NOTES FROM THE BENCH
Clock Repair Archive - - Two spring Westminster chime Sessions:
The sessions westminster chime mechanism with only 2 mainsprings can be
recognized by the silver colored large hammer lift assembly on the back plate that is
quite obvious when you open the back door. This is not present on time and strike
mehanism. The assembly is spring loaded . If there is not a coil spring in the cap
on the end, there should be! This mechanism has 2 racks and 2 snails. The front rack
and snail controls the hour count, the rack and snail behind these control the quarter
hour chime. the two racks work together, in other words they both always drop, and
the gathering pallet cam picks both of them up together. They are offset from each
other, that is they drop to different levels. The snail for the hour has 12 levels;
the one for the quarter hour has four levels. Behind the hammer lift assembly on the back
plate is a fixed indexing pin permanently attached to the plate; it should not move,
or be moved unless someone has tampered with it. the hammer lift assembly has a
hole in it that snaps onto the indexing pin at the end of the hour chime sequence ,
allowing the hour count to finish the remaining gear travel allowed for by the hour
strike rack action.
The power to run the chime and strike is transfered through the
long shaft that runs through the hammer lift assembly. The cap on the back end of
the hammer lift assembly has a pin that catches either all the discs in the hammer
assembly, or just the hour strike disc depending on the position of the assembly
as determined by the fixed pin on the outside for the back plate.
To set these mechanisms up after rebushing them, first set up the snails
and racks on the front plate to the 12 o'clock position with the trip cam on the inside
of the plate with the high side having just released the trip lever. The quarter hour
snail should be set so the corresponding rack drops to the deepest spot. Set the hour
snail to the 12 o'clock position of course. The hour snail has a set screw on it so when
the snails are set on the front very carefully tighten that setscrew; be absolutely
certain nothing moves when you do (except the set screw, of course!). Be absolutely
certain that the hour tube still has endshake after this cam is secured. Now move
your attention to the back plate. There is a cam friction fit on the back of the
centerpost that needs to push the hammer lift assembly out (via the swivel lever
on the back plate) far enough to clear the indexing pin so the hammer lift assembly
is in position to lift the hammers that will sound the quarter hour chime after the trip
lever releases. On the hour this cam must just be starting to lift the swivel lever in
order for the hammer lift assembly to be in the correct position when the quarter
hour chime starts. This mechanism can take as long a 1 and a quarter hours to self
There is an idler gear on the front that meshes with the gear on the quarter hour
snail. This gear is often friction fit on. It should be absolutely tight. It must not
move or the clock will never work. What usually happens if this gear is too loose is that
the clock will mysteriously keep getting out of sequence. It needs to turn of course , but
it must be tight on the shaft. this idler gear, as you will probably notice turns the
quarter hour snail.
There are usually 2 setscrews on the cap on the back of the hammer lift
assembly; be sure to loosen these when you set the chime sequence at the hour.
There is not a lot of spin on the governor before the first hammer picks up on this
clock. The sequence of the hammers is the 1,2,3,4 down the scale at quarter after
similar to the modern german w.c mechanisms.
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Copyright (c) 2002 David Tarsi.
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