Gents Bell Ringer Part 2. The Mechanics.

The overall view from the rear of the striking mechanism. Note the large size of the wormwheel and cam. It is the cam which lifts the bell hammer via a rope or cable. The ratio of the wormwheel is determined by the number of teeth. With a single start worm the system is usually designed to strike the bell once every 3 seconds. This period gives a sense of authority to the bell striking without dragging it out too long on the later hours.[10-12]

The strike count plate ensures the correct number of hammer blows are struck on the bell. The number of blows depends on the length of the land between the slots as the count plate slowly rotates. The locking tab is resting in a peripheral slot. This is the normal, rest position with the switching lever raised and all switches off. The count plate must rotate once in 12 hours but is driven only intermittently during the actual striking. Not that the tab does not physically stop the striking. Given the torque amplification of two wormwheels it is impossible to resist the motor power at this point in the drive chain.

A view of the worm drive to the count plate. The initial drive is via 1:1 bevel gears from the main  wormwheel/cam shaft. There follows a considerable speed reduction via a second worm and smaller wormwheel. There appears to be 60 T on this wormwheel. I have yet to discover the purpose of the coiled spring. It may well be safety device to protect the count plate from damage if the tab should become lodged in one of the strike locking slots. If this should occur the count plate would still be driven against the resistance of the locking detent. With the considerable amplification of the motor torque via 2 wormwheel reductions the damage could be considerable!

The main wormwheel and worm reduction. It looks like a single start worm. So the reduction ratio is a direct result of the number of teeth on the wormwheel. Always a difficult task to count teeth from photographs. Made worse by odd numbers of wheel spokes. After repeated counts I make the wormwheel approximately 180 teeth.

                                                                                                                                            The flexible coupling between the motor and the main worm shaft is seen.  This reduces shocks in the drive system and ensures alignment of the motor and shaft. The load on the hammer lifting cam is heavy at times [of lift] and highly variable. Falling to almost zero after the hammer is dropped.

One of the two, brass worm shaft bearings is next in line and supports the main worm in contact with the wormwheel. An oiler cap is provided.                                            

The main wormwheel/cam shaft, bearing, bevel gears and secondary wormwheel seen from above. Gent's certainly did not stint on providing adequate strength in the wormwheel casting and other components. Long life and reliability are important when a device is subject to dirt and unskilled care. Even if a covering box was provided it takes only one failure to replace it for typically dirty working conditions to do their worst.

End view of the mechanism from the bell hammer rope pull end. An original length of rope is seen clamped in the linkage on the end of the bell hammer, lifting arm.

Heavy loops of iron or steel help to ensures that no damage occurs if the connection to the bell hammer, lifting lever is broken. This lever is normally held up by the tension of the bell wire or rope.

The motor shaft brake from the rear. A brass disk is fitted to the end of the motor shaft. A fibrous brake pad normally rests against the disk. When the solenoid is activated by low voltage electricity the brake pad is lifted clear of the disk. Allowing free rotation. A strong coil spring pulls the brake on when the solenoid is not powered. The spring pulls below the brake pad, pivot bearings.

The motor shaft brake from the front. Once deprived of electrical power the motor must be stopped quickly to avoid random over-run of the gear train. The count plate striking system is sensitive to its rotational position relative to the tab. [Or locking detent as it is known in clock circles.]

No comments: