In an automatic thread cutter for nuts and similar mass-produced parts where the nuts or the like are taken from a magazine and moved through a feed trough into a guide where they are held secured against rotation and are then pushed by means of a pusher over a rotating thread cutter from where they are subsequently removed while the pusher is returned to its starting position, the improvement comprising:
- a. a pressure medium operated double acting actuating cylinder including first and second displacement chambers and a piston separating said chambers and being slidably received therein;
- b. a piston rod affixed to said piston and projecting from said cylinder and carrying said pusher;
- c. a pressure medium supply means including a conduit circuit coupled to said first and second displacement chambers and pressurizing means connected in said conduit circuit for maintaining said pressure medium under pressure;
- d. a solenoid valve connected in said conduit circuit for controlling the admission of the pressure medium into at least one of said displacement chambers, said solenoid valve having an energized state effecting a greater pressure in said first displacement chamber than in said second displacement chamber for displacing said piston, said piston rod and said pusher in a first direction;
- said solenoid valve having a de-energized state effecting a greater pressure in said second displacement chamber than in said first displacement chamber for displacing said piston, said piston rod and said pusher in a second direction which is opposite said first direction;
- said pusher performing its work during the course of its movement in one of said directions and performing its return motion to its starting position during the course of its movement in the other of said directions;
- e. electric circuit means connected to said solenoid valve for placing the same alternatingly in said energized and de-energized states, said electric circuit including
- 1. a settable pulse generating means for controlling, dependent upon its setting, the length of the alternating energized and de-energized states;
- and
- 2. drive means for driving said thread cutter;
- f. a first electric safety means having
- 1. a first control switch formed of a first stationary switching member and a first movable switching member cooperating with said first stationary switching member and attached to said piston rod for moving in unison therewith;
- said first control switch emitting a first pulse in response to a predetermined position of said first movable switching member relative to said first stationary switching member in the course of travel of said piston rod in its normal, predetermined path;
- 2. a first settable time-delay relay connected to said first control switch for receiving said first pulse from said first control switch;
- said first settable time-delay relay being connected to said electric circuit means for applying a second pulse to said electric circuit means solely in the absence of said first pulse within a predetermined period set at said first time-delay relay;
- said second pulse de-energizing said electric circuit means for switching off said drive means;
- and
- g. a second electric safety means having
- 1. a second control switch formed of a second stationary switching member and a second movable switching member cooperating with said second stationary switching member and attached to said piston rod for moving in unison therewith;
- said second control switch emitting a third pulse in response to a predetermined position of said second movable switching member relative to said second stationary switching member in the course of travel of said piston rod beyond its normal predetermined path;
- 2.