Deep thoughts

In our last episode your local horologist was polishing pivots and finally got the Thomas Adams Astro Regulator English Bell Strike clock to run.  

But despite that which is first amongst this horological mechanic's principles: first getting the thing to run; often that isn't enough.

Getting a clock to run well can be quite a different story.

And indeed our English friend, now running, still evidenced several concerning behaviors.

The escapement (that part of the clock movement that transmits and regulates power from the wheel train to the pendulum) was noisy. Instead of an even tick-tock it had a few "extra" clicks and other bits including a subtle but quite noticable scraping sound.

Hmm...

Reader, your correspondent will spare you the details of the endless listening and examination that ensued. Instead we will focus on the two primary underlying causes that were made apparent.

To be fair YLH has heard noisy escapements before and had an idea of where to look. Our first suspect, a "depthing" problem. In short the term depth in horological parlance refers to how closely the teeth of a wheel are meshed with those of another or, as in this case, the anchor's pallet faces. This observer of small things took the plunge on this topic a year ago. 

When an escape wheel tooth lands too deeply on a pallet face it means that the teeth are landing too far up the locking face of the pallet. 

Here is a repurposed graphic from that earlier plunge to help explain.

As that pointy escape wheel turns clockwise a tooth lands on that long edge of the black (Exit) pallet arm. The tooth slides along the face and then reverses and slides off. 

YLH suspected that the Thomas Adams escape wheel teeth were landing too deeply on one of its two pallets (the opposite one is the Entrance pallet). There are several problems that can result and a common side effect is "extra" clicks or noises from the escapement.

The escapement on the Thomas Adams looks a bit different than our American example above but they operate largely in the same way and with our English friend there was no way for your intrepid photographer to get a side view.

But here is the escapement from above.

Sure enough, on close examination, it did appear to YLH that the Entrance pallet was locking very deeply.

So what do do?

Well friends we are back to that endlessly problematic versatile suspension bridge.

Let's take a new angle on the dingus.

Here is a straight on view of the back plate of the movement with the bridge cock pointing towards us.

See anything... askance?

The observant reader might note a few things. (Firstly, Jeff's riveted supports were slightly cockeyed, but they are sound and not the source of this problem.)

One can see that the two large screws that connect the bridge feet to the back plate have different slot sizes. Hmm... 

Now consider those bridge feet (wing shaped brass plates) behind each of those two screws.

See how the right foot is sitting slightly lower than the left relative to the top edge of the back plate?

There are a few dents on that right foot and in its far bottom corner... a hole. It's a bit large to be a pivot hole...

Vas is das?

Vat does all this mean?

Turns out that the right foot of the bridge is adjustable. And yes YLH has seen variants of this plate adjustability before on a Schatz clock though never explicated here on the blog.

How is that adjustable you ask?

Well thank you for asking...

That right foot... its screw hole... well it isn't exactly round.

The oval hole in the right foot allows the clockmaker to loosen the screw and gently shift the foot up or down a tad. This has the effect of slightly raising (or lowering) the anchor arbor with more of that lift going to the Entrance pallet (the lower one in the view below) albeit the Exit pallet goes up a smidge as well.

Here is yet another highlighted variant of a view the kind reader has enjoyed before.

OK we can see how the right suspension bridge foot (bottom in this view) sits lower on the back plate vs. the left foot. 

Lifting that right/lower foot will lift the anchor arbor in such a way that the Entrance/right anchor pallet will raise a bit more than the Exit pallet. In doing so this creates just a bit of extra separation from the escape wheel teeth such that they will now drop just a bit less deeply AKA more shallowly than before.

We can also see that the mystery hole is an accommodation for the fly (fan) pivot (end of its arbor) that pokes out beyond its pivot hole in the back plate and would wedge against the foot were it not for that extra hole giving it some room.

In the photo below the gap from the top edge of the right foot to the top of the plate is quite evident.

Also look at the gap between the back of the foot and the back plate. You can just see a bit of the fan arbor pivot poking through.

Speaking of that gap yes that right foot didn't seat flush to the plate. It required a thin washer to support it.

And the result of all these micro realignments?

Alas this photo hound failed to capture an "after" snap but suffice it to say that a nudge up on the right foot of the suspension bridge resulted in an improved depthing of the Entrance pallet and eliminated the extra clicking sounds from the escapement!

Yay!

Except there was still that scraping sound.

Sigh.

This one confounded your clock doc for a while as the sound was very hard to pinpoint. 

Until it wasn't.

It was coming from the escapement too. YLH had wondered if one of the pivots had some strange wear or the crutch pin was scraping inside the pendulum rod slot.

No, you see dear reader, YLH had noted early on that the pallet faces of the clock were pitted with wear. Many, many decades of escape wheel teeth hitting and sliding along pallet faces.

The effect of this wear (and often very visible) is a groove cut into the face of the pallet that has the rough shape of the edge of the escape wheel tooth. Like this example.

Remedy needs to proceed with caution. The pallet faces of these old clocks are typically made with very hard steel. In extreme cases pallet faces can be rebuilt with new metal. 

But that is major surgery and is beyond the ken of this aspiring clockmaker.

For now.

Meanwhile careful filing and burnishing can smooth the worst of the wear without so much material removed as to change the face of the pallet such that it no longer has the correct angle to the teeth. 

With our English friend the groove cut was wide so the edge was pronounced. 

Filing helped considerably.

Before and after.

Yes there was definitely some groove left but it was much reduced and smoothed out. An effort to completely eliminate the groove would have risked changing the pallet geometry too much.

The last step was a mild application of a clock specific grease on the smoothed pallet faces.

Movement now reassembled and back on the stand... 

No more scraping sound!

Yes!

And the clock ran strongly overnight and for several more nights.

But...

It was running slowly. Probably about 2-3 minutes lost per day.

Well that requires a change in the pendulum. For many clocks adjusting the pendulum bob up a bit with a few turns of the rating nut is the easy peasy adjustment.

No biggie right?

Well speaking of biggie...

Going back to one of our earliest posts on this giant bell strike clock.

The pendulum is huge.

See that disk at its base there on the far right? That's its rating nut for the bob. It's the size of a half dollar coin.

The bob weighs a ton. 

It's a gorilla of a bob.

Turns out this adjustment was going to be far from simple.

And that friends is a whole 'nother story.