|P.O. ENGINEERING DEPT
Issue 1, 8.10.38
“Clocks Nos. 3, 5, 7 and 9”
” Clocks Nos. 3, 5 and 7” are 8 day general-purpose timepieces which have a spring-driven chain and fusee movement. The movement is housed in a circular polished mahogany case.
Clock No. 9 is similar, but is without glass and bezel (see picture below).
||Dia. of dial
||Depth (back to front)
2. Description of movement
A simple train of wheels is associated with a fusee (F) which acts as a multi-ratio gear to secure a uniform motion of the wheels (i.e. to keep correct time), whilst the torque decreases as the spring in the barrel (Q) runs down. The spring driving power is transmitted to the fusee by means of a chain (C), and thence by wheels (W3 and W4) to the escape wheel (S). The pallet (J) allows the escape wheel to move round one tooth for every swing of the pendulum (P).
3. The 1en~th of the pendulum rod is designed to permit a certain number of escape-wheel teeth to pass per minute, the actual number depending on the design of the wheels. Wheel W3 is coupled directly to the ‘minute’ hand and, by a 12 to 1 reduction,
gear to the ‘hour’ hand. The pendulum is suspended from a cockpiece (B) by means of a very flexible
spring (E). The pendulum rod is slotted to embrace the pin (G), which forms part of the crutch (H) This, in turn, is fixed to the pallet staff carrying the pallet, which engages with the escape wheel. An adjusting screw (K) enables the effective length of
the pendulum to be adjusted by raising or lowering the lead bob.
4. A safety device (L), to prevent over winding the spring, is attached to the pillar plate (A) adjacent to the fusee. It is operated by the side-thrust of the chain during the last two turns of its winding, bringing into operation a positive locking device, which engages with a stop fixed to the fusee, and thus prevents over-winding.
5. The crutch is made of soft brass, to permit bending in the plane of swing of the pendulum. This operation is sometimes necessary to bring the clock into beat.
6. To expose the movement, remove the wooden pegs which secure the back of the case.
The clock is provided with a concealed mirror-plate suspension and fixing plates for wall mounting.
A winding key is supplied with each clock.