Pinning (for the Fjords?)

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(Yes it's a spelling error in service of a terrible pun.)

Your local horologist grew up on Monty Python. 

In our last episode we examined the ailing innards of Chip's gravity clock which revealed some problems with the pin pallet escapement.

As shown in this earlier photo the two principle issues were that one anchor pin was missing entirely and the other was badly mispositioned. 

So the pin repairs were obvious but trickier than immediately apparent.

Several complicating factors:

  1. The pins in the pin pallet escapement need to be made of steel to reduce wear and to engage properly with the teeth of the brass escape wheel (EW). 
  2. The pins need to extend about 2.5mm from the base of the anchor plate to their tip to in order to be long enough to engage with the EW teeth but not rub up against the wheel at the base of the crutch. 
  3. The pins need to be fairly specific in diameter; in our case about 0.37mm. There is room for a bit of play so something in the range of 0.35-0.4 would probably suffice.
  4. The replacement pin needs to have some taper where it meets the hole in the arbor plate to ensure a secure fit, but it cannot be glued or permanently bonded in place as sometimes pins require repair or replacement. Case in point.

Where to get steel pins that narrow in diameter? After considerable researching YLH tried several great suggestions from the NAWCC geniuses (of course). 

One was a thin sewing needle.

Nope. 

You'd think it would work but all options were considerably too thick.

A piece of guitar string. 

Ah interesting. As most guitarists know the strings of electric/acoustic guitars are made of steel and highly specific in diameter. 

14 gauge is 0.014 inches AKA 0.36mm!


Snippety snip.

Everything about this choice was great but...

See factor 4 above. No taper!

It wouldn't stay in place snugly no matter how this metallurgist tried.

Your experimental engineer tried so many different pins to make this work but will spare the kind reader the details.

Ok long story short it turns out that about 5 years ago your local hoarder horologist had purchased a set of taper pins for a project that required somewhat softer pins and the ones he first purchased were steel. So they were put aside at the time.

A candidate was found in the cache.

The right pin did require quite a bit of trimming as well as honing of the taper.

Et voila!

So the movement was reassembled and tested.

The new pin nicely engaged with the EW teeth.

But...

The movement stopped after just a few ticks!

Grrr...

Testing of the whole apparatus revealed the next problem. 

It was subtle.

Let's go back to the earlier photo of the escapement, fresh out of the clock. The anchor sits on an arbor that connects directly to the pendulum crutch. The ends/tips of the arbor are the pivots and they are inserted into pivot holes in the front and back plates.

That's how most arbors and pivots work. 

Except each of these plates have a section that is sort of a cut out. Both front and back plates have this.

Why?

Well the answer lies in the fact that the anchor must have some way to be adjusted; meaning that the pin pallets need to be able to be finely tweaked either closer or further from the EW teeth. This is referred to as "depthing."

Your essayist wrote an earlier lengthy treatise (with diagrams) that explain this and why it's important. 

These two cut outs on these plates are a meant to enable a clockmaker to bend the shit out of adjust the pivot holes up or down slightly. 

Now look closely at this photo.

There's the arbor with pivots on each end (their tips protruding from the pivot holes).

Can you see the problem?

Yeah both plates were bent to the left (towards the back).

AND...

One of the two adjustable plates was twisted / bent such that it was no longer parallel to the rest of the plate. 

Meaning the pivot hole was not perpendicular to the plate but now slanted away from the pivot itself.

Creating friction between pivot hole and pivot.

Equals... stopping the anchor.

Whomever adjusted this clock last...

Ahem.

Un-twisting and straightening ensued.

Movement reassembly resumed.

The movement ran! Weakly!

Hmm...

It's out of beat.

A few minor adjustments to the pendulum crutch.

It was running strongly now!

Everything fully reassembled and installed back on the rack.

Chip still hasn't picked it up.

YLH is enjoying it in the shop.


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