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Record 1955-2 / Longines 505 auto bridge bronze bushes


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I thought it better to start a new thread on this than confuse the one about train counting.

So this watch will need 2 new bushes for the auto reverser wheels - one in the auto bridge and one in the train bridge.

These bushes appear to be bronze and are quite small. I think they are listed on the bottom of the parts diagram on Cousins, but even if I could identify them from there, they don’t stock any of those parts https://www.cousinsuk.com/PDF/categories/3662_Longines 501.pdf

The lower bush is 0.27mm high, 1.6mm OD and 0.9mm ID with no oil sink

The upper bush is 0.27mm high, 1.0mm OD and 0.22mm ID with an oil sink

I have only ever seen brass watch bushes for sale and never anything this thin.  They will be quite fiddly to make on a lathe, but I’m willing to give that a go. I have some brass wire, but would rather stick to bronze although not sure what type of bronze to look for and can’t find any described as being for watch use.

Anyone got any clues?

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This was an unfortunate problem with early automatic watches before the manufacturers grasps that they should be Using jewels rather than bushings. I've seen for some Omega watches they replace the bushings with jewels. So that's another option to look into if you can find one the right size and thickness.

As the tech sheet only has the pictures and numbers and doesn't explain what the parts are what is the number for the automatic bridge that you need the bushing for?

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Thanks for the idea John, although I’m struggling to find jewels of the right size.

If I were to look for new or used bridges then unfortunately I would need both the train bridge (110) and the auto bridge (1142) as I need both the upper and lower bush.

I’m heading towards buying some bronze bar from eBay, but the smallest diameter of SAE 660, which appears to be the most suitable, is 0.5” which will give me a chuck problem to start with. What I really want is 1/16” so I’ll keep searching...

 

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Thanks John, I’d never seen that site before until yesterday, but that's where I’m getting the 4th wheel from.

After a lot of research I ordered some PB104 phosphor bronze bar in 3/16” diameter, so will see how that goes. Will also need to buy some new tiny drill bits as the ones I have aren’t fit for this job :)

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When you mentioned bronze I called a friend who makes clocks to verify something? I had seen a reference before to someone else who made a clock and they used bronze for the plates because it be really really hard. Unfortunately the bronze they picked wasn't suitable for plates and cause the Pivots to disintegrate. So you just have to be careful that you picked the right bronze suitable for bushings.

Then you may not actually have to use bronze at all? If you look up the age of the watch it's roughly 50 years old so it's taken a very long time to wear out its brass bushings. So at a 50 year replacement interval brass should work just fine. Especially if you drill the holes undersize and use a smoothing broach to harden the inside of the hole.

Then the other thing is you do need to verify that the pivots that go in the holes are not rough.

 

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Hi John,

Yes, selection of the correct bronze is important. The original bushes are bronze, not brass, so I was trying to follow suit.

Ideally I would take an old bush to work and ask someone to put it in an SEM and tell me what the composition is... but that would be an abuse of my position so not going there!

I worked from this summary of options broadly available http://www.holmedodsworth.com/materials/bronze/bronze-specifications and would ideally have gone for a lead bronze alloy, but they only come in 1/2” bar minimum. The PB104 I’ve ordered was the next best thing, and it is described as suitable for bearings and bushes.

The complexity here is that the auto winding mechanism will move intermittently and therefore never set up a hydrodynamic oil film, so there is likely to be some metal to metal contact. In a normal engineering environment, the answer to this is to use a high viscosity oil, or a molybdenum type coating / grease, but here that may result in too much resistance. I may try building it with 9141 which is designed to carry high loads but shear easily.

The pinions are in a pretty good state so clearly the existing bronze has done a nice job of being the sacrificial part of the bearing.

No claim to have the right answers here - will tell you how it all goes after 10 years of use...

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Hi @StuartBaker104 - you've obviously done your bronze research but just thought I'd add in something for consideration...

I know you're looking at phosphor bronzes in the main but there are also silicon bronzes. A good overview here ... https://www.avivametals.com/collections/silicon-bronze ... mentions "offers added strength in conjunction with the self-lubricity of silicon for excellent bearing and load properties". Handily, because silicon bronze is used for brazing, then rods of 1.6mm and 1.0mm OD can be sourced ... just the OD dimensions you need.

 

Edited by WatchMaker
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I was looking in my ancient bergeon Catalog. So in the watch material section  is a reference to jewels and metal bushings for automatic watches..  Basically a comment that Jewels are preferred  but for variety reasons metal bushings are used and material is hardened Beryllium. So they at one time had an assortment  which was basically for AS, ETA & Felsa.. There is a reference that there designing another assortment for others Swiss factories.. But on the current website I can't seem to find bushings for watches anymore.

 

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Now then Watchmaker... that’s given me something to think about. Although I have ordered some material now, I know that the addition of silicon would make it easier to machine, so I will see if I have any difficulty there. I did order a couple of new drill bits just smaller than each size to give myself the best chance of a clean cut. Will obviously have to broach to finish.

As for Beryllium, that is now locked up in the nasty box with other wonder materials of the 1950s and 60s like asbestos, so not surprising that it has been removed from the Bergeon catalogue.  Maybe that’s what this watch has, but I’d rather live with a shorter watch life than a shorter watchmaker life :huh:

All this armchair watch repair is where I do my best work. Will have to wait till the weekend, but lets hope my machining abilities live up to that standard :chainsaw:

Thanks for replies both.

S

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If you look up bearing bronze comes in a whole variety of numeric representations and slightly different names. Including such things as C954 Aluminum Bronze. So basically there's a whole bunch of bronze material for bearings and  bronze for other stuff that is not good for bearings. Which is why I have the caution of make sure you know what you're purchasing otherwise you're going to regret this.

Your word lesson for the day what is Glucydur?

So it's used primarily for balance wheels and Wikipedia indicates possibly other parts unfortunately it doesn't say what those other parts are.. It's basically a bronze  with the addition of a forbidden metal.. Fortunately we usually don't have to machine these parts so it should be relatively safe.

https://en.wikipedia.org/wiki/Glucydur

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