Slava alarmclock mainspring broken

[orbanp]

Hello Everyone,

I am new here and new to watch/clock repair.
If I am posting in the wrong forum or my posting is not appropriate in some form or shape please advice me.
Looking at a number of watch repair videos they advice you start with repairing a pocket watch, because of its size.
The Slava alarm clock was called an "overgrown" pocket watch as it has a Swiss escape mechanism.
I felt this would be a good place to start repairing watches.
Here is a good description and of servicing such a Slava alarm clock:

The clock is a 11-jewel alarm clock, made in the USSR for decades, and it has a broken mainspring.
The clock is from the '70s, it is a "newer" version, it already has the plastic alarm-spring barrel.
It belonged to my mother in law, I would like to repair it. It probably would not be that hard to find a replacement spring in Russia...
The spring is 2.9 x 0.2 x 611 mm, the barrel inside diameter is 20.8 mm.
The outside of the spring has a "T", spot welded to the main spring, the inside has a hole. The inner 80 mm or so part is broken off.
Failing to find a replacement spring I wonder if I can make a new inner ending for that broken spring. The broken 80 mm is about 13% of the total length of the spring.
One solution would be to grind a hole to the end of that spring with a Dremel tool. I would also need to "tighten up" the inside of the spring so it would catch with the arbor. I wonder if the tightening would lead to eventual spring breakage.
The other solution would be to anneal the inside of the spring and then make the hole and tighten the radius.
Any of these ideas viable? On the other hand I could not loose much by "ruining" this broken spring.
I took out the main spring and did reassemble the clock to get some understanding how hard is it and if I would be able to do it.
The cover of the main spring barrel would not snap back, like I could see it on the repair videos. There is probably some burr, or these are the "normal" tolerances of Soviet manufacture.
I did manage to put back the main bridge, it covered three jeweled wheel axes and the main spring barrel. It took about 15 minutes and two trials.
The rest of the watch definitely needs a cleaning and I need to demagnetize the tools that I used.
Here is a picture of the broken spring:

Thanks, Peter

[orbanp]

Hello,

Looks like the link and the picture did not get through.

Here is the link: https://soviet-box.com/post/vintage-slava-11-jewels-alarm-clock/

and here is the picture:

I am learning

Peter

[RichardHarris123]

Hello and welcome from Leeds, England.  The closest I could find is below, ideally the strength would be the same or slightly lower than the original.  

[AndyGSi]

Welcome to the forum.

Looking at the GR Catalogue you'll be looking for a spring in this range.

Depending where in the world you are there are a few 47301 & 47333 for sale on eBay.

[HectorLooi]

I think @nevenbekriev would be the best person to answer this question.

[nevenbekriev]

The mainspring repair is with more or less unpredictable result. Many times the result is good and long lasting, but often the spring breaks again with the first attempt for winding. Sometimes it will break after month or week. For sure, annealing of relatively long part when the internal end is broken is needed and annealing in many cases means heating to red and slowly retracting from the flame as just leaving the spring to cool in air may harden it again. Often people think that after shaping the internal end they must harden the spring. This is useless, wrong and it is impossible to harden the annealed part without leaving soft area between the rest of the spring and it.

My experience with Slava springs is not gathered with many cases, may be 2 or 3 and very long time ago. This clocks were produced long time and many changes of technology and materials were made, so can't make general conclusions. Parts for such clocks we have plenty here. But yes, I have tried (with old springs, made in 60-70s, brown temper color like the one on the picture) and came to the conclusion that this springs are wicked and it is bad idea to repair them. Possibly bad luck, but was not able to wind to the end without new breaking happening.

[AndyGSi]

1 hour ago, nevenbekriev said:

The mainspring repair is with more or less unpredictable result. Many times the result is good and long lasting, but often the spring breaks again with the first attempt for winding. Sometimes it will break after month or week. For sure, annealing of relatively long part when the internal end is broken is needed and annealing in many cases means heating to red and slowly retracting from the flame as just leaving the spring to cool in air may harden it again. Often people think that after shaping the internal end they must harden the spring. This is useless, wrong and it is impossible to harden the annealed part without leaving soft area between the rest of the spring and it.

My experience with Slava springs is not gathered with many cases, may be 2 or 3 and very long time ago. This clocks were produced long time and many changes of technology and materials were made, so can't make general conclusions. Parts for such clocks we have plenty here. But yes, I have tried (with old springs, made in 60-70s, brown temper color like the one on the picture) and came to the conclusion that this springs are wicked and it is bad idea to repair them. Possibly bad luck, but was not able to wind to the end without new breaking happening.

Do you have any details showing what the correct mainspring should be for this 5671 movement?

[nevenbekriev]

I have never seen published manufacturer data about the sizes of soviet watches and clocks main springs. OP has the spring measured. I can try to measure one later too.

[orbanp]

Many thanks for the replies and for the help!

I guess I will be looking for a donor movement as well.

I did try to repair that broken main spring. I did manage to make the hole with a Dremel tool but the end snapped off as soon as I tried to tighten up the radius. I did not anneal the end of the spring though. 

I am not surprised that the spring broke, it is quite brittle.

I enclose a picture of the broken off end with the new hole.

Peter

[AndyGSi]

I'd just get one of the Illinois springs.