Component record · Regulation
Balance Screws (Timing Screws)
VerifiedSmall screws set into the rim of a balance wheel, used historically to adjust the balance's effective mass distribution (poise and timing) and, in compensation balances, temperature response.
What it does
Allow fine adjustment of the balance's moment of inertia and static balance (poise) by removing, adding, or repositioning mass at the rim.
How it works
A screwed balance carries numerous small timing screws around its rim rather than a plain, solid edge; selectively lightening a screw (by filing its head) or repositioning screws alters the balance's effective inertia and hence its rate.
In bimetallic compensation balances, some rim screws (sometimes called compensation or mean-time screws) are positioned near the free ends of the bimetallic arms specifically to fine-tune the balance's response to temperature change, distinct from ordinary timing screws used for basic rate and poise adjustment.
Poising a balance — ensuring no heavy point causes it to settle preferentially in one orientation — is done by selectively adjusting screw mass around the rim so the balance is in static equilibrium in every position.
Evolution
Screwed balances with compensation screws were central to 19th- and early-20th-century precision watchmaking; modern balances more often use uncut, monometallic alloys (such as Glucydur) with weighted timing screws purely for poise and rate rather than temperature compensation, since modern alloys already resist temperature-driven rate changes.
Known variations
- Plain timing/poising screws
- Bimetallic-balance compensation screws for temperature adjustment
- Free-sprung balances using screws or eccentric weights instead of a curb-pin index for rate adjustment
Identification for collectors
- Small screw heads visible around the balance rim distinguish a screwed balance from a plain annular or solid balance
Common failure modes
- Loose screws altering poise or, in the worst case, working free and jamming the escapement
- Corrosion or damage to screw slots complicating adjustment
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- Daniels, G., Watchmaking
- de Carle, D., Watch and Clock Encyclopedia
Where sources disagree, the disagreement is stated rather than resolved silently.