Friction fitting

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Friction is often considered the enemy in clockmaking. Us horology hounds often spend many an hour trying to unearth what is slowing or stopping a clock and most of the time it is some source of unwanted friction somewhere. Friction between wheels. Friction between a pivot and its hole. There are many sources of friction that can stop a clock.

In today's story my friends... we want friction where it is missing.

What!?

In our last episode your local horologist was wrestling with pulley arms and pinning for the fjords suspension springs on the pendulum of the Thomas Adams "Astro" Regulator English Bell Strike clock (whew).

One of the repairs highlighted in that essay was the replacement of the suspension spring and subsequent testing and alignment of the pendulum with the crutch pin. And towards the end of that story it was clear that this effort was lacking something.

The regular reader will likely understand that this (any) clock must have some ability to adjust / set its beat... the even tick tock of it's movement. And beat setting is done by adjusting the relationship of the crutch to the anchor via the anchor arbor... commonly by bending the crutch. Here is a beat setting how-to from the NAWCC.

Our English Bell Strike (EBS) has a friction fitting to enable its beat adjustment. Very common in EBS clocks which typically have fairly rigid steel crutches. It allows the anchor arbor to be slightly turned on its axis in one direction or another while the crutch remains vertical to the clock and aligned with the pendulum hanging straight down. In reality this is all about very slightly tweaking the angle by which the pallets of the anchor engage with the escape wheel teeth and whether that angle enables the pallets to push the pendulum in equal amounts on both sides of the pendulum swing.

Sorta. It's even more complicated than that.

This horology major will not republish his senior thesis about said topic today. You're welcome.

A photo from the Ruttmann and Klein Vienna clock in YLH's living room clearly displays its friction fit.

The kind reader may recall in our early examination of the Thomas Adams clock that one of the many issues revealed was a problem with the anchor arbor and that friction fitting.

Yes the arbor had separated from that rusty "friction" fit which had been soldered together thus transforming the design to enable a desired friction to one of missing friction entirely née immobility.

It's not like your bender-of-metal hasn't seen a soldered crutch / anchor arbor before.

Here again is the compete anchor unit.

And a close up of the friction fitting and related components.

That fit ain't turning.

Oh and that anchor arbor pivot... Ugh.

We'll address that another time. 

Back to the friction fit.

Early in the look at our English friend YLH thought about how to get that anchor arbor to tightly reconnect to the fitting. He discussed with Jeff the master clockermaker the idea of perhaps using some Loctite there. 

Jeff thought that could work.

This idea was put away for future contemplation.

Contemplation now upon us.

Revisiting how to address the "broken" arbor your horological sleuth suspected that its separation from the fitting may have been something a bit more than a simple break. 

If we lock the arbor to the fitting then the whole connection between anchor arbor and crutch is er... locked.

Loctite was becoming a less compelling option.

But how would we connect these things so we can adjust the beat?

Well we could remove the entire friction fit and build a new one.

Oh boy there's a long, long and very complex effort.

And such a extensive repair might unnecessarily break two of our principles in clock repair: 

  • Preserve and protect original parts as much as reasonably possible
  • Minimize the nature of the changes needed to enable the healthy running of the clock

YLH doesn't want to be an overly devout acolyte to those principles but in spirit they ain't wrong.

Let's think about this harder.

Can something else be done that could stick to those principles, would work and be a lasting repair?

Hmm...

[Turning this whirligig over and over in the hand]

That steel arbor did slip into the fitting hole snugging with a modicum of resistance. Not much but...

Hmm...

[Gears grinding... No not those gears!]

We have to be able to adjust beat...

Hmm...

Well if that arbor shaft end and the fitting hole could be made to snug a bit more securely...

But not that securely...

OK reader have you guessed?

Maybe that hole in the friction fit (where the arbor is inserted) could itself serve as an ersatz friction fitting!

That would restore the ability turn the entirely fused friction fit and enable beat adjustment.

Furthermore beat setting is not a daily occurrence. Realistically, a big clock like this... once the movement is reinstalled its case and the last beat adjustment happens (if even needed at that point)... 

The beat on this clock may not need to be adjusted for a long time. Maybe not until a future full service / overhaul and that may be many, many years down the road.

So...

Any new solution for the anchor arbor requires:

  1. Something that holds the arbor to the friction fitting well and will not just wiggle loose as the clock runs but not so tight that it prevents...
  2. A fit that will allow for beat adjustment with some careful effort 
  3. That the repair be reversible if a real clockmaker ever wanted to take a stab at fully replacing that friction fit

Hmm...

After some careful experimentation...

YLH created some raised ridges on the arbor shaft ends with a sharp-edged file. To the whole end of the arbor he applied a very, very thin layer of a hard-bonding cyanoacrylate and let it completely dry. The resulting very slightly enlarged and roughly-edge of the diameter of the arbor shaft created a most excellent, snug, adjustable and resilient binding with that hole in the friction fit when inserted.

Huzzah!

No pictures. From the outside you can't even see the repair.

Whew!

Now we can revisit getting the crutch pin to sit correctly in the pendulum slot.

But of course it wasn't that simple.

Next time! 

Comments

  1. SaknussemJuly 30, 2026 at 9:09 AM

    But how can you create a friction fit with sufficient 'hold' given the constant torsional stress at the arbor?

    ReplyDelete
  2. CubroJuly 30, 2026 at 9:56 AM

    Good question. The torsional stress is only the small amount needed to create a tick or tock from the landing of the escape wheel teeth on the pallets. Just enough to nudge the pendulum. The ridges on the shaft hold it pretty tightly in place. Turning the shaft in the fit hole for beat adjustment takes some force.

    ReplyDelete

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