Anyone know how this works?

Hello,

Can someone tell me how this mechanism works, I am unsure of how the large brass wheel engages and drives the shaft.

At the moment it is driven by the horizontal worm gear at the top, but the brass wheel spins freely on the shaft as there is no keyway or other connection to it.

The rear wheel that is used to set the hands has a connection to the shaft via a key way and pin.

I can get it working by inserting a screw that engages with one of the spokes of the large brass wheel, I know this is not correct but would like to hear from anyone that would know how this should work.

Thanks,

Paul.

Looking at the drive, I suspect that there should be some sort of spring friction drive between the worm wheel and the hand setting dial. A view on the other side of the hand setting dial may show some signs of this.

This would allow the hands to be moved in relation to worm wheel.

I am sure that others on this forum will have a better idea of the details of these types of drives than I do.

Neil

Just had a thought, usually the springs are in the form of a dished washer giving just enough friction to drive the hands, but still allow the parts to be moved in relation to each other.

Edited By Neil A on 19/08/2018 12:21:22

Hi

There are two clues that make me think there is a missing part. Maybe just a nut.

1. there is a round pin on the shaft that I assume engages the keyway on the outer plate.

2. There is a shiny mark just below the teeth on the gear wheel.
Could this indicate a friction clutch surface engaged there, or just the back of the outer plate. Is it relieved
engaging on the outer edge only?

It is in the right location for maximum friction torque to be applied.

Maybe the plates were simply clamped together after setting with say a wing nut or knurled nut.
Once set the only way to change the time would be to access the mechanism directly.
simple clamping is all that is needed.

Image below.
I have marked the areas in red.

Regards
​John

I think John is right about there being just a simple knurled nut clamping the setting dial to the worm wheel.

It has been a long time since I saw one of these clock mechanisms with the cover off, but it does jog my memory of watching someone reset the time when the clocks changed from GMT to BST. They had no special tools and it was done in a matter of minutes.

Neil

Thanks John and Neil,

There must have been a knurled nut, that is missing.

I found a few snippets that relate to these type of mechanisms, the sketch is very similar to the one I am dealing with and clearly shows a knurled nut.

I will find an imperial nut from somewhere and try it out, if it works I will make a knurled nut.

Will let you know how I get on.

Thanks again, Paul.