NOTES FROM THE BENCH

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Clock Repair Archive - -     Cuckoo clock repair:

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Determining the correct type of chain:

If you have a cuckoo clock that does not
have any chains or has chains that do not work correctly there is a way to determine
what chain to use. First ,count the number of teeth on the sprocket and measure
the effective diameter of the sprocket. Keep in mind that most cuckoo clocks
sprockets / chains use every other link , so the distance between sprocket teeth must
match the distance between 3 centers of links. Use the formula to find the circumference
of a circle; to find the distance around the sprocket exterior ; then divide that by the
number of teeth to determine the required distance between every other link ie: the
distance between sprocket tooth ends. The wire diameter must be such that the links will
set in the saddle of the sprocket enclosure without climbing out as the sprocket turns as
the clock is running or when the clock is being wound. The links should sit approximately
50% of the way down on the tooth. The final test, however, is whether or not the chain
pulls through without any places that bind up. The chain must run though SMOOTHLY or the
clock will not work. If the links climb up on the sprocket teeth when the chain is pulled
though, then the chain is not the correct link per foot count or the wire diameter is wrong.
Many times the chain will climb up on the sprocket teeth on the side opposite the weight (the
loose end side). You will not see this if it is up inside the clock. Sometimes the chain
will climb only intermittantly. This is a very difficult thing to catch. It will happen
when the customer has the clock at home. They take it off the wall , bring it back in to
you and by the time you get it the chain problem has vanished. You will hang the clock up
and it will perform perfectly. I am not suggesting that you check each link on every chain
on every cuckoo you repair. What I am saying is to check each chain by pulling it through
the sprocket and watching it carefully. If you have a cuckoo come back and there appears to
be nothing wrong , then you need to check the chain VERY carefully. This is also true for
most chain drive clocks. Brass chain does stretch more than steel chain , but it tends to
wear the sprocket teeth less. It is usually easier to replace a chain than a sprocket.

Most cuckoo clocks do not have suspension springs. They depend on
gravity and the power in the gear train to make the pendulum move. They do ,
however have a suspension. It consists of 2 loops and one hook. The hook is on the
end of the suspension rod. Always check this system. The loops get grooves worn
in them and this is enough to stop the clock. Also check the top loop on the
suspension post to be sure they are not loose. The clock will stop if either one of
these are loose. They must be tight, absolutely tight. If the post is threaded in the
threads can be tightened by closing the hole in the plate slightly with a hole closing
punch. This will adequately tighten the suspension , providing the hole is not closed
too tightly. These loops in my opinion are best served by light oiling. Light meaning very
small amounts of oil , and a very light weight oil. Only enough oil to cover the friction
points with a thin film of oil should be used.

Many of the cuckoo clocks you see will have music mechanisms in them. They
will usually be weight drive. watch for worn governor assemblies, worn bushings on
the player drum assembly, and missing or ineffective dampers on the sounding fingers.
the governor assemblies that have plastic worm drive gears often have cracked gears;
and will make a clicking sound as the cracked part of the gear passes the worm gear.
these must be replaced once the gear cracks.
An irritating squeaking noise as the music plays is often caused by bad or
missing dampers on the music sounding fingers, to fix this simply glue
new tiny plastic pieces on
the inside bottom of the fingers. The originals are glued on. The plastic you
use to dampen the vibration must not be too stiff or too flexible. If there are any
of the originals left you can tell from them what the required flexibility must be. If not you may
have to order a new mechanism and take the dampers off of the new one. Why would you
want to do this, you may ask? Because the customer may not want to change the tune
and you may not be able to find a replacement mechanism with the same tune. I have been
through this hundreds of times.
The squeak can also be caused by loose hardware in the
clock  anywhere. Check very carefully for loose screws or wood parts.
The governor assemblies can be rebushed if they aren't worn too badly, and
this is preferable , because the original tune can then be saved. There are some
replacement governor assemblies available, but quite ofter the correct gear ratios are
not included. Also, it is possible to rebush the player drum assembly. Use the appropriate
reamer and very carefully, by hand , open the holes on the frame and press the bushing
in with a pair or flat parallel jawed pliers. Make sure the bushing fits the shaft before
it is pressed in.
DO NOT EVER PUT ONE OF THESE IN AN ULTRASONIC  CLEANING
MACHINE , THE DAMPERS WILL BE BOILED OFF AND IT WILL BE RUINED.
There are music mechanisms that have only the tune part separate , and the gear
train is in the main mechanism. The usually have large vertically mounted governors,
with adjustable fan blades . Watch out for these ; if the worm gear has worn teeth , it
will never work correctly . On music cuckoos , if the return spring on the side mount
music mechanism it too tight; the entire time/strike mechanism will bind up and stop.

Most cuckoos have what is sometimes called an "Anchor escapement" system or a "Recoil
escapement". This type of system does not have a lock action , it is simply impact, slide ,
and release. The recoil escapement is less critical to adjust, and generally speaking ,
is more efficient in that it does not take as much power to run. However this type of
system is less accurate because the motion of the pendulum is less isolated from the
gear train. The escape wheel tends to bounce backwards at each impulse ; and as the
spring runs down the arc of the pend slows causing less bounce or recoil in a nonlinear
manner. In the case of weight drive cuckoos this is not as much of an issue.
Make sure that the verge-escape wheel depth is set such that the pendulum will not
swing far enough to hit the sides of the case enclosure. The depth settings will vary
from clock to clock. If the original depth setting is lost; a general rule I use is
this: the working surfaces of the escape wheel tooth contact with the verge surfaces
( the slide and release ) should be 20 percent of what the total depth would be if it were
taken all the way to the point at which the verge surfaces would not release the escape wheel
teeth.
If possible the escape wheel should move equally on each
side of the tick. Often the verge has either been bent or replaced and the escape
wheel will impact,slide and release  further on one side than the other; and in many
cases the clock will run. My experience has taught me that this is not an extremely
critical adjustment on this type of verge with respect to whether or not the clock will
run.If the goal is just to get it to run ; then don't be fussy. To charge a customer a
premium price for this kind of work , however is quite another matter. The majority of
clocks (excluding cuckoos) that I have seen over the years have an even release distance
on the impact ,slide , and release. If you want to do accurate, original , restoration;
then set both sides of the sequence equal.

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Copyright (c) 2002 David Tarsi. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being no invariant sections, with the Front-Cover Texts being no Front-Cover Texts, and with the Back-Cover Texts being no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

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