Hamilton 917 hairspring terminal curve?

[Dawagner]

Hey WRT,

Ive got a Hamilton 917 movement I am working on to get better at my hairspring techniques.  I was wondering if anyone had a link to a good copy of the terminal curve diagrams and knew what terminal curve these movements are supposed to have?  Pretty much the terminal curve is the only thing messed up on this piece and would like to try and fix it instead of replacing it.  Thanks!

[praezis]

Hi,

the curve is determined by the ratio "distance of the regulator pins from center" to radius of the hairspring. Multiplied by 100 gives the curve number (eg 75) that you can look up in tables. If still needed, I can post one next week. 

Frank

[Dawagner]

Perfect thank you, yes the table would be much appreciated!

[Orville]

Amazing answer by praezis above.  I never knew.  When I was super focused on hairspring manipulation as a learning module, I could figure out the termination by the sweep of the regulator and get it right most of the time. The important thing is that if it's not dead on, it's dead off.  Maintaining the coil of the spring is another key.  Distorted hairsprings don't work and I have a boxfull of them to prove it.  

[praezis]

I supposed in my reply that with terminal curve you mean a Breguet terminal curve.

Frank

[praezis]

Just found one in an older post of mine.

There were different authors of overcoil diagrams with different design, but they all match the theoretical rules.
These are from Helwig, Glashutte.
You must size the picture so that the diameters match your vibrated hairspring. Length of the overcoil (from knee to regulator pins) is about 180° of outer coil.

Regards,

Frank

[Dawagner]

Perfect thank you sir, yes I am taking about a breguet overcoil.

Any tips you have for redoing one? The spring was fairly mangled and there was no good way to save what bends were in it so I have made it back to flat and concentric in preparation of redoing the terminal curve overcoil.

Thanks again!

[praezis]

Hi,
Making an overcoil is one of the most challenging tasks in watchmaking.
I recommend finding a book that discusses this topic. Surely other members can help, as I know mainly German literature. 

Essential for bending are special curve tweezers with )) tips. New ones are no more made today, you can find them used or make your own. 

Frank