mainspring not catching arbor

[PostwarO27]

Im doing a teardown of simple HMS movement to get to the mainspring that was broken.  Before putting the barrel assembly back together I like to test the fit of the spring around the barrel to make sure it catches.  However, sometimes after winding a mainspring in a winder the initial coil with the hole in it no longer conforms to the barrel arbor and the tab will no longer engage with the spring when wound.

Whats the best method to eliminate the spring from getting misshaped and the best method to getting the notch in the spring to line up with the tab on the arbor if and when the spring becomes misshaped?

Thanks

George

[mikepilk]

Ideally you have the correct size winders, with the winder arbor smalll enough for the mainspring.

This isn't always possible - I only have a small set of winders. You have to improvise. The winder I use most is the 10.5 mm but the arbor is often too big for the inner coil of the spring. I use a bit of brass tube in the winder body, so that I can use the arbor from one of the smaller winders.  

If the spring does get distorted, use some round nose pliers to gently reduce the diameter of the inner coil. Once in the barrel, it's hard to do without scratching the barrel. DO NOT just squeeze the outside of the inner coil - it will kink and wreck the spring. Put something inside the inner coil to stop it bending too far.

Edited January 23, 2022 by mikepilk

[PostwarO27]

Mike,
Yes....ideally I would like to have winders with a wider range of arbor sizes.  But, this is all I have and the arbor sizes range from 2.3mm to 4.7 mm.  I've seen countless vids on YouTube of mainsprings being put back in the barrels and every single time the arbor snaps right into place and grabs the spring.  I know those vids are edited but you would think at least one would cover what to do when the arbor coil gets distorted.

I've done the needle nose pliers and yes have scratched a barrel or two AND tried squeezing the outside of the inner coil around the arbor which ended up with the arbor disappearing into the void of space never to be seen again as well as kinking the spring.

I did have success on one occasion of bending the very tip of the spring around the arbor not by squeezing the coil but by pushing the spring at the very end, just in front of the slot.  I did this by placing the arbor in the barrel with the end of the arbor in a hole of a staking block and holding it in position with a piece of plastic pushed down into the threaded end of the arbor.  Taking a small pin punch and pushing perpendicular to the arbor axis (or as close to perp as the barrel wall will allow) until it hits the arbor.  Mind you, the notch on the arbor and the hole of the spring need to be lined up to do it this way and any slip will result in a barrel hole that looks like a football.

Alas, I'm going to be forced into getting the proper tools and buying a full set of winders but the toolmaker in me.

 

George
 

[mikepilk]

The 2.3mm arbor should be small enough for most springs. That's about the size of my smallest arbor. Though I had an Eterna which was smaller than that. I broke 2 springs before I could get the inner coil bent correctly.

Don't worry too much about lining up the hole in the spring with the arbor. As long as the inner coil is small enough, use some strong tweezers to push the arbor in, start it at an angle, then just twist it until it the hole catches on the arbor.