The inner depths

Persistence.

It's a virtue.

About six months ago your local horologist wrote a series of posts about a Vienna regulator as seen here, here, here and most recently here. We explored adjustable deadbeats, the Biedermeier design aesthetic and the entertaining conundrum of the second hand that swept a full trip around its dial in 45 seconds. 

And the clock doc did get our European friend to run.

But not well.

Here she is.

Sadly, its pendulum swing was... anemic. 

The pendulum had low amplitude (distance of the swing).

So what does that imply you ask?

The amplitude of the pendulum reflects the amount of power being transmitted to it. Not enough power and a clock will stop.

And that's what happened with our Vienna.

Let's step back.

How do we evaluate the amplitude of the pendulum and what's good vs. not so good?

To start it's not strictly how far left and right the pendulum swings. It's more nuanced. Some pendulums need big swings and others less so. 

It's about amplitude and overswing. 

Let's dive in.

Here's an animation your essayist used to explicate the mysteries of the deadbeat escapement. 

from Wikimedia

A brief outline of what we're looking at... Up top we have the anchor with its two pallet arms swinging back and forth. The escape wheel (EW) is ticking forward (clockwise) to each beat / swing of the pendulum crutch (OK for the sake of ease of explication let's just call that a pendulum swinging for now).

As the pendulum swings to the right, the anchor collides with a tooth (locks) on the entrance pallet (left side) and then, as the pendulum does its return swing (to the left), it releases (drops) that tooth. Through that same return swing / beat the exit pallet (right side) snags another EW tooth and it in turn drops on its return pendulum swing. 

The observant reader will note that the EW teeth lock on the outside face of the entrance pallet and the inside face of the exit pallet. 

Those little locks and drops are at the heart of the regulation of a clock.

Here's a diagram of an entrance pallet drop and an exit pallet lock.

When each EW tooth drops off the pallet face it creates a measurable gap from the tip of the escaped tooth to the tip of the pallet face. Similarly when it lands (locks) an EW tooth can slide a measurable distance along the locking face of a pallet.

The length of the gap of the drop and the distance of the slide of the lock tells us a lot about the power of the escapement.

Look again at the animation. 

As the pendulum and anchor pallets swing the EW tooth drops and continues to travel a bit -- widening the gap between the tooth tip and the pallet face. Similarly observe the length of the slide of the locks. The EW teeth land and then slide along the face of the pallet. These distances represent what is called "overswing" meaning how far the pendulum swings "over" what is needed to lock or drop.

For a real world example of locks, drops and overswing have a look here at the animated gif that your local computer geek horologist made in the examination of Charlene's Ingraham Regulator.

In this escapement the black bent strip anchor is below the EW so the EW teeth enter the escapement from the right. Watch as an EW tooth hits the outer edge of the entrance pallet on the right side. The tooth lands and slides. Landing is the lock. Sliding indicates overswing. Then the swing reverses and the tooth drops. 

It's the same on the other side of the anchor. An EW tooth locks on the inside of the exit pallet, slides (overswing) and then reverses and drops with some overswing.

So summarily regarding overswing:

• Big overswing means that the escapement has plenty of power to drive the pendulum ie. big amplitude
• Little/no overswing indicates low power and will manifest in low pendulum amplitude and the clock will barely run
• Sometimes the power from the escape wheel is so low the EW teeth can't escape to drop at all. 

If the EW teeth don't drop, the escape wheel cannot advance. And the clock stops.

As did our Vienna.

In brief the most basic research on these lovely creatures revealed that Viennas classically operate with low amplitude. Healthy, normally operating Viennas typically demonstrate low pendulum amplitude. 

So... anything that saps power from a Vienna can take an already modest pendulum amplitude to zero.

But this aspiring clockmaker had just done a full service on our Austrian timekeeper. The pivots were clean. There was very little wear. The movement was freshly lubricated and put in beat.

The clock did run when it was reinstalled in the case on the wall. 

The pendulum amplitude was low but isn't it supposed to be with Viennas?

Yes but our clock did eventually stop. 

Restarted, it ran for a few more days.

Weakly.

Then it stopped again.

Something was wrong.

And there is our question: 

Why was it stopping?

What was sapping the power of our Vienna?

To help us solve this riddle let's rewind once more.

When YLH was servicing the movement it all seemed to go without much issue. There were some interesting things to observe and learn. The clock movement only needed a simple cleaning. Nothing appeared broken or overly worn.

But there was a challenge in it's servicing that was a bit of a conundrum and turns out became key to understanding why this clock stopped.

Horology 101:

Before (and after) servicing a movement it is important to test / observe the movement on a test stand. Early analysis of a movement on a stand can tell the clockmaker many things.

Well with our Vienna YLH couldn't run the movement out of the case.

Why not?

Because the pendulum does not attach directly to the movement.

Huh?

Let's go back to Charlene's movement. Here it is up on the test stand with it's pendulum attached. 

And a tighter shot shows the suspension of the pendulum and how it hooks directly to the pendulum rod which is connected to a suspension spring which is attached to a cock on the front plate of the movement.

The pendulum is suspended from the movement itself. It is a singular unit. And those units can be heavy so those test stands have to be clamped down tightly. 

Further to the example above, those images from the service of Charlene's clock... once up on the stand it stopped too. It's good to run the movements on test stands and see what happens.

But the Vienna's pendulum is not suspended from its movement. It is suspended from a bracket on the back of its case (as noted in the first post about our Viennese friend).

And once it's up in its case that clock movement cannot be observed for testing. All that an aspiring clockmaker can do is see if the dingus runs and is in beat.

No goodski for real troubleshooting.

And we did have to troubleshoot the movement.

Zo vat did zis horology hund do?

Perhaps you can guess.

Find out next time!