Clock repair blog

WHAT ABOUT THE IDEA THAT THE WEIGHT HAS NOTHING TO DO WITH THE PERIOD OF A PENDULUM? 

Well you can believe what you want. And if you are a physics major you may say that this is true. In theory you are correct. In clock repair not true at all. There are several reasons for this. First, the “center of gravity” of a pendulum determines its effective length as far as the clock is concerned. This has been determined by exaustive empirical study. So if you put a “different” weight on a pendulum the timekeeping will change. In other words if you change the pendulum bob you will probably change the timekeeping characteristics of the clock. It is important to understand here that if you “add” weight to a pendulum, you will change its effective center of gravity. To better understand this concept; think about it this way: How do you determine how long a pendulum is? Is it the pendulum rod, the suspension, the pendulum stick, or the pendulum bob? If you were doing a physics experiment, how would you make the pendulum shorter? You would probably shorten the string holding the weight. To adjust the timekeeping of a clock you move the bob up or down depending on whether or not it is running slow or fast. This changes the effective length of the pendulum, thereby changing the period. If you add weight to a clock pendulum, you will change the period of the pendulum and you will change the characteristic timekeeping of the clock, unless you add the weight in such a manner so as to NOT change the center of gravity, and you add enought power to the mainspring or or weight that supplies power to compensate EXACTLY for the weight you have added. Consider this: Lets say you have a wall clock that has a pendulum that produces one tick per second ( This is typical of many large wall clocks ). How many seconds in a day? 60 * 60 * 24 = 86,400. Now take that times 7 and you have 604,800 seconds in a week. In most repair situations and customer service situations, if a clock is more than 5 minutes a week off, you will get a call from your customer. This error is not acceptable to most people. Lets say you change the length of your pendulum so the period is one tenth of one percent slower that it should be on each swing. That is .001. One thousandth. Doesn’t seem like much? Better think again. 604,800 * .001 = 604 that is 604 seconds in a week. Depending on the gear ratio, the clock could be ten minutes off or more. Ok, lets say the error was only .0001 one ten thousandth. That would still be a minute a week. Annoying, but ok. However, lets say you had a 30 day clock ( there are clocks designed to run for 4 weeks on one winding ). That would be a half hour in a month. Probably not acceptable to most people. A tiny set screw on a small wall clock pendulum will make more difference than the .001. This does, as you can see, illustrate the fact that a heavier pendulum will be more accurate, because adding a small amount of “change of center of gravity” will have less overall effect on a heaver pendulum. Clock timkeeping error is additive in a way most people do not consider, and weight change on a clock pendulum does make a difference; sometimes a large difference. This theory mentioned above is precisely why clocks have been designed with temperature compensating pendulums, and suspension springs. If the temperature changes 10 degrees and the suspension rod expands say .01%, it will change the timekeeping. If the pendulum bob expands, and does so in a non-uniform way, the timekeeping will change, because the center of gravity will be altered by the changing shape of the pendulum bob.

Second: If you put a heavier weight(pendulum bob) on a pendulum the pendulum arc will decrease because you have not changed the amount of power that is pushing the pendulum yet you have added to the friction. With a shorter arc there will be less time between ticks. The escape wheel will move faster and the clock will run faster. Too much weight here and the clock will stop. This problem is worse with spring drive clocks than with weight drive clocks because of isochronal error. That is a fancy way of saying there is less power available from a mainspring when it unwinds. The reduction in power is not linear. Generally speaking the mathematics needed to design a clock was available many years ago. Most clocks have been designed well and the “stock” pendulums and mainsprings are crucial in providing good timekeeping. For this reason, I recommend when ever you can, keep the clock as original as possible. Unless you are a skilled mechanical engineer with years of experience in designing slow moving grear trains, you probably will not be able to improve much on the design of an old clock.

Third: If you put a lighter weight on a clock pendulum ( that is to say if you put a pendulum that is lighter on the clock ) the arc on the swing of the pendulum will increase slightly because you have reduced the amount of friction on the pendulum. Maybe I shouldn’t call it friction. As the weight of the pendulum increases it takes more energy to push it. As the weight of the pendulum decreases, it takes less energy to push it. Then there will be more time between ticks. The escape wheel will move more slowly and the clock will run slower. Remember that this effect is additive here; most clocks will tick hundreds of times in one day.

The strength of the suspension spring will also determine the arc of the pendulum. A thicker (stronger) suspension spring changes the arc , or swing of the pendulum ; it usually makes it shorter. Too thick (strong) and the clock will stop. Too thin (weak) and the clock will stop. A thinner (weaker) suspension spring changes the arc , it usually makes the pendulum arc increase. Remember, when the pendulum arc (swing) increases there is more time between ticks and the escape wheel turns more slowly which makes the clock run slower. All of these factors interact in a very complex way mathematically. Sometimes timekeeping is affected in ways that seem illogical at best. If a clock has an excess of power , sometimes you can get away with putting a stronger suspension spring on it. The key word here is sometimes. As soon as you start changing things you will need to be very careful. I strongly advise against changing a clock suspension spring or pendulum unless you use an exact replacement. If you have a clock that has no suspension or pendulum this may help you devise one by emprical study.

This is a phenomena that sounds unbelievable at best, but it does exist and is a common cause of many clocks stopping. Sympathetic vibration can be described as the transfer of energy from one object moving with a steady frequency to another object (initially not moving) connected to it. The objects will transfer energy very efficently if they are the same length; however, they do not have to be exactly the same length to transfer energy . A classic example is a large grandfather clock with a heavy pendulum and a case that is set up on a rug. When the weights travel downward and get even with the pendulum bob, the weights will absorb enough energy from the pendulum to either stop the clock and or start the weights swinging and stop the clock. Also the clock case can absorb energy from the pendulum because the case is not solid on the rug. Even the slightest instability can cause the clock to stop. On old cases ; if they are loose, if the case is not solid, the pend moving will cause the case to oscillate (this may or may not be visible) and the case will absorb enough energy to stop the clock. correct this by securing the case to the wall. be sure the case is solid.

If there are several clocks running on a shelf with similar pendulum lengths , and the shelf appears solid it still may be possible that the clocks on this shelf will transfer energy back and forth. The result may not be just stoppage. One or both of the clocks may not keep time or may be un-regulatable because they will affect each other.

Sympathetic vibration may be demonstrated by a little device with weights and strings. Suspend 2 weights ( at least 8 ounces ; fishing weights would work nicely ) from a small frame like a scale model of a swing set with strings. Make the strings the same length. Start one weight swinging and very soon the other one will be swinging, and the first one will be stopped. This is sympathic viabration. The less solid your frame the quicker the energy will bea transferred. The frequency with which the energy is transfered back and forth ( the weights will start and stop alternately) is related to the length of the strings and the amount of friction present and the time it takes to transfer the energy.

There are a number of things that will cause timekeeping problems. Some
are true generally speaking and some are specific to certain clocks. The following is
a list of the generally speaking problems:
a “set” mainspring
improperly lubed mainspring

damaged mainspring— scratched ,rusted or pitted spring : or a spring with lumps
caused from the shape of the spring upon itself being wound for years and years.

worn weight pulley
gummy oil
worn or loose bushings
loose suspension post
incorrect mainspring
sympathetic vibration
damaged threads on the pendulum adjusting nut
regulator end of key damaged
bent suspension spring
loose verge
worn gear teeth
worn roller pinions and or worn roller pinion bushings
incorrect weight on time gear train
loose hand clutch
scored pivots or pivot
too much play in impulse loop
incorrect gear ratio
incorrect center of gravity on the pendulum bob
incorrect pendulum weight
incorrect suspension spring thickness
mainspring run down
unstable running position
out of beat
mainspring catching on gear teeth or click rivet or click spring hooks
damaged escape wheel teeth
moon dial gear binding
incorrect verge escape wheel depth (shallower depth will generally make the clock
run faster because the swing is reduced making less time between ticks.

You may have to check all of these if you have problems after moving a 
clock. It doesn't take much to stop a clock. The most common problem is 
failure to wind the mainsprings up all the way! This is a user/owner 
problem. Generally speaking if a clock is stopping after it has been 
rebuilt check the following: 

Check the beat setting 

check endshake on all gears and levers 

check for tight bushings on all pivots and levers 

check the position of the impulse arm vs susp rod check for bent 
escape wheel teeth 

check for bent teeth (even slightly) every where in the gear train 

check for a mounting bind: with the mechanism mounted in the case 
if one of the mounting feet is even slightly bent it can cause any 
one or all of the gear trains to bind) 

check for barrell teeth hitting #2 wheel teeth on endshake minimum or 
maximum. 

check for worn gear teeth 

check for proper gear depthing 

check to be sure the mainsprings the correct strength 

Check to be sure the suspension is the correct strength 

check if possibly the pendulum is the wrong weight 

check to see if the Hands are rubbing on the glass at any point in 
the 360 degree rotation: (put your finger on the glass over where  the minute hand is located and if the hand looks closer to your finger 
than the glass is thick then the hand is probably hitting on the glass.) 

check for a bushing not oiled 

check to see are the hands touching each other at all anywhere? 

when the clock stops , very carefully check to determine if there is 
any power to the escape wheel; if there is power then be more concerned 
about pendulum friction, sympathetic vibration, or suspension problems. 
If there is absolutely no ; or very little power, 
then there is probably a gear train problem. 

Check if there is there any air circulation around the pendulum, it does 
not take much to stop a clock. 

Check to see if the weights are magnetized and is the pendulum brass 
plated steel? 

Check if the pendulum is touching the back of the clock ? 

Check if the clock case is sitting on a solid surface? 

check if the clock is hanging plumb on the wall? 

Is the hour tube binding? 

Are the chime or strike levers binding because of lack of oil or 
rough edges? 

check the suspension post to see if the suspension is loose--- 
If it is loose the clock will probably stop. 

check for pallet face wear 

check all lubrication points.

All clocks must have maximum power transfer to the pendulum or they will not run dependably. This means they must be in beat. What does this mean? Some call this “setting the balance”. Try to imagine the pendulum and verge as a swing and the person pushing as the escape wheel. When the clock is in beat the escape wheel gives the pendulum a push at just the right time in the same way as a person gives the swing a push just as it arrives back and at the instant it starts back on its return trip. When a clock is not in beat the situation is similar to the person pushing the swing taking five or six steps forward before the person on the swing starts on their way back. What happens? There is a collision and the arc of the swing is disturbed. If a clock is out of beat the verge collides with the escape wheel teeth, and the clock eventually stops before it is run down.

The verge clutch will usually allow the beat to be set by adjusting the position of the impulse arm until it is at the true center at rest with the mechanism and case set level and plumb. Be very careful when setting the beat; sometimes the verge clutch is set so tight that the escape wheel teeth can be bent without realizing it. If the clock is “in beat” then as you watch the pendulum swing you will hear a “tick” or “tock” precisely at the point when the pendulum passes the center ( true center as mentioned above) of its arc. This must be its characteristic arc , not the one you give it when you swing the pendulum. How do you know its “true arc” ? Do this with the clock perfectly level while you can see the escape wheel and verge: starting with the pendulum at rest move it slowly until you hear a tick or a tock which is the sound of the escape wheel releasing.(You must know which way to move the pendulum of course because the escape wheel will only release once on each side of the arc. If you are doing this for the first time it would be a good idea to be able to watch the escape wheel and verge interaction so as to know which way to move the pendulum to allow the verge to release the escape wheel. To get an idea how this works, take the pendulum off and GENTLY move the suspension arm back and forth to observe and learn the action of the escape wheel / verge combination, then put the pendulum back on and continue.) As soon you hear the tick or the tock release the pendulum. DO NOT PUSH IT. If the clock is in beat you will hear the other side tick when the pendulum gets to the other side of its arc.

If the beat is set, but the clock gets in beat and they out of beat; check for bent escape wheel teeth if the “in beat and out of beat” sound has a regular repeating pattern. If there is not a regular pattern then the problem is probably a loose verge. The clutch can be ok but the verge can be loose on the shaft. when setting the beat on a clock, if possible do it by sight and sound.

Setting the beat on a balance wheel is just as important as the beat on the pendulum units. The hairspring collar can usually be moved if need be, it is a delicate operation. Practice on spare parts

Clock Repair Archive – –

Clock Repair Archive – –     

Clock Repair Archive – –

The sonora chime by Seth Thomas that has dual chimes (whittington
and westminster ) has 2 small dials about 1 inch in diameter on the top of the
face. One of them is for the chime selection and the other is for the timekeeping
adjustment. The mainspring in the chime unit is larger than in the single chime
unit; it’s dimensions are: strength: .0215inches thick by 1.375 inches wide by
approximately 106 inches long.Be careful with this spring. When it is wound fully it
has a lot of energy stored in it. If you are installing this with a spring winder, I
would strongly recommend wearing a face shield; not just eye protection, but a face
shield and eye protection. The sequence of the hammers is as follows: looking in the
back of the case assign numbers to the hammers and let the hammer closest to the back be #1 .
The wittington sequence is as follows at the quarter hour chime: 1, 4, 6, 7, 2 ,3 ,5 ,8.
The westminster chime at the quarter hour is: 6, 7 ,2 ,8.

This clock has two mechanisms. The one closest to the front of the clock powers
the strike and the time gear trains. It also trips the chime. The chime mechanism is
closest to the back of the clock. The chime mechanism has a huge mainspring and mainspring
barrell. Pay very close attention to the teeth on this barrell; if this mainspring or
barrell lets go , it will do much damage to the mechanism and possibly to someone’s finger.

Most of these clocks are not self correcting on the chime or the strike.The
mechanism that runs the strike and the time is very similar to the 8 day
time and strike american clock mechanisms. The chime usually is sounded on a row of bells
mounted above a resonating box. These clocks have a beautiful sound in my opinion. The hammer
sequence is different on these clocks than on the modern german w/c self correcting
mechanisms.

The time and strike mechanism is activated by the chime mechanism,
however, the chime mechanism is activated by the trip lever and the trip cam in the
time and strike mechanism. It is a good idea to be very sure you have the lift wires
correctly adjusted before you re-install the mechanisms in the case. I have usually
set them up on a couple of blocks outside of the case to get the adjustment reasonably
close before installing the mechanisms.

Be absolutely sure to check the ratchet dog system on
the chime mechanism; I have seen many of these loose when they come in for repair.
If one of these lets go, the results will be disastrous indeed. The mainspring in one
of these mechanisms is powerful enough to easily break someone’s finger. There is usually
a pin on the inside of the ratchet that the click spring pushes on to make the click
work. Be sure to check this pin very carefully, it must not be loose or the
ratchet system will fail.

The pendulum on these mechanisms usually will have at lease 2 inches of
swing, and the pendulum bob is one of the heavier (2+ ounces typically) types.
Before getting too far on the repair of one of these clocks . it is very wise to check
the gear teeth on the chime mainspring barrell. If the barrell is bad , there is no point
in doing the rest of the work until the barrell problem can be resolved. If the chime
mechanism won’t work, then neither will the strike . The hammer throw is critical
on these clocks ; it may have to be reduced if it has been tampered with. Take the
hammer assembly out, take it apart and clean it throughly. If you do not do this
you will be insulting the integrity of the owner and the quality of the clock.
I have frequently seen these mechanisms bind up because of excessive hammer friction
due to too much throw or gummy oil.

Unless you are working on a family heirloom, be prepared to have trouble with
these clocks. Not that they are bad; on the contrary, they are excellent clocks in my opinion.
Many of them I have seen have been butchered, or have had so much oil slopped on the gears that
the chime mainspring barrell has teeth that are dangerously worn. You can save yourself a lot
of headache and embarrassment by checking the chime mainspring barrell while the customer is
there, if possible. If you have too many customers to check it at the counter, be sure to
check it BEFORE you get into the repair. Look at the teeth on this barrell carefully. If you see
grooves worn in the teeth be alerted. It has been my experience that more than 10% wear on
these teeth will cause the chime to bind up sometimes. I have seen them with more wear that
will still make the chime work. This is an extremely dangerous situation. Here we have a situation
of what you can get by with, and what is a good restoration. The damage has already been done.
Now the owner has to decide if they want to keep the original barrell and risk destroying the rest
of the clock by running it until the thing explodes, or not running it and having it original.
It is a judgement call as far as the antique condition of the clock is concerned.

The hammer sequence on the single melody westminister chime is different than usual.
It is as follows: looking in the back of the clock and assigning numbers to the four bells
used for the quarter hour melody starting with the bell closest to the back door
and calling it #1 and the one next to it #2 ,Then #3 and finally #4 , not counting the
bell used for the hour strike or course , the order for the quarter hour chime (down
the scale westminster) is ; 2 ,4 ,1 ,3 . This same sequence would also apply to the
3rd measure of the 3/4 hour chime.

Clock Repair Archive – –    
The seth thomas a-200 movement strike mainspring is .018in strong by .682in wide ; and the time mainspring is .014 in strong by . 682 in wide and both 96 inches long. This is the mechanism that is used in their banjo clock of the early 1900’s.The return spring on the Seth Thomas time and strike 891m shutoff is .010in. and is usually 5 turns. Regulation on the Seth Thomas A- 200 series movement : turn to the left for slower or to the right for faster .4 1/3 minutes per day – 1 turn.

Clock Repair Archive – –