REALLY tiny pivots - what to do?

[TJ Cornish]

I'm working on an unsigned time-only Vienna. The clock was running when I disassembled it. Checking it over, some of the pivots have a fair amount of wear - a couple have a fairly significant groove in them. Normally I would polish that out and rebush the movement, however the pivots are already microscopic - 0.5mm. I'm fairly comfortable with larger movements, but this is my first foray into something this small. I've also heard that often Viennas have hardened pivots. Would that likely be the case with this clock (I'm assuming no since they're so worn)?

What's the best path forward? grinding down the existing pivot and repivoting with new wire perhaps slightly larger than the original pivot size to compensate for plate wear? Should I try polishing? If so, how small is too small?

Thanks in advance for any advice.

 

[Karl Burghart]

It is likely hardened. Try lightly scratching with a razor blade. If it doesn't dig in then it's hardened. The general rule of thumb I use is that you can reduce the pivot size by 1/3rd to remove imperfections. Your's looks to be well within that. When dressing the pivot ensue the arbor is supported. Go slow.

This article has some very good information on Vienna clock pivots. . Tid-Bit 19 - Restoring Clock Pivots - SNClocks

When re-pivoting you can get away with a little larger but the pivots have a smaller diameter for a reason, to reduce friction in the wheel train. Making it too large may cause the clock to stop.

 

[wow]

I do not re-pivot in most cases like this. I turn the pivot down till even and polish it well. I then bush with a bushing that fits the new pivot size. These arbors are usually vey hard and must be annealed in order to re-pivot. Same thing with French clocks. Very hard. Just what I think.

 

[R. Croswell]

I'm working on an unsigned time-only Vienna. The clock was running when I disassembled it. Checking it over, some of the pivots have a fair amount of wear - a couple have a fairly significant groove in them........

If the clock was running OK before you disassembled and cleaned it, it should run even better after cleaning and oiling. If the pivots have groves and irregular wear it is likely that the pivot holes have corresponding wear. The real question is how sloppy are the pivots in the pivot holes? One option may be to just do nothing except clean and oil and wait until there is a problem, especially if you own this clock..

RC

 

[TJ Cornish]

If the clock was running OK before you disassembled and cleaned it, it should run even better after cleaning and oiling. If the pivots have groves and irregular wear it is likely that the pivot holes have corresponding wear. The real question is how sloppy are the pivots in the pivot holes? One option may be to just do nothing except clean and oil and wait until there is a problem, especially if you own this clock..

RC

I actually had that thought. It is my clock; my work on it was an attempt to be proactive. My fear is that if a pivot fails, the whole movement will let go and I'll have a much bigger problem, including possibly dropping the weight.

 

[TJ Cornish]

It is likely hardened. Try lightly scratching with a razor blade. If it doesn't dig in then it's hardened. The general rule of thumb I use is that you can reduce the pivot size by 1/3rd to remove imperfections. Your's looks to be well within that. When dressing the pivot ensue the arbor is supported. Go slow.

This article has some very good information on Vienna clock pivots. . Tid-Bit 19 - Restoring Clock Pivots - SNClocks

When re-pivoting you can get away with a little larger but the pivots have a smaller diameter for a reason, to reduce friction in the wheel train. Making it too large may cause the clock to stop.

Thanks for the link.

 

[TJ Cornish]

I do not re-pivot in most cases like this. I turn the pivot down till even and polish it well. I then bush with a bushing that fits the new pivot size. These arbors are usually vey hard and must be annealed in order to re-pivot. Same thing with French clocks. Very hard. Just what I think.

I will give this a try I think. The smallest bushings that are available off the shelf are 0.6mm which may already be too big (haven't measured the plate), but I think I have blanks and could drill them. I'm sure there's some work needed where even if I don't decide to rebush the plate I will need to at least go in there with a smoothing broach to make sure I don't leave an issue that will cause problems later.

 

[R. Croswell]

I'm sure there's some work needed where even if I don't decide to rebush the plate I will need to at least go in there with a smoothing broach to make sure I don't leave an issue that will cause problems later.

Old parts that have run together for years conform to one another's shape and irregularities and are frequently quite happy until disturbed. The real performance issue here is misalignment of wheels and pinions due to wear of the pivots and pivot holes (looseness). Smoothing the pivot holes and leveling out the irregularities that conform to the irregularities of the pivot will increase the clearance of the pivot in the hole and exacerbate the problem. In this case, I cannot recommend removing any more material than what has already worn away from the pivots. I would suggest that the desirable way forward, if and only if you are comfortable replacing fine hardened pivots, would be to replace the pivot and bush to worn pivot hole to match.

I would either go "all in" or leave it alone until it fails to run correctly.

RC

 

[TJ Cornish]

Old parts that have run together for years conform to one another's shape and irregularities and are frequently quite happy until disturbed. The real performance issue here is misalignment of wheels and pinions due to wear of the pivots and pivot holes (looseness). Smoothing the pivot holes and leveling out the irregularities that conform to the irregularities of the pivot will increase the clearance of the pivot in the hole and exacerbate the problem. In this case, I cannot recommend removing any more material than what has already worn away from the pivots. I would suggest that the desirable way forward, if and only if you are comfortable replacing fine hardened pivots, would be to replace the pivot and bush to worn pivot hole to match.

I would either go "all in" or leave it alone until it fails to run correctly.

RC

Clarifying - by "all in" do you mean polishing pivots and bushing, or by "all in" do you mean drilling and installing a new pivot?

 

[R. Croswell]

Clarifying - by "all in" do you mean polishing pivots and bushing, or by "all in" do you mean drilling and installing a new pivot?

Replacing the pivot with a new one of the original size and bushing the worn pivot hole with a bushing that fits the new pivot. That will restore the movement to original specifications if you get the new pivot perfectly centered in the arbor, and get the bushing perfectly centered over where the original pivot hole was.

RC

 

[matthiasi]

The smallest bushings that are available off the shelf are 0.6mm which may already be too big (haven't measured the plate), but I think I have blanks and could drill them.

I have bought bushings as small as 0.2mm in the KWM sizes (they go down even smaller) , off the shelf. Available from Timesavers.

If they're too high, I install them"almost" flush to the outside of the plate (i.e.- just around 0.05mm from being flush), then apply thin, low-tack painters tape around the bushing on the inside of the plate and file the bushing flush with the plate. You don't want to file/scratch the plates. Remove the tape, then press the bushing in to be flush with the inside of the plate. Run a small broach through to clean it up (and size the hole correctly), then use the smoothing broach to harden the new bushing.

Forgot to mention, I use a bushing machine (Bergeon).

When polishing the pivots, I tend to go with the 85% rule - very small imperfections allowed.