-Finger Scratch / Mar Tester is based on the apparatus described in automotive specifications (including Ford BN 108-13; General Motors GMN3943; and Daimler-Chrysler LP-463DD-18-01) , which is commonly referred to as a five-finger (five-arm) scratch & mar tester.
The instrument includes a pneumatically driven, moveable sledge to which the test sample is mounted. The sledge moves in a linear fashion, and is operated by a control knob for one or multiple pass testing. An electronic timer displays the rate of speed, which can be controlled by reducing or increasing air pressure.
A gantry supports five independent splined-fingers, which provide a constant, vertical load on interchangeable scratch pins (1.0mm or 7.0mm diameter hemisphere). The gantry system includes a handle to raise and lower the arms. In addition, five support rests are incorporated to allow one or more arms to be moved to an upright, rest position such that the arm does not contact the specimen during testing.
Individual weights of varying loads mount to the top of each arm finger to exert a standard force on the surface of the test material. Each instrument includes a weight set of 2N, 3N, 4N, 5N, 6N, 7N, 10N, 15N and 20N loads. Other weights are available for 8N, 13N, 18N and 25N.
Although flat specimens up to 22mm thick are normally tested, the ‘free-floating' arms fingers enable you test evaluate slightly contoured specimens provided they are rigid or adequately supported. A spring-loaded specimen holder is standard and can be mounted to the end or side of the moveable sledge for greater flexibility. To mount contoured specimens, an optional set of ‘moveable' hold-down clamps is available