|A Monthly Sample of Clock Repair Projects
This month's patient is a British 30 hour longcase
movement from the early 1800's.
Both the time and strike are powered by the same single
weight on the "endless loop" pulley system first
introduced by Christiaan Huygens in the late 1600's
(though this system is typical of most 30 hour clocks up
through the 19th century). The mechanics are quite
interesting in that, while designed to provide an
affordable clock to the common man, the 'run of the mill'
30 hour clock had some unique shortcuts built into it
which surely came from basic - historically sound - ideas
that came into being long before our subject was made.
First--- 1 weight!!! An excellent way for the clockmaker
to cut expenses. And while you're at it: use rope to drive
it instead of brass chain or cable and save a few more
pence: the winding arbor carries a spiked winding wheel
that "digs in" to the rope to prevent slippage.
Second--- The ratcheting system>>>>>>>>>>>>
Because there is only one weight there is only one
ratcheting assembly needed. But that's not all folks: they
needn't the usual click (or pawl) and click spring and
the ratchet wheel with all those annoying teeth that must
be shaped and all those screws and pins that would hold
that whole expensive, time-consuming assembly
together (as you'd see on an 8-day clock from this or
any period). Here's what we're left with: a sort of
O-shaped circular disc spring with a raised pawl which is
partially riveted onto the back of the winding wheel.
(Notice also that the lifting pins needed to raise the
hammer to strike the hours are located on the great
wheel instead of a separate "pin wheel". That's 1 less
gear and arbor that needs to be made!).
When the chain or rope is pulled to raise the weight the
winding wheel is drawn clockwise (in this case). This
action draws the raised pawl around with it - imagine the
pawl being sucked under each "crossing" arm on the
great wheel during the wind due to the springiness of
the disc. When winding is completed the natural action
of the weight on the winding wheel is to pull back
counter-clockwise. This motion is stopped by the pawl
face brought 'round against the first crossing arm that it
This meeting re-introduces power back to the strike side.
30 hour clock ratcheting system on great wheel arbor (tthe great wheel also acts
as the 'pin wheel' in this case).
Third--- Maintaining Power. Yes, that's right folks.
Huygens' "endless loop" pulley system also provides
constant power to the time train during the wind.
Because there is only one weight, AND, because the
ratcheting mechanism for winding this one weight is built
onto the strike side, it is only the strike side which loses
momentary power during the wind (which is nice
because a strike train never needs maintaining power).
It's amazing - I see so many more complex (albeit
creative and mechanically brilliant) solutions in other
clocks, but a bare bones system like this makes me
smack my head in wonder at the sheer practicality of it
and ask: "What is truly necessary?"
The pawl face is brought around by the weight to meet the crossing arm (notice the
wear on other crossing arms). The weight is now bearing upon the crossing arm
and ready to drive the strike train.