Procedures for mainspring cutdown

[bacgoff57]

Hello All
Can anyone give me a complete procedure to cut down a mainspring that is too long?
Thanks Ben

[Bob Tascione]

Hi Ben,

Repairing or shortening a hole end mainspring is a fairly easy, rewarding and often necessary job.

As stated in your previous post you just want to shorten a new spring to about 64″ so if the the spring you purchased is say 96″ you could cut off 22″ from the new spring using a tin snips. If you make the cut with roughly the same curve (shape) as the original you save yourself a little filing time. Next you’ll need to anneal (soften) the end of the spring back about 1 1/2″ to 3″. To do this you can use a hand held propane torch. Bring the end of the spring to a cherry red color and then begin “slowly” moving the spring away from the flame taking about 30 to 40 seconds to clear out of range…about 6 inches or so. Then let the spring air cool for a few minutes. The cherry red color and slow cooling is critical. If not done correctly the metal will not soften enough to punch a new hole into it. If it doesn’t work the first time there’s no harm done, just do it again until it’s soft enough. You can test the hardness by running a small file on the spring end. If it “cuts” then you’re probably where you need to be. You can now shape the end with a file to match the original end. At this point you can use the original end with the hole in it as a template. Place and line up the cut piece on top of the spring, then place them on a piece of wood and with a pointed metal punch and hammer punch a hole through the spring in the appropriate place. Again use a file and follow the template to get the exact hole shape needed. Sand and or stone off all sharp edges and burrs. I rarely harden the end after this as there is no real springing taking place at the end of the spring. I know that some people do heat treat and then temper the ends when done so it’s your call here but this technique has worked well for me countless times.

Hope this helps Ben,
It’s a fun job so Enjoy!

Bob

[samspade]

Good question excellent answer and information. Perhaps we should have this as a sticky in a ‘How to……..section?

Regards.
Scott.

[Bob Tascione]

Great suggestion Scott…I’ll add this topic to the new material that’s to be added to the course soon.

Thanks!
Bob

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