Reusing mainsprings in an automatic and slipping

[JohnL]

Hi all,

Might a posit a theory and people can chime in and tell me if I'm barking up the wrong sycamore:

If a mainspring is a bit coned and returned to its barrel for reuse, is it less likely to slip when the spring gets to fully wound? 

For a bit of background: Slava 2427, barrel walls greased with 8217, six dots evenly spaced around each of the barrel walls, then smeared/ spread along the wall before popping the springs in. 

[AndyGSi]

By coned do you mean it sits proud of the barrel before you fit the lid?

[rehajm]

1 hour ago, JohnL said:

six dots evenly spaced around each of the barrel walls

…to clarify, you placed it here, yes?

[JohnL]

Hi Andy, 

Yes, the arbor and a few coils would be a bit higher than the rest of the spring. 

I'm wondering if an alternative possibility is that there is a slight kink close to the end of the spring where the spring overlaps the end of the bridle just before the joint at the end - where the bridle and the end of the spring are joined. This was a bear to wind in/ feed in when winding the spring to put in the barrel. That was on both springs. If it was tough turn against the wall of the washer when winding to go into the barrel, it's probably going to be the same in the barrel, no?

I should probably say, the kink was in both springs, one more than the other, before I got my grubby little paws on them.

@rehajm, I placed it at six spots rather than five, but yes, around the wall evenly spaced as in your diagram. 

Edited 11 hours ago by JohnL
clarity

[AndyGSi]

You may get some extra friction on the barrel lid so may not slip as easy but I wouldn't think it's a problem.

My suggestion would be to finish the assembly and see how it runs.

[JohnL]

2 minutes ago, AndyGSi said:

My suggestion would be to finish the assembly and see how it runs.

Assembled and running well, I'm asking after the fact. I'm waiting on a new oscillating weight as this one was worn (they have a reputation for it apparently, no bearings). So I've been winding it by hand, but meeting quite a bit of resistance at the end, more than I think an automatic weight will overcome. It's not quite as sudden as a manual mechanism, but there's very little in it, certainly enough that I would be concerned about breaking something if I continued.

[AndyGSi]

If the weight was worn how does the post look as normally you'd have to replace both.

There should be no real resistance at the end and just be able to keep on winding.

Did you insert both springs the same and is the idler gear OK.

[JohnL]

Ah, well there is the rub. I ordered a post and oscillating weight, but clicked on the wrong thing when adding the weight to the basket adding an automatic bridge. Ordered a weight, and it's somewhere in the ether after our customs and excise folks rejected it because of the documentation. 

14 minutes ago, AndyGSi said:

Did you insert both springs the same and is the idler gear OK

Yes, both springs inserted the same. "Is the idler gear ok", and here's why I posted to the newbie area: So, reading between the lines, and again correct me if I'm wrong here, the automatic winding mechanism will have an ideler gear, along with the reverse wheels, that prevents over-winding? There is nothing (that I'm aware of) between the crown pinion, crown wheel, and the ratchet wheels to prevent over-winding other than the mainsprings slipping in the barrels. 

This is only the second automatic I've worked on. The other, a Vostok, had a very obvious mechanism. 

I shall look at the automatic winding mechanism in a bit more detail when I've a bit more time. At the moment I'm taking a glance here now and then when work is dragging 

As ever, thank you for your help. Always appreciated.

 

Edited 9 hours ago by JohnL
punctuation

[AndyGSi]

The idler gear I'm referring too is the one between the 2 barrel wheels.

These movements just rely on the spring slipping to prevent over winding.

[JohnL]

Ah, well that's a relief, though the parts document does list a 1520 which is a coupling clutch. This threw me for a while (it's a quiet day in the office) until I realised I couldn't see a listing for the reverser wheels.

So, we're back to the mainspring should slip in the barrel. It can really only be one of three things (that I'm aware of)

• mainspring 'coned' and pressing slightly on the lid
• the kink, close to the  end of the spring, which puts a sort of a self lock grip on the spring and may not allow the spring to release enough there to allow slipping
• quantity of lubrication, either not enough, or too little

Two of those require new mainsprings, which aren't readily available, though I may post a query about alternative mainspring sizes. The third, will more grease or less be required? The word breaking in breaking grease suggests more means more breaking?

[AndyGSi]

Does your parts list actually have the description as mine just shows the parts.

Is 1520 the gear that sits in the auto bridge to couple to the barrel.

You could try letting the power down and then remove the idler gear between the 2 barrels and see how it winds then.

I presume you're doing all this at the moment without the auto bridge in place.

[JohnL]

I've had a look at what I have and compared it to what I can see on a video of the automatic works being dismantled and I'm happy at this stage I'm not missing some part that supposed to slip that I'd overlooked. Everything links as I thought it did. 

I suspect we have similar parts lists. Just pictures of the parts with a number beside them. 1520 is, according to Best Fit, a coupling clutch. I suspect the reverser wheels are what it's labelled as 1520. The reason I'm ready to question the complete vallidity of the document is because it has a part numbered 2574 and I'll be damned if I can find that in either Ebauche or Best Fitt (the pdf copies I have anyway).  I think the wheel that connects the automatic works to the barrel should be 1482, the driving gear, it's either that or 1481 which would be the reduction wheel. Have to say: it would be really handy if they did those parts documents as an exploded diagram. 

Yup, auto bridge isn't in place yet. But weight turns reverse wheels, reverse wheel turns reduction, turns drive gear which turns ratchet. So the mainspring has to slip, and logically both have to as the inter doesn't, and if they don't the weight can't turn. 

The movement is currently in it's holder with face and hands attached so I've examined it while winding. Both ratchet wheels turn happily, the intermediate wheel/ ratchet winding wheel/ idler gear is doing its job. I'll see what happens if I take out that inter wheel and wind it a little later. 

 

[AndyGSi]

I've found with Russian watches they don't stick to the Swiss numbering system.

The problem with the mainspring is that as this is a dual barrel system they're very small compared to most automatics.

If you look on Cousins the weakest 1.45mm high spring is 0.085mm which could be too powerful for this movement and is also designed for a 7.5mm barrel.

If you then look at the GR Catalogue and work back from the GR3930X, this is the first auto with correct power rating.

Although you'd probably have to go back further to this one to make sure it fits.

 

 

[JohnL]

Andy, thank you again for all your help. You are a true gent.

I removed the winding stem in order to pop it into the case so I could play with the movement more easily while the dial and hands were still in place, but it appears the setting lever spring has sprung. So, unfortunately I need to address that before looking at anything else. 

25 minutes ago, AndyGSi said:

this is the first auto with correct power rating

If I might be so bold: I presume (given I know what everything else is) that the 3930 is the power rating? How do you know what a suitable rating is for a watch, how do you know 3591 (assuming that's the power) is correct for the Slava 2427? I just know it's 1.5 mm wide, 0.06mm thick (assuming my measurements were correct) and fits in a 7.0mm barrel. The magic art of knowing whether a thicker or less wide spring would be suitable is eluding me, the maths didn't turn out as I thought they would.

Again, thank your for all your help thus far. 

[AndyGSi]

The 3930 is just the reference from GR who make these springs and the X after signifies it's for a auto.

So from a google search.

1.45 is the height

7.0 is the size of barrel this will fit from the washer

0.075 is the thickness which is where the strength comes from

240 is the length which equate to running time

The critical part is the strength. If you fit a stronger one i.e. 0.085 then the potential is the watch would run faster, especially as these are newer materials.

Obviously the height is also significant and you can't fit a higher spring in the barrel, but going down 0.05mm won't make a difference.

[JohnL]

Excellent. Thank you. I knew the power differences in width and thickness, but I was trying to figure out an equivalent mathematically. Having it explained like that makes things much clearer.