Critical torque detector

An apparatus for detecting the critical torque imposed on a rotating drill, comprising:

• a rotating input member,
• an output member for supporting said drill and connected in a flexible driving connection with said rotating input member, and
• means for detecting the difference in rotational speed between said input and output members, when said drill is subjected to a torque greater than the predetermined critical torque,
• said rotating input member including:
• a first rotating sleeve,
• a pulley operatively connected with said first rotating sleeve for rotating the sleeve,
• a second rotating sleeve attached within said first rotating sleeve for movement therewith and having a longitudinal slot formed therein,
• said flexible driving connection and said detecting means including:
• a reaction rod slidably accommodated within said second sleeve and having a pin projecting into said longitudinal slot, said reaction rod being releasably connected to said output member for rotating the output member when said drill is subjected to a torque less than the predetermined critical torque, said reaction rod being retained against rotation relative to said second sleeve by said pin in said slot,
• and biasing means for maintaining said reaction rod in an axial position in connection with said output member for rotating the latter in response to rotation of said second rotating sleeve, said reaction rod being operatively connected to said output member to move axially against said biasing means when the predetermined critical torque is reached and thereby to signal that a difference in rotational speed between said input and output members has occurred.