ETA 2892 How much endshake on second wheel ?

[mikepilk]

Assembling an ETA 2892 (my first, been waiting a while to get my hands on one ) I noticed far too much endshake on the second wheel, due to the train wheel bridge being bent.

I noticed that the centre tube was not pushed all the way home. This could have caused the bridge to bend when screwed down, or someone's pushed the hands on with too much force ?

Anyway, I've got the centre tube pushed home, and now have excessive endshake  - the bridge will have to be bent back  down.  

How much endshake should I have on the  centre wheel, minimal or should it have bit or room to move ? 

 

 

[clockboy]

Every wheel and arbor in a watch must have endshake, or they will bind stopping then watch. The amount of endsahke must be enough to see with magnification, BUT should not be to excessive. The amount of end shake should be no more than half of the pivot length.

[mikepilk]

8 minutes ago, clockboy said:

Every wheel and arbor in a watch must have endshake, or they will bind stopping then watch. The amount of endsahke must be enough to see with magnification, BUT should not be to excessive. The amount of end shake should be no more than half of the pivot length.

Thanks, it's hard with endshake to define how much a 'bit' or a 'lot' is - but 'half the pivot length' is just what I needed to know.

[rogart63]

Looks like it's a little to much. Did you take the picture before you bent it back?  Looks like the jewel could be sitting to high also. Shouldn't that be the same level as the other jewels?  

[mikepilk]

34 minutes ago, rogart63 said:

Looks like it's a little to much. Did you take the picture before you bent it back?  Looks like the jewel could be sitting to high also. Shouldn't that be the same level as the other jewels?  

Good point, I'll push the jewel back level 

[mikepilk]

I pushed the jewel level, a very slight bend of the bridge, and the endshake looks OK.

One weakness of a cantilevered bridge like this, is if someone is heavy handed fitting the second hand, you can end up with a bent bridge or displaced jewel. 

[clockboy]

I must apologise I did not read your original post in full. The fact that the bridge is not straight could cause other issues when the watch is in different positions because the wheel is not sitting straight. Poor meshing of the gears could cause binding and erratic performance.  In may opinion the bridge needs to be straightened if that is possible that is.

[mikepilk]

Finally got round to assembling this movement, but ended up stripping it again due to poor amplitude. I'm not happy with the gear train - there's some 'stiction' sometimes.

I pushed the second wheel jewel level at the top as Rogart63 suggested, but now it sticks out the bottom.

Also the pivot is a VERY loose fit in the hole - the picture isn't very good , but the pivot is only about 2/3 the hole width.

Is this correct, or has the jewel been changed ?

 

[mikepilk]

I've managed to answer my own question, looking at Mark's video (12:00 m) there's a lot of play at all 3 jewel pivots

https://www.youtube.com/watch?v=xh3uH4t5mKw

[khunter]

That is the wrong jewel for that wheel, a little side shake is normal but that jewel looks almost twice as big as it should be. I recently replaced a fourth wheel lower jewel, the pivot measured 0.31mm, the proper jewel was 0.32mm. 1/100 of a mm is roughly 0.0004 inches. The pivot should be measured and a new correct jewel fitted. Looks like someone tried to "just get it running" with whatever was handy.

[mikepilk]

Thanks for confirming that. It's going to be tricky measuring the jewel as it's so small. I bought a box of assorted jewels, looks like one of those should fit. 

[rogart63]

The jewel looks like it's very worn. Wouldn't it be a better alternative to find a new bridge . 

[khunter]

4 hours ago, mikepilk said:

Thanks for confirming that. It's going to be tricky measuring the jewel as it's so small. I bought a box of assorted jewels, looks like one of those should fit. 

A good digital caliper would be fine to measure the outside dimension, use the wheel arbor to confirm the hole size. A jewel press would be the best way to press out and install a new jewel, not a difficult job at all.

Edited March 19, 2018 by khunter

[mikepilk]

3 hours ago, khunter said:

A good digital caliper would be fine to measure the outside dimension, use the wheel arbor to confirm the hole size. A jewel press would be the best way to press out and install a new jewel, not a difficult job at all.

I measured the OD with digital calipers (too hard to hold in a micrometer) at 0.70 mm.

From my mixed box of jewels I've found a suitable candidate - I've no means of measuring the hole, but it sits on the pivot with just a little bit of wobble. 

I have a jewel press, only used it a few times, and not on such a small jewel. I'll make sure I don't have too much coffee before trying 

[khunter]

Should be good to go. I've found that slowly pressing in the jewel in small increments, then checking the endshake works best as opposed to trying to get it right the first try. Check the hole/pivot size under high mag to make sure it's not too sloppy but it sounds like you're on the right track...

[mikepilk]

New jewel fitted and looking good !

In the end it was pretty easy to fit. The seconds wheel now spins nicely with correct endshake.

With the pallet out I still have some 'stiction' - usually the gear train moves with the slightest turn of the crown, but  sometimes it takes a full turn or more to move.

The gear train on it's own seems fine - spins nicely when I use the blower.  The barrel and intermediate wheel also seem OK when isolated so I'm at a bit of a loss to work out what the problem is. 

Could the arbor be binding in the barrel ?  Any other suggestions ?

 

[khunter]

That looks MUCH better!!

As for the stiction, I had a similar problem lately, and turned out one of the train wheels was not perfectly flat/perpendicular to the arbor. Took a little work on the truing caliper and it works great now. I'd also check the barrel arbor for free spin (without the mainspring of course). Wonderful job on the jeweling!

[mikepilk]

On 20/03/2018 at 7:11 PM, khunter said:

That looks MUCH better!!

As for the stiction, I had a similar problem lately, and turned out one of the train wheels was not perfectly flat/perpendicular to the arbor. Took a little work on the truing caliper and it works great now. I'd also check the barrel arbor for free spin (without the mainspring of course). Wonderful job on the jeweling!

Had another go at sorting this watch out - it would run OK for a while and suddenly stop. Took me ages to determine the problem. I always assume it's pivots/jewels etc. Turns out it's the mainplate. As you can see in the pic, there's distortion at the recess for the escape wheel. You can also see the web holding the centre tube is not vertical. 

There are also raised dimples under the base of the balance cock. This watch has had a hard life!

I don't expect I'd be able to straighten the mainplate - there's no flat references to work to. 

So if anyone knows where I can get a 2892 mainplate, please let me know

 

Edited April 5, 2018 by mikepilk

[khunter]

Wow, looks like someone used a miniature jackhammer on the plate. The dimples are "somewhat" common, old timers would do this to adjust the endshake on the balance wheel. Not the best practice, but not totally surprising.