Clearing the upper and lower registers is accomplished by rotating the respective carriage support shafts through an angle of about 30°.
The motion is generated by a pair of cams and clutches at the rear of the control unit. The clutches are controlled by a linkage from the clearing keys at the front of the machine.
There is also a "Clear/Return" function which clears both registers and returns the carriage to the right, and an automatic counter clear function at the start of a division.
The clearing cams and clutches.
The clearing cams and clutches are mounted on the No.4 shaft at the rear of the control unit. The outer end of the shaft has an eccentric bearing to adjust the clearance on the fibre drive gear.
The two cams at the bottom right operate the clearing linkages via the two roller-equipped lever arms (top right).
The third cam (next to the drive gear) operates the Clear/Return function via a linkage which releases both the clearing cams and initiates a carriage shift.
The clutches are controlled by a linkage which starts the motor, releases the clutch pawls, and then disengages, allowing the cams and clutches to make only a single revolution.
The three dog clutches rely on a deliberate friction load from an internal wave washer to hold them in their rest positions against the release dogs at the end of their cycle. The friction load is present at all times, and helps to bring the gear train to a stop whenever the motor is switched off.
The clearing links.
This view shows the links which connect the two operating arms from the control unit to the carriage support shafts.
The bushings which rotate the shafts are attached to the brass support bushings in the frame plate. They are built up from seven layers of pressed steel so as to distribute the turning force along the double keyway. The counter mechanism is relatively light, but clearing the main register requires a force of about ten pounds on the horizontal connecting link.
The carriage clearing arms.
The rear carriage support shaft has a simple lever arrangement at the right-hand to transfer the rotation to the counter register clearing shaft.
The main register clearing arms are much larger to cope with the higher loads. The front support shaft has a double arm and roller at each end of the carriage, which transfers the rotation to the main register clearing shaft. The linkage allows for the vertical movement of the register as it is pulled down into the dip.
The clearing clutch operating linkage.
The clutch operating linkage can be installed as a complete sub-assembly after the control unit has been attached to the rest of the machine. The shaft is held in place by two retainer plates attached to the frame side plates.
The forward-pointing yoked arms on the left (in this rear view) connect to the clearing keys at the front of the control unit via three long links and levers on the outer right-hand side. They operate the three clutch release dogs on the lower vertical arms.
The yoked lever on the right of this assembly engages with a pin on the right-hand carriage pull-down lever, and relays the carriage position through the cross-shaft to a series of interlocks in the control unit.
The rightmost lever arm initiates the carriage return function via a long link to the shift mechanism at the front of the control unit.
The clutch linkage installed.
This view shows the clutch operating linkage and the carriage dip interlocks installed on the right-hand rear corner of the machine.