**** What makes a fusee movement a fusee movement ****

[is that my watch]

Richard Shrivell, Brighton - Verge fusee pocket watch -. 1800

Well was looking at pocket watches and seller's and feedback and one caught my eye telling the seller off for calling a pocket watch a fusee when it was not their was a link to the sale and from my limited experience it looks like a fusee to me they called it a spring driver and I thought in this instance aren't they all as they have a main spring but also the fusee which controls the torque constant or am I mistaken ?

So was looking at a few threads, links, and sites and this seem to best explain it to me and hopefully to you of how at least the fusee worked and why with time it became obsolete.

The mainspring is coiled around a stationary axle (arbor), inside a cylindrical box, the barrel. The force of the spring turns the barrel. In a fusee clock, the barrel turns the fusee by pulling on the chain, and the fusee turns the clock's gears.



When the mainspring is wound up (Fig. 1), all the chain is wrapped around the fusee from bottom to top, and the end going to the barrel comes off the narrow top end of the fusee. So the strong pull of the wound up mainspring is applied to the small end of the fusee, and the torque on the fusee is reduced by the small lever arm of the fusee radius.
As the clock runs, the chain is unwound from the fusee from top to bottom and wound on the barrel.
As the mainspring runs down (Fig. 2), more of the chain is wrapped on the barrel, and the chain going to the barrel comes off the wide bottom grooves of the fusee. Now the weaker pull of the mainspring is applied to the larger radius of the bottom of the fusee. The greater turning moment provided by the larger radius at the fusee compensates for the weaker force of the spring, keeping the drive torque constant.
To wind the clock up again, a key is fitted to the protruding squared off axle (winding arbor) of the fusee and the fusee is turned. The pull of the fusee unwinds the chain off the barrel and back onto the fusee, turning the barrel and winding the mainspring. The presence of the fusee means that the force required to wind up the mainspring is constant; it does not increase as the mainspring tightens.
The gear on the fusee drives the movement's wheel train, usually the centre wheel. There is a ratchet between the fusee and its gear (not visible, inside the fusee) which prevents the fusee from turning the clock's wheel train backwards while it is being wound up. In quality watches and many later fusee movements there is also a maintaining power spring, to provide temporary force to keep the movement going while it is being wound. This type is called a going fusee. It is usually a planetary gear mechanism (epicyclic gearing) in the base of the fusee "cone") which then provides turning power in the opposite direction to the 'winding up' direction therefore keeping the watch or clock running during winding.

Most fusee clocks include a 'winding stop' mechanism to prevent the mainspring and fusee from being wound up too far, possibly breaking the chain. As it is wound, the fusee chain rises toward the top of the fusee. When it reaches the top, it presses against a lever, which moves a metal blade into the path of a projection sticking out from the edge of the fusee. As the fusee turns, the projection catches on the blade, preventing further winding.

The fusee was a good mainspring compensator, but it was also expensive, difficult to adjust, and had other disadvantages:

It was bulky and tall, and made pocket watches unfashionably thick.
If the mainspring broke and had to be replaced, a frequent occurrence with early mainsprings, the fusee had to be readjusted to the new spring.
If the fusee chain broke, the force of the mainspring sent the end whipping about the inside of the clock, causing damage.
Achieving isochrony was recognised as a serious problem throughout the 500-year history of spring-driven clocks. Many parts were gradually improved to increase isochronism, and eventually the fusee became unnecessary in most timepieces.

The beginning:

The origin of the fusee is not known. Many sources erroneously credit clockmaker Jacob Zech of Prague with inventing it around 1525, The earliest definitely dated fusee clock was made by Zech in 1525, but the fusee actually appeared earlier, with the first spring driven clocks in the 15th century. The idea probably did not originate with clockmakers, since the earliest known example is in a crossbow windlass shown in a 1405 military manuscript. Drawings from the 15th century by Filippo Brunelleschi and Leonardo da Vinci show fusees. The earliest existing clock with a fusee, also the earliest spring-powered clock, is the Burgunderuhr (Burgundy clock), a chamber clock whose iconography suggests that it was made for Phillipe the Good, Duke of Burgundy about 1430, now in the Germanisches National museum The word fusee comes from the French fusée and late Latin fusata, 'spindle full of thread'.

Again just a collator of this thread as some bits come from various sources and I have just gather them for my needs

As always Ismy