French clock running too fast

[gerene]

I just assembled the French clock that had a problem with the fly arbor (was occupied by other things lately).
Everything seems to work well at first sight, but the clock is running fast for about 5 min. an hour. I already lowered the pendulum weight as far as I can, but still 5 min/hour fast.
I did change the tension spring with a new one of the same dimensions as the broken one that was in the clock. Don’t know if this was ok before since it was broken.
I am not sure on how I should fix this. Can I use a tension spring which is a bit longer and would that solve the problem? I don’t know if one can buy tension springs of different stiffness and if that would do anything. Cousins does not seem to sell tension springs by stiffness.

any ideas?

Jan

[bernie weishapl]

I have always remembered that a thicker suspension spring will make the clock go faster and thinner will slow it down. If the suspension spring was broke can you measure it’s thickness and order something close? How is the pendulum swing. A shorter swing can cause that. I had one that had about 1/2″ to 3/4″ total swing from side to side. I adjusted the depth of the verge to escape wheel which gave it a longer swing of about 1″ or slight longer from side to side. The longer it takes to swing the pendulum the slower it is. Be interesting to see what you come up with.

[gerene]

Thanks Bernie,

unfortunately I no longer have the original spring and did not note down the thickness, only the other sizes since Cousins only sells them by length etc… not the thickness of the spring itself. Don’t know if any material house sells different thicknesses of the same size spring (did not look yet). I also don’t know if the broken suspension spring that was in the clock was the right suspension spring for that clock, since I never saw it working.
Anyhow, the swing of the pendulum is rather small: 1.5 cm measured at the bottom of the pendulum weight. I measured the total distance travelled, so 0.75 cm each side. (sorry for the metric sizes, but that’s what I am used to ) It is about 1/4″ total swing.
The clock has a brocot escapement and according to De Carle the escape wheel teeth should drop on the centerline of the pallets. (Practical clock repairing page 172). This is the case and there is no recoil as it should be. So for the moment I am inclined to think that lock and drop are ok.
I have another question regarding pendulum length: does one take into account the length of the spring or only the length of the pendulum itself? I measured the pendulum from the point where the suspension spring is attached to the bottom of the suspension weight and it is 20 cm or about 7 11/32″.

Thanks for your help.

Jan

[bernie weishapl]

Jan I am guessing spring since it is a brocot and seems to be working well. As far as measurement of the pendulum goes I am hoping someone will jump in. I have been told you measure from the suspension post, some say from the bottom of the suspension spring and some say just measure the leader with the bob. So most times I play it by ear and try longer leaders, etc till I can get it in the middle of the adjustment range. I would measure the thickness of the spring you have and then call cousins to see if they have anything. There was one I had I just recalled this morning. The spring was missing but to make a long story short the small piece of spring that was still on the clock measured as close as I could tell .003″. I tried a number of springs I had in stock and most worked except they were all about .0038″ to .0042″ so the clock ran fast. Steve at Timesavers found me a couple that were .003″ and one worked. It may end up a guessing game/trial and error.

[arutha]

Hi Jan,
I would imagine you measure from the post as any adjustment in length of the suspension spring would affect the overall length of the pendulum. It sounds like you have watched and checked the escapement so we can be sure the escape wheel is not tripping through the pallets due to too shallow depthing. Next thing I would ask is do you know if it is the original pendulum and is the clock original? If any of the wheels have been swapped out it could affect the overall length of pendulum needed?
If you are satisfied that this is all ok the next thing is to look for is a loose wheel on an arbor, if it is slipping now and again this can cause a problem. Clutching at straws now obviously
Will keep on thinking about this one!
Paul.

[willofiam]

Hey Jan, is it possible to get a couple of straight on photos of the escapement? I have a idea but would like to see that first. thank you, have a nice day, William

[arutha]

A picture of the movement with the pendulum would also help and an idea of how much space you have between the bottom of the pendulum and the bottom of the case.
Paul.

[gerene]

Here are some pictures of the movement and details of the escapement. I tried to get as much as possible of the escapement and hope you have enough detail. If not let me know what is needed and I will do my best to get better suited pictures.
I believe the pendulum belongs to the movement since the number 931 is stamped on both pendulum and movement.
There is about 5 cm room in the case beneath the pendulum.

Jan

• This reply was modified 2 years ago by Tamas Richard.

[willofiam]

Hey Jan, hard to see exactly in the photos but what I was suspecting may be the issue, you will have to look closely at the D shaped pallets, as DeCarle shows in his book page 172, the flat part of the pallets needs to be radial from the center of the escape wheel or you will not get full impulse, impulse area would be 1/4 of the radius of the pin, so if the pin flats are out of adjustment you can lose impulse surface. Do you have a depthing tool? it would would help with adjusting because you would be outside of the plates and get a good view of it all but you can get the job done without one. With such a small oscillation this would be my best guess. Have a great day, William

[arutha]

Is it my imagination or is one of the steel pallets larger in diameter than the other?
Paul.

[willofiam]

Sure looks like it doesnt it Paul. I see the one on the left appearing quite large, could be the angle, have to wait for Jans response. William

[bernie weishapl]

I have to agree with Paul that one of those pallets is way bigger than the other. I am thinking both pallets should be the size of the smaller one. I agree with William about De Carle’s book page 172. I have it bookmarked with a sticky note. 😆

[gerene]

I had noticed the difference in size of the pallets as well, but since it is my first brocot escapement, I was not sure if it would be original or not. I doubted it to be original but forgot to mention it in my original post 😳
Here are some detail picture of the pallets. The diameter of the smaller pallet is 1.5 mm while the larger one is 1.96mm which is a distinguished size difference. Furthermore the bigger one is not radial with the pallet.
I did not try to adjust it yet.

Jan

• This reply was modified 2 years ago by Tamas Richard.

[gerene]

I have been thinking about this over the weekend and before I start fiddling with the pallets I would like to have other ideas about this.
Please understand that I am not questioning anyone’s knowledge or trying to be smarter, it is just that I am confused about the matter and would like to have a better understanding.
Bernie, who’s advice I certainly appreciate very much, says that a small swing would have an impact on the period of oscillation of the pendulum and William says that when the pallets are not radial the pendulum might not receive its full impulse and hence result in a smaller pendulum swing.
The point that confuses me is the fact that a smaller swing might result in a shorter oscillation period. It was my understanding that the period is only function of the length of the pendulum, provided that the amplitude is small. Bigger amplitude will give circular error. I don’t want to go into too much math here, but with small amplitude (less than 15°) the period T = 2*pi*sqrt(l/g) where l = length of the pendulum and g the gravitational acceleration. Since g is constant (at least for a specific place on earth) and pi obviously also, the only other variable in the formula is the length of the pendulum.
That leads me to think that changing the escapement to have a bigger swing would not change anything to the period.
Hope someone can enlighten me a little.

Jan

[willofiam]

Jan, What I was referring to was, as a example, if the entrance pin (pallet) in the shape of a D were to be out of adjustment @willofiam wrote:

the flat part of the pallets needs to be radial from the center of the escape wheel or you will not get full impulse

The flat edge being the releasing point of the escape wheel tooth, too far one way will cause binding with the previous teeth, too far the other way and your escape wheel tooth will prematurely release from the pallet not giving full impulse. William

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