Automatically-applied friction braking means for a portable electric tool

Claim 1

IN A HAND-OPERABLE PORTABLE ELECTRIC SAW OF THE TYPE COMPRISING A SUBSTANTIALLY-FLAT SHOE PLATE FOR SUPPORTING THE SAW UPON THE TOP SURFACE OF A WORKPIECE, A HOUSING STRUCTURE ON THE SHOE PLATE, A MOTOR IN THE HOUSING PROVIDED WITH A SHAFT, A SPINDLE JOURNALED IN THE HOUSING, GEAR REDUCTION MEANS TO DRIVE THE SPINDLE FROM THE MOTOR SHAFT, A BLADE MOUNTED ON THE SPINDLE AND EXTENDING THROUGH THE SHOE PLATE TO ENGAGE THE WORK, AN UPPER CONTROL HANDLE ON THE HOUSING FOR MANUALLY GUIDING THE SAW ALONG THE TOP SURFACE OF THE WORK, AND AN ELECTRIC SWITCH MOUNTED IN THE UPPER HANDLE, THE SWITCH BEING PROVIDED WITH A MANUALLY-ACTUATED RESILIENTLY-BIASED TRIGGER FOR ENERGIZING THE MOTOR FROM THE ELECTRIC LINE: THE IMPROVEMENT OF MEANS TO AUTOMATICALLY BRAKE THE BLADE TO A STOP SUBSEQUENT TO DISCONNECTING THE MOTOR FROM THE LINE, WHICH COMPRISES: (A) A BRAKE DRUM MOUNTED ON THE MOTOR SHAFT WITHIN THE HOUSING; (B) A BRAKE SHOE WITHIN THE HOUSING AND ENGAGING SAID DRUM; (C) MEANS CONSTANTLY URGING SAID BRAKE SHOE AGAINST SAID DRUM, WHEREBY SAID BRAKE SHOE TENDS TO EXERT A RADIAL BRAKING FORCE ON SAID DRUM; AND (D) LINKAGE MEANS INCLUDING AT LEAST ONE PIVOTED LEVER IN THE UPPER CONTROL HANDLE, CONNECTING SID BRAKE SHOE AND THE SWITCH TRIGGER, AND COUNTERACTING SAID RADIAL BRAKING FORCE OF SAID LAST-NAMED CONSTANTLY-URGING MEANS WHEN THE OPERATOR ENGAGES THE SWITCH TRIGGER IN MAKING A CUT; (E) SAID PIVOTED LEVER HAVVING A DISTINCT MECHANICAL ADVANTAGE, THEREBY REDUCING THE PRESSURE REQUIRED BY OPERATOR AGAINST SAID CONSTANTLY-URGING MEANS IN THE NORMAL USE OF THE SAW IN MAKING A CUT; (F) WHEREBY SAID LINKAGE MEANS AUTOMATICALLY WITHDRAWS SAID BRAKE SHOE AWAY FROM SAID DRUM AND ALLOWS THE MOTOR SHAFT TO ROTATE WHEN THE SWITCH TRIGGER IS MANUALLY ACTUATED; AND (G) WHEREBY SAID BRAKE SHOE AUTOMATICALLY RETURNS INTO BRAKING ENGAGEMENT WITH SAID DRUM CARRIED ON THE MOTOR SHAFT WHEN THE SWITCH TRIGGER IS MANUALLY RELEASED TO DISCONNECT THE MOTOR FROM THE LINE, WHEREBY THE BRAKING FORCE IS APPLIED AUTOMATICALLY TO THE HIGHER-SPEED MOTOR SHAFT RATHER THAN TO THE LOWER-SPEED SAW SPINDLE.