Chapter 2 The Going Train

First, let's talk about the entire system, the going train. In a clock, the large gears are called wheels. The wheels engage small gears called pinions, and a group of gears and pinions that interact with each other to accomplish a specific function, like telling time, is called a train. The going train is the time train of our clock. It's called the going train because this part of a clock must operate or go continuously if the clock is to accurately keep time. Clocks may have more than one train. Many clocks have a strike train, or both a strike and a chime train, as well as the going train. No matter how many wheel trains a clock may have, they're all dependent on the going train. Our movement is a time-only movement, so it has only one train, the going train. The complete train is made up of five major building blocks, the power source, the escapement, the timing source, the wheel train, and the motion works. Here we're looking at the front of the clock movement. The square winding arbor is facing forward, as is the center arbor where the hands of the clock are attached. Associated with the center arbor is a special set of wheels and pinions called the motion works. The gears curving around the center arbor to the right make up the wheel train. The clock movement is held together by these two flat pieces of brass called plates. A clock movement must have at least two plates, but they can have more. Our time-only movement has two plates, a front plate and a back plate. The plates here are held together by these posts or pillars. These pillars are riveted to this plate. Often the pillars are riveted to one plate, with threaded nuts or taper pins holding the other plate in place, so at least one plate can be removed to service the movement. Between the plates are the gears and other parts that make up a movement. This is an arbor. Arbors support things that rotate, like pinions and wheels. This short section, with a smaller diameter, is a pivot. It slips into this bushing hole here, and together they make up a low-friction bearing that allows the arbor to rotate freely between the plates. This is a wheel in clock speak. It's usually made of brass. Generally, wheels have 20 or more teeth. This is a cut pinion, usually made of steel. These teeth are called leaves in clock speak. Pinions usually have fewer than 20 leaves. Cut pinions are difficult to repair. If damaged or worn, they usually have to be replaced. This is a lantern pinion. These are common in most American kitchen and mantel clocks. Notice the hardened steel wires taking the place of the leaves. Lantern pinions are inexpensive to make, and they have less friction than a cut pinion of the same number of leaves. An eight-wire lantern pinion is equal to a 10-leaf cut pinion. They're easy to repair, too. Just replace the wires. The two different metals used in clocks is not by accident. Parts that move against one another have significantly less friction if they're made of different metals. Most often you'll find cycloidal gearing in antique clocks. Cycloidal refers to the shape of the wheel and pinion teeth. This is a cycloidal tooth profile. Notice the almost vertical sides, and the tops look somewhat like a gothic arch. Your thumb is the general shape of a cycloidal gear tooth. This profile only works well when large gears drive small pinions to increase speed, where overall power transfer is very low, and there's lots of backlash or looseness between the wheels and pinions, the exact conditions we find in a clock. This is an involute tooth profile. Notice the sloping sides and the squared-off top. This is the profile used in most modern machinery today. In clocks, you'll often find involute gears in the motion works, where a smaller pinion drives a larger gear, and rotational speed is reduced rather than increased. We'll discuss this more in detail when we get to the motion works.