Top Reference for Drilling
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
Fixed depth holes, also known as blind holes, can be precision drilled by air turbine driven drills. As shown in the drawing, a drill turbine 1 is fitted with a Hall effect eddy current sensor 2 that detects a tick mark 3 in the rim of the journal bearing 4. The sensor emits an electrical signal each time the tick mark passes by, one impulse per revolution. The period between pulses, or one revolution, can be timed very accurately with a microprocessor. As the drill 5 comes in contact with the panel, the drills's RPM rate will drop because of an increased load on the bit. This change in the frequency of the RPMs is a signal to the microprocessor that a top reference point has been established. This RPM reduction sensing concept can be used in conjunction with microprocessor controlled vertical motion.