To re-bush or not to re-bush?

[mjj1543]

Hi all,

I'm servicing my Junghans mantle clock again. I restored it in 2019 and it ran well for a while and then became a little erratic in its timekeeping. I've pulled it apart and there are a number of issues, the main two being; the pallet is very worn, grooved on both the entry and exit pallets, and the trains are what i think to be very loose in their pivot holes. I've read various posts on the forum about the former so my question relates to the latter issue - how do i know when to re-bush these holes? With one possible exception there are no obvious ovalled holes, it's just that the pivots appear to rattle around in the holes and there looks like a lot of play. Now, I've heard one repairer state that 'rattling is good', but then i see photos of pivots in a very snug fit in their holes. Is there a rule of thumb i can go by to establish if the holes need re-bushing (and the 5 degree rule is actually quite challenging to estimate so ideally i was hoping for a measurement or percentage) - i've heard someone quote 30% of the pivot circumference as one rule, another repairer (YouTube) fitted bushes that were 0.1mm (tenth of a mm) larger than his pivot sizes which seemed excessive to me (and probably wouldn't be a significant improvement on the current situation).

Difficult to provide close-up photos to illustrate but i've attached one of the plate marked up by me to show the holes that i consider to be the most worn.

Any advice will be gratefully received.

Mark.
UK.

 

[John P]

Loose pivots are not good in a clock movement. If you have the tools and skill, why not re bush the holes and have confidence that the clock will run on for many years.

johnp

 

[bkerr]

Worn pivots are a problem that gets worse over time. One thing I was taught is, a clock will run loose but it will not run tight. The best inspection, in my opinion, is to take the power off the train and inspect each pivot applying a bit of pressure to power the train, At this point also check for end play. If you see the pivot sliding in the hole with the naked eye it is likely it may need to be bushed. It is hard to put a value on this but I would say 10 - 20 % of the diameter is a good guess. It really become more of a feel and experience than an exact measurement. So if you have the tools and feel confident then by all means bush the plates. I would also advise checking the pivots. A bad or worn pivot will wipe out all of your work in short order. You likely have seen post about pivot polishing on the site. To each there own on the procedure chosen. I also use a smoothing broach on each hole now after fitting the pivot.
This may be extreme but it only takes a few minutes, use a piece of peg wood to clean each hole before final assembly. I say this because I see a can of Brasso in the background. I like a clean plate too but, left unchecked the cleaning material will contaminate the bushing loading it up with abrasive. I have recently been doing a few French carriage clocks for my collection. I buff the cases and plates until the reflect very well. The compound gets in the holes and it is amazing how much comes out with the peg wood. All that is required is a knife to peel away the contaminate and sharpen the stick. I do this until the peg wood looks clean for each hole.
Best of luck

 

[David Hill]

Just my 2 cents worth. I have found thru trial and error working on clock movements that the movements made prior to 1900 were overpowered to keep the clock running and egg shaped bushes were much less forgiving. By the early 1900s I think clock manufacturers became more cost conscience regarding material cost and engineered their clock movements to run on minimal power and reduced plate thickness which can be seen in the movements made by Hermle and other manufacturers over the years. When I get a 20th century movement in my shop that is not running correctly I've learned the slightest amount of egg shaping to the bushes has compromised the movement and it's time to rebush. I find this to be true for the 1st and 2nd wheel bushes primarily and especially on the wheel side of a shaft. When I find numerous bushings needing rebushed I calculate the cost to tear down, rebush and reassemble vs. the cost of a new movement and let the customer decide.

 

[Willie X]

Look downward into the movement while applying a strong finger pressure (back and forth) on the 2nd wheel.
Anything jumping around needs attention.

Pick the very worst one and post a 'straight on' extreme close-up photo, with good
(left-right) lighting. This is about the only way the pivot hole fit can be judged from here.

Same for the pallet faces.

Also, could you explain "a little eratic".

Willie X

 

[R. Croswell]

Hi all,

I'm servicing my Junghans mantle clock again. I restored it in 2019 and it ran well for a while and then became a little erratic in its timekeeping. I've pulled it apart and there are a number of issues, the main two being; the pallet is very worn, grooved on both the entry and exit pallets, and the trains are what i think to be very loose in their pivot holes. I've read various posts on the forum about the former so my question relates to the latter issue - how do i know when to re-bush these holes? With one possible exception there are no obvious ovalled holes, it's just that the pivots appear to rattle around in the holes and there looks like a lot of play. Now, I've heard one repairer state that 'rattling is good', but then i see photos of pivots in a very snug fit in their holes. Is there a rule of thumb i can go by to establish if the holes need re-bushing (and the 5 degree rule is actually quite challenging to estimate so ideally i was hoping for a measurement or percentage) - i've heard someone quote 30% of the pivot circumference as one rule, another repairer (YouTube) fitted bushes that were 0.1mm (tenth of a mm) larger than his pivot sizes which seemed excessive to me (and probably wouldn't be a significant improvement on the current situation).

Difficult to provide close-up photos to illustrate but i've attached one of the plate marked up by me to show the holes that i consider to be the most worn.

Any advice will be gratefully received.

Mark.
UK.

Mark, you said, "I restored it in 2019 and it ran well for a while....". Just what was done during this restoration? Were the mainsprings removed from the barrels, cleaned and lubricated? A clock should not fail in four years unless something was overlooked or done incorrectly. Is there now a lot of black stuff (pivot poop) around the pivot holes? A lot of black stuff or black oil indicates that something isn't just right.

Clocks stop running when not enough power gets all the way to the pendulum and the most common cause is friction caused by wear. You said, "pallet is very worn, grooved on both the entry and exit pallets". Although your question is about bushings, you can't expect this clock to run properly until you address the problem of the badly worn pallets.

There is a lot of advice given on-line, in You-tube videos, and even in this forum by all sorts of individuals with all levels of experience. Some is good, some not so good, and some will get you in trouble.

To answer your question, the pivot and the bushing must be considered as a unit. The pivot should be evaluated first. It may just need polishing or burnishing, but if the pivot hole is worn enough to require a bushing, very likely there will be some issues with the pivot as well. A bushing cannot be properly sized until one knows what the finished size of pivot will be.

If the pivot has grooves and uneven wear, you can be pretty sure that the pivot hole is going to have a matching set of groves. So one rule of thumb should be, if the pivot requires any significant work, the pivot hole should be bushed to properly fit the reconditioned pivot.

Another rule of thumb is, if the pivot hole is visually out of round, it should be bushed.

Most of the other "rules" such as degrees of tilt, percent of pivot diameter etc. are, as you mentioned, difficult to measure, often do not apply well to some types of clocks, especially clocks with very small or very large pivots and clocks with very thick or very thin plates. It is also often unclear whether the "rule" defines the limit of wear or the desired clearance when fitting a new bushing.

If the pivot bounces around or "dances" in the pivot hole as power is applied by hand in alternating directions, it probably needs to be bushed even if it is not visually out of round, but just how much wiggle room is needed and how much is too much is mostly something that one has to experience and learn when it just feels right. One objective test is with the arbor in place on one plate, place the other plate directly above the pivot. Tilt the arbor around 360 degrees (N, E, S, and W) and the pivot should orbit the pivot hole at least a pivot diameter beyond the edge of the hole.

Finally, ask yourself, considering my skills and the tooling available, can I make it better by installing a bushing when there is not extreme wear? If a pivot hole is only slightly worn, a bushing installed just a little off center, or just a little off perpendicular to the plate, could actually make the situation worse.

Sorry for the long-winded reply but I hope it provokes some helpful thought.

RC

 

[shutterbug]

I've been repairing clocks for quite a number of years, and have just recently found my first ever movement that needs no bushings! There are several bushings installed, apparently recently. It appears that the movement was abandoned after the suspension spring broke. Not needing at least a few bushings is a very rare find.

 

[R. Croswell]

I've been repairing clocks for quite a number of years, and have just recently found my first ever movement that needs no bushings! There are several bushings installed, apparently recently. It appears that the movement was abandoned after the suspension spring broke. Not needing at least a few bushings is a very rare find.

That would be a rare find for an American clock. But I guess the operative word is "needs". I have a somewhat distressed ST column and cornice 1-day clock that came in as partial payment on a repair job. It really "needs" some bushings, but I just cleaned it and oiled it and it runs just fine. Its a real rattler and I just don't have the time to restore the case. Someone was going to buy it for $xx.00 but never came to pick it up. Point is that there are a lot of clocks like this, and some that have been to a quickie shop and got one or two bushings when they really need a lot more to be reliable for several decades.

RC

 

[mjj1543]

Firstly, thanks indeed for taking the time to give your really useful replies. Secondly, apologies if I'm about to use the 'quote' feature far too much...

I say this because I see a can of Brasso in the background.

It is hard to put a value on this but I would say 10 - 20 % of the diameter is a good guess. It really become more of a feel and experience than an exact measurement

Bkerr, I may have misled you with the photo; i do indeed use brasso but not on clocks, the tins you see are just used to hold my tools. That 10-20% is the sort of figure i would have thought as well and that would indicate that all the holes in both plates on my clock need re-bushing.

I'll attach a few more photos including a couple of the pallet for your opinions. I think, having read your responses, that these holes will need bushing, there is too much play, especially the escape wheel (which would explain the wear on the pallet). I will also now consider the main wheel as there's a lot of play in that one as well.

You said, "pallet is very worn, grooved on both the entry and exit pallets". Although your question is about bushings, you can't expect this clock to run properly until you address the problem of the badly worn pallets

I suppose part of the problem for the enthusiast like myself, as opposed to the professional, is that it is very tempting to do what you can do and ignore or put off the parts you can't. I am more used to working on watches and have rebushed watch plates and also another clock and am comfortable with my ability, but effecting a repair to this pallet I recognise is beyond my skill set.

When i got the clock in 2019 it was in a very poor aesthetic condition, i put up a series of posts on it here - Junghans clock refurbishment and i enjoyed learning how to resilver a chapter ring and blue hands, tidy the walnut case etc.

Just what was done during this restoration? Were the mainsprings removed from the barrels, cleaned and lubricated?

RC - yes the springs were removed, i discovered a split strike spring barrel which still needs a repair (may be laser welded), I'll attach a photo of the spring's condition as well. As per advice on this forum, if i remember correctly i used motor oil to lubricate the movement after cleaning it.

So one rule of thumb should be, if the pivot requires any significant work, the pivot hole should be bushed to properly fit the reconditioned pivot.

You're of course correct, and studying the escape wheel pivots under 20x mag there are horizontal striations all over it. I will attempt to polish these out.

One objective test is with the arbor in place on one plate, place the other plate directly above the pivot. Tilt the arbor around 360 degrees (N, E, S, and W) and the pivot should orbit the pivot hole at least a pivot diameter beyond the edge of the hole.

That's a terrific bit of advice - very easy to see and assess the lean of each wheel by eye - and as the photos might show there is significant lean of several of the wheels. Both the escape wheel and the next wheel to it significantly exceed that metric.

Also, could you explain "a little eratic".

Willie, it started to lose time by a few minutes a day and then on occasion it would gain by a similar amount. The clock was especially difficult to set up, it never sounded perfectly in beat, and was very sensitive to how it was positioned on the shelf!

Thanks again for all your input, this forum is great for wisdom and is why i keep coming back to it rather than any others. I've attached further photos.

 

[bkerr]

Oh ya, now you can see the tilt on the wheels. Those plates need bushings. The crack / split on the barrel is not unusual for that maker and I don't really know why. So here is a thought and maybe one of the other guys will chime in. Is it possible to make a ring with a slight press fit (I.D.) to go over the barrel? it looks like the teeth are good and there should be clearance within the movement. Maybe covering 3/4 of the barrel and open toward the teeth? Silver Brazing would be my first choice but that will anneal / soften the barrel, not good! Silver bearing solder would be okay but it is not overly strong by it's self. A sleeve silver soldered on might work. Just a thought.

 

[Willie X]

Now those photos tell the tale but don't leave the new bushings to tight. The side play should be easily visible with oil and moderate magnification (Optovisor).

On the pallet ... in my shop that one would get a resurface on the entrance pallet and a 'slipper' added to the exit pallet. The slipper usually needs to be about .010" thick. It's best to make the slipper protrude some small amount (.010") over the edge. This will give you plenty of room for adjustment. All angles (geometry) will stay the same.

Willie X

 

[mjj1543]

Oh ya, now you can see the tilt on the wheels. Those plates need bushings. The crack / split on the barrel is not unusual for that maker and I don't really know why. So here is a thought and maybe one of the other guys will chime in. Is it possible to make a ring with a slight press fit (I.D.) to go over the barrel? it looks like the teeth are good and there should be clearance within the movement. Maybe covering 3/4 of the barrel and open toward the teeth? Silver Brazing would be my first choice but that will anneal / soften the barrel, not good! Silver bearing solder would be okay but it is not overly strong by it's self. A sleeve silver soldered on might work. Just a thought.

Having reviewed other threads on this subject on this board I'd considered the idea of soldering a patch over the split. I've got some 4mm brass sheet but I'm not entirely convinced by the idea. Mainly because if a barrel with 1.2mm walls has split right through, how secure will a much thinner patch be. I contacted someone about laser welding who says it's do'able without imparting too much heat and potentially separating the two-piece barrel.

On the pallet ...

Willie, i understand the theory of what you describe, unfortunately i don't have the facility or skills to manage that myself so i will need to find a professional over here who can help.

 

[R. Croswell]

......for the enthusiast like myself, as opposed to the professional, is that it is very tempting to do what you can do and ignore or put off the parts you can't........... effecting a repair to this pallet I recognise is beyond my skill set.

We have all been there and done that as part of our learning process. That's OK with your own clock, but not good practice when working on someone else's clock. This clock may run with those pallets like they are if you fix everything else, but it won't run as well as it should. You should be able to grind and polish the surface on the entrance pallet. The problem with doing the same for the exit pallet is that the distance between the pallets is critical and will be increased by the amount removed from the exit pallet. Soldering a "slipper" of spring steel over the exit pallet (after removing an equal amount to maintain spacing) as Willie is describing is a good repair. However, just grinding and polishing the entrance pallet may give some improvement until you are comfortable with the slippering process, which isn't that difficult to accomplish.

That's a terrific bit of advice [the pivot should orbit the pivot hole at least a pivot diameter beyond the edge of the hole.]- very easy to see and assess the lean of each wheel by eye - and as the photos might show there is significant lean of several of the wheels. Both the escape wheel and the next wheel to it significantly exceed that metric.

That test also shows when the hole is out of round because the "orbit" will be greater or smaller as it completes the circle. At least one pivot diameter from the hole is not a wear limit. It's a theoretical limit when two bushings are precisely aligned one over the other and the hole has parallel sides and is perfectly perpendicular to the plate. Some clocks demand a little more pivot clearance to accommodate flexing of the plates. Most clocks will run OK with several pivot diameters of "orbit" before demanding a bushing. The pictures indicate that the pivot holes and/or pivots in your clock exceed acceptable wear limits by any and all standard for when to bush.

.......... i discovered a split strike spring barrel which still needs a repair (may be laser welded),

If you can laser weld the barrel (or have someone do it), I think that would be an excellent repair. In the mean time, I would not try to use it.

RC

 

[Willie X]

Make sure the repairer knows to drill a small hole just past where rack stops and the crack should be chased with a fine jewelery saw before brazing. If they don't know about these steps, you should probably go somewhere else.

I am not familiar with Lazer welding but all other forms of welding require the above treatments. Otherwise the barrels diameter will increase and the crack may contunue.

A rotary tool, with a largish dovetail cutter, will make short work of restoring the step where the cap goes.

Willie X

 

[mjj1543]

Further to this, having looked at the inside of the plates under high mag it's evident that some of the holes have been re-bushed in the past, it's also easy to see that the inside of those bushes are not at all smooth, so i think attempting to re-bush most if not all the holes would be sensible.

In respect of the pallet, again looking at it under high magnification I can see that if I attempted to grind back to the depth of the groove in the entry pallet it'd result in an almost knife-sharp edge which I'd have thought wouldn't last long and would cause further wear to the escape wheel teeth. The groove in the exit pallet, whilst clearly visible, is much shallower. The pallet itself also looks quite roughly finished underneath - is this usual on a Junghans clock of this age or does this suggest this may be a replacement itself?

Looking at the pallet assembly, the arbor is tapered and it looks like the pallet is held friction-tight to the arbor (let me know from the photo's if you disagree). I wonder if it would be a better option to remove the pallet from the arbor and have a replacement made? If i could get it laser cut the dimensions & tolerances should be pretty much exact to the original and it would be a case of 'just' reassembling the new pallet to the arbor in the same orientation.

I wanted to get your thoughts before i attempt to loosen the pallet from the arbor.

 

[Willie X]

There is no need to remove the pallet, unless you want to make a new problem for yourself?
You can send it out to be repaired, or just smoothe it up a bit, as already mentioned.

If you are new to doing bushing work, replacing all those bushings is probably a really bad idea. Willie X

 

[R. Croswell]

......having looked at the inside of the plates under high mag it's evident that some of the holes have been re-bushed in the past, it's also easy to see that the inside of those bushes are not at all smooth, so i think attempting to re-bush most if not all the holes would be sensible.

Based only on your description, I agree, re-bush most if not all the holes would be sensible. However, looking at your pictures, I do not see convincing evidence of the holes having been previously bushed, and I have to agree with Willie, "If you are new to doing bushing work, replacing all those bushings is probably a really bad idea". Even small errors in bushing / rebushing that many pivot holes cumulative and the sum of all of them together can add up to a big problem. On the other hand, if you are comfortable with properly installing bushings, go ahead and do what needs to be done. The option of doing nothing isn't going to solve the problem(s) that are why you took it apart in the first place.

RC

 

[mjj1543]

thanks, i do take on board your warnings. I have re-bushed plates before but no I don't profess to be an expert (I wouldn't be here asking questions otherwise).

There is no need to remove the pallet, unless you want to make a new problem for yourself?
You can send it out to be repaired, or just smoothe it up a bit, as already mentioned.

I asked this because it would seem to me if the pallet is 'removable' from the arbor it would be more efficient to remove it and have an exact replacement made from new stock, rather than have a damaged part repaired. I'm aware of the importance of correctly repositioning it afterwards but that didn't strike me as necessarily more complex than fine-tuning a repaired pallet to run correctly. I mentioned the problem I foresee if the entry pallet is smoothed as you suggest, it would leave a very fine edge which I imagine would further wear the EW.

The option of doing nothing isn't going to solve the problem(s) that are why you took it apart in the first place.

Absolutely the point of this isn't it. I didn't buy it because I wanted a clock, I bought it because I wanted a clock to repair. I don't want a non-working clock on my shelf, and equally i don't need another clock on my shelf if it's been repaired elsewhere. It cost me all of £30 so I don't have money tied up in it, but it does feel like a lot of clock for little money.

 

[Willie X]

It's supposed to have a sharp corner on the trailing edge of both impulse faces.

You will have to make many adjustments to the new, or repaired, anchor. Are you going to remove and replace the anchor 10 or 15 times??

Look up 'repairing an English style anchor' or just 'slippering'.

Also, 'Practical Clock Escapement' by: Laurie Penman has good information on both making, or repairing, English style anchors.

Willie X

 

[mjj1543]

I realise I probably owe you a closer to this Junghans thread. I did end up re-bushing 8 holes that were the worst offenders, but left the one's that were less obviously worn. I polished all the pivots by mounting the wheels in my drill press and using two lollipop sticks with very fine sandpaper attached, they came up a treat. I had the wear grooves in the pallet faces laser welded, it wasn't very well done in my opinion, but it was good enough for me to dress back sufficiently to create a clean face on each pallet. The split in the strike barrel was also laser welded but failed almost immediately. I managed to obtain a spares movement with identical barrels so ended up substituting it with the strike barrel from this instead. I fitted two new springs. The clock appears to be running better than before so i guess my work has helped. My biggest disappointment was with the walnut case; i should've left well alone, but once a tinkerer always a tinkerer...I used shallac, and as the case has a decorative flourish, i had to apply it with a brush rather than pad. Long story (and boy was it a long story...) short, after many coats and knocking them back i eventually got it to a point i was reasonably ok with, but it's still not perfect. However, that all said, i enjoyed the restoration and hopefully i've extended the clock's life a little. Thanks again for all your insightful input, much appreciated as always. Mark

 

[Simon Holt]

Nice work, Mark!

Simon

 

[TEACLOCKS]

I realise I probably owe you a closer to this Junghans thread. I did end up re-bushing 8 holes that were the worst offenders, but left the one's that were less obviously worn. I polished all the pivots by mounting the wheels in my drill press and using two lollipop sticks with very fine sandpaper attached, they came up a treat. I had the wear grooves in the pallet faces laser welded, it wasn't very well done in my opinion, but it was good enough for me to dress back sufficiently to create a clean face on each pallet. The split in the strike barrel was also laser welded but failed almost immediately. I managed to obtain a spares movement with identical barrels so ended up substituting it with the strike barrel from this instead. I fitted two new springs. The clock appears to be running better than before so i guess my work has helped. My biggest disappointment was with the walnut case; i should've left well alone, but once a tinkerer always a tinkerer...I used shallac, and as the case has a decorative flourish, i had to apply it with a brush rather than pad. Long story (and boy was it a long story...) short, after many coats and knocking them back i eventually got it to a point i was reasonably ok with, but it's still not perfect. However, that all said, i enjoyed the restoration and hopefully i've extended the clock's life a little. Thanks again for all your insightful input, much appreciated as always. Mark

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Who did the spot weld Good Job.