Clock Mainspring Repair

[rauman]

Okay, I’ve had a class that included repairing the end of a hole-end mainspring when it breaks and done it successfully on practice springs, but, believe it or not, this is the first time I’ve had to actually make the repair on a clock I was servicing for someone. I’ve cut off the end, punched and filed out a new hole twice on this spring and it has snapped both times. I suspect my problem is in the hardening of the area around the new hole.
1) I annealed the end first, then when the repair was done I hardened it again.
2) the first time I heated the end (to cherry red) from the spring end to the bottom of the new hole. The second time I only heated from the end of the spring to the start of the hole. In the first case the spring snapped and the end (below the hole) when I had the spring pulled out to clean it. In the second case I was putting it in the barrel and it looks like it broke on the barrel hook and came lose when i was tightening it up to remove the barrel ring.

I’ve decided either the spring is bad – I’ve never seen this before – or I’m just not hardening the end of the spring correctly.

Can one of you experts help me out here?

[bernie weishapl]

When I repair the end of a hole in mainspring I heat about 2 or 2 1/2 inches of the end. I use a tin snip to cut the end slightly rounded while cutting off the damaged end. I use my power punch to punch the hole and the file to shape if needed and file any burrs off. i do not re-harden the end as it is a wasted step IMHO. I think if you look at new mainsprings the ends are not hardened. Been doing this for over 30 yrs and no problems with springs breaking.

[willofiam]

Hey guys, to add to Bernies response…slowly take the heat away and let it air cool slowly. If you cool it too fast it will harden. I have also had a few recently that needed a new end made, must be that time of year. 🙄 William

[willofiam]

maybe you know this but for some reason I want to mention that after working on your mainspring and making the new hole end, remove any burrs and smooth out any tool marks on the surface and the hole…a small scar and it can possibly start a tear there. Hope that makes sense. William

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