Moon phase clock dial drive missing

djhaggarty

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Dec 11, 2015
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I have a moon phase longcase clock where the moon dial does not rotate. .Further investigation shows the drive to the dial is missing. I am guessing that there was a wheel with a tab that rotates once every 12 hours to drive the 118 tooth moon phase wheel, and there is a threaded hole on the upper RHS of the plate that might have held it. The wheel was probably driven from the chime wheel below? If anyone has a picture of a similar clock, I'd much appreciate a look before I have a go at making a replacement drive wheel. I see that some moon phase dials were rotated by a lever arrangement but I don't see how that would work on this movement.

IMG_20220615_114055944_HDR.jpg IMG_20220621_103908751.jpg IMG_20220621_095424054.jpg
 

kinsler33

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Aug 17, 2014
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I'm going by faint memory here but I think the teeth in the moon dial directly engage a little stud of some sort in the motion work. The wheel that carries the stud rotates at half the speed of the hour hand--I think.

I always wondered where they got that horrible sheet iron. It looks like boiler plate.
 

Simon Holt

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Mar 21, 2017
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It looks like there's a long pin sticking out of the snail. Is that in such a position that it would nudge the moon dial once every 12 hours?

Simon
 
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RJSoftware

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Apr 15, 2005
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Yes, a missing pin. But it looks intact on the snail. So I guess you only assume it incorrect/incomplete. Advance hands 24 hours and see.

The wheel that drives the snail looks to be the one responsible for initiating the strike as the lever is aligned with it. So the existing pin I see on the snail should be it.

If you can observe from side while advancing hands you can see if pin engagement happens. It could be slightly missing if somehow moon dial arbor is off.

A beautiful clock btw...!
 
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shutterbug

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I suspect that either the movement has been replaced or several parts are missing from the plate it sets against. Probably the latter, and they will be hard to find. You need a mechanism for advancing the wheel, a spring to hold it in place and a lever to activate it. The mechanism usually looks a bit like the figure 4.
 

Room 335

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Aug 16, 2018
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I can't find any pics at the moment but you are basically right in what you suggest.
The moon drive wheel would be the same diameter (or very close) as the 12 hour wheel (behind snail) with the same number of teeth. This mounts on a post in the threaded hole and rotates anti-clockwise driven from the 12 hour wheel with a pin to knock on the moon disk by one tooth per rotation. You can see where the falseplate has been cut away to allow room for the protruding pin to rotate freely.
If the post is not there it's normally best to re-tap the hole for 3BA rather than try to find a thread that fits (it needs to be secure), John Wardle do a post and collet kit for this purpose. The moon drive wheel will need to be parallel to the plates with minimum run-out because the wheels obviously need to stay engaged for the full rotation - they are biggish wheels and normally only around 1.5 mm gauge brass so can easily mis-align. Also make sure that you carefully measure the size for the moon wheel, it may be the same size as the hour wheel but frustrating if you make up the parts and it doesn't quite fit (yes I have done this!). The moon wheel will run quite close to the seconds hand arbour so worth checking that as well - should be ok though if it is the original layout.
You should also re-instate the spring which holds the moon disk in position until the next 'knock-on'. It may work without this but not reliably.
BTW the pin on the snail is almost certainly to drive a date wheel, sometimes they can also drive a moon lever but probably not on this one.
Hope this helps,
Richard
 

Peter John

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Sep 4, 2018
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I don’t see how the pin on the snail can drive the moon dial and still allow the seconds hand to be on the escape wheel. The moon dial edge needs to be above the seconds bit. The photo in post 7 has it right. Peter
 

shutterbug

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Or a mechanism like I explained above. Similar to this, but may be positioned differently. The pin on the large wheel would lift it, and gravity would lower it. A spring interacting with the wheel teeth would hold it in place.

Moon Dial Lever.JPG
 
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