My friend asked me if I could bringn her grandmother's French clock back from the dead. "Probably," I replied glibly.

Turns out, her father took it apart to "repair" it in the late 1940's and lost the original suspension spring. I assume it must have been broken, because he disassembled it from the upper and lower blocks.

The upper block rides in a typical fine rating system, which is stamped "L.PIGEON". The movement itself is a typical round Marti.

Here is a photo of what I have, along with a piece of suspension spring material (0.002mm thick) I propose making the new suspension from.
(Incidentally, that's block of invar the pieces are lying on - I have no idea why it looks brownish in the photo)

But how long should I make it?

Well - I got tired of waiting, so I decided to take a chance. Laurie Penman says the suspension spring length is not critical, provided it does not place the pendulum outside the range of regulation. So I attached the upper end, and placing it ibn the chops, ran the regulator all the way u. I then marked the spring about 1 mm below the chops, and placed the lower suspension blocks at that point. The clock is on the test stand, and has been keeping time since about 10 o'clock this morning. So far, I am within one minute. I used to use a Timetrax 500, but it gave up the ghost, so I am back to testing clocks the old way - by running them, and making a note of time differences each day over their full running time.

Does anyone have a schematic for the Timetrax 500? I could probably repair it, if I knew what the circuitry was. Where are Sams Photofact Series when you need them? :-)

Good idea and good luck. I suppose the length of the pendulum spring is critical but there is adjustment to the pendulum itself. keep us informed.

Well, it has been running for a week on the test stand. I had to run the bob up 1/4 turn, but it seems to be keeping pretty good time now. It lost a little over a minute in the first two days, but made up for lost time at the end of the run. (Assuming, of course, that the clock in my phone is correct) That's not too bad for a spring-driven clock - most of the ones I have encountered run a little slow when fully wound, but make up for it when the spring isn't pulling quite so hard on the train.

So I guess Laurie Penman is correct when she says the length of the suspension spring isn't critical. I suppose, when one thinks about it, that makes sense; the portion above the chops can only be bowing very slightly (in the opposite direction)as the spring is bending with the pendulum. I suppose that slight bowing may theoretically give a little more impetus to the pendulum, but the force imparted must of necessity be miniscule by comparison to that imparted by the free portion of the spring.

Yes, what they said

regards,
bb

Here is a photo of the assembled movement, clamped up on the test stand.

Good job David!

Upedate: Ran the clock on the test stand for one week. at the end of day one, it had lost two minutes. Knowing that often spring powered clocks lose when fully wound but gain when nearly run down, I left it alone. at the end of a week, the clock had lost about (near as I could tell with a loupe) 1/2 minute.

I figured that was close enough, and took the movement back to its hoime, and installed it in it (heavey and ornate, alabaster case. It was horribly out of beat, but a little fussing with the crutch soon set that to rights. The owner talked with me this morning, and said the clock has been running for several weeks now, and is keeping very good time - never more than one minute off from her quartz kitchen clock.

The final overall length of the suspension unit is 14.58 mm, measured between the mounting and suspension pins. (Pins are 0.60 mm diameter) Length is 17.57 mm overall, including the brass upper and lower blocks.

Nice work Mr. Booth! Another job well done.
Your skill is worth congrats !

Thanks, Mike. I try to follow two rules passed on to me by Bob Goodman, a retired Hamilton Factory master watchmaker.
Rule number one: Don't do anything that cannot be undone.
Rule number two: See and follow rule number one.

I am not a horologist but only an enthusiastic amateur. I recently noticed my French 4 glass regulator (I think you guys across the pond call them crystal regulators) had a suspension spring that looked out of kilter. I had a spare although it was quite a bit shorter so I tried that and now the clock works even better than before so I agree, the suspension spring length is not critical (although it's still important). I did adjust the mercury pendulum length and this can be done on those that have the weighted bob instead of mercury pendulum. My movement is also Marti by the way.