free sprung vs. regulated

Feb 16, 2010,05:59 AM

Also no expert, but the basics as I understand them:


Free-sprung balances vs. regulated balances reflect two different ways of adjusting the rate (fast/slow) of the oscillating timekeeper.  Free-sprung have a fixed-length hairspring, and thus the rate is adjusted by changing the inertia of the balance itself by moving weights (screws and such) either out from the center (increasing inertia and slowing rate) or in towards the center (decreasing inertia and increasing rate).  Regulated balances have a fixed-inertia balance (mostly – more on this later) and a variable-length hairspring.  The hairspring’s effective length is changed by the regulator: as you move the index on the balance cock, a pair of curb pins slides along the hairspring: in toward the center shortens the spring and increases rate, and vice versa.


Many watches with regulators, especially these days, also have screw balances.  Sometimes these are timing screws (ie, with slots) which can be used to change the balance inertia, and sometimes these are weight screws (no slots) that serve an aesthetic purpose and to some extent to move the mass of the balance out the rim as a stabilizing factor.  On screw balance watches with a regulator, the timing screws can be used to make large changes in rate, and the regulator for fine changes.


For a free-sprung system, the main advantages are reported to be stability of rate, once properly timed (no regulator to knock about, as Steve said), and better inherent positional accuracy.  This is because the hairspring, particularly when paired with a Breguet overcoil, is free to “breathe” concentrically as it contracts and expands with balance oscillation.  This concentric breathing theoretically means than the watch’s rate changes less when put into different positions.


The main disadvantage to the free hairspring is the difficulty in regulation.  Rate is changed only by fiddling with the balance, and any non-symmetric changes will throw the balance out of poise (like a wobbly bicycle wheel).  The main disadvantage to the Breguet overcoil is its height: it adds something like 1mm to the balance assembly.


For a regulated system, the main advantages are the ease of regulation (move an index) and the fact that you never (almost) have to adjust the balance, so it stays poised.  The main disadvantage is the distorting influence of the regulator pins on the breathing of the hairspring: the breathing is asymmetric, and thus there are inherent positional rate issues arising from gravity which must be addressed for high performance.


After all that, I am entirely with SteveG: both adjustment methods can and are employed in the highest quality watches and can be and are adjusted to the highest level of timekeeping performance.


Lastly, I believe that Lange has retained the swan’s-neck regulator on its free-sprung watches not a a rate adjuster, but rather to adjust the beat (impulse from the pallet fork to the balance should be symmetric in both directions of the fork swing) by centering the fork at rest between two guide posts.




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Free-Sprung Obsession: Am I alone?

 By: brandon1 : February 15th, 2010-23:16
Friends- When my watch obsession was beginning to take hold a few years ago, I read an article which stated that free-sprung balances are more ideal than those with regulators. And while I have only a vague understanding of engineering (I am a business ma...  

Not entirely alone.

 By: mkvc : February 16th, 2010-00:28
I certainly have a preference for variable-inertia regulators, of which the most typical examples are free-sprung. However, I have a particular soft spot for the old IWC system that combined a variable inertia balance for large adjustment with a regulator... 

i have absolutely no idea what a free sprung balance is.

 By: G99 : February 16th, 2010-04:31
i probably own a watch with one, but i'm not technically minded so wouldnt know. i have several with no regulater, but i dont think that is the true explaination. someone please enlighten me. best Graham


 By: BDLJ : February 16th, 2010-04:49
Hey Graham, In a (very small) nutshell, a free-sprung balance is where the balance spring length is fixed and the adjustment is via the polar moment of inertia of the balance...hmmmm. Bit techy, sorry. From the other direction: On a balance with a regulat... 

sometimes you can have both ...

 By: donizetti : February 16th, 2010-05:02
... the Richard Lange has a free-sprung balance with a swan neck regulator I believe. Now why that would make sense (outside of esthetics) I don't know. Best Andreas

The reason for the RL swan neck...

 By: brandon1 : February 16th, 2010-06:29
as far as i know is that it adjusts the stud holder...much like the new GP Microvar setup. This is used to control the beat. Many (most?) watches that have a free-sprung balance have an adjustable stud holder of some kind. B

thanks Ben, i think i've...

 By: G99 : February 16th, 2010-05:06
thanks Ben, i think i've got it. from a money a saving point of view i like the vintage pieces to have regulaters so i can adjust them, but aesthetically i can see that a free sprung looks better and probably is of higher quality. cheers G

I am not an expert, but I believe this falls into

 By: SteveG : February 16th, 2010-05:06
one of those instances where while one solution (free-sprung) offers at least a theoretical advantage (a more perfectly-formed hairspring, no regulator to get knocked out of position), in most practice there is a huge overlap with the performance of other... 

free sprung vs. regulated

 By: tee530 : February 16th, 2010-05:59
Also no expert, but the basics as I understand them: Free-sprung balances vs. regulated balances reflect two different ways of adjusting the rate (fast/slow) of the oscillating timekeeper. Free-sprung have a fixed-length hairspring, and thus the rate is a... 

I wish I was a non-expert like you....

 By: JMan : February 19th, 2010-17:12
Tom: That quite comprehensive. Thanks. J.

I don't know about the theory...

 By: SteveW : February 16th, 2010-08:33
... but I find the ones with free sprung balances tend to run very regularly. They seem more immune to positional errors. The manufacturers I have had experience with are Rolex, Patek Philippe and Audemars Piguet. On the other hand a few carefully built w... 

I think for me its about philosophy and emotion...

 By: brandon1 : February 16th, 2010-09:21
Rather than actual rate results or real world stability. I am fully aware that many fine watches with regulators keep time just as well as their freely sprung brethren, but I like the "idea" of stability that a free sprung balance conveys, and for me (pro... 

Not always high end

 By: nickd : February 16th, 2010-10:33
Elgin produced the Durabalnce free sprung balance, though I don't know if it was ever used in production. FHF produced a free sprung production movement the FHF 72 . You see it from time to time on ebay in various watches around the $150 mar... 

That's a good point...

 By: brandon1 : February 16th, 2010-10:48
That's a good point, I don't have any experience with watches/movements in segments that low, and thus they don't really enter into my thought equation. Obviously, the execution is a major factor. B


 By: eterna-fan : February 16th, 2010-11:49
elgin produced tens of thousands of durabalance grade watches. the finishing was spartan, at best, but the movements were excellent time-keepers. i believe the free-sprung caliber 730a was the first wristwatch approved for US railway service. they were no... 

I did not mean to imply the Elgin mov't was low end...

 By: brandon1 : February 16th, 2010-11:59
I was referring to the "$150 ebay" watches when I made the low end comment. Sorry for the confusion! B

The movement Nick cited has a regulator of sorts

 By: brandon1 : February 16th, 2010-11:54
After careful inspection of the movement in the link posted by Nickd, it seems that the rate can still be adjusted with the "cylinder" because the text states that this adjusts the length of the spring, which is what a regulator does. However, I don't kno... 


 By: nickd : February 16th, 2010-13:18
The index pins of a watch with a regulator don't grip the spring perfectly tightly, otherwise you'd have to slacken them to adjust the regulator. Classic theory says the balance is isochronous due, in part, to this gap. As the balance spring oscillates it... 

I think you're talking about this system (pics)

 By: ei8htohms : February 19th, 2010-19:14
g This one was in a Mido (if I recall correctly) and the system was identified in some reference book or another as "Incastar". And it's a terrible idea by the way. You can't regulate it without not only putting it out of beat, but also effectively "peeni...  

Elgin Durabalance

 By: aaronm : February 16th, 2010-16:36
In its freesprung form made it into production in the 760 automatic movement. I know I've seen some other dials marked with the 'db' but some of the durabalances were not free-sprung. A

There's something about those little screws...

 By: pplater : February 16th, 2010-17:47's kinda like needing to see a carbie or three in the engine bay of a classic sportscar. Cheers, pplater.

Well said!

 By: brandon1 : February 16th, 2010-18:27
YES! Those are my sentiments...very well said! B

Technical Ture vs Aesthetic Right

 By: Ogygia : February 16th, 2010-22:18
Most of the designs of watches are a gimmick nowaday. They are for perfectionists! Free sprung is a solution for dislocation of hair spring, regulator and index which is caused by shock. But the problem is past. Now we can weld the hair spring end with la... 

Another great technical discussion

 By: Bill : February 23rd, 2014-11:55
Over my head by fun to observe. Bill

This is a great thread which is worth a revisit... thanks!

 By: Brandon Skinner : July 14th, 2020-22:46
-from a fellow Brandon