Pivot Holes Worn - But Still Round

[Mike Mall]

In your experience:
There are some widely varying opinions here, on when a bushing needs to be installed, for a proper repair.
I have seen the opinion that if one hole is worn, they should all be bushed, because they all wear at the same rate.
I have also seen the opinion that if it's worn with less than 30% slop, that's OK.
In my experience, I have seen pivot holes worn into an obvious oval, while others have play but the hole appears to be completely round.
It's true that the force applied to a pivot is usually from one direction, as it transfers the power through the train.
Obviously nobody takes a movement apart until it's old, and has problems.
So how do we know if a pivot hole was designed, and manufactured a little sloppy?
When pivot holes wear - how often do they wear and remain round?
Is it possible to measure pivot holes for "out of round?"

 

[R. Croswell]

In your experience:
There are some widely varying opinions here, on when a bushing needs to be installed, for a proper repair.
I have seen the opinion that if one hole is worn, they should all be bushed, because they all wear at the same rate.
I have also seen the opinion that if it's worn with less than 30% slop, that's OK.
In my experience, I have seen pivot holes worn into an obvious oval, while others have play but the hole appears to be completely round.
It's true that the force applied to a pivot is usually from one direction, as it transfers the power through the train.
Obviously nobody takes a movement apart until it's old, and has problems.
So how do we know if a pivot hole was designed, and manufactured a little sloppy?
When pivot holes wear - how often do they wear and remain round?
Is it possible to measure pivot holes for "out of round?"

Lets say the clock is 100 years old and three pivot holes are very obviously worn egg shaped, and the escape wheel pivot hole is round but sloppy (it does happen) and this clock is not running or is having problems running. What is your objective? Bush the four obviously worn pivot holes and the clock will probably go on running, but the other holes already have 100 years wear and I think it is reasonable to expect that the rate of wear increases as wear increases. It doesn't make a lot sense to bush a pivot hole that's only 20% worn out after 100 years in most ordinary clocks. Then there are some clocks that seem to not tolerate any wear at all, so you will treat these differently. If you are doing a total restoration back to as close as possible to original factory tolerances, then you will replace any detectable wear.

I think it is safe to assume that cheap clocks were fitted to looser standards and overpowered to compensate for lack of precision.

One rule of thumb is, if the clock is being serviced at a regular interval, bush any obviously out of round and excessively loose pivot holes, and any that are questionable, and check again at the next service in 3 to 6 years. If you do not anticipate ever seeing the clock until it stops, better give it the works.

Finally, just how good are you (not personally, but whoever is doing the job) at installing bushings? A lot of bushing jobs really are not very precise, so if you install 29 bushings, and bush a lot of pivot holes that have very little to no detectable wear, are you sure that you are actually improving anything?

RC

 

[Mike Mall]

Lets say the clock is 100 years old and three pivot holes are very obviously worn egg shaped, and the escape wheel pivot hole is round but sloppy (it does happen) and this clock is not running or is having problems running. What is your objective? Bush the four obviously worn pivot holes and the clock will probably go on running, but the other holes already have 100 years wear and I think it is reasonable to expect that the rate of wear increases as wear increases. It doesn't make a lot sense to bush a pivot hole that's only 20% worn out after 100 years in most ordinary clocks. Then there are some clocks that seem to not tolerate any wear at all, so you will treat these differently. If you are doing a total restoration back to as close as possible to original factory tolerances, then you will replace any detectable wear.

I think it is safe to assume that cheap clocks were fitted to looser standards and overpowered to compensate for lack of precision.

One rule of thumb is, if the clock is being serviced at a regular interval, bush any obviously out of round and excessively loose pivot holes, and any that are questionable, and check again at the next service in 3 to 6 years. If you do not anticipate ever seeing the clock until it stops, better give it the works.

Finally, just how good are you (not personally, but whoever is doing the job) at installing bushings? A lot of bushing jobs really are not very precise, so if you install 29 bushings, and bush a lot of pivot holes that have very little to no detectable wear, are you sure that you are actually improving anything?

RC

Thanks for your time, and effort replying. Thanks also for filling in a few blanks for me.
This is exactly the type of information I'm seeking. I know there are tolerances in any mass produced item, especially a fine machine.
I have been repairing clocks for a little over a decade now, but not professionally. So I don't have the experience background many here do.
As my experience has grown, I've gotten to the point where I repair all egg shaped holes, and pick which round holes I repair subjectively.
I am just seeking a better framework to make those decisions - this has helped.
I read here, exponentially more than I write here.
Thanks again

 

[POWERSTROKE]

I bush all holes that are sloppy. But this doesn't mean much because most people are movement replacers.
Round or not, sloppy is causing poor mesh

 

[shutterbug]

Round is probably as important as size. The movements coming from Hermle are often sloppy, but they are round, and seem to function OK.

 

[Mike Mall]

I bush all holes that are sloppy. But this doesn't mean much because most people are movement replacers.
Round or not, sloppy is causing poor mesh

Your right about that!
Cuckoo movements seem to be normally a little looser in their pivots, than others I've encountered.

 

[Mike Mall]

Round is probably as important as size. The movements coming from Hermle are often sloppy, but they are round, and seem to function OK.

I guess the final test is always function.

My thoughts are:
How much slop is too much?
Is the shape of the hole any indication?
It functions now, but for how long?

Thanks for your insight!

 

[Willie X]

Noise can be a factor when holes are big but still round, on the fly arbor. Usually the noise will just be louder than normal gear noise but I've seen a few that will howl like a coyote. This is often intermittent. Willie X

 

[POWERSTROKE]

If I had a movement apart and saw too big a hole, I'm bushing it. New cuckoo movements aren't sloppy in the bushings when new. They have lots of endshake.

 

[NEW65]

All new hermle movements have sloppy pivots BUT they all rotate in round holes.
I have fitted loads of new hermle movements with sloppy pivots and never had a return yet. And some were fitted over 20 yrs ago.
I think the secret is to ensure that the pivot is in good condition and is fitted in a round hole.
I bush by hand and have the most basic lot of tools imaginable but make a good job of all the rebuilds that i do.
If the hole is elongated it has to bushed. If its just 'slightly' off round I use a smoothing broach which is very effective. (Which Willie suggested).

 

[R. Croswell]

When the hole is round, and the pivot is round but a bit smaller in diameter, the pivot has a small contact area with the hole and adequate running clearance and room for oil. When the hole is worn egg shaped, the small end for all practical purposes is the same diameter as the pivot - no running clearance at all as the power train forces the pivot into the small end made in its own image. Aways bush out of round holes, and bush "sloppy" round holes.

RC

 

[GA Hal]

I realize it is a judgment call, but being a newbie, I don't trust my judgment. I too have seen the various percentage wear numbers stated, but I must admit, I am unsure of what those really mean.

I saw one that was going by the contact area around the circumference. Frankly, that one is hard for me to comprehend. How do you even estimate that? On a microscopic level if there is any difference at all between the diameters, then there's only line contact. We know we have to have some clearance, so there's not really any contact "around" the circumference, only at one point.

I've seen others that seemed to be going by the the difference in diameter between the pivot and pivot hole. Say you have a pivot that measures .050" and you are going to allow 30% wear. Are we saying that a .065" pivot hole is the cut-off? If so, that one is a bit easier to measure. I'd have to invest in some pin gauges (or hope some numbered drill bits were close enough...). My interest lies mostly in American spring driven clocks from the late 19th and early 20th centuries. Is 30% based on the pivot diameter a good rule of thumb for these?

Thanks,

Hal

 

[Mike Mall]

I realize it is a judgment call, but being a newbie, I don't trust my judgment. I too have seen the various percentage wear numbers stated, but I must admit, I am unsure of what those really mean.

I saw one that was going by the contact area around the circumference. Frankly, that one is hard for me to comprehend. How do you even estimate that? On a microscopic level if there is any difference at all between the diameters, then there's only line contact. We know we have to have some clearance, so there's not really any contact "around" the circumference, only at one point.

I've seen others that seemed to be going by the the difference in diameter between the pivot and pivot hole. Say you have a pivot that measures .050" and you are going to allow 30% wear. Are we saying that a .065" pivot hole is the cut-off? If so, that one is a bit easier to measure. I'd have to invest in some pin gauges (or hope some numbered drill bits were close enough...). My interest lies mostly in American spring driven clocks from the late 19th and early 20th centuries. Is 30% based on the pivot diameter a good rule of thumb for these?

Thanks,

Hal

That's kind of the same boat I'm in.
I think RC addressed this topic the best in Post #2, and summarized in #11.
That's a lot of years of experience, very well stated.

I believe "I think it is safe to assume that cheap clocks were fitted to looser standards and overpowered to compensate for lack of precision. " Would probably apply to most of the American clocks you're interested in.

 

[POWERSTROKE]

I believe "I think it is safe to assume that cheap clocks were fitted to looser standards and overpowered to compensate for lack of precision. " Would probably apply to most of the American clocks you're interested in.

I disagree. I have 15 new Regula movements at my shop right now. None of them have loose pivots. I checked. All tight. I don't know where the idea comes that cuckoo clocks have loose pivots when new. My assumption is that they will run with tons of wear and people think they are loose when new. The rattle you hear is the end shake between the plates.not the pivots rattling in the holes. This is because the plates are thin. These movements (I know you aren't talking about them specifically) are hardy and will run in almost any environment for a long time.
Now to the point. If you have a clock with jokes that are too large and you have it apart, why would you not tighten everything up? You're asking because in the back of your mind you know it shouldn't be sloppy. I'm here to say to bush a sloppy round hole. Silly to leave it. Take a couple minutes to mic it and bush it. Then when it leaves the shop you know it isn't coming back for a long time. I do mostly cuckoo clocks. I have noticed in close examination let's say, that all 4 second wheel pivot holes need bushing. After I do that. It makes other wear that was no completely noticeable more apparent. Just yesterday I had a Regula 25 just like that. Bushed all the second wheel holes and afterward, the slop in the escape wheel and 3 of the main wheel bushings were done as well. Could I have left them because they were still "ok"? Yes, but it's already apart and it took me another 1/2 hour at most to do it the right way. I don't want a call 11 months from now.
Again, I'm not being mean or anything, but if you're asking, you have doubt about leaving it like that. Put a bushing in. It will be better than new

 

[R. Croswell]

.......I've seen others that seemed to be going by the the difference in diameter between the pivot and pivot hole. Say you have a pivot that measures .050" and you are going to allow 30% wear. Are we saying that a .065" pivot hole is the cut-off? If so, that one is a bit easier to measure. I'd have to invest in some pin gauges (or hope some numbered drill bits were close enough...). My interest lies mostly in American spring driven clocks from the late 19th and early 20th centuries. Is 30% based on the pivot diameter a good rule of thumb for these?

An easy way to measure a pivot hole is to insert a tapered smooth broach and mark how far it goes in, then use your micrometer or caliper to measure the diameter of the broach at the mark. The result will be as they say, "close enough for government work". That of course assumes that the pivot hole is round. There are really two dimensions or limits of concern, the diameter of the hole in the new bushing being installed, and the permitted diameter of the worn pivot hole before it should be bushed. It is difficult to quantify the limit because some clocks demand tighter tolerances than others. For the type of clocks you are working with, a pivot hole with 30% wear may run, but will no longer be round. If you are looking for a visual wear limit, if the hole is visually out of round you are over the limit. If you stand the arbor upright in the pivot hole and note how much it leans all the way around a 360-degrees circle and find that it leans more in some directions, then the hole is out of round and over the limit. With the movement assembled but not powered, pivots that "dance around" in the pivot holes as hand power is applied back and forth in both directions to the main wheel are over the limit.

Something that's seldom mentioned is that a movement with a bunch of work pivot holes where the arbors are all tilted way over is much more difficult to assembly. This includes the strike control lever pivots that are often ignored.

RC

 

[R. Croswell]

I disagree. I have 15 new Regula movements at my shop right now. None of them have loose pivots. I checked. All tight. I don't know where the idea comes that cuckoo clocks have loose pivots when new. My assumption is that they will run with tons of wear and people think they are loose when new.

I suspect that idea goes back to the older wooden frame movements that reportedly had barrel shaped pivots fitted more loosely to compensate for movement and changes in the wooden movement frames from humidity etc. One would expect a bunch of new Regula movements not to have lose or sloppy pivot holes. On the other hand, these are mass produced and relatively low-cost clocks that are what they are. I don't do a lot of Regula cuckoo clocks, but I've found that the 8-day ones (including one of my own) can be pretty finnicky about worn pivot holes.

RC

 

[Mike Mall]

If you are looking for a visual wear limit, if the hole is visually out of round you are over the limit. If you stand the arbor upright in the pivot hole and note how much it leans all the way around a 360-degrees circle and find that it leans more in some directions, then the hole is out of round and over the limit.
RC

Great suggestion!
I observe tilt when broaching a new bushing, but I haven't thought to use it this way.
This is a good way to test if a hole is concentric.

 

[GA Hal]

Thanks guys.

When one says 30% wear or whatever percentage, do they mean the diameter of the hole is 30% larger than the diameter of the pivot?

 

[POWERSTROKE]

Not sure how you're measuring this stuff. All I know is that if I see the pivot moving around, I just bush it. It's ridiculous not to.

I suspect that idea goes back to the older wooden frame movements that reportedly had barrel shaped pivots fitted more loosely to compensate for movement and changes in the wooden movement frames from humidity etc. One would expect a bunch of new Regula movements not to have lose or sloppy pivot holes. On the other hand, these are mass produced and relatively low-cost clocks that are what they are. I don't do a lot of Regula cuckoo clocks, but I've found that the 8-day ones (including one of my own) can be pretty finnicky about worn pivot holes.

RC

8 days can be finicky if they're worn. They jump back to life when you bush them. One days are the best. They run for a long time with wear.

 

[Swanicyouth]

I usually do not bush round holes. I’m from the school of thought that a hole can only wear oblong. I bought one of those wifi iPhone microscopes too look at pivot holes, and you can blow a hole up the size of your screen to see what is going on with it much better.

I use the rock The gears back & for method when the movement is together & also how far the pivot leans in the hole when the movement is apart. I tend to think people put too much emphasis on bushings .

I never had a clock not run because I didn’t put a bushing in a round hole. I have had a clock not run because bushings were too tight. So, I say if the hole is obviously oblong bush it. If not, it probably was designed that way. Most of the clocks I’m working on are mass produced, maybe tolerances are tighter on hand made movements.

Im also bushing by hand, which I’m sure is not as perfect as original or if you have a fancy bushing machine. I fix pretty much anything mechanical and feel like if something isn’t broken or damaged - don’t try to fix it. It just creates extra work & headaches.

 

[JimmyOz]

My interest lies mostly in American spring driven clocks from the late 19th and early 20th centuries. Is 30% based on the pivot diameter a good rule of thumb for these?

Those type of movements, the arbors are soft steel and the pivot will most likely need a bit more than a light polish. Once the pivots are addressed put just the wheels back in and then check what you have. After bushing put T1 and S1 in and give them a spin (check for end shake) take them out and put in T2 and S2 and spin, do it like this till all spin okay, then put all wheels in and with finger pressure on the T1 and S1 they should spin easy. By doing it this way you will learn what works for you and after a while most of it can can be eliminated, Just take your time.

When one says 30% wear or whatever percentage

I doubt that would work on a French movement.

 

[JimmyOz]

I usually do not bush round holes

As I said in my last post, do the pivots 1st then see what you have, the pivot may have worn instead of the hole?

 

[Mike Mall]

Thanks guys.

When one says 30% wear or whatever percentage, do they mean the diameter of the hole is 30% larger than the diameter of the pivot?

My original post gave two examples of opinions here on when to install bushings, that I believe are the extremes. One is to bush them all, the other is only if there is at least 30% wear. I would not use either recommendation.

As RC pointed out, the repairer's ability to install a bushing accurately is a very important factor too.
My intent was to pick the brains of these older experienced folks to get their perspective.
I have seen the advice given here by one of them in the past "Don't become a bushaholic."


The thrust on a pivot is usually in one direction, I believe Willie gave an example of one that is probably an exception.
As stated above if the pivots are loose, and the hole is still very round, the pivot itself is probably worn. But that should be evident by the condition of the pivot's surface.

I have seen many pivots, that are not as tight as most, with round holes and pristine pivots. I believe they were manufactured to looser tolerances.
I have also decided to bush a few in that condition, because I wanted to improve the movement.