Of pins and needles

In our last episode your local horologist was contemplating Newton and how his famous force enabled was presently unsuccessful in the proper operation of the so called Gravity clock. 

As a brief reminder our round friend rides a metal rack and when raised to the top and released it should slowly descend along the rack over the course of a day. See the prior post for details.

Except our chonky ticker wouldn't. 

It mostly fell (well if allowed to).

This burgeoning clockmaker had a sneaking suspicion of what lay underneath the dial and the nature of the problem. 

No time like the present!

The dial is retained with two screws (crude design says this clock snob) and when lifted up and away must be carefully snaked along the hole from which protrudes the pendulum (as there is no way to remove the pendulum first) for proper extrication.

A confession. 

That's actually not a pendulum in the strictest sense because it cannot swing independently from the movement. It's actually a crutch that acts like a pendulum (in this cost cutting design) and has been called such (incorrectly) by YLH but going forward will be referred to correctly as to its true identity. 

A crutch. 

With an adjustable pendulum bob on its end.

Ahem...

Sorry if that's confusing. Just keeping it real.

So what is now revealed is the modest movement ensconced in the solid metal case with the pendulum crutch hanging down the front.

That's the name of the maker of the movement embossed in that front plate, Gebruder Allgaier from "Schönwald im Schwarzwald", a region of the Black Forest area of Germany. This horological historian had never heard of that maker or makers ("Gebruder" translates to "Brothers") but a quick check showed him/them to be one of the major producers of this type of clock. 

The Black Forest region of Germany has been a major clockmaking center for centuries. Many clocks, especially cuckoos, are still made there today.  

Back to the clock, note in the photo above that curved cutout of the case edge on the left to accommodate the gear and wheel that engages with the rack.

Here is the movement removed and flipped back to front. There's the gear that engages with the rack. 

Imagine the toothed rack descending directly down the middle of the back of this movement and you can see how its teeth would catch that gear.

And in this side view you can see how that gear is on an arbor connected to a wheel which in turn transfers the energy from the gear to the rest of the movement.

That photo also shows just a bit of the (unhappy) escapement of this clock. 

Before we go any further it is important to explain that this clock utilizes what is known as a pin pallet escapement.

To help the lay reader understand the general (not pin pallet) action of escapements here is one of YLH's earlier expositions.

Borrowing from that post linked above, here is a more traditional escapement.

Two items to note in our example above: 

A. The classically pointed teeth of the escape wheel

B. The anchor with its two pallets that engage with escape wheel teeth. That anchor and its pallets are a classic design seen in many movements.

Pin pallet escapements work in nearly the identical fashion as that traditional escapement but they are often (and in this example especially) more cheaply constructed and have a few key differences that are important to distinguish. 

The anchor is largely a flat sheet of metal and its pallets are two metal pins inserted in and protruding out perpendicularly from the anchor plate. A bit different from most clock anchors/pallets.

And here is closeup of the escapement of this clock, fresh out of the case. 

It has several problems.

Yikes. 

See the pendulum coming up on the right then bending and connecting to the movement? 

Oops.

See the crutch coming up on the right then bending and connecting to the movement? It's been soldered in place! That's an old (ugly) repair. Likely the crutch broke at some point. The solder makes it really hard to adjust it.

Then there's the anchor and its pins. 

Well...

One pin is missing entirely and the other is protruding out in front of the anchor plate. It should be protruding the other way (towards the crutch) so that it can engage with the escape wheel teeth.

Here's another angle of the dingus.

Two additional points to this photo. 

First, note the teeth of the escape wheel. They are commonly referred to as being "club" shaped instead of classically pointy. In short that club shape is needed because the pallets of this escapement are those pins which are basically shaped like columns. 

Albeit 3mm long and 0.3mm in diameter columns. 

Small. He means small.

By utilizing pins for pallets the escapement requires a different type of escape wheel tooth surface to transmit an impulse from the movement. Pointed escape wheel teeth won't work with pin pallets. 

Second (and it's not easy to see but look at both photos above), note that the escape wheel is aligned and rotates between the arbor plate and that soldered section. In the angle of these photos the escape wheel sits behind the arbor plate (as it should) yet the one pin that was still present is sticking out in front of the arbor plate. 

Well mostly. There's a nub sticking out in the correct direction that you can just see in the first photo.

Here is an example of a pin pallet escapement with club toothed escape wheel from a clock that YLH worked on long ago (and ashamedly has yet to fully repair).

Note in this photo we are looking at the escapement from the opposite direction from the photos take of the gravity clock but regardless of photographic angle it clearly shows how the pins extend out directly over the escape wheel teeth. And also note the more robust arbor plate. This is a better built pin pallet escapement than today's example on the bench.

OK back to our gravity defying friend.

Here is the anchor / crutch combo removed and laying out on the bench. 

As shown above, the missing pin is now obvious and the existing pin has been temporarily tapped back into an improved position (towards the crutch) by your clock doc. The escape wheel slots in between that thick brass wheel where the crutch connects and the thin arbor plate. With that one pin sorta realigned correctly it would engage with escape wheel teeth (sorta) but without it's partner... no go. 

This photo was taken while horological brain cells were burning over the different choices for possible replacement pins. 

And here's a glimpse into the future: none of those worked.

So what does this all add up to?

One more point. 

Clocks 101: in a mechanical clock the pallets receive power from the teeth of the escape wheel and transmit that power down the pendulum. The pallets also act effectively like brakes. They allow only one single tick of the movement forward at a time. One tick with each swing of the pendulum. 

Remove the pallets and no more brakes... a powered movement would spin uncontrollably.

So yes the missing pin and its waywardly pointing partner were the reason the clock would "fall" down the rack. With the pallets missing / misaligned the movement would just spin out of control as Newton's force pulls this movement, uncontrolled, down that rack. 

Perhaps that one pallet pin would occasionally catch a club tooth or two. Ergo the stuttering quality of the fall of the clock when YLH first examined it.

Abundantly clear now to all on what repair was needed, right?

Well of course it wasn't that simple for this simpleton aspiring clockmaker.

Next time: Travails in pinning (and other things that could go wrong)