What beat is and how to set it in your clock to keep it running. BEAT AND BEAT-SETTING
----------------------------------------------- THE REALLY, REALLY BASICS
A clock is in beat when its ticks and tocks are even....tick...tock...tick...tock..., and is out of beat when they are uneven...ticktock...ticktock...ticktock...or tick...tocktick...tocktick...
When a clock is out of beat, either it won't run at all, or it will run for a bit and then quit.
There are two ways to put a clock in beat. The first, and simplest, is to tilt the clock sideways, one way or the other, and listen for the beat to even out. When the beat is even, prop the clock to stay tilted that way. Now it will run, but it will look funny tilted.
The second way is to adjust the crutch to one side or the other, until the beat is even. The crutch is the rod that extends down from the pallets the things that rock back and forth. The pendulum rod passes through either a loop or a forked foot at the end of the crutch.
If the crutch is a simple rod or wire, it is adjusted by bending it to one side or the other. If it attaches to the pallets with a friction joint, it is adjusted by holding the pallets still with one hand, and shifting (pushing) the crutch right or left on the friction joint.
Which way to tilt it? Rich Jones has formulated a simple rule, known here as Arjay's Maxim:
Tilt her till she ticks with pride
Then adjust the crutch toward the high side
First, use the tilting procedure to make the beat even. Note which side is the high side. Now, straighten the clock so it's vertical, and adjust the crutch toward the side that was the high side.
How much to adjust it? Trial and error. Adjust the crutch, then start the pendulum swinging and listen to see if it's in beat. If it isn't, repeat the procedure. If it goes out of beat the other way, you adjusted it too much: adjust it back a bit. Generally, in two or three tries it will be in beat so it runs AND it will be level, so it doesn't look funny.
The working heart of any pendulum clock consists of the escape wheel, (EW).the escape wheel pallets & their attached crutch, and the pendulum. The EW is powered by a spring or weight through the gear train. The pallets rock back & forth, allowing the EW to rotate one tooth at a time. The pendulum passes through the crutch loop, and regulates the back & forth rocking of the pallet; and therefore regulates the speed at which the EW is allowed to turn, by how fast it is swinging. To work properly, the crutch loop must be level that is, at a right angle to the pendulum rod.
As the pallets catch and release the teeth of the EW they make the characteristic tick...tock... sound. The rhythm of that tick...tock... is the BEAT (the "heartbeat") of the clock.
The pendulum swings back & forth by gravity, and left to its own devices it would eventually slow and stop. What keeps it going is the escape wheel. As each escape-wheel tooth slides off the pallet, it gives the pallet a little push, or impulse. That impulse travels down the crutch to the pendulum. The little push in each direction is what keeps the pendulum swinging instead of running down.
An irregular heartbeat in a human can be fatal. An irregular beat in a clock will cause it to stop running. In order for the pendulum to keep going, the pushes have to happen at exactly the right moment in the pendulum's swing, in order to assist it instead of interfering with it. At the bottom of each swing of the pendulum, it gets a little "boost" from the escape wheel, pushing it a little further than it would have gone on its own. If the push comes too LATE (after the bottom), the pendulum will start back before it has benefited by the extra distance it needs to keep swinging, and will slow and eventually stop. And if the push going one way comes too EARLY (before the bottom), then the push going the other way will come too late.
When pushes, or impulses, occur at the wrong time, the clock is "out of beat". Each impulse is accompanied by either a "tick" or a "tock". So when the clock is out of beat, one will be too early and the other too late in the pendulum's travel. Their sounds will be uneven: tock...ticktock...ticktock... or tick...tocktick...tocktick... instead of a smooth tick...tock...tick...tock...
The crutch loop is the part that delivers the impulse from the EW to the pendulum, so the crutch is what determines when the impulses will be given. Putting the clock in beat is therefore a matter of adjusting the crutch.
The Beat Center
Imagine a line that extends along the pendulum rod at the moment when the pendulum receives its "tick" impulse and "tock" impulse from the crutch. I call that line the "beat-center". The pendulum passes back and forth across the beat-center in its progression from tick to tock and back. The clock is in beat when the beat-center is perfectly vertical: tick and tock impulses are delivered at the exact bottom of the pendulum swing.
The location of the beat center is marked by the crutch loop, which is what delivers the impulse to the pendulum during each swing.
Vertical is determined by gravity. Imagine it as a line from the suspension post of the pendulum to the center of the earth: straight down.
Beat-center is determined by the angle of the crutch relative to the escapement (the pallets interacting with the escape wheel).
When the beat center is slanted from the vertical, the clock will be out of beat, and will eventually stop. There are two ways to bring it back to vertical.
One way is to lift one side or the other of the clock, rotating it until beat center and vertical line coincide.
The other way is to adjust the angle of the crutch relative to the escapement.
In figure B, the beat center is deflected to the right. The tick is closer to the bottom of the swing than the tock is. The beat is uneven. Now imagine how you would have to rotate the clock to bring the line to vertical. You would lift the lefthand side (tilting it to the right), until the beat center matched the vertical line. You put the clock in beat by lifting its left side.
In the diagram, the pink dot represents the position of the crutch loop as it delivers an impulse to the pendulum in the course of the pendulum's swing.
Since the crutch loop marks the beat center, you can shift the beat center by holding the clock level and moving the crutch. In the diagram, you would put the pink dot on the vertical line by moving it to the left...toward the side you raised to put the clock in beat.
This reflects Arjay's Maxim:
"Tilt her 'till she ticks with pride, then adjust the crutch to the high side."
Adjusting the Crutch
There are two basic types of crutch: the wire crutch and the flat crutch. Some examples are shown in the pictures. The wire crutch is solidly fixed to the pallet arbor. The flat crutch is attached to the pallet arbor with a friction joint or friction clutch.
A wire crutch is adjusted by bending the wire to move the crutch loop in the desired direction. How much to bend it is a matter of experiment. Bend it a bit a listen to the beat. If it's still out of beat, bend it a little more. If you go too far and it's out of beat the other way, unbend it a bit. Usually, you can get it in two or three adjustments.
A flat crutch has a foot which serves the same function as the loop: to transmit impulse to the pendulum. The usual way to adjust it is to turn the crutch on the friction joint. That means keeping the pallet arbor still while turning the crutch.
One simple method is to gently move the crutch in the desired direction until you feel resistance the pallet will be "bottomed out" on escape wheel, so the arbor can't turn any further. Then push the crutch just a bit more to move it on the arbor.
That isn't always possible. The design of some clocks prevents the crutch from being able to "bottom out" the pallets. In that case, reach into the movement with one hand and hold the pallets in place while you move the crutch in the desired direction.
A third type of connection between crutch and pendulum uses neither a loop nor a foot, but a pin. You find this in Viennas and some other clocks where the pendulum is suspended from the case, rather than from the movement.
The pendulum stick has a slot in it, protected by a metal wear plate. A pin on the crutch extends through the slot. These employ a screw adjuster that moves the pin back and forth in the crutch to adjust the beat.
The Overswing Method of Setting Beat
this segment contributed by Scottie-TX
The overswing of a pendulum is the distance it travels after receiving an impulse after you hear the tick or tock. This is illustrated in figure I. The impulse occurs as the pendulum crosses the beat center. The distance it travels after that is overswing.
An alternative or supplement to setting a clock's beat by only listening to the ticks and tocks and sometimes can even produce a more accurate beat setting, is by observing supplemental arc or overswing of pendulum bob. Supplemental arc is the distance the bob travels after you hear the tick. See diagram below. Clock is in perfect beat when supplemental arcs, left and right, are equal.
As mentioned above, Each impulse is accompanied by either a "tick" or a "tock". So when the clock is out of beat, one will be too early and the other too late in the pendulum's travel. Their sounds will be uneven.
So it is also with overswings. They also are equal when impulses are neither early nor late and unequal when out of beat - especially applies to 400 day and torsion clocks.
The method requires you to use both sight and hearing. Here's one way. Manually move the pendulum to the left just until you hear it tick; then make a mark on the back panel where the pendulum rod is. Do the same to the left. The marks show where ticks & tocks happen. Start the pendulum swinging. Any pendulum movement beyond a mark is overswing. Determine by eyesight. If a beatscale would aid your analysis - create or find one to place behind pendulum for a reference. A beatscale is simply any kind of calibrated scale with a center mark and equally spaced hashes left and right of center to observe behavior of pendulum.
If left side has a lot of overswing and right has little - adjust beat by whatever method available until overswing is equal on both sides. When overswing is equal on both sides - clock is in beat. The beat center will be vertical.
With torsion clocks, where the pendulum rotates instead of swinging, this method is crucial. The difference is that the beat center isn't a vertical line, but a point on the pendulum's arc, so equal overswings MUST be used to determine beat.
The advantage I see to this method is using both audible and visual assessment of beat may be superior to listening, alone. Another possible advantage is that some have difficulty acquiring an ear for, "in beat", and for them may be helpful.
Adjusting Beat in a 400-Day Clock
Scottie has pointed out that a regular pendulum clock is in beat when overswing is equal in both directions. The same is true for torsion clocks.
A 400-day torsion clock is in beat when its pendulum has equal overswing in both directions.
Overswing is the amount of pendulum rotation AFTER a tick or a tock.
Adjusting beat in a torsion clock is a matter of both watching and listeningor rather, of watching two places at once: listening for the tick (or tock) or watching for the EW tooth to drop off the pallet, since the tick of these clocks is barely audible while watching what the pendulum does. A beat amplifier helps. Make some radial marks on the base with a felt tip (clean off later with alcohol) to help judge the amount of rotation. OR make a gauge out of a circle of paper with lines for "spokes", and put it under the pendulum.
Mark one ball of the pendulum with a piece of tape or something. Keep your eye on that ball of the pendulum as it rotates. Note the location of the marked ball when you hear the tick or see the tooth drop, and watch how far it rotates after that. ("It was at THAT mark at the tick, and it traveled to THIS mark before it reversed direction.") Do the same for the tock. The two quadrants the amount of circle traveled must be equal.
Overswing is adjusted by turning the saddle holding the top of the suspension spring...in LITTLE TEENY increments. They make a 400-Day Beat Adjuster that clamps onto the saddle, providing a lever. You can also do it by sticking a jeweler's screwdriver into the cleft of the saddle, and using that as a lever to adjust it.
Moving the lever to the LEFT will increase CLOCKWISE overswing (and decrease counterclockwise overswing).
Moving the lever to the RIGHT will increase COUNTERCLOCKWISE overswing (and decrease clockwise overswing).
Use tiny movements just fractions of a degree at a time. A small change at the saddle makes a big change at the pendulum.
Tick! (overswing)...Tock! (overswing)...and so on. Make adjustments back and forth until they are equal. The clock will then be in beat.
Adjusting the Beat of a Hairspring Movement
These illustrations are of a Big Ben lever balance movement. The general principle applies to any lever balance movement.
The hairspring is attached to the balance staff with a brass collet which has a slit in it. The collet can be turned on the staff.
To make the adjustment, let down the mainspring so there is no power to the escapement. Put the blade of a small screwdriver into the slit of the collet, to hold it and keep it from turning. While holding the collet steady, turn the balance wheel so the impulse pin points directly toward the lever arbor. Remove the screwdriver and check the pin's position. You may have to refine the adjustment a time or two.
When the three items are perfectly in line, the movement will be in beat.
IMPORTANT ADDENDUM: Thanks to "Les" Lesofsky for this bit of wisdom. When a balance is set in perfect beat, it won't self-start from a dead stop. It will require a push from a finger to get going. Instead, set it just a tiny bit ... a degree or two... out of perfect beat. That keeps the lever fork pressing on the impulse pin, ready to give it a boost as soon as there's power to the train.