Alloy vs Steel

[LiamB]

This may seem like a stupid question, but are there strength differences between an alloy and steel mainspring of the same dimensions? 

I have to replace mainsprings in two pocket watches (18s Waltham and 18s Illinois) and I am concerned that fitting a modern mainspring will result in knocking. 

Any advice, 

Thanks

Edited December 4, 2018 by LiamB

[nickelsilver]

The general thinking is that modern alloy springs are stronger for the same dimensions. Usually it's not an issue, especially in older watches that may need a little boost anyway. There are also two alloys offered by Generale Ressorts (the primary maker of mainsprings), one they just refer to as "stainless" and the other is Nivaflex. The Nivaflex is definitely a little stronger. In an old 18s watch the little extra power would probably be welcome.

On knocking (rebanking) in older American pieces- the American companies tended to flatten the ends of the balance pivots which reduced the amplitude in horizontal positions, bringing vert- horizontal closer. Replacements staffs from Switzerland would have rounded pivots, which if combined with a modern spring did present a good chance of rebanking. Though, the escapements on these old pieces have usually been "adjusted" so poorly that it cancels out.

[oldhippy]

There are a number of reasons why a watch is knocking, one that can cause it is the mainspring is too strong.

[praezis]

There is little danger to get a Nivaflex spring, as their price is a multiple of the stainless ones, so wholesalers will order the cheaper springs.

Frank

[rodabod]

I've suffered knocking when using modern a modern white spring of matching dimesnions to replace a blue steel spring in an Omega Cal 350. Just be aware that there can bve differences, and to check the amplitude.