Invisible problem with barrel arbor - A lesson learned

[Simeon]

I finally got back around to an ETA 1093 that I had started servicing and then gave up in frustration a few weeks back (See this thread for self-pity and complaining, or don't bother).

Basically, the train was running perfectly free until I installed the barrel bridge, at which point it seemed to bind up.  Anyway, moving on I lubricated the escapement and installed the balance.  As expected, the movement started running but with really low amplitude (around 150 degrees) - not surprising considering how tight it became with the addition of the barrel bridge - I had also over oiled the train with the removable end stones so I intended to strip and clean the movement again anyway. 

I slowly started stripping the watch again, checking each wheel for end shake and giving it a general look over to try and find what was binding.  Once I removed the barrel bridge, the train freed up again and turned over well with just a few puffs on the escape wheel.  I now had a donor movement in hand, so I pulled the barrel bridge from this one and tried that in place of the original.  The train bound up again.  Looking at the two barrel bridges side by side, I couldn't see any differences - they both looked flat and there wasn't any signs of rubbing (I suspect that this 'fault' was present when- I got the watch and it was running with low amplitude because of this - rather than specifically needing a service).  The centre seconds wheel, also has a slight wave to it and is not running entirely true - this probably wouldn't effect running too much but I at least get the chance to try and true the wheel up again or replace from the donor before installing.

I then turned to the barrel and swapped in the barrel complete from the donor, reinstalling the original barrel bridge it was like night and day - so much better.  I then pulled the barrel arbor from both the serviced original barrel and the donor barrel and compared them with my 15X loupe.  I couldn't see any difference - if anything the serviced orignal looked better because the square ratchet drive on the donor was a little chewed up and it was yet to be cleaned.

I installed the donor arbor into the serviced original barrel (it had a new mainspring so I wasn't ready to give up on that yet), installed it back into the movement with the original barrel bridge and again it seemed so much smoother and free.  Now I have the correct combination of parts, I am going to reclean everything and reassemble tonight and see what I get.

There was no appreciable endshake or play with either barrel arbor and it seemed the same with both barrel bridges so I am going to rule out the barrel bridge becoming oval and binding but I can't for the life of me determine what was the problem with that barrel arbor unless it had always been slightly too big for the barrel bridge bearing from the factory or misshapen in some other way.  I can't see the barrel arbor wearing and not the brass barrel bridge.

Perhaps if I had a microscope (hoping Santa Claus brings me one this year) I could see a microscopic difference between the two.  It's also a lesson to check each component for free running as well as endshake when inspecting it.  Barrel arbor to barrel, barrel complete to barrel bridge and the rest of the train when installed.  If you install each wheel individually and inspect in isolation of the rest of the train, you can determine easily which wheel is dragging.  It takes a bit longer but it avoids having to fault find on an assembled movement.

[nevenbekriev]

7 hours ago, Simeon said:

There was no appreciable endshake or play with either barrel arbor and it seemed the same with both barrel bridges so I am going to rule out the barrel bridge becoming oval and binding but I can't for the life of me determine what was the problem with that barrel arbor unless it had always been slightly too big for the barrel bridge bearing from the factory or misshapen in some other way.  I can't see the barrel arbor wearing and not the brass barrel bridge.

Perhaps if I had a microscope (hoping Santa Claus brings me one this year) I could see a microscopic difference between the two.  It's also a lesson to check each component for free running as well as endshake when inspecting it.  Barrel arbor to barrel, barrel complete to barrel bridge and the rest of the train when installed.  If you install each wheel individually and inspect in isolation of the rest of the train, you can determine easily which wheel is dragging.  It takes a bit longer but it avoids having to fault find on an assembled movement.

OK, so You came to the conclusion that the barrel arbor is the reason and somehow is not working, but You don't know why? But... the same way some day You may come to the conclusion that this chair is not working or this spoon is not working too, but again, You don't know why...

Well, I feel need to explain that in You case there is no need to check how the arbor behaves in the bridge bearings as the arbor doesn't turn at all when the watch works, it turns only when winding. So consider the arbor as part that stays still. The bridge/plate bearings here are important as they support the arbor to stay upright, but nothing more in the long time between the winding.

So, You barrel doesn't turn free? Then, follow You own logic. Put the barrel only with no spring inside with the arbor in the plate/bridge, put the ratchet wheel with the ratchet to hold the arbor still and turn the barrel to see if it is free or stuck. Then, if it is stuck, You will have to find out why - may be it is rubbing somewhere, may be there is no radial free play in the bearings barrel/arbor.