Pilot pin-locking device in drilling machines

Claim 1

A drilling machine comprising: a hollow shaft, mounted for reciprocal vertical and rotational travel between a lower working position and an upper resting position; an annular cutter mounted to said hollow shaft for rotational and vertical movement in unison with said hollow shaft; a pilot pin axially mounted within said annular cutter for independent vertical reciprocal movement from an upper unrestrained position to a lower locked position, relative to said hollow shaft and said annular cutter, said pilot pin having a head portion and a shank portion, said shank portion having a groove extending from a lower portion to an upper portion spaced from said head portion, thereby forming an upper shank portion without a groove; an engaging member separate from said pilot pin and disposed within said hollow shaft, said engaging member being biasable against said head portion of said pilot pin by a first spring means having one end fixed in place, said engaging member thereby following the reciprocal vertical movement of said pilot pin from an upper unrestrained position to a lower locked position, said engaging member being biased against said head portion of said pilot pin only during said reciprocal vertical movement of said pilot pin or when said pilot pin is in said upper unrestrained position; an internal oil reservoir within said hollow shaft adapted to be automatically supplied with oil by an external oil supply means; said oil flowing from said internal oil reservoir past said engaging member and down said pilot pin when said engaging member and said pilot pin are in an upper position, and said hollow shaft and annular cutter are in said lower working position; said engaging member being seated on a ring and substantially blocking the flow of oil down said pilot pin when said engaging member is in its lower position, said engaging member including a horizontal cavity alignable with an annular depression in the inner wall of said hollow shaft when said engaging member is in its lower position; a ball received in said horizontal cavity and biased outwardly by a second spring means, said ball being extendible by said second spring means to a position within said annular depression when said horizontal cavity is aligned therewith, said position maintaining said ball partially within each of said cavity and said annular depression, thereby releasably locking said engaging member to said hollow shaft to maintain said pilot pin in said lower locked position while centering said drilling machine and to substantially block the flow of oil down said pilot pin when in said lower locked position.