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Watch Mainspring Barrels

Ever since clockmakers figured out that you could use a spring to drive a clock, and later a watch, they have been trying to figure out the best way to do it. They have come up with several methods, none are wholly satisfactory.

Plain Barrel
Elgin Database Mainspring Barrel Code:   None, Elgin didn't use this.

The easiest solution is to take a post, fasten one end of the spring to the post, and fasten the other end of the spring to a barrel with a gear attached to it. To wind up the spring, you turn the barrel/gear one way, and the spring tightens up around the center post. When the clock or watch runs, the gear slowly turns the other way.

One problem with this solution is that while the clock or watch is being wound, there is no maintaining power to keep the gears turning. Thus, you lose time every time you wind the timepiece.

Another problem is that when the spring is fully wound, it pushes the gears much harder than when it is wound down.

A third problem is that when the spring breaks, and any watch made before around 1960 you can count on breaking, the spring will whip around and slam against the outside of the barrel, turning the barrel in the opposite direction that would normally go. This is exactly like what happens when you pull a rubber rubber band apart and let go of one end. The other end receives a nasty snap. This snap can damage gear teeth, break jewels and cause a great deal of other damage.

While there were probably watches made using this kind of plain barrel, they were probably all made before 1850 when the Americans started making watches.

Barrel and Fusee
Elgin Database Mainspring Barrel Code:   None, Elgin didn't use this.

To solve some of the problems of the plain barrel, watchmakers invented a somewhat conical shaped device called a "fusee".

The spring barrel was attached to the fusee via a tiny chain, or in earlier times, cat gut. When the spring was fully wound, most of the chain was wound around the fusee all the way up to the narrow end of the cone. As the watch runs, the chain unwinds down the fusee to the wide end of the cone and wraps around the spring barrel. This means that the lever arm of chain pulling the fusee is weakest (shortest) when the watch is fully wound and strongest (longest) when the watch is unwound.

By carefully crafting the shape of this cone like device, the spring can be made to deliver almost a constant force to the gear train.

Another advantage of the fusee is that when the spring breaks, the barrel may whip around, but since you can't push a chain, this watch is much less likely to be hurt.

The Barrel and Fusee system still has the problem of not having any maintaining power while the watch was being wound. Some watches that used a fusee solved this problem with some extra springs and ratchets and gears.

While the fusee solved some problems, it created others. First the fusee took up a great deal of space in the watch, and required the watch to be quite thick. Secondly, the fusee and the fusee chain are very hard to make and greatly increase the cost of the watch. This is especially true if you add in all the extra springs and stuff needed for the maintaining power.

The Barrel and Fusee system was heavily used by the English in their watches up until the 1890's, and were used in marine chronometers through WWII.

Going Barrel
Elgin Database Mainspring Barrel Code:   gb

Another technique to solve some of the problems with the plain barrel is to turn the center post into an axle, or in watch terms, an arbor. You can then turn the axle (arbor) to wind the watch, and as the watch unwinds, the outside barrel will turn. This means that there is always tension on the spring so the "gears keep going".

There are a couple of techniques can be used to solve the problem with unequal power. These are discussed in the isochronic adjustments section of the adjustments web page.

The problem with the damage caused by a broken mainspring can be solved by using a "safety pinion". The gear that is driven by the spring barrel is screwed onto the axle (arbor). When the spring is wound up and trying to turn the gear in the right direction, it just screws the gear on tighter. If the mainspring breaks and the gear gets turned the other way, it unscrews and disconnects that rest of the gear train from the spring. The barrel just twirls for a while and stops.

The going barrel was used in most American and Swiss watches since the 1850's.

Motor Barrel
Elgin Database Mainspring Barrel Code:   mb

Another technique is to reverse the connections that the going barrel uses. Instead of winding with the axle (arbor) and driving the train with the barrel, you can wind the barrel and drive the train with arbor. Then, when the spring breaks, all the damage is done to the winding gears, which can easily be made strong enough to handle the force. The result is called a motor barrel or a safety barrel.

You still have the problems with unequal forces, but you solve them the same way as with the going barrel.

The motor barrel required significantly more parts, mostly plates and screws, than a going barrel. It has the advantage that since the power comes off the center arbor, the barrel only has to slide on its bushings when it is being wound. This means that a weaker, less breakable mainspring can be used to transmit the same amount of power to the gear train.

Elgin started using the motor barrel on some watches, mostly the higher grade ones, starting in the late 1890's. I believe several other companies had been using the motor barrel for years by that time.

You can tell if an Elgin watch has a motor barrel by the three small screws on the mainspring wheel.

Jeweled Motor Barrel
Elgin Database Mainspring Barrel Code:   jb

Since the mainspring arbor of a motor barrel is just like all the other arbors in the watch, it too can be jeweled in order to reduce friction. While these jewels doesn't provide that much of a real benefit, they are "functional jewels" and they can be used to increase the jewel count of a watch. As explained in the Watch Jewel web page, many people will think a watch is better just because it has more jewels.

While I'm not an expert, I believe the information on this page is correct. Please send suggestions and corrections to the webmaster.
This web site runs on 100% Open Source Software. This web page was last changed on 10/04/2002 at 00:42:26.