Drilling experiments were conducted in bovine cortical bone specimens. A surgical drill (Stryker-100) was fitted with a custom-designed speedometer for measuring rotational speed, and the drill was mounted on a drill press. Three series of tests were conducted. In the first one, tests were performed using forces in the range of 1.5 to 9.0 N, and free-running speeds in the range of 20,000 rpm to 100,000 rpm. Measurements were made for applied force, rotational speed, electric power and temperature rise. The simultaneous measurements of speed and load show that the average operating speed changed with force: at low starting speeds, the speed increased slightly with force; at high starting speeds and high forces the speed decreased by as much as 50%. The results also show that the temperature rise, the duration of 10{dollar}spcirc{dollar}C temperature elevation and the total energy consumed generally decreased with speed, primarily because of decreased drilling time. In the second series of tests, drilling was performed at the same speed, 49,000 rpm, and at various forces in the range of 1.5 to 9.0 N. The temperature increased with force up to about 4.0 N and then decreased. This dependence of temperature rise on force was found to be statistically significant (p {dollar}ll{dollar} 0.01). The third series of experiments were performed at a speed of 49,000 rpm, and a force of 4.5 N. Temperature measurements were recorded in two directions: longitudinal (L) and transverse (T). The temperature was consistently higher in the longitudinal direction than in the transverse direction. This directional variation in temperature rise was attributed to anisotropy in bone thermophysical properties.
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