Help To bush or not to bush, that is the question

focusrsh_b07732

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(I posted this in the general clock discussion forum and then realized this is a clock repair question, so please excuse the double posting.)
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I'm working on a weight-driven, strike, tall-case movement for a friend. I've measure the winding arbors and plate holes as follows:
Strike, front side arbor: .355", plate hole: .370"
Time, front side arbor: .340", hole: .362"
Strike, rear pivot: .193", hole: .195
Time, rear pivot: .175", hole: .193"

So there is a gap of .015" and .022" in the front side arbors and holes, and
.002" and .018" on the rear side pivot/hole.

The plates are quite thick at .148", and 4-5/8 x 6-1/2 inch. Unfortunately, I don't have the weights at this moment, but the winding drums have heavy braided metal cable, so I suspect they are heavy weights.

So, the question is, do I rebush the two arbors and the one pivot? Is a gap of .015" to .022" too large?
Interestingly, neither arbor hole is oval. I can see where the clock has been repaired once before and someone closed-up one of the timing-side hole by hammering around it.

(Two opinions expressed in the general-clock discussion forum said that these clock like some play and to just leave it alone. Agree?)

---------------------------------

The second picture is of the assembled movement. There aren't any maker marks I can find. The bell is non-magnetic, perhaps bronze. The movement is a mix of brass and steel parts. Everything is "substantial". Unfortunately, the case and dial are in his brother's home a long way from me. Any guesses on the maker?

front 1600.JPG winding arbors 1600.JPG
 

bruce linde

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re: double posts... better to ask rather moderators to simply move a post to the right forum by reporting the post. now that you’ve double-posted, you should report the original and ask them to delete it.

re: should you bush... Let me qualify my response by saying that I am a hobbyist and not one of the repair pros who hang out here… The way I decide whether I need to bush or not is (unless it’s already totally obvious) by first trying to tilt the arbor in all different directions and making sure the amount of tilt is consistent. if it isn’t, the next step is magnification... and measurements to confirm what i’m seeing. from there, it’s needle filing opposite the wear to preserve hole center, and then bushing. slop is good... but it should be even all the way around. i will re-check tilt after bushing, and then do the spin test with just that gear between the plates to make sure it looks... and, most important, feels... good. if you do that for every major arbor, you know you’ve eliminated pivots from any remaining issues. i find the entire process fun and rewarding.... love the feel of it all. :)
 
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shutterbug

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I determine when to bush by rocking the main wheel and looking for lateral movement in the pivots. If they move side to side, then for sure it's time to bush. In your case, I believe I'd wait for the weights so I could see how it's responding to the current wear. Then you can make a decision.
 

R. Croswell

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I determine when to bush by rocking the main wheel and looking for lateral movement in the pivots. If they move side to side, then for sure it's time to bush. In your case, I believe I'd wait for the weights so I could see how it's responding to the current wear. Then you can make a decision.
I believe that wear begets wear so the rate of degradation will likely proceed somewhat exponentially going forward, especially under the load of a heavy weight. The question is now or later.

RC
 

kologha

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My criteria is: Is the hole round or oval? If the hole is round, I leave it alone even if the pivot is a bit sloppy, and if the hole is oval I will bush. <EDIT> Of course this only applies if nothing had been done previously such as punching around the hole, or if the pivot needs polishing to remove wear.
 
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POWERSTROKE

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I’ve not been doing this long. But I can tell you both from reading the forums and watching how clocks operate I. The real world, I’d say people over-Bush. I think you need to look for gear mesh and how the wheels are moving from a profile view. You can always Bush, but it’s possible to create more problems than you already have. (Potentially) if a clock has good time keeping and runs well, I hesitate in my short experience to Bush unless it shows. Not sure if I worded the above correctly, but as an example, I’ve seen movements already that have tremendous wear that still run. I think it matters what the purpose is and how bad the pivot hole actually looks. If it’s round, I say leave it be. If it’s starting to oval out Bush it. I would say 1/3rd of the pivot diameter is about the limitation of wear in a hole before it becomes erratic.
P.S I don’t know why my phone is capitalizing Bush.
 

Bruce Alexander

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The shape of the pivot hole must be taken into account as well, but assuming that you're looking at roughly round holes
a very general rule of thumb is to look for a 5% clearance for the pivots you've measured.

For example:
Time, rear pivot: .175", hole: .193"
The .175" Time rear pivot in your example should have a round pivot hole measuring about .184".
In my view, if you plan to service the movement, that pivot hole should be bushed while you have the plates separated.

Bushing pivot holes which are only marginally above the plus 5% mark is a judgment call. Chances are the pivot holes are not round and if the pivot requires refinishing, its diameter may be decreased of course.

Unlike the amount of Arbor Tilt, this method is consistent regardless of plate thickness which is one of the reasons that I like it.

Arbor Tilt is a very useful and quick way to check tolerances, but like any other method you just need to be mindful of its limits.

Regards,

Bruce
 

Bruce Alexander

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I also think that a lot must depend on the method(s) one uses for bushing. If bushing by hand, for example, one might want to take more of a "If it ain't broke..." approach. I tend to agree with RC. Wear results in accelerated wear and gears which are starting to drift off center lose/waste more power. Power loss is a cumulative effect and well designed/maintained clock movements should not need an overabundance of power to run well.
 

JimmyOz

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I'm working on a weight-driven, strike, tall-case movement for a friend. I've measure the winding arbors and plate holes as follows:
Strike, front side arbor: .355", plate hole: .370"
Time, front side arbor: .340", hole: .362"
Strike, rear pivot: .193", hole: .195
Time, rear pivot: .175", hole: .193"
All those hundreths add up as you go up the train, however till you have the weights you can't tell if it will work well enough to leave as is. Also you say you are working on it for a friend, what was the reason for it needing worked on.
 

POWERSTROKE

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In my short time with clocks, I’ve seen them run rather well, with even oblong pivot holes. I’m not trying to start an argument, but bush the holes if it’s obvious or it runs poorly. I have movements in the workshop that are 50+ years old and never touched. I’ve cleaned and oiled them and they run perfectly. I think bushing a hole for 5% is a little much. Just my two cents.
 

Kevin W.

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If hole is oblong i bush. I have seen some repair people rebush everything on a clock movement, i do not.
 
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shutterbug

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I think a lot depends on whether you own the clock or are doing work for money. If the former, you can leave some things for later. If the latter, you need to get the clock in like new condition so the customer doesn't have problems later on.
 
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Uhralt

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(I posted this in the general clock discussion forum and then realized this is a clock repair question, so please excuse the double posting.)
-----------------------------------
I'm working on a weight-driven, strike, tall-case movement for a friend. I've measure the winding arbors and plate holes as follows:
Strike, front side arbor: .355", plate hole: .370"
Time, front side arbor: .340", hole: .362"
Strike, rear pivot: .193", hole: .195
Time, rear pivot: .175", hole: .193"

So there is a gap of .015" and .022" in the front side arbors and holes, and
.002" and .018" on the rear side pivot/hole.

The plates are quite thick at .148", and 4-5/8 x 6-1/2 inch. Unfortunately, I don't have the weights at this moment, but the winding drums have heavy braided metal cable, so I suspect they are heavy weights.

So, the question is, do I rebush the two arbors and the one pivot? Is a gap of .015" to .022" too large?
Interestingly, neither arbor hole is oval. I can see where the clock has been repaired once before and someone closed-up one of the timing-side hole by hammering around it.

(Two opinions expressed in the general-clock discussion forum said that these clock like some play and to just leave it alone. Agree?)

---------------------------------

The second picture is of the assembled movement. There aren't any maker marks I can find. The bell is non-magnetic, perhaps bronze. The movement is a mix of brass and steel parts. Everything is "substantial". Unfortunately, the case and dial are in his brother's home a long way from me. Any guesses on the maker?

View attachment 573644 View attachment 573645
You've got lots of (partially diverging) opinions regarding bushings so I won't comment on that. Your movement is English or Scottish. Often the maker's name could be found on the dial. If it is not, it is very hard to identify the maker. The braided metal cord is not original and should be replaced by what has been used for centuries, animal gut. A good source for high quality gut is a natural gut replacement cord for tennis rackets.

Uhralt
 

Bruce Alexander

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Just based on the information you've given see the remarks I've added to your quote below...

Strike, front side arbor: .355", plate hole: .370" I would leave as is if round
Time, front side arbor: .340", hole: .362" I would bush
Strike, rear pivot: .193", hole: .195 I would leave as is if round (you might even want to broach this one a little. Two thousandths is kind of tight for most clocks)
Time, rear pivot: .175", hole: .193" I would bush

So there is a gap of .015" and .022" in the front side arbors and holes, and
.002" and .018" on the rear side pivot/hole.
The 5% clearance rule of thumb has been very useful for me.
As you can see, it doesn't mean you "bush everything in sight" but it does give you an objective standard which you can take into consideration.

As you build more experience, your judgement will begin to play a bigger role in your decisions. The Strike, rear pivot, for example, needs some thought.
As is, does the clock currently run? Is that tight pivot hole original to the clock? Is there sufficient end-shake on that gear?
If your measurements are accurate and if you answer "yes" to all of these questions, you should consider that this clock may have been designed to run with very tight tolerances.
You say it is a "substantial" movement. What do you mean by that?
If it is a tight movement, (I've never serviced one that tight before) all of your other measurements could indicate a lot of wear and that could change things as far as your maintenance decisions are concerned.
You see, measurements alone are only part of the picture.
Personally, I would not attempt to bush this movement by hand.

Regards,

Bruce
 
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POWERSTROKE

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Hi Bruce, you bring up another important point which is endshake. When bushing a hole, what happens if the endgame is reduced and it is deemed insufficient or not enough. How does one created more endshake in an acceptable manner.
 

kologha

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I always ensure that the bush (which must be pressed in from inside the plate) is flush with the plate thus mantaining the endshake.
 

R. Croswell

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There seems to be one factor to consider when deciding whether to bush that has not been mentioned. That is, will the movement be disassembled for some other reason such as to replace a broken spring or general cleaning or to bush one or two extremely worn pivot holes. Most of the time required to install a bushing is the time to disassemble and reassemble the movement, so when I have a movement apart I usually install bushings at some locations showing wear but not as much as might otherwise trigger the need to do so right now.

A minimal guide line for a running clock not showing any symptoms associated with pivot hole wear is whether any operational issues are likely to show up before the clock is seen again for scheduled maintenance. We know that scheduled maintenance is often extended or overlooked entirely, so if the clock can't be expected to run at least 10 to 15 more years in the present condition it probably should get some bushing work now.

Finally, while this may be the underlying reason some defer bushing work, I have not seen it stated specifically. The question being will installing 18 or so bushings really make the clock run better than just bushing 1 or 2 severely worn pivot holes? The answer may depend on the methods used and the skills of the repairer. Returning the movement to within original factory specifications will, at least theoretically, make a better running clock and greatly extend its service like. However any deviation from the exact original pivot hole location will degrade performance and the effect is cumulative across the total number of bushings installed. It is entirely possible for an inexperienced repairer, especially an inexperienced repairer using simple hand tools, installing a large number of bushings may actually introduce more problems than are solved. It is probably a good idea for beginners using such methods to confine their early efforts to severely worn pivot holes where a less than perfectly accurate bushing placement may still improve things enough to return the clock to running status.

RC
 

shutterbug

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If you determine that you need to increase end shake, you can take a little off the back of the bushing, or tap it through a little more.
 

POWERSTROKE

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I’ve bushed a bunch of movements already. I’m a beginner. I’ve used a hand reamer, files and broaches. I’ve used a pin guage and my work seems pretty good and all the clocks are running well so far. I agree that bushing every hole by hand greatly increases the probability of changing the geometry.
 
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shutterbug

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You're making good progress, powerstroke. :thumb:
 
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R. Croswell

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I’ve bushed a bunch of movements already. I’m a beginner. I’ve used a hand reamer, files and broaches. I’ve used a pin guage and my work seems pretty good and all the clocks are running well so far.
Powerstroke, this comment isn't directed specifically to you or any individual, but how can you know, how can I know, how can anyone know how close we come to "hitting the mark". If the clock runs we assume that all is well but most clocks have excess reserve power to compensate for wear over the life of the clock so they will usually run with a less than perfect bushing job. Unfortunately bushing installation is one job that is difficult to accurately and quantitatively evaluate. We, pretty much all of us, rely on our faith in the methods we use to achieve an anticipated outcome that is difficult to verify. Some methods are more likely than others to yield high precision results, and experience is likely to improve the outcome with any method. So if one has the required skills and tools to bush a moderately worn pivot hole and restore it to, or close to, factory spec. then it should probably be be bushed. If one isn't yet completely comfortable that they can hit or come close to "hitting the mark" then preemptive bushing might best be postponed.

RC
 

POWERSTROKE

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I’m sure if you have a bushing machine it can be more accurate. I’ve onot worked on about 20 regulas and Hubert herrs so far. I’ve taken things that are in either a very poor working state or non working state, to working well, with good pendulum swing and good time keeping over the course of a couple weeks already. I’m no expert, but I’ve working and taking things apart my whole life. I would say that the way the gears mesh when looking at the profile of the movement is important. Most of the holes I have bushed except for one, showed maybe 1/3rd diameter of pivot wear in the hole. I find it no great stretch of workmanship to ream that fairly accurately by hand. Maybe it’s just me. One pivot hole in an 8 day was severely worn. More than double the diameter of the original hole in one direction. I bushed it by hand and it’s been running for about 2.5 weeks. I’m sure there are clocks with super fine pivots and tight tolerances where this becomes more important. Maybe I’m wrong.
 

shutterbug

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The smaller the movement, the more important it is ;)
 

Bruce Alexander

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Hi Bruce, you bring up another important point which is endshake. When bushing a hole, what happens if the endgame is reduced and it is deemed insufficient or not enough. How does one created more endshake in an acceptable manner.
Hello POWERSTROKE,

It's a pretty safe bet that the movement came out of the Factory with adequate end shake on all wheels, or gears. If it was present before you bushed the pivot hole, then you've altered something. If the gear didn't have enough end shake as found, it may be the source of problems for the movement. Maybe it never ran quite right after it was last serviced...

As has been said, you need to make sure your bushing is flush with the inside surface of the plate. It's also a good idea to place a short chamfered edge around the inside ID of your newly placed bushing because sometimes there's a rounded joint between the Pivot and the shoulder of the Arbor. That can cause binding.

Check to make sure that the pivots haven't been slightly bent. It may not be obvious and it doesn't have to be in order to cause problems with binding or gear depths. Slightly bending a pivot is very easy to do upon reassembly of the plates and one usually does so several times during bushing work.

Is the plate warped, or slightly bent. If so, why? Can you tell if it was accidental? If you straighten the plate, re-evaluate everything carefully.

Has the Wheel/Gear Arbor been worked on? If so, how does the length of the arbor compare to its neighbors?

As has been mentioned, with the proper tooling you can push the bushing outward a little. If you have a small end-cutting mill you could relieve it slightly. Either way, it shouldn't take much and you don't want to shorten your bushing any more than necessary or cause it to loosen.

In regards to hand bushing, I think it's a good idea to broach with the plates assembled so that you can direct the end of the broach through the opposite pivot hole. Even if you don't need to enlarge the ID to size, you should lightly broach (cutting or smooth). You have to select an appropriately sized broach in order to reach the other plate's pivot hole and still be able work on your new bushing. If you don't have a broach that can do so in your set, get as close as possible so you can eye-ball it with some accuracy. Doing this can ensure that your bushing's ID is properly aligned.

If one pays close attention to detail, they can do a very fine job hand bushing, but when working on machines, there's nothing quite as accurate or reliable as using another machine. Especially if you use one made for the job at hand.

Regards,

Bruce

Edit:
The smaller the movement, the more important it is ;)
Absolutely!
In my hands, pivots smaller than 1 mm can get very hit or miss. Small pivots, small teeth and small pinions are very unforgiving. :(
 

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