Toothsome

In our last episode we discussed the roughly 100 year-old Sessions York banjo clock emblazoned with Betsy Ross on its glass tablet and an eagle sitting on top. 

And while in very good shape overall it was ticking and tocking in an uneven manner, what clockmakers call a "beat" problem....

What is a beat problem?

Being in beat mean the clock is ticking and tocking very evenly, eg. tick-tock-tick-tock. That is a healthy beat for a clock.

A tick or tock of a clock is the sound made when an escape wheel tooth hits a pallet... well... look at the gif above.

You can see the escape wheel with its pointy teeth turning and gently colliding with the pallets of the pallet fork (that bent strip of grey metal). There are two pallets, one curved on top (the entrance pallet) and a second flat one on the bottom (the exit pallet). 

See each one hitting a tooth?

That pallet fork, also called an anchor, is attached to a crutch (the brass rod that is bent and then descends down below the image) which connects to the pendulum. The anchor rides on a pivot and goes back and forth with the movement of the crutch/pendulum. The swing of the pendulum moves the crutch and causes a pivoting action on the anchor which catches and releases a tooth of the turning escape wheel which is driven by the mainspring.

I diagramed a Seth Thomas movement for Nana's Adamantine clock a couple years back. The escape wheel and crutch layout is slightly different (anchor sits below the escape wheel) but all the parts are essentially the same. You can see that diagram and read more about that clock here.

Back to Betsy, the two pallets catch and release in turn as the anchor pivots back and forth. When one releases, the other catches and vice versa. Watch closely in that gif above. It's like each pallet hands the turn of the wheel off to the other pallet.

A tick (or tock) is the sound made when one escape wheel tooth collides with the face of a pallet. 

Basically any time you hear a mechanical clock going tick-tock that is what is creating the sound.

Whew.

An in beat clock will tick-tock such that the escape wheel turning and its teeth pushing the pallet back and forth happens with a very even pattern. Tick-tock-tick-tock.

The gif at the top of this post shows a nice, even beat.

Being out of beat means there is a clustering of the tick and tock with some extra time in between. Rather like a heart beat e.g. tick-tock, space, tick-tock, space, etc. 

A clock that is out of beat will still have an even pendulum swing but the ticking of the escape wheel and anchor will have that slight double beat quality. This is a problem but typically not a serious one.

Clocks being out of beat is extremely common and "setting the beat" is usually and simply addressed by either changing the level of the clock or adjusting its crutch. More details can be found here.

So what's different here? Couldn't you just set the beat Doctor Clock?

Not exactly...

Typically when a clock is in or out of beat it generally remains that way unless something changes (like re-leveling the clock or adjusting the crutch). In other words, a simple out of beat clock stays out of beat until you adjust it.

Our Yorkie went in and out of beat over the course of a single minute, every minute.

Over and over. 

Sounds in beat. Good. 

Wait, no. It's out of beat. 

Wait, no. It's back in beat. 

What?

Roughly 45 seconds of being in beat and then suddenly out of beat... and slowly coming back into beat over 15 seconds or so.

Then the movement runs fine for about 45 seconds and is suddenly out of beat again. Rinse and repeat.

But the change was happening every minute.

That beat problem / condition is much more unusual but something YLH has seen (heard) before in a (yet-to-be-blogged-about) clock acquired about year ago. A New Haven calendar clock. 

"Heard" being the key word. Visualizing a beat problem is very tricky. Hearing it is almost invariably the first signal to an experienced clockmaker.

That symptom of going in and out of beat indicated what might be some modest, but still concerning damage, to that escape wheel shown earlier.

Hey Clock boy! How do you know it's the escape wheel?

First clue to the problem: going in and out of beat

Second clue to the problem: going in an out of beat every minute.

Guess which wheel is the only one on a clock that makes a full rotation precisely once per minute?

Yep. The escape wheel.

Sometimes in the handling of a clock the movement can become damaged. A bump or even a poor turning of the key at the wrong time can result in a little shock wave that can travel throughout the movement and sometimes result in damage to many parts of a clock or, perhaps, just to a single tooth of the escape wheel that happened to be engaged with a pallet at that moment. 

Which can result in a bent tooth. 

Typically a single bent tooth (although more severe variations do occur). There can be other causes of clocks going "in and out" of beat but a bent escape wheel tooth is far and away the most common reason. 

So says Willie X, one of the geniuses on the NAWCC boards.

The bend of the tooth can be a very, very small deflection off of normal and very hard to easily visualize. A 0.1-0.2mm bend to the tip of a tooth is enough to cause this.

YLH encourages the kind reader to review this photo of the movement of the clock. Take a look at the escape wheel. 

You can see an escape wheel tooth resting on the face of the entrance pallet (the curved one) of the anchor.

Back to the wheel. Can you tell which tooth is bent?

Just visually, this horology hound could not either.

Oh and here's a tease... The bent tooth is clearly visible in this photo but good luck trying to ascertain that just visually.

What is essential to finding the errant tooth is careful observation of the escape wheel and anchor as the movement is running. 

And listening is key.

After several attempts your local videographer was able to capture a clear example of the movement going from in beat to out of beat.

Have a look / listen and then more shall be revealed. Turn up the volume.

Did you hear it?

About halfway through the video the beat changes.

In this video you can actually see it happen as well as hear it.

Look / listen closely.

If you didn't catch it, the movement is going out of beat on the catch of the escape wheel tooth marked with a red dot. As the wheel turns you can hear the extra long beat occur as that tooth slides off the entrance pallet (the curved one). It's literally taking the tooth a longer time to slide off that pallet face because the tip of the tooth was slightly bent.

Listen again. It sounds like it just takes extra time for that tooth to release from the pallet.

That extra slide time puts the movement out of beat. Listen for the more double beat variation of the tick-tock right after that.

Tick-tock-space, tick-tock-space.

Not seen in the video, over the next 15 seconds or so the anchor and the escape wheel settle down to a regular, in beat pattern.

And then it starts all over again.

If you go back up to the photo above where YLH asked if you could see the bent tooth... it's visibly marked there in red. On the upper left of the escape wheel. A tooth at about the 10 o’clock position has a red dot at its base. That’s the culprit.

Sure looks similar to the other teeth.

Well how do you fix this professor?

A very, very gentle and subtle bend with flat jawed pliers made to the tooth by drawing the pliers outward.

As demonstrated by another clock genius, Dave LaBounty.

From Dave LaBounty (abouttime-clockmaking.com)

But first the movement must be disassembled and checked for any other problems.

Turns out there were a couple more.

But that's for next time.

OK Scooby?

R'ok R'aggy.