- This topic is empty.
October 30, 2014 at 6:15 pm #49293
Has anyone repaired a Junghans clock movement that when you have taken it apart found some of the pivots much shorter than the others? I have did several of these movements with anywhere from 2 to 4 pivots that were very much shorter than any of the others. In fact these short pivots in these thick plate movements barely come half way up thru the hole. Well what to do when they need a bushing? I have found thru the years of doing these that I started repivoting the arbor with a longer pivot. I then bush the hole and use a ball end mill for a dremel tool to cut a oil sink slightly deeper. It has worked well for me on several of these Junghans movements. I should have mentioned the reason for bushing these shorter pivots is because of tunneling. Just thought I would pass this on. One I tried a shorter bushing that fit the length of the short pivot then used the ball mill to cut a deeper oil sink. To put it mildly it looked like crap. Hence the repivot to a longer pivot.October 31, 2014 at 6:37 am #60100willofiamModerator
- Topics Started: 75
- Total Posts: 1437
Hey Bernie, Is there a reason to have the pivot all the way thru the plate? Do you think that originally they were? Trying to remember the last Junghans I have worked on, cant seem to find the photos of it…. Better get some coffee so I can think straight 🙄 Have a great day, WilliamOctober 31, 2014 at 8:23 am #60101
Thanks for sharing this Bernie, it may come in handy one day if I acquire a Junghan, although I have a couple of their PWs.
seeing as you’ve had a few of these with short pivots, it strikes out the possibility someone doing an incorect rebuild.
One thing that did come to mind… IF these particular clocks were manufactured between 1941-45 in Germany, materials were in short supply, also due to bombing, many industries were disrupted. You know the old saying about a stich in time saves nine, how many short pivots would make up one complete shaft? A saving measure?
The other possibility is that they changed to thicker plates but used old style shafts for the thinnner plate models? Again, fun conjecture
William, the more material you have in contact, the better/stronger, more effecient. Kinda like if they put your tire on your car but only used the first two threads of the wheel studs. So if a shaft pivot is only half way through a plate, the full thickness support is not being utilized, only the tip. Not sure if the shoulder of the shaft is up against the plate, but if it wasn’t, there would surely be unwanted lateral play.October 31, 2014 at 9:31 am #60102
Chris, have you considered that too much surface contact could cause unwanted friction?
Bernie, I am doing a junghans at the moment and some of the pivots are quite short. The oil sink seems to be cut quite deep. This is only on the smaller wheels towards the top of the train. If the pivots are way to short it could be because a previous repairer filed them back if they were badly tapered. Obviously not the way to deal with the problem!October 31, 2014 at 9:46 am #60103willofiamModerator
- Topics Started: 75
- Total Posts: 1437
That was my thinking Paul, also there are alot of clocks that do not have oil sinks. I too have noticed the shorter pivots, my thinking was that they were made that way for assembling, as you work your way up the train in assembly each consecutive pivot was a bit shorter making assembly easier and less dangerous to the pivots, I may be way off on that thought but it was a good way to justify what I was seeing and experiencing, these pivots are pretty small.
Just looked at my personal Junghans clock and I see the pivots getting shorter up the train, they do have the oil sinks too.
WilliamOctober 31, 2014 at 10:18 am #60104
Well, its hard to say for sure what Jughans were thinking, but contact area vs friction is not necessarily related to length of contact, it can also be related to diametric contact which I think you might be thinking of? The thin pivots on a watch, those that utilize bearing jewels were designed for thinner pivots, thus reducing friction and improving performance, but these watches were under a very different set of operarting conditions than clocks, as in movement, various positions, temperature change and shock, plus they utilized a fast gear train, which I don’t think clocks use, although I don’t know for sure.
This is why nearly all clocks use bushings, I know I’m preaching to the choir here So with a clock, that really never changes its position from the vertical, where temperature is at a near constant and there is no shock, a longer area of pivot contact on a wear brass bushing is much preferred as frequent lubrication is what minimizes the friction. So what is better, a short thin pivot, a long thin pivot, a short fat pivot, or a long fat pivot? For this type of application, I really think a longer thicker one would provide better support for gear shock and certain forces applied by the train. It would also, in the case of this Junghans, utilize the whole length of the bushing, which would reap better, longer wear resistance.
Any idea what year your clocks were made, this could provide clues as to why?October 31, 2014 at 10:26 am #60105
Oh, Paul, I forgot to add, that it seems a constant on Bernies several, yours and Williams, so the odds of a repairer making a bad job seems slim, if it was only one or two, possibly.
Like I mentioned, Germany suffered many bad years of depressions, war, shortages, occupations etc, we can see this on many items mand in the DR from 1813- 1952 when the economy began to pick up, so another possibility, but who knows, they could be Monday or Friday clocks 😆October 31, 2014 at 12:53 pm #60106
I don’t know if they were made that way or what. I know on the two I have hanging in my house there was some tunneling on the short ones and have read complaints from others of this problem. William I made the pivots just long enough that they just peaked out of the oil sink. The two I have hanging and running in the house had the pivots done about 13 or 14 yrs ago. Both are running well an 4 yrs ago both were taken down for a cleaning and oiling. No tunneling or wear that I could see. Didn’t seem to have a problem with reassembly with them either or any others I did. On another forum one gentleman said when he rebushed he used a bushing that fit the pivot diameter and height. Problem with that is the plates are thick therefore the bushing maybe half the thickness of the plate. So right or wrong it has worked for me. Haven’t had anyone ever explain to me or come up with a reason why they are short.October 31, 2014 at 1:14 pm #60107
Well, these are interesting topics Bernie, so thanks again for raising this. Anything that is out of the ordinary is food for thought and I figure are nice to discuss, gives us a better insight into what the hell went on waaay back then, were these guys dipping their oilers into the Schnapps supply 😆 CAUTION OR ACHTUNG, SCHNAPPS MAY MAKE PIVOTS APPEAR LONGER THAN THEY REALLY ARE 😮October 31, 2014 at 2:39 pm #60108
contact area vs friction is not necessarily related to length of contact, it can also be related to diametric contact which I think you might be thinking of?
If there was diametric contact I would imagine the pivot would be binding in the pivot hole, this is why we allow 5 degrees of lean on the pivots so the oil acts like a bearing. When the pivot is in use and has the pressure from the previous wheel against it, it will tend to run on just one part of the pivot hole which is why you tend to see oval holes as the dirty pivot slowly chews its way through the plate. I am right in thinking diamteric contact is contact around the whole diameter? You will have to forgive me if I have this wrong as I don’t do well with big words
Paul.October 31, 2014 at 2:51 pm #60109
Surely if you have a pivot 1mm long and a pivot 3mm long (and both the same diameter) there would be greater friction from the 3mm pivot as there would be a greater surface contact area? My head hurts, I am going to make a cup of tea
Paul.October 31, 2014 at 3:18 pm #60110
Well, there are different fits, press fit for example would cause binding, interference fit etc, sliding fit would have less friction, and so on down the line…
But back to the short pivots… If a weight, load or pressure is spread out over a longer area, then it is less on one spot and distributed evenly across a longer surface, so therefore less friction on one spot. The same principle as a tank track. As Bernie mentions, with the short pivot, tunelling was noticed and if for example, the tip of a pivot, say 5mm was resting on a 10mm bushing, then that would not fully utilize that load across the whole available surface. So now, you have only half the bushing wearing down, and the tip of the pivot would be touching, or jamming itself in the lip it has created. this would cause friction, slowing down and eventual stopage.
The oil bearing you mention can only be achieved at very high speads, its called oil lift and requires a constant flow of pressurized oil to maintain the lift on a shaft. The oil is “whipped” around the shaft and acts as a sort of fluid bearing. In the case of a clock, we only have low speed and no constant oil supply, so the “wedge” is not created. we rely more on slipping sliding lubrication for this type of application, which again, dries, is squeezed out, or wears out, hence the use of a brass wear bushing, as brass itself is a soft lubricationg material and will not wear a steel pivot. Our drop of oil is only to provide the temporary resistance free slip and to prevent the bushing from wearing out too fast. As you noted, bushing are ovaled out when pressure from one gear exerts force, so any oil is pushed out.
On our steam turbines we use a similar method called a babbit bearing, which is basically like a clock bushing but with much tighter tolerances, high speed and a lot bloody heavier 😆 The weight of the turbine shafts are distributed over a long babbit area, more support, better load carrying and wear, more stable..
Maybe the Junghans boyz tried it to see what happened, who knows, but all Junghans clocks don’t have short pivots, do they ? What about other makes ?
I tried not to use too big words this time my English brother, go and enjoy your tea and possibly a digestive;)October 31, 2014 at 4:27 pm #60111
Chris you had my thoughts exactly. I thought with a longer pivot that used the whole plate instead of half of it would cause less friction. It definitely will have less friction than tunneling and the tip binding up. Like I said the two of mine had virtually no wear on the pivots that I did and made them slightly longer when I cleaned and oiled them. No tunneling. Chris no not all Junghans clock movements have short pivots. I just did a 77 model and all pivots were the same length as I measured them. I think I have did 7 or 8 of these Junghans not including mine that have had short pivots. One of them I know has been running for 14 yrs with no problems. I called her today after reading these conversation to see if it was running ok and if they had any problems. She said they haven’t had any problems. She said it is keeping great time and chimes great. She did say that it is probably about time to have it cleaned and oiled again. I always tell my customers 10 yrs it should be serviced.
As for short pivots these Junghans are the only clock movements I have seen short pivots on. I have run across very few but have seen some on antique clocks. Maybe 4 or 5 in 30 yrs. Anyway those were replaced also.October 31, 2014 at 10:23 pm #60112Bob TascioneModerator
- Topics Started: 38
- Total Posts: 1559
Hey interesting subject!
I can’t add much here since I’m not sure. I tend to lean toward Pauls longer pivot higher friction theory though. The pressure would be distributed along the longer pivot but I would think that there would still be increased surface friction since more metal is involved in the sliding of the two parts ie: pivot and hole wall. I can’t remember and would probably fry my brain trying to figure it out but we would be dealing with kinetic or sliding frictional coefficients of dissimilar metals vs static frictional coefficients as the wheels are not actually in continuous motion due to the starting and stopping of the escapement. If that makes any sense to you then you’re doing better than I am.
I can say for sure though that a shorter pivot as compared to a longer pivot will absolutely help when it comes to power loss effects to timekeeping and run duration due to changes in oil viscosity over time. This is the very reason that Olive jewels are used as balance jewels, pallet arbor as well as escape wheel jewels. Less surface contact between parts for dry gummy oil to cling onto. Watches will run longer using these olive jewels over straight sided plate type jewels. Also William made an interesting point about possible ease in assembly. Never thought of that one but makes sense.
I’m not considering the effects of tunneling etc. or what effect any of this would have on this movement. Just addressing the subject of pivot length.
So…beats me why they would design their movements this way. Maybe they wanted to reduce the adverse effect of aging oil or if the pivot length to friction theory holds water they may have been trying to cut down on friction or maybe they wanted to leave us wondering. Or perhaps they just had a bad batch of parts they needed to get rid of.
BobNovember 1, 2014 at 4:15 am #60113
Bob, is that why clocks don’t have jewels 😆
- You must be logged in to reply to this topic.