Hydraulic stop

A hydraulic stop for use with a rotating drill and drill bit to limit the depth of penetration of the bit into the workpiece comprising:

• a body member attached at its first end to the spindle of the drill and designed to rotate about the axis of rotation of the drill, said body member having a cylindrical cavity at its second end;
• a first sliding member to fit within said cavity of said body member, said sliding member engaging and rotating with said body member and capable of movement along the axis of rotation of said body member, said sliding member having a cylindrical cavity on end within said body member and drill engaging means on the opposite end;
• a first chamber member to fit within the cavity in the body member engaging said first sliding member and capable of sliding along the axis of rotation of said drill to form with said body member a first variable fluid chamber to hold hydraulic fluid providing stiffening of said stop during the cutting stroke;
• a second chamber member to fit within the cavity located in said sliding member forming a second variable fluid chamber to receive and exchange fluid with said first fluid chamber through the valve means;
• valve means located in said first chamber member to control the passage of fluid from said first variable fluid chamber to said second variable fluid chamber;
• sensing means engaging said valve means, said sensing means opening said valve means when said drill bit has penetrated said workpiece to the desired depth permitting passage of fluid from the first chamber to the second chamber and the collapse of said stop.