Arnfield Gravity Escapement

[Michael GilliganParticipant @michaelgilligan61133]

The October 2024 issue of The Horological Journal arrived today, and p407 has a brief article about Jim Arnfield’s amazing Inertially-Detached Gravity Escapement.

Apparently there is a good animation of this on the Instagram channel

@Vecthor_Animation

Not being Instagram-inclined, I have not viewed it … but browsing-around, I also found this:

https://engineezy.com/products/the-arnfield-gravity-escapement

… which looks like a jolly-fine introduction for those with 3D printers, or just some general curiosity.

MichaelG.

[Grindstone CowboyParticipant @grindstonecowboy]

Thanks Michael, very interesting – also the other escapements at the bottom of the page too.

Rob

[duncan webster 1Participant @duncanwebster1]

Just googling around I found https://www.trin.cam.ac.uk/about/the-college-clock/ which describes the Dennison gravity escapement. It appears to me that the left hand lever will be lifted by more than the right, and so it gets a lopsided drive. Am I correct or this there some other trickery that I haven’t spotted? In any case, would it matter?

[Martin KyteParticipant @martinkyte99762]

Not sure I understand your thinking on that Duncan. Could you explain a little more.

regards Martin

[duncan webster 1Participant @duncanwebster1]

The curved pusher element (the bit that contacts the rotating 3 pin wheel) of the left hand rod is closer to the pivot than the right, so for the same horizontal displacement will be pushed through a larger angle.

[Martin KyteParticipant @martinkyte99762]

Yes I see. I think the drop can be controlled by the position of the stop pin each side which would give a way of equalising the energy input. I had the pleasure of winding that clock a few years back. It’s a very interesting machine.

regards Martin

[Michael GilliganParticipant @michaelgilligan61133]

Just a quick experiment, to see if that animated GIF will embed here:

.

 

… evidently not 🙁

MichaelG.

.

Edit: __ Yet, curiously, the copy in my Gallery appears to work

[duncan webster 1Participant @duncanwebster1]

That makes sense, there would be a tad more clearance ar rest twixt the left hand pusher and it’s pin than the right

.

[Martin KyteParticipant @martinkyte99762]

Just had a look at Denison’s comments in Clocks, Watches and Bells and he states that the lifting pins should be no further from the centre than 1/24 the distance from the centre to the pendulum suspension, which indicates he was aware of the issue. However his arrangement omits the stop pins and relies either on adjustable tails or bending the tails of the legs to equalise the beat. He states that great care must be taken to ensure that the leg coming to rest must be at the same instant of the lift of the other.

It is maybe useful to recognise that the primary objective in the design is to isolate the impulse from the large variation in drive from the train in tower clocks where the weather acting on the hands causes large variations in force.
There have been occasions on the Trinity clock where pigeons perching on the hands have massively altered the rate albeit temporarily despite the gravity escapement.

Regards Martin

[John HaineParticipant @johnhaine32865]

I have to admit to occasionally using Instagram (for family reasons mainly) but I can’t find any sign of this animation – another case of the BHI being internet-incompetent I think.  Has anyone else had better luck and if so please could they post a link?

[Martin KyteParticipant @martinkyte99762]

Hi John

Just to repeat Duncan’s link to the Trinity Clock which has the animation along with a slew of detail.

https://www.trin.cam.ac.uk/about/the-college-clock/

regards Martin

[Michael GilliganParticipant @michaelgilligan61133]

No objection to that, Martin … But my post was specifically about Jim Arnfield’s masterly development of the concept.

MichaelG.

.

Edit:__ Here is the page into which I chose not to delve deeper:

https://www.instagram.com/vecthor_animation/

 

 

[John HaineParticipant @johnhaine32865]

Thanks Martin, it certainly has the animation but not of the Arnfield escapement!

[John HaineParticipant @johnhaine32865]

Thanks Michael, I found that one but it seems to have only watch escapements on it.

[Michael GilliganParticipant @michaelgilligan61133]

Sadly, John … it appears to be a ‘communication problem’ in HJ

MichaelG.

.

[Michael GilliganParticipant @michaelgilligan61133]

In the absence of that which was ‘advertised’

https://youtube.com/shorts/jl4gJZ_sx_I?feature=shared

MichaelG.

[John HaineParticipant @johnhaine32865]

https://youtu.be/KjZmMF5-u24?feature=shared also

[Michael Gilligan]

On 27 September 2024 at 12:02 Michael Gilligan Said:

I also found this:

https://engineezy.com/products/the-arnfield-gravity-escapement

… which looks like a jolly-fine introduction for those with 3D printers, or just some general curiosity.

MichaelG.

Nice. I’ll try and get one printed for this Saturdays exhibition

South London Branch of the BHI – Time is what prevents everything from happening at once (slbbhi.co.uk)

[John HaineParticipant @johnhaine32865]

…while space stops it happening in the same place…

[John HaineParticipant @johnhaine32865]

Someone from the BHI who is Instagram-savvy provided me with the following link after my plea on the BHI member’s forum.

https://www.instagram.com/p/DAa9P3ItiyV/?hl=en-gb

 

[Michael GilliganParticipant @michaelgilligan61133]

Well done, John !

Thanks

MichaelG.

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