MEASUREMENTS OF SHAFT SPEED WHILE DRILLING THROUGH BONE

Purpose: This study investigated the effect of force on drill speed and measured the energy consumed during the drilling process. Material and Methods: Applied force, drill speed, and energy consumed were measured during drilling in bovine cortical bone specimens. A commercial surgical drill was fitted with a custom-designed speedometer for measuring the rotational speed. The handpiece was attached to a laboratory drill press and positioned above a bone specimen mounted on a load cell. To apply steady loads, weights were placed on the drill platform, and tests were conducted for forces between 1.5 and 9.0 N and for free-running speeds from 20,000 to 100,000 rpm. Results: The simultaneous measurements of speed and load for the electrically powered instrument showed that the average operating speed changed with the force applied: at low starting speeds, the speed increased slightly with force; at high starting speeds, the speed decreased with force by as much as 50%. The measurements of electric power showed that the total energy consumed generally decreased with speed and force, primarily because of decreased drilling time. Conclusion: The decrease in energy suggests that drilling at high speed and with a large force may be desirable because bone temperature is reduced.