Waltham mainspring - Factory vs. generic

[Wesley881]

Hi folks,

I measured up the mainspring in a Waltham model 1894 12s and came up with (in mm)  2.10 x 0.14 x 490 or so mm, hole end, with 15.5 barrel ID.  For a few dollars at Cousins, I can get a 2.10 x 0.15 x 480, 15.0 ID, TR end.

Otto Frei has a factory mainspring for this watch that they are saying is 2.15 x 0.16 x 19 1/4 in (488mm) with end hole, for about 4 times the cost.

One thing I'm sure of is that I might need a better quality set of calipers . With the variability in sectional area between the springs, can I expect significant differences in power delivery, or negligible?  Thoughts?

[StuartBaker104]

Everything you need to know (and some things you don't) is here.

http://www.vintagewatchstraps.com/blogmainsprings.php

In practice, any of those springs should work fine.

 

[Wesley881]

StuartBaker104, this is a great read and is definitely dusting off some old engineering concepts that I haven't played with in quite a while!  What an excellent site, thank you very much indeed.

C