Mantle clock – unfamiliar suspension spring arrangement

[Bodger BrianParticipant @bodgerbrian]

[Bodger BrianParticipant @bodgerbrian]

After managing to get my wall clock into some sort of better state than it was when it came into my possession, I rashly told my father that I would attempt to get a non-working mantle clock of his going again. This one is non-striking & I figured that it would be a far easier thing to cut my teeth on with regard to a total overhaul.

Having taken the movement out of the case, it does indeed look a lot simpler. However….

There is mechanism that I have never seen before (nor can I find anything similar from trawling the internet). It consists of a rod that protrudes through the face just above the 12 o'clock position & is connected though a pair of small gears to a vertical shaft within the block that holds the suspension spring. Turning it doesn't appear to do anything. What is the purpose of this? It may become more obvious before I strip it down but I would like to know what to be prepared for.

My other question is with regard to the suspension spring itself. It is obviously bent & will need to be replaced but I having trouble locating a suitable replacement from one of the on-line clock part suppliers. To my un-tutored eye it appears to be a simple strip, the top end of which is clamped into the afore-mentioned block, whilst the other end has a slightly thicker section that carries the pin(s) for suspending the pendulum.

I cannot find a single-ended spring like this (only double ended) – am I merely looking for the wrong thing or is it something that will need to be made form scratch?

Brian

[RedsetterParticipant @redsetter]

Google "Brocot suspension."

[Bodger BrianParticipant @bodgerbrian]

Posted by Redsetter on 02/07/2018 14:20:41:

Google "Brocot suspension."

Many thanks – it's amazing what can be found on the internet when one knows what to look for! Having researched a bit more, I think it's actually a Vallet suspension. I might be wrong but my understanding is that in a Brocot, a block slides along the spring, effectively altering it's length, whereas in a Vallet the spring is physically raised or lowered so the effective length is what is exposed below the two halves of the assembly – very nicely illustrated at the bottom of page 1 in a post here :-

https://www.model-engineer.co.uk/forums/postings.asp?th=87189

I've disassembled the suspension & ordered a replacement spring but one question remains. There appears to be little or no clearance between the two halves when they are screwed together. I'm concerned that having fitted a new spring I'd immediately wreck it by forcing it through too small a gap if / when attempting to lower it. Should it be lightly lubricated to allow a smooth passage?

Brian

[RedsetterParticipant @redsetter]

That is a good question. No experience with these, but my feeling is that a trace of lubrication would do no harm, as clearly a nice sliding fit is required. However it doesn't move very often, and the metals are dissimilar, so it is probably OK dry.

I am absolutely certain that others, with equal lack of experience, will advise you differently.

The NAWCC forum is worth a look for this sort of thing.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Redsetter on 04/07/2018 07:04:30:

I am absolutely certain that others, with equal lack of experience, will advise you differently.

The NAWCC forum is worth a look for this sort of thing.

.

Having equal lack of experience, I shall offer no advice.

But I have found a decent illustration of a Vallet suspension

https://mb.nawcc.org/threads/vallet-or-brocot-suspension-whats-the-diff.140907/

MichaelG.

Edited By Michael Gilligan on 04/07/2018 07:26:22

[Russell EberhardtParticipant @russelleberhardt48058]

If the suspension is Vallet style you may have to buy suspension steel and make the suspension yourself. Ian Cobb at http://www.clockmaking-brass.co.uk/ supplies suspension steel in a wide range of thicknesses. He can also make up complete suspensions.

Russell

[Bodger BrianParticipant @bodgerbrian]

Posted by Russell Eberhardt on 04/07/2018 10:35:03:

If the suspension is Vallet style you may have to buy suspension steel and make the suspension yourself. Ian Cobb at http://www.clockmaking-brass.co.uk/ supplies suspension steel in a wide range of thicknesses. He can also make up complete suspensions.

Thanks for the link Russell but I've managed to locate what I think is a direct replacement spring from Meadows & Passmore. Every dimension of the two end blocks appears to match (it seems to fit & adjust correctly) but I must confess that I haven't checked the thickness of the spring itself. However, I now have a slight diversion to negotiate before I can try it out.

After I let the mainspring down, the end came unhooked from the winding arbor (correct terminology?). I've prised the end cap off the barrel and am having a bit of trouble re-hooking it. Oh, and before anyone says anything, I'm well aware of the dangers of coiled mainsprings – I have no intention of trying to remove it from the barrel unless there is no alternative!

Brian

[Bodger BrianParticipant @bodgerbrian]

A little update.

Mainspring sorted and new suspension spring fitted. The clock now runs with an even beat & without any obvious problem. However…..

Despite adjusting the pendulum bob as low as possible, with the suspension spring also adjusted to it's lowest point, the clock still gains approx 10 minutes per day. My initial thought was that perhaps the new suspension spring is wrong in some aspect (thickness?) but now I've turned my attention to the pendulum.

I'm working on the assumption that the clock is French. Using the formula on the M&P website, I used the figures stamped on the rear plate (4 & 6) to give a pendulum length of 122mm. This gives rise to further questions as the pendulum in the clock is more like 145mm, whereas I was thinking it might be too short.

1) Am I right in my assumption that the clock is French?

2) If so, am I using the right figures for the calculation? (Serial number on the right?)

3) I've recently been told by my father that when his father was still alive, two other people attempted to get the clock working without success. Is this the sort of pendulum that would be expected in a clock like this or is it likely to be non-original?

Any thoughts? I'm very confused!

Brian

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