French silk suspension running too fast

[heifetz17]

I got this clock up and running and it’s running beautifully now, but way too fast. It’s gaining 7.5 minutes per hour.

I can’t lower the bob any more than it already is as it’s just a few mm’s above the table at the bottom of the case.

Could this clock possibly have a missing pedestal it was supposed to sit on? Or is there something I’m missing with getting it set up? This was my first silk suspension and the entire suspension was missing when I got the clock, so perhaps I set it up wrong somehow.

 

[Dick Feldman]

You may have a correct sized movement that bolts up but not the correct movement for that case.
If all of the mechanics are correct and the verge is not skipping teeth, that could be the situation.
If you take the movement apart, there is a formula to calculate the proper pendulum length by counting teeth on the wheels.
I normally test run movements for a week or so on a stand to make sure proper timekeeping is possible.
What is the history on the clock?
Best Regards,
Dick

 

[JTD]

I looked to the base of the back plate where often the pendulum length is given in pouces and lignes but there was nothing there. The I saw the 7 5 further up on the left hand side.

I wonder if this might be the pendulum length stamped in an unusual position?
You could take the movement out of the case, put it on a test stand and hang a pendulum of the 7 5 length and see if it keeps better time.

This may be a foolish suggestion but it might be worth doing before taking things apart.

Others may have better ideas.

JTD

 

[wow]

Show us a photo of the bottom of the case and we may be able to tell you if it is missing part of the case.

 

[Uhralt]

I looked to the base of the back plate where often the pendulum length is given in pouces and lignes but there was nothing there. The I saw the 7 5 further up on the left hand side.

I wonder if this might be the pendulum length stamped in an unusual position?
You could take the movement out of the case, put it on a test stand and hang a pendulum of the 7 5 length and see if it keeps better time.

This may be a foolish suggestion but it might be worth doing before taking things apart.

Others may have better ideas.

JTD

JTD may be up to something. Worth a try. I believe I read 7 and 3, but I'm not 100% sure.

Uhralt

 

[JTD]

JTD may be up to something. Worth a try. I believe I read 7 and 3, but I'm not 100% sure.

Uhralt

Yes, upon looking again, more carefully, I believe you are right - 7 and 3 it is.

JTD

 

[heifetz17]

So the funny thing is I used the formula Dick mentioned at first and it gave me a 4.5 inch drop, so I cut my pendulum rod at 4.5, set it up, and it gained almost 15 minutes per hour.

I then noticed the 7 3 on the back and ordered a new rod and started again. Right now it’s hanging at 7.5 inches (I also mistook the 3 for a 5) and still gaining 7.5 minutes every hour (I came back after 4 hours and it has gained 30 minutes).

So unless I’m measuring incorrectly or not understanding something I don’t think the 7 3 on the backworks either. I’m measuring from the post below the regulator where the thread comes out and down to the pendulum rod, then to the center of the bob.

Upon further inspection it does appear that maybe something was broken or detached from the bottom of the case. A pedestal perhaps?

 

[Ralph]

I think the base of your case is missing. . It would add another 2” or so to the height of the case.

Ralph

 

[JTD]

I then noticed the 7 3 on the back and ordered a new rod and started again. Right now it’s hanging at 7.5 inches (I also mistook the 3 for a 5) and still gaining 7.5 minutes every hour (I came back after 4 hours and it has gained 30 minutes).

Well, if lengthening the pendulum by about three inches made no difference at all, then something is clearly wrong.

I can't see very well from your photos, but they look wrong to me. If I were you I would would start from the beginning - forget about fitting it in the case, just try to find the right pendulum length. At the moment, your pendulum hook is far too low, the thread loop is much too long. I don't think it will ever work properly hanging like this.

Wind the thread loop back to a normal position and then hang your 7 3 pendulum. Thern see what happens, and start your alterations from there.

JTD

 

[heifetz17]

JTD,

I guess I had measured wrong initially. I raised the pendulum as you suggested and now it’s sitting at a length of about 7.25 if I’m measuring correctly.

 

[shutterbug]

I don't think you have the silk suspension correct. Let us see a close up of that area where it hangs from. We need to see it with the pendulum in place so there's weight on it.
Edit: Sorry, you added the above pic as I was typing. It looks OK there.

 

[JTD]

JTD,

I guess I had measured wrong initially. I raised the pendulum as you suggested and now it’s sitting at a length of about 7.25 if I’m measuring correctly.

That looks much better. Now set it going on the test stiand and see if it keeps something nearer the right time.

JTD

 

[Uhralt]

The silk loop should be only about 1 cm long. If 7 and 3 really indicates the length of the pendulum for this clock, the pendulum needs to be about 18.4 cm long, that's about 7.4 inches.

Uhralt

 

[heifetz17]

I don’t think the 7 3 is the pendulum length. The clock is still gaining 8-9 minutes per hour (after raising it from seen in my original photos). The escape wheel doesn’t seem to be skipping teeth, so I either missed something in my rebuild or just need a much longer pendulum than I have, in which case I’ll need to build some sort of pedestal to set the clock on.

 

[JTD]

I don’t think the 7 3 is the pendulum length. The clock is still gaining 8-9 minutes per hour (after raising it from seen in my original photos). The escape wheel doesn’t seem to be skipping teeth, so I either missed something in my rebuild or just need a much longer pendulum than I have, in which case I’ll need to build some sort of pedestal to set the clock on.

Well, as said before, if lengthening the pendulum either makes no difference or makes the clock run even faster, then there is clearly another problem.

You say the escape wheel 'doesn't seem to be skippng teeth', but you don't sound 100% sure. Skipping teeth on the escape wheel would certainly make the clock run faster, regardless of pendulum length.

JTD

 

[shutterbug]

It's also possible that your pendulum is the wrong size. A heavier bob would run slower. It doesn't look like you have a lot of room for a longer pendulum.

 

[Uhralt]

So the funny thing is I used the formula Dick mentioned at first and it gave me a 4.5 inch drop, so I cut my pendulum rod at 4.5, set it up, and it gained almost 15 minutes per hour.

I then noticed the 7 3 on the back and ordered a new rod and started again. Right now it’s hanging at 7.5 inches (I also mistook the 3 for a 5) and still gaining 7.5 minutes every hour (I came back after 4 hours and it has gained 30 minutes).

So unless I’m measuring incorrectly or not understanding something I don’t think the 7 3 on the backworks either. I’m measuring from the post below the regulator where the thread comes out and down to the pendulum rod, then to the center of the bob.

Upon further inspection it does appear that maybe something was broken or detached from the bottom of the case. A pedestal perhaps?

View attachment 756461 View attachment 756462 View attachment 756463 View attachment 756464 View attachment 756465

The bottom of the case seems to have some plaster residues. So, maybe you are right and there was something attached underneath the bottom.

Uhralt

 

[heifetz17]

JTD, the reason I said that is because I looked first at the escape wheel to make sure it wasn’t sipping teeth as I know that would cause this issue. The clock runs beautifully, just fast.

Shutterbug, I also thought of that but unfortunately this is the only solo suspension I can seem to find. Do you have a recommendation to possibly fit a heavier bob? This one is from Timesavers.

 

[Peter John]

I don’t think the 7. 3 is an inches measurement. That’s not an American movement.

 

[R. Croswell]

7 Pounces 3 Lignes (old French measures) works out to 7.727 inches US in most cases. Seems the French changed things a few times. Dave Labounty has a great article on this for free download. At the end of the article is a table s you don't need to do the calculations (where this figure came from). I would try a pendulum of 7.727 and see if it keeps time. then see if it fits the case.

RC

 

[Tim Orr]

Good afternoon, Heifetz!

This reminds me of another thread we had a while back where a clock was gaining at an enormous rate and folks were suggesting all sorts of things, including suspension spring stiffness adjustments, etc., rather like trying to empty a bathtub with a thimble. (Not applicable here, at least!) I haven't done the math in a long time, but I believe it works out that if the pendulum is currently about 7-1/2 inches long and it's gaining 8 or 9 minutes per hour, it would need to be on the order of about 2 inches longer.

Plus, the fact that you already lengthened it once and things got no better – maybe even worse – lends credence to JTD's hypothesis that it's not the pendulum length that's the issue.

As I calculate it, this clock is running something like 10 percent too fast. In clocks, that is enormous! It's on the order of more than 2 hours a day. Plus, the case is too small for your trial pendulums already. I'm betting pendulum length is barking up the wrong tree, unless, of course, this isn't even the right movement for this case.

As JTD points out, tooth skipping isn't always obvious or consistent, but it certainly can account for huge speed increases. I suspect this will be one of those where when you finally find it, will result in slapping your forehead!

I think I'd get a nice long, thin, dowel or even a long broomstraw and find out whether pendulum length actually changes anything.

Also, in your photos, I can't quite see what's going on with the crutch. Is it actually bumping against the leader on each side of the swing? It almost looks as though it is fixed fast to the leader. It almost appears as though there's yet more thread between the suspension loop and the brass hook on the end of the leader. Shouldn't be that way.

Best regards!

Tim Orr

 

[heifetz17]

Robert,

Upon closer inspection it actually is 7 5. The 5 looks really closely like a 3. I guess that would put the actual measurement close to 8 inches, which might be exactly what I need. I’ll download that article and read through it. Thank you.

Tim hello!

I do want to clarify that the clock has slowed down from 15 minutes an hour to 8 minutes an hour upon lengthening the pendulum, so I am indeed seeing progress, just not enough. Regarding your question about the crutch, it’s indeed tight and holding the leader firmly. How much clearance should there be in each side and would that cause an issue such as this? There isn’t any extra thread, the hook goes through the loop and the thread goes back up and around the regulating arbor.

Regards
Chris

 

[R. Croswell]

Robert,

Upon closer inspection it actually is 7 5. The 5 looks really closely like a 3. I guess that would put the actual measurement close to 8 inches, which might be exactly what I need. I’ll download that article and read through it. Thank you.

Tim hello!

I do want to clarify that the clock has slowed down from 15 minutes an hour to 8 minutes an hour upon lengthening the pendulum, so I am indeed seeing progress, just not enough. Regarding your question about the crutch, it’s indeed tight and holding the leader firmly. How much clearance should there be in each side and would that cause an issue such as this? There isn’t any extra thread, the hook goes through the loop and the thread goes back up and around the regulating arbor.

Regards
Chris

7 5 works out to 7.904 inches.

....... about the crutch, it's indeed tight and holding the leader firmly.

That may be the main problem! It cannot run properly that way. You want minimal (0.001" or 0.002") clearance between the crutch and the leader. It cannot be zero or "tight". The point of contact should be polished smooth and a bit of oil.

RC

 

[Tim Orr]

Good evening, Chris!

As RC pointed out, the crutch must not "hold onto" the leader. It must have clearance, so that it sort of "taps" the leader on one side, then the other as the crutch swings back and forth. If it holds the leader, the pendulum is being more or less "driven" from one side to the other.

Consider what happens in a lot of clocks when you remove the pendulum leader altogether, just leaving the crutch in place: Oftentimes, if it runs at all, the crutch flicks back and forth at a great rate. Sometimes, we use that as a diagnostic: If the clock will run that way but not when the pendulum and its leader is in place, there's a "lack of" power problem.

Some old clocks,, notably those called "tic-tacs," had a driven pendulum. No leader. Just the bob connected to what would have been the crutch. They also were hard to regulate and often inaccurate. The crutch and leader creates a sort of "almost free" pendulum.

I still can't see what all is going on. Why isn't the hook on the pendulum leader hooked to the silk suspension? It looks as though there's the silk suspension, some kind of string attached to that, then the brass hook through the string. We really could use a better picture.

In any case, I would appreciate someone who knows the math better checking mine.

Best regards!

Tim

 

[Ralph]

You’re missing the base. Check. Out the case styles.

Lot - Two French Black Marble Mantel Clocks, 19th c., the taller with an enamel dial, time and strike, by Japy Freres, lacking the pendulu...

www.crescentcityauctiongallery.com

Ralph

 

[R. Croswell]

You’re missing the base. Check. Out the case styles.

Lot - Two French Black Marble Mantel Clocks, 19th c., the taller with an enamel dial, time and strike, by Japy Freres, lacking the pendulu...

www.crescentcityauctiongallery.com

Ralph

Very likely, but regardless of the case, the movement has to keep time. Once it is keeping time the OP will know if it needs a taller base, or if someone put in a short pendulum movement because the base is missing.

RC

 

[shutterbug]

Shutterbug, I also thought of that but unfortunately this is the only solo suspension I can seem to find. Do you have a recommendation to possibly fit a heavier bob? This one is from Timesavers.

Here's a 3 ounce bob with rod, made for French clocks. That might be a better choice for you.

 

[Ralph]

It's also possible that your pendulum is the wrong size. A heavier bob would run slower. It doesn't look like you have a lot of room for a longer pendulum.

That's not necessarily true. If the heavier bob is larger in diameter and the bottom of the bob ends up in the same place at the max, the period might shorten, because the actual center of oscillation will be raised.

Ralph

 

[R. Croswell]

I would say fix the known problem first, that being that the crutch loop must not be tight on the suspension rod. The weight of the pendulum has little to do with the rate except where the heavier bob is also larger as Ralph described. f the pendulum is made longer the clock
will run slower. Once the pendulum is lengthened to the point where it keeps time on the bench it will be clear if the movement will work in that case without, or with an additional base.

RC

 

[heifetz17]

Tim,

I’ll try to explain until I get home later and can post another picture. I have the thread started at the regulating arbor, comes down through the post directly below that arbor, makes a loop that the pendulum is suspended from, then comes back up through that post and winds up around the regulating arbor. Does it sound like I have this incorrect?

I did widen the crutch a bit as suggested and while the pendulum looks to have a much healthier swing to it, it didn’t seem to change the rate. I’ll follow the tips about lengthening the pendulum with the correct weight and go from there!

Thank you all!
Chris

 

[Tim Orr]

Good afternoon, Chris!

JTD is still right, and RC's latest is 1000% right! At the risk of being extreme, forget the bob weight! Make sure the crutch is tapping the leader on alternate sides of it with each swing, It must NOT be gripping the leader, ever. If you need to make a test leader, you could also try piano wire, hobby wire or even that brassy-looking thinnish coathanger wire. The advantage is that you can easily make a hook to hang on the suspension.

If making the pendulum leader longer does not slow the clock down, that's not where the problem is.

There is a very very very long shot that the bob could be SO light that it's effectively not even there (See my post, #24). I doubt that – a lot – but I suppose it could happen. You could check the rate with and without the bob to verify that.

And, close-up photos of the suspension and of the crutch's interaction with the leader would still help.

Best regards!

Tim

 

[heifetz17]

Thanks again Tim. Hopefully these pictures will help. I widened the crutch so there’s just enough room on each side that it’s not actually touching or holding, but not enough for a bunch of slop. Let me know your thoughts on the clearance.

 

[Dick Feldman]

Please refer to this link for calculating pendulum length from wheel tooth counts:
Calculate Pendulum Length | Horology - The Index
If you calculated the pendulum length using the appropriate formula and the calculation determined a pendulum of some unbelievable length, start over--you made an error. The calculated pendulum length should be near what is required for proper timekeeping.
The physics of pendulums applies to this clock as well as any ever produced. It will be nearer than any error introduced by a light or heavy pendulum bob, too heavy or too light a suspension spring (rigidity) etc.
Each pendulum length has a corresponding BPH. (See The Modern Clock, Pg. 10-16) Have you tried to measure the BPH? You can interpolate BPH values against timekeeping to come up with a target BPH if you run the movement for a while. That target BPH should steer you towards a target pendulum length.
It sounds like double speak but the proper pendulum for a movement is the one that makes it keep good time.
Think about what you are really trying to achieve. You want a pendulum length that will make the speed of the hands be proper. If you are sure the escapement is not skipping and that everything else is proper, the solution has to be to lengthen the pendulum.
The length of the pendulum can easily be varied using paper clips, wire, masking tape, popsicle sticks, etc. with trial and error. If a longer pendulum does not slow the rate down, there is an error in your calculations. Your clock is not devoid of the physics of pendulums, guaranteed.
Have you removed the movement from the case and run it on a test stand, adjusting the pendulum length till the movement kept close time?
If the movement has a pendulum fitted that will keep time and the movement no longer fits in the case, it is obvious what the problem is.
That is what I know,
Dick

 

[Tim Orr]

Good evening, Chris!

The way to tell if the clearances are right is to note that the opening in the crutch is slightly larger than the width of the leader. If you want an actual measurement, use what RC suggested, about a mil or two. The thickness of a piece of paper would probably be about right. If you hold the leader and move the crutch from side to side, it should be possible to get it into a position where it is not touching the leader and "ticks" against each side when you move it.

Looks like you've got that.

As both Dick and RC say, you must establish that changing the pendulum length affects the rate. Once you assure yourself of that, you can either go with the total trial-and-error method of just changing the pendulum length until you get it right.

Alternatively, you can go with the method Dick suggests, and "count the train," then use the calculator he referenced. Eventually, when you get close, you will have to go to fine regulation by trial-and-error.

Meanwhile, before you get there, you will have the answer to whether or not your "works" will work in the case you have.

Good luck!

Best regards!

Tim

 

[R. Croswell]

You have the general idea that there must be clearance between the leader block and the crutch, but you can't (shouldn't) attempt to do it that way. On this type of crutch the loop or foot is a closed rectangle. It needs to have straight parallel sides and it cannot (should not) be pried open like that. You now have curved sides and excessive clearance in the middle, but because the loop is closed, you still have the same tight condition at both ends. It may run OK if the leader block is exactly centered in the middle, but leader block should have clearance anywhere in the rectangle, including at each end of the rectangle.

The fact that your leader block doesn't fit the crutch suggests that this is not the original (not the correct) pendulum for this movement. One possible explanation is that the base of the case got broken or lost and the seller just stuck any short pendulum on that would fit in the case as it was sold. He/she may or may not have known that the pendulum length controls the clock's speed.

I would suggest that you reform the crutch back to a rectangle with parallel sides and, if you are going to use that leader block, file it down and polish it so it fits the crutch opening as it was designed.

Regarding calculating the pendulum length, be aware that the result is the length from the point where the suspension flexes (where the thread passes through the post) to the center of mass of the entire pendulum-leader assembly. The center of mass will be just a little above the middle of the pendulum weight.

RC

 

[heifetz17]

Ok, looks like I’ve got just a little more work to do. I’ll revisit the formula and make some more adjustments to the crutch.

I’m not able to find many silk suspension rods. I’m getting these ones through Timesavers, but I see Merritt’s also has one. Perhaps I’ll try that one although it looks the same in the picture and file down the block a bit if necessary.

 

[R. Croswell]

Ok, looks like I’ve got just a little more work to do. I’ll revisit the formula and make some more adjustments to the crutch.

I’m not able to find many silk suspension rods. I’m getting these ones through Timesavers, but I see Merritt’s also has one. Perhaps I’ll try that one although it looks the same in the picture and file down the block a bit if necessary.

The suspension rods from these places never fit the crutch (are usually tight). It is easier to reduce the leader block that it is to reduce the crutch opening so I suppose they make them oversize for that reason. That's not going to change the speed the clock runs, you need to make the pendulum longer for that.

RC

 

[shutterbug]

If all of that doesn't slow it down and you are hitting the bottom of the case, you'll either have to raise the case or try the pendulum I suggested. If you lower the center of oscillation (heavier bob) it will slow down. Also lengthening the pendulum will slow it down. Keep us posted on your progress, and what you have done. Maybe the missing platform under the case is the solution.

 

[R. Croswell]

We really need to see how much too long the pendulum is for the case once it is keeping time.

RC

 

[heifetz17]

My apologies shutterbug, I see your post above but there’s nothing attached in the post. What is the pendulum you meant to suggest?

I will certainly post back with my end results and the length of pendulum I end up with to keep time!

 

[Tim Orr]

Good evening, all!

Clearly, RC, you have knowledge way beyond mine on such things! One question, though: Can you explain the thinking behind the design of the crutch system on Chris' clock? Why the big block on the leader? Why the rectangular hole in the crutch?

Thanks!

Best regards!

Tim

 

[Rod Schaffter]

If the depth of the verge into the escapement wheel is too shallow, it can essentially become a recoil escapement and run fast...

Good Luck, Rod

 

[JTD]

Can you explain the thinking behind the design of the crutch system on Chris' clock? Why the big block on the leader? Why the rectangular hole in the crutch?

Well, I can't explain it, I just know that almost all the French clocks with silk suspensions that have come my way have been the same.

The replacement pendulum often has an oversize block which you have to file down (see RC's post #37) and the rectangular slot in the crutch is to accommodate the block.

But I don't know why, it just is, and I've never thought to wonder about the reason.
JTD

 

[R. Croswell]

Good evening, all!

Clearly, RC, you have knowledge way beyond mine on such things! One question, though: Can you explain the thinking behind the design of the crutch system on Chris' clock? Why the big block on the leader? Why the rectangular hole in the crutch?

Thanks!

Best regards!

Tim

The silk thread is so flexible that the pendulum would have a tendency rotate without the square peg in the square hole to keep it lined up, at least that's what I understand. I haven't seen very many silk thread suspension clocks.

RC

 

[R. Croswell]

If the depth of the verge into the escapement wheel is too shallow, it can essentially become a recoil escapement and run fast...

Good Luck, Rod

There are quite a few factors that can cause small changes in the clock's rate, but the primary determining factor is the pendulum length. More specifically, the distance from the flex point of the suspension material to the center of mass of the total moving pendulum assembly.

The pictures do not clearly show the verge and the OP did not state if it is a recoil or a deadbeat escapement (it could be either in this type of clock). It is true that if it is a deadbeat escapement and the verge is "too shallow" the escape wheel teeth will land on the impulse faces of the verge instead of the dead faces and the escapement will attempt to run as a recoil escapement. These cocks typically will run weakly or not at all like that. The resulting small pendulum amplitude may sometimes result in the clock running very slightly faster. Recoil escapements do not run faster than deadbeat escapements and both are regulated the same way by pendulum length and the same rate-length formula applies to both. Many recoil escapements have large pendulum amplitudes, especially is some overpowered American clocks, but a larger amplitude does not result in a faster clock. Pendulum amplitude has only a very small affect on the pendulum rate.

It was already mentioned that if the verge into the escapement wheel is too shallow the most likely cause of the clock running faster is a tooth occasionally skipping past the verge unnoticed.

RC

 

[shutterbug]

My apologies shutterbug, I see your post above but there’s nothing attached in the post. What is the pendulum you meant to suggest?

Ooops. I forgot to post the link. Senior moment Here it is.

 

[JTD]

Ooops. I forgot to post the link. Senior moment Here it is.

This pendulum is not intended for clocks with silk suspension. The hook would be wrong and the shaft might be too thick for the rectangular opening in the crutch.

JTD

 

[R. Croswell]

This is the one for silk thread applications (not saying it will fit this clock).

Silk Thread Pendulum 1-1/4" x 11-3/8" (timesavers.com)

RC

 

[JTD]

This is the one for silk thread applications (not saying it will fit this clock).

Silk Thread Pendulum 1-1/4" x 11-3/8" (timesavers.com)

RC

Yes, that's the right sort - I think it's what the OP already has.

JTD

 

[Uhralt]

The silk thread is so flexible that the pendulum would have a tendency rotate without the square peg in the square hole to keep it lined up, at least that's what I understand. I haven't seen very many silk thread suspension clocks.

RC

I think that is exactly the reason. I have an American clock, made by Terry Clock Company, that has a silk suspension and no square peg on the pendulum rod. The style of the clock mimics the look of a French clock of that period. I need to push the pendulum very carefully to prevent it from wobbling around.

Uhralt