Bush or Not?

[wow]

It amazes me sometimes why some bushings wear more than others. This is a 451-050 I just got in. It needs 5 bushings and four are not bad. Just sloppy enough to bush. But why is this S-1 so worn? None of the other winding arbors need bushings on either end and this one is worn only on the wheel (front) end.?

 

[J. A. Olson]

Wear can happen anywhere and is not consistent. It'd be interesting to evaluate the metallurgy and tensile strength of an entire movement plate to see where any 'weak spots' may have occurred during manufacture.

 

[NEW65]

Also, it may not have been completely lubricated. Also, because the history is often unknown, the quarter chime weight may have been used to drive the strike train.
I rebuild the weight driven Hermle's almost on a daily basis and even the later models require a crazy amount of bushings to be fitted! Regarding the chain wheels, much more likely to need bushings ( in my experience) in the front plate than in the rear plate which has always puzzled me!
I started overhauling another 0451 earlier today. So far, I have had to bush every pivot in the time train. It takes me a while to do any Hermle but i would sooner do this than buy their crappy new units.

 

[Willie X]

It probably had an obvious flaw that wasn't noticed, because no human being ever saw or touched it ... Willie X

 

[TEACLOCKS]

Plated Pivots.

 

[John P]

New if you look at the gearing from the side, you will see all the wheels work the hardest near the front plate.

johnp

 

[wow]

Plated Pivots.

I examined the pivots of the winding arbors and there is no flaking. All three look the same. All pivots look good except for being dirty. The weights were in their proper place when I picked it up so the theory about the chime weight being on the strike side is not what caused it. Who knows! I Maybe just no oil from the get go. Put in a bushing and all looks good. It should be a reliable movement for many years when done.

 

[POWERSTROKE]

Im convinced that hermle movmwnts are trash. They come from the factory in poor shape. They get sent out to clock repair people, send back to hermle, they "test" them, put them back on the shelf, wash repeat. The one I sent back a couple weeks ago, was being tested when I called about the second failure. I was told it was running great. Lol.

 

[R. Croswell]

Just a thought, I suspect that a new and properly finished pivot and pivot hole, initially well-oiled would wear rather slowly up to the point where the lubrication began to fail. At that point bare metal to metal contact would begin to roughen up the bearing surfaces and wear would continue at an exponentially faster rate. Perhaps that one got contaminated with a bit more dust or a bit less oil or whatever and was the first to break down. My guess is that had no one intervened it wouldn't be long before the other pivot holes would soon fail. This one just started downhill first is what I think.

RC

 

[wow]

Well it’s up and running on my test stand. Pivots polished well. Should be good for a long time.

 

[bkerr]

Good that you got it going again! I looked at the photo closer and noticed the bushing height verses the plate thickness. Is there a reason why this stands proud? I have always thought that the arbor should stand out of the bushing / plate. There again maybe it was my screen and camera angle?

 

[shutterbug]

The pivot should stand proud of the oil sink, not necessarily proud of the bushing. It should also clear the plate.

 

[wow]

The pivot should stand proud of the oil sink, not necessarily proud of the bushing. It should also clear the plate.

Yep, on these big bushings I like to use a bushing that will cover the full arbor but still leaves an oil sink. More surface=slower wear?

 

[shutterbug]

Yep. At least in theory

 

[R. Croswell]

Yep. At least in theory

......on these big bushings I like to use a bushing that will cover the full arbor but still leaves an oil sink

I can think of two possible exceptions, 1) If the pivot contact area of the proud bushing is greater than the original contact area of the pivot hole and the worn pivot is not turned down to a uniform cylindrical diameter the slightly larger unworn end of the pivot will be the only surface in contact with the bushing. Initially there will be faster and uneven wear. 2) If this were a restoration job (not a repair) and there was a perceived need for an invisible restoration as close as possible to original dimensions, then the bushing should be as small as possible and flush with the plates.

So yes, I agree, in theory maximizing the pivot contact area should promote longer life.

RC

 

[bkerr]

Maybe learning something new and that could be a good thing.

Let me preface by explaining that I purchased a Rollimat last year to try to do the very best job I could on a rebuild / restoration of any clock that comes across my bench, BTW I really like this tool.

So with the pivot polished and straight I then go to the bushing, selected for height and diameter ( most of the time KWM to keep the o.d. smaller).

Once the bushing is installed I fit each arbor to the pivot with a tapered reamer. Both from the from and the back of the plate shooting for the same distance on the reamer on each side. If you could see inside the bushing you will see a slight taper from the outside of the plate to the center of the bushing on both front and back. I then follow up with a tapered smoothing broach again from each site of the plate.
Reamers are tapered I am guessing for that purpose? I was told by a very good clock guy that this will reduce the amount of friction verses a straight bore? Was he wrong? I finish up the bushing by cutting or dressing the bushing with a circular cutter to create an oil sink. This also reduces the i.d. length slightly, keeps the arbor proud of the bushing.
Please comment if I am off base.
Regards

 

[wow]

I think, just because it makes sense, that a straight smooth pivot in a straight smooth hole will last longer than any taper. Am I wrong? You got me wondering, Bkerr.

 

[Willie X]

I would leave off the "cutting for the oil sink part", especially at the bottom end of a modern clock. And, straight pivots in straight sided bushings are ideal but very hard to do. Where are you Jerry?

Note, I think some people visualize a big hump at the mid point of the bushing hole but if you do things exactly as bkerr just described that hump is close to a fictional thing. Unless the .0003" bothers you and you think that will make any difference over time?

There are basically two camps on this. The RC camp and the Gerry camp. I think both make very good arguments. RC toward the practical and Jerry toward the ideal/theoretical.

My 2, Willie X

 

[R. Croswell]

Maybe learning something new and that could be a good thing.

Let me preface by explaining that I purchased a Rollimat last year to try to do the very best job I could on a rebuild / restoration of any clock that comes across my bench, BTW I really like this tool.

So with the pivot polished and straight I then go to the bushing, selected for height and diameter ( most of the time KWM to keep the o.d. smaller).

Once the bushing is installed I fit each arbor to the pivot with a tapered reamer. Both from the from and the back of the plate shooting for the same distance on the reamer on each side. If you could see inside the bushing you will see a slight taper from the outside of the plate to the center of the bushing on both front and back. I then follow up with a tapered smoothing broach again from each site of the plate.
Reamers are tapered I am guessing for that purpose? I was told by a very good clock guy that this will reduce the amount of friction verses a straight bore? Was he wrong? I finish up the bushing by cutting or dressing the bushing with a circular cutter to create an oil sink. This also reduces the i.d. length slightly, keeps the arbor proud of the bushing.
Please comment if I am off base.
Regards

I do pretty much what you do but like Willie said, this is where the theoretical and the practical/possible come head-to-head. Ideally, the full length of the pivot should be supported but unless you have ultra-precision tooling to set the bushing and true-bore it, it isn't going to initially contact the full length of the pivot, and if there is any misalignment or flexing of the plates (common in mass-produced clocks) the pivot will be pinched. If the bushing is slightly tapered from both ends to the middle, it will be more tolerant of any slight misalignment of the plates. I maintain that either way (double tapered or straight) the pivot will initially be in contact with only a small part of the bushing - inside opening, outside opening, or center. After some time, the pivot and bushing should wear in and become in full contact either way. Obviously the straighter the bushing and the smaller taper, if any, the shorter the wear in period and the less debris that will accumulate during the process.

I have not seen this mentioned, but ideally, I think it would be desirable to disassemble the movement after the first year and just clean all the pivot holes and pivots with no broaching or additional machining unless a problem is found. Of course no one is going to want to pay to have that done so we just give it our best shot.

RC

 

[bkerr]

RC I agree with you and with Willie. Like I said it was the way I was taught and it did make sense to me. I am sure like you said that both ways work so, at the end of the day?
I would like to add that if you are fitting a bushing to the arbor after it is pressed into the plate how do you do that? My guess is with a tapered reamer not a straight reamer. If done with a tapered reamer from both sides then you end up with a bushing with a taper from both sides like RC describes. For what it is worth, the guy that taught me said that is was the way he did fine Vienna Regulators, weight driven because it reduced the amount of friction. Folk Lore - you decide.

Willie, I like the way the oil sink looks. It is nothing too big. Just breaks the surface. I will look for a pic to show. It takes a bit longer but I think that when someone sees a movement that was done with care it shows. I have seen too many job that " got it running" and look like crap. Drives me crazy when I see soldered parts too. When bushing I believe your eye should not be driven to the bushing either, that is why I prefer KWM style to keep the o.d. smaller.

It may all be just a preference to the one who does the work. Thanks All

 

[wow]

I would like to add that if you are fitting a bushing to the arbor after it is pressed into the plate how do you do that? My guess is with a tapered reamer not a straight reamer. If done with a tapered reamer from both sides then you end up with a bushing with a taper from both sides

Bkerr, in that bushing I polished the arbor pivot and fit the bushing to it before anything else. I then used a KWM reamer in my bushing machine to cut and center the new bushing hole. It fits automatically without reaming/broaching the ID of the bushing at all. I use this procedure with every bushing. The bushings are already straight and smooth so I hardly ever broach any bushing. If the bushing hole is cut perpendicular to the plate, it is almost never necessary to do anything to the ID of the bushing.
Where I have trouble is when I have to use a hand reamer and get the hole cut crooked. Then I sometimes have to broach slightly to get a good fit.
Hope this helps.
Will

 

[David Provan]

You guys leave me in the dust. I can't help asking if you've looked at the new way of bushing, HERE

 

[R. Croswell]

Yes, a real hack job!

 

[Willie X]

Just for another visual ... Willie X