Low amplitude. Again!

[VWatchie]

I’ve just serviced the same Unitas calibre 6380 for the second time around trying to find out what’s causing its low amplitude. In the horizontal positions (dial up/dial down) the amplitude is approx. 245 degrees and in the vertical (pendant) positions about 200 degrees.

I’ve checked and adjusted just about everything I can think of from the mainspring arbor to the balance staff pivots but without any noticeable difference. The last thing I checked (and that I often have ignored) was guard pin clearance, in banking positions and towards the crest in the safety roller (no remark). Anyway, this movement just doesn’t want to come fully alive.

The only thing I can think of now is the hairspring. Please see the images below.

In the last picture I have rotated and locked the balance wheel at about 315 degrees from its dead centre between the banking pins (fixed and non-adjustable on the main plate). What I suspect is that the outermost coils might start to collide when the amplitude reaches about 245 degrees. Anyway, it is a guess as I have found no way to verify this, as it (if it really occurs) would only be visible under the balance cock.

I’ve never really heard about colliding hairspring coils being the cause of low amplitude and perhaps it would be visible on my Chinese (Weishi 1900) TM if the coils actually were colliding? However, the graph on the TM looks reasonably straight without anything, except amplitude, looking abnormal.

So, could there be any substance to my theory (colliding HS coils) and if so, what could I do about it? Or should I look elsewhere? Any input would be extremely welcome! Thanks!
 

[Plato]

Are you getting the correct amplitude from the timing machine? The lift angle of the 6380 is 49deg rather than the default 52 deg.

[VWatchie]

  On 10/29/2021 at 3:40 PM, Plato said:

Are you getting the correct amplitude from the timing machine? The lift angle of the 6380 is 49deg rather than the default 52 deg.

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Thanks! Yes, I'm pretty sure about that. I placed the movement directly on the pick-up stand and tried with several gain settings. And to make absolutely sure I shot a slow motion video of the balance wheel as well.

So, the HS looks good/OK?

[Plato]

Is the hairspring centred over the balance jewel without the balance wheel attached? Best wait for advice from one of the pros before delving too deep!

[VWatchie]

  On 10/29/2021 at 4:00 PM, Plato said:

Is the hairspring centred over the balance jewel without the balance wheel attached?

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Thanks @Plato, but can you rephrase that question? I really tried to understand your question, but I don't want to speculate. Perhaps you can explain what you want me to do, like... "remove the hairspring from the balance wheel, then... etc."?

 

 

[VWatchie]

  On 10/29/2021 at 4:00 PM, Plato said:

Best wait for advice from one of the pros before delving too deep!

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Yeah, it would be great with a comment from a pro like for example @nickelsilver 

 

  On 10/29/2021 at 4:00 PM, Plato said:

Is the hairspring centred over the balance jewel without the balance wheel attached?

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Ah, maybe I got what you mean? Remove the HS and then replace it on the underside of the balance cock, replace the stud in the stud holder and see if the center of collet ends up is right in the center of the jewel hole?

[Nucejoe]

 Hairspring itself looks good, if anything last coil is a little bit close to the stud, due to imperfectly centered coil, the whole coil looks a bit pushed to the side which has pushed the last circle close to the stud, if it was me I adjust the coil to push it to exact opposit side, to reduce chances of last coil colliding with the stud.

Didn't you examine the lock on this movement before? 

[Nucejoe]

The H/S should leave slot of the stud at the slots mid point, so I make H/ S adjustment( push towards center) close to the stud.

[Plato]

  On 10/29/2021 at 5:56 PM, VWatchie said:

Ah, maybe I got what you mean? Remove the HS and then replace it on the underside of the balance cock, replace the stud in the stud holder and see if the center of collet ends up is right in the center of the jewel hole?

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Yeah, I remember it from one of Mark's videos. 

[nickelsilver]

Hairspring is slightly out of center but that's not the cause. It could still be a lot of things, center wheel bearing worn (often in the plate), wear in bridge bearing for barrel arbor, general pivot condition, wear on the actual pinion leaves, etc. But if I was working on it, at this point I would have a good look at the escapement. Just a movement of 0.005mm on both pallet stones could easily give a 30 degree boost- but you have to know if they can be moved in. It could stand to have the bankings closed a bit, if the run to the banking is too large. But these checks can't really be explained correctly in a post or two unfortunately.

[Plato]

  On 10/29/2021 at 6:18 PM, nickelsilver said:

0.005mm on both pallet stones could easily give a 30 degree boost

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If the locking on the pallets is too deep then energy is wasted? Would the adjustment be needed because of wear on the escape wheel? If so, would replacing the escape wheel give the same boost? 

Also, if the balance wheel pivot has too much play (excuse the terminology) would energy (amplitude) be lost? I recently serviced my brother's 2824 an the amplitude in that wasn't great, I put it down to a worn pivot due to late servicing (worn every day for 6yrs before I did it).

[Nucejoe]

 If memory still serves me, VWatchie got this watch brand new and its been giving him a hard time, lock on the pallet weren't excessive, he did check all side shakes, all jewels, holes including center hole bearing were OK any part examined was as expected in a new watch, but gained time on active wrist.

No issue was found , the fault remained undiscovered.

[Plato]

  On 10/29/2021 at 8:25 PM, Nucejoe said:

 If memory still serves me, VWatchie got this watch brand new and its been giving him a hard time, lock on the pallet weren't excessive, he did check all side shakes, all jewels, holes including center hole bearing were OK any part examined was as expected in a new watch, but gained time on active wrist.

No issue was found , the fault remained undiscovered.

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New or New Old Stock? Many unscrupulous sellers the world over. 

[Nucejoe]

  On 10/29/2021 at 8:26 PM, Plato said:

New or New Old Stock? Many unscrupulous sellers the world over. 

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New I think, unless VWatchie has several unitas movements.   Either this or I am going crazier. 

Regs 

[VWatchie]

  On 10/29/2021 at 8:25 PM, Nucejoe said:

If memory still serves me, VWatchie got this watch brand new and its been giving him a hard time

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I can understand why you think so joe, but that was a used Unitas 6325. This is a used Unitas 6380 that I picked up on eBay. The first time I serviced it (same poor amplitude) I made a service walkthrough of it which you'll find here (Note: the talk about "great TM results with Unitas movements" was before the assembly). There's a picture there showing the locking depth which @nickelsilver mentions! Anyway, I had been meaning to get back to it once I had acquired more experience and skill, but obviously there's more to learn 

Edited October 29, 2021 by VWatchie

[Plato]

@VWatchie your guides are superb. I used your eta walkthrough as a guide to my brother's 2824 (Sellita 200).

Something is f**ked up or worn out on your watch which will soon be pointed out by our more experienced friends on this forum. 

[mikepilk]

I started servicing watches about 9 years ago. To start with I often struggled for amplitude, but now I have the problem much less ofter.

 I'm now re-servicing some of my original watches and often get better amplitude now (20-30deg) than I got when I started.  I'm now using better cleaning methods/fluids and work under a stereo microscope so that I can see any dust specs. Also, I over oiled.

If I get low amplitude, my first step is re-clean and oil the balance jewels. Although they may look spotless, many times re-cleaning + oiling has fixed the problem.  One thing I always now do (thanks to @nickelsilver) is peg the pallet arbor jewels - cleanliness here is essential !!  I recently serviced a watch and lost 40 deg amplitude because one of the jewels wasn't clean enough.

Then work along the gear train. As @nickelsilver mentions above, wear in the bridge bearing for the barrel arbor is often a problem I've had. Wish more watches had replaceable bearings or jewels here (e.g. Seiko) 

[Graziano]

Please read the Watch cleaning section especially page 8 it's good practice to also peg fork of pallet taking care of guard pin and impulse jewel surface, I have done this combined with burnishing fork with ladies mainspring wired to pegwood,with great results. 20 to 40 degrees difference. This article on cleaning will recharge your approach to cleaning and amplitude. Obviously mechanical issues sorted first. 

Graziano 

626914013_December2012(1).pdfUnavailable

Edited October 29, 2021 by Graziano

[rodabod]

Always start with he really simple and common stuff: how does the barrel and centre wheel sideshake look with the power let-down?

Rubbing hairspring coils tend to cause very noticeable rate changes which are obvious.

Improperly adjusted escapements are more common on older watches in my experience, say <1950's.

[Plato]

  On 10/29/2021 at 9:12 PM, Plato said:

@VWatchie your guides are superb. I used your eta walkthrough as a guide to my brother's 2824 (Sellita 200).

Something is f**ked up or worn out on your watch which will soon be pointed out by our more experienced friends on this forum. 

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Pardon me, I get a bit carried away after a few glasses of

[VWatchie]

  On 10/29/2021 at 6:18 PM, nickelsilver said:

Hairspring is slightly out of center but that's not the cause. It could still be a lot of things

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In this case I feel pretty confident it is not a matter of cleanliness or lubrication that is the culprit but something mechanical. I agree, the HS can likely be removed from the cause list. Nevertheless, I won't rule out anything.

 

  On 10/29/2021 at 6:18 PM, nickelsilver said:

wear in bridge bearing for barrel arbor

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I did check this, and wasn't super happy about it. I'll try to record a video while tugging on it up and and down and you can have a look. In this case, I feel very unsure of what is acceptable as I normally never investigate this, something I should start doing.

 

  On 10/29/2021 at 6:18 PM, nickelsilver said:

Just a movement of 0.005mm on both pallet stones could easily give a 30 degree boost- but you have to know if they can be moved in

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In my eyes the pallets lock to deeply!?

Not sure the pallets can be moved in enough, but it looks like there is a bit of play (I don't have the equipment to shorten the pallets). Maybe I have a few Seitz pallets that might fit. I will have to look into it. Anyway, even a 30 degree boost would be on the shy side...

  On 10/29/2021 at 6:18 PM, nickelsilver said:

It could stand to have the bankings closed a bit, if the run to the banking is too large.

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The banking is fixed and I would assume that it can't be adjusted?

  On 10/29/2021 at 6:18 PM, nickelsilver said:

But these checks can't really be explained correctly in a post or two unfortunately.

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That's OK! Just pointing in the right direction is a great help! 

[nickelsilver]

Total lock is definitely too heavy. It could be reduced by 25% easy, and that would fix your amplitude. You could probably just move the stones in, but often it's a mix of closing the bankings a moving the stones.

[Plato]

  On 10/31/2021 at 2:09 PM, nickelsilver said:

Total lock is definitely too heavy. It could be reduced by 25% easy, and that would fix your amplitude. You could probably just move the stones in, but often it's a mix of closing the bankings a moving the stones.

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Is this a result of wear on the banking pins (mainplate) or on the fork etc.? Is the space for the pallets to be adjusted part of the original design to fix a potential low amplitude problem if it occurs?

[Nucejoe]

In case you don't have spare pallet stones, fine sand paper spread on top of glass works to file this pallet stones to size. 

I have a 3×3 meter white nylon sheet which I spread on floor to work on. 

 

[xyzzy]

It seems like you could reduce the space for the banking by putting some small pieces of tape on the plate so as to build up the thickness where the fork hits.

Not a proper repair, but would let you see what happens easily and non-destructively.