Joining broken mainspring

[dnhb]

I want to rejoin two halves of a broken mainspring in order to be able to run a clock movement I'm cleaning - and which may require repairs to its components - to see if it will be worth purchasing a new mainspring. So it doesn't need to last longer than it's going to take to diagnose - & hopefully fix - any problems. I can think of 2 approaches: a) riveting the two pieces; & b) cutting a slot in one piece and a 'T' at the end of the other. I'd be grateful for any suggestions/comments. Doing such a repair will also be useful experience for future repairs to the ends of mainsprings which seem to be a common requirement to master.

[rjenkinsgb]

If the break is near one end, could you heat it at the broken end and let it cool slowly, to remove the tempering, then drill & file a slot to re-attach it?

It would not run as long as with a full length spring - but if it's just for diagnosis it should not matter?

 

[Nucejoe]

How long is each piece?

Which end of the longer piece is broken?

 

[dnhb]

16 minutes ago, rjenkinsgb said:

If the break is near one end, could you heat it at the broken end and let it cool slowly, to remove the tempering, then drill & file a slot to re-attach it?

It would not run as long as with a full length spring - but if it's just for diagnosis it should not matter?

 

Yes: I've done that on a pocket watch spring recently - to my surprise ! Unfortunately, RJ,  the break is right in the middle of the spring and in any case I'm just interested to see what the options are & how I get along trying exercise them....

[Nucejoe]

11 minutes ago, dnhb said:

 the break is right in the middle of the spring 

If there is an eye into which the barrel arbour hook locks. 

Heat the other end ( broken end)  to a glow, then shaping a spindle is easy, I done bend them with a pair of cheap tweezers.  

Good luck

Edited April 5 by Nucejoe

[dnhb]

1 minute ago, Nucejoe said:

How long is each piece?

Which end of the longer piece is broken?

 

I appreciate where you're coming from, N, but I'd like to try to reconnect them all the same.....

[dnhb]

I've gone with a 'T' & 'tear drop' slot approach as this provided some filing practice. My question now is: do I reheat each piece (to Straw or Red ?) & quench or just leave the material as is following the initial annealing to make it workable? (I did woodwork not metalwork at School!).

[nevenbekriev]

Leave the ends soft. Two reasons: 1. The harder they are, the easier to break again. 2. No mater how perfect You have hardened the end, next to the hardened place always lefts annealed soft part between the end and the rest of the spring. So it is not possible to achieve uniform hardness unles You harden the whole spring, which is not easy thing to do.

Then, hardening a steel needs knowlage about the steel and what is the correct regime for hardening. It is easy to damage a steel by overheating or burning the carbon in it for example.

[oldhippy]

Joining in the middle I don't recommend it. Don't you have a complete m/s you can just try it doesn't have to be the correct one. 

[nevenbekriev]

I agree, such spring doesn't behave as normal spring.  But, You can try it. It mainly depends on the type of clock and what torque is needed to keep it working. The isochronism is the thing thart will suffer the most.

[dnhb]

17 hours ago, oldhippy said:

Joining in the middle I don't recommend it. Don't you have a complete m/s you can just try it doesn't have to be the correct one. 

No: I haven't built up a store of bits & pieces yet, OH, having only begun my journey last year as I would down my consultancy business. If I can get the clock working then I'll get a new M/S. (BTW I'm still hoping to hear from you as to what you mean by "platform" in your comment on my "Charity Shop purchase" thread in which you did helpfully tell me that the clock was of the French 8-day variety).

[transporter]

Buy a new mainspring, they only cost a few quid, and if you don[t require it then you'll have started your spare inventory

[nevenbekriev]

On 4/9/2024 at 1:41 PM, dnhb said:

No: I haven't built up a store of bits & pieces yet, OH, having only begun my journey last year as I would down my consultancy business. If I can get the clock working then I'll get a new M/S. (BTW I'm still hoping to hear from you as to what you mean by "platform" in your comment on my "Charity Shop purchase" thread in which you did helpfully tell me that the clock was of the French 8-day variety).

Platform is the small separate plate with the escapement and balance on it.