SETH THOMAS CLOCKS
The Seth Thomas clock company has made millions of clocks, many of which have 2
mainsprings , two gear trains ,and one count wheel. Most of these types of mechanism
have a wire lock arm system which usually consists of two small shafts with wires
attached
to trip the strike in conjunction with the count wheel. The bushings for the
lock arms are critical. They must be loose , but not too loose. Any thing over
about.006in maximum play. Oil in this area will probably cause problems;
unless the shutoff wire has a return spring.
If the actual shutoff wire has a return spring , it may forgive some slop however ,be
careful, and be sure to check the operation of the wire very carefully. The slop in the
bushing will cause sideways movement of the arm and may be enough to disrupt the action
between the shutoff lever and the count wheel. The slot in the count wheel that the flat
wire end drops into is not very wide.
Another part of the strike system that is critical is the lift cam attached to
the
centerpost. This cam is almost always press-fit. It must be tight enough so
that it cannot be moved by even the strongest hand. If this cam is soldered, beware,
this almost always means that it has either come loose , or someone didn’t know
what they were doing. The lever hooked to the count arm that works with this cam must
contact that cam at the center of both the cam and the lever. PICTURE. If the cam
does not have a beveled edge , then the minute hand should not be turned backwards.
If the cam has a beveled edge , then counter clockwise motion is probably an option.
The lever will usually gave an angled edge so that it will spring back out or the way
of the cam when it moves counterclockwise.
All of the levers that are hooked into the count arm axles must be absolutely
tight. They must not be able to move under normal operating conditions. It is not
necessary to solder these parts to make them stay put. However if they gave been damaged,
as a last resort from a practical standpoint, soldering may be the only option. Remember
to use only enough solder to do the job. Again, let me stress, be absolutely certain that
all the flux is removed when the job is done before the clock is reassembled.
Many of these clocks have escape wheels with somewhat long fine teeth. Be
careful , they bend very easily. The Dead Beat type of escapement is common on this
type of mechanism. Be aware of this and keep in mind that the tolerance of the bushings
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
corr
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
corr on the escape wheel and the verge are critical if the clock is to keep good time. If the
verge is located on the front or back outside of the plate; it still must not have sloppy
bushings.
Always check for worn main wheel gear teeth, and worn pinions (wire pinions
can be replaced of course) these two situations will cause stoppage and timekeeping
problems. Also check for bent gear teeth ;even slightly bent teeth can
cause the clock to stop.
The seth Thomas Adamatine clock regulator: 1 turn is 2 min
in 24 hours. The mainsprings in these clocks are of the standard .018in. by .750in. by 96in.
american manufacture. They must be thoroughly cleaned and all the old oil must
be removed without scoring the spring. They must be unwound ;opened up entirely
and all the surface cleaned by other than an ultrasonic cleaning machine. The ultrasonic
can and probably should be the first cleaning step. There are in fact some movements
that don’t take the standard size spring so be sure to measure the springs carefully. A
sticky or fatigued mainspring can cause the clock to stop erratically , and or not keep
time. Problems with the strike will also be experienced; such as sequence getting off
and or the speed or the strike varying.
Some of these mechanisms will have a return spring on the shutoff, and some
will not. Care must be taken to insure that the strength of the return spring is not
strong enough to make the clock stop. Also make sure that the surface of the trip cam is
not rough enough to add enough friction to stop the time gear train. The cam lift surface
must be smooth.
I have found that cleaning mainsprings with an abrasive substance such as
sandpaper is ok as long as the spring surface is not scratched excessively. If the
surface of the spring is scratched, then friction will be added in direct proportion
to the extent of the scratches , quite possibly more than the old oil that was removed
by the substance in the first place. A self defeating situation at best!! Use fine steel
wool with cleaning solvent to remove the old oil. The old oil will often look like a
yellowish brown stain and can be mistaken for the color of the steel if you are not
aware of this. Some springs do have this color; so check if the stain can be removed
by fine steel wool and solvent, it is probably not the steel color!