The gear train of a watch… (more)
Forum: TimeZone – Advanced Forum
Re: What Does ‘Jeweled To The Center” vs ‘Jeweled To the Third” Mean? (NT) (Michael Friedberg)
Date: Fri, 28 Nov 1997 21:20:54 GMT
From: Walt Odets
The standard gear train of a watch follows the power flow from the mainspring to the balance. Through gear ratios (wheel to pinion to wheel to pinion, etc.) this train converts the slow torque of the mainspring into increasingly faster, lower torque, movement:
- The main spring barrel, which revolves approximately 0.15 turns per hour (depending on spring length, etc.).
- Center wheel, which revolves exactly once per hour (and thus drives the minute hand of the watch).
- The third wheel, which revolves approximately twice per hour.
- The fourth wheel, which revolves exactly 60 time per hour (i.e., once per minute, and thus drives the seconds hand of the watch).
- The escape wheel, revolving approximately 1,200 to 2,400 times per hour (15 tooth wheel, balance at 18000 to 36,000 BPH).
- The “anchor” or pallet fork, which engages and releases the escape wheel, pivoting back and forth 18,000 to 36,000 times per hour.
- The balance wheel, which engages and releases the pallet fork, making a complete swing 9000 to 18,000 times per hour (18,000 to 36,000 half swings per hour).
Starting from the balance wheel and moving backwards in the train, each component is moving more slowly. Because faster movement means more wear, jeweling “starts” at the balance (which is almost always jeweled except in extremely cheap watches) and moves backward in the train.
“Jewelled to the third” means: the balance, anchor fork, escape wheel, fourth wheel, and third wheel are jewelled (usually 15 jewels in a hand wound movement).
“Jewelled to the center” means: the center wheel is also jewelled. This is common in high quality watches (usually 17 or 18 jewel hand wound movement).
“Jewelled to the barrel” means: the barrel is also jewelled. This is unusual because the very slow speed of the barrel doesn’t really warrant such a hard bearing.
Some of the variations in jewelling include extra “cap” jewels, in which each end of the shaft is supported in two jewels: one with a hole through which the shaft runs, the other against which the very tip of the shaft rests (this reduces friction because there is actually less contact between shaft and jewel than with single jewels). Thus some hand wind movements have 19 jewels (the extra two being cap jewels on the escape wheel) or 21 jewels (cap jewels on the pallet form). The balance always has cap jewels in high quality watches, and the escape wheel very often does (e.g. all JLC, Patek, etc.) Cap jewels on the escape wheel are very often described as “escape wheel with combined jewel housings.” Sometimes the escape wheel with cap jewels is shock protected like the balance wheel.
1. Thanks, Walt…and one for the archive, Richard? (NT) by Michael Friedberg, 11/29/97