Pendulum length for french clock.

[binman]

On the movement of my french clock it has the numbers 4 8 at the bottom. the number on the weight matches the number on the plate. it is just one item i want to check. from the top of the hook to centre of weight is 115mm say 4 1/2 inches. only having trouble getting it to run, ihave checked the pivots they appear okay, i wondered if the spring is getting tired. The pendulum hasn't a drilling all the way through. i thought about drilling it right through.

 

[gmorse]

Hi,

The effective pendulum length is 4 pouces and 8 lignes; a pouce is an old French inch, and is 27.07 mm or 1.066", and a ligne is a twelfth of that, 2.256 mm or 0.88". So your pendulum should be approx. 126 mm long, remembering that this is supposed to be the effective length.

If it won't run, have you checked the pallets?

Regards,

Graham

 

[harold bain]

The length won't keep it from running, and putting holes in it won't make it run either. Your movement likely needs to be torn down, cleaned and lubed, especially the mainsprings.

 

[binman]

Hi Harold. The movement is in good nick, I have a spare japy im going to try a particle swop, verge and escarpment and see what happens first. The maker is different but distance between plates same plus thickness of arbor. I find some clocks give you a little more leeway when setting in beat, but no room for error on this French movement. Which could point to trying the swop.

 

[Scottie-TX]

Well, first we don't know whether this is a brocot type deadbeat or a more conventionial anchor type deadbeat. Which is it? I suspect the latter. Lack of drop can be the cause for the type behavior you describe. In the case of a brocot pallets that are too thick can be the culprit. In that case increasing locks can cause it to not unlock while decreasing locks can cause it to not unlock.

 

[jmclaugh]

French clocks can be quite tricky to get in beat so it may just be that or a kinked or bent supsension spring. If when you remove the pendulum and it will run quite happily it will most likely be one of those. Many French movements have a facilty to adjust the depthing of the pallets by changing the position of the front pivot hole of the anchor using a screwdriver to rotate a sort of turntable. It should only be attempted if you know what you are doing. However it rarely needs adjusting so unless someone has been fiddling with this I doubt it will be that.

Swapping parts would be a last resort imo.

 

[shimmystep]

They are tricky to get into beat if there is not enough impulse due to the verge height, getting as much amplitude as you can makes these easier to put into beat. Also making the final finer adjustment to beat can be done by loosening the two movement/case door retaining long screws and turning the movement a tiny fraction by the bezel, soooo much easier, you're probably were aware of that though.

Does it go in and out of beat? If so check the EW teeth and the EW pivots. Not so sure I'd swap the parts BM

 

[Thomas Sanguigni]

Just a quick check on the calculation from Graham in post #2. If the ligne is a 1/12th of a pouce, and a pouce is 1.066", then wouldn't the ligne be .0888 instead of .88?

I am working on a French movement without a pendulum, and calculating this becomes more crucial. Thanks in advance.

 

[jmclaugh]

Blimey this is an old one. I think Grahan's post was just a typo, it is 0.088" and the crucial point is as he said is 4 8 is the effective length. If it is longer or shorter it wouldn't stop it running but will just impact timekeeping.

 

[Thomas Sanguigni]

So, does the effective length theoretically just get you in the ball park?

 

[Willie X]

The trouble is, that you never know how each company made their determinations and there were thousands of clock manufacturers. Just go long and shorten as necessary works for me. And if you look closely, there are often ghost marks made by the old pendulum that once lived there. Willie X

 

[Thomas Sanguigni]

Thanks, I planned on going long just in case. No ghost marks to see on this.

 

[jmclaugh]

So, does the effective length theoretically just get you in the ball park?

No, there's a formula to calculate it from counting the teeth in the wheels of the going train which would have been how the example of 4 8 was derived. It's a tedious process and you need to take the movement apart.