How the full power system works

The animation includes a horse mill to provide the power, a belt and pulley system to transfer and distribute that power, and then shorter shafts carrying their own belts and pulleys to control the power as it is provided to each individual machine. The animation only shows a lathe, but there would also have been saws of various kinds, sanders, planers and grinders. Each of these would have required their own clutch and speed control. Let us walk through the power system in more detail, following the steps shown in the animation:

The horse mill shown is what we imagine it to have been like, from what limited evidence we have. One or two horses would be brought in for the day to walk around a circle about 16 to 20’ in diameter, pulling “sweeps” attached to some kind of structure which would support the turning of a large horizontal wheel, perhaps 8’ in diameter, and high enough to be above the horses heads. There is just room enough for such an arrangement in the post & beam construction of the Campbell Carriage Factory.

We do not know exactly what kind of teeth this large horizontal wheel would have carried, wooden pegs or iron teeth, nor the style of gear that would have meshed with them. But it is clear that at this one juncture a meshing of gears was required, as there is no arrangement of belts and pulleys that could have done this job. That job is twofold: first the slow, lumbering turn of the 8’ wheel (at the speed of plodding horses) needs to turn this small gear at much higher speed, and also the turning of the large wheel around its vertical axis needs to be converted to turning a short shaft on a horizontal axis. Belts cannot carry power around corners, so this shift in the axis of turning needs to be handled by a gear which meshes at right angles to the teeth on the large horizontal wheel. From this step on, all the power can be carried by shafts, and each shaft can run parallel to all the others. That allows pulleys fixed to shafts and belts tying together pulleys to do all the remaining work.

Animation: a&b  If the horizontal wheel at “a” was 8’ in diameter, and the small gear at “b” was likely 6” or perhaps only 4” across, then every time the horses pulled the horizontal wheel around once, the small gear (and the shaft to which it was attached) would turn approximately 20 times! That’s a gain of 20 x the speed of the horses, even if there was an accompanying loss of power. If we imagine the horses walking around their circle once a minute, that has become 20 revolutions per minute

Animation: c&d  The large pulley at “c” is also turning 20 times faster than the horses, and is now turning at right angles to the circle round which they plodded. This pulley is known to be 4’ in diameter (it is the only piece of this horse mill we still have in the factory) and the pulley on the longer lineshaft at “d” was likely 1’ in diameter. So the belt carrying the power from “c” to “d” would gain another 4 times the speed, or 4 x 20 = 80 revolutions per minute. This is the speed at which the main lineshaft, stretching the full length of the machine room, would continually turn (so long as the horses were at work!).

Animation: e&f
  Each machine would draw its power from the one pulley on the lineshaft dedicated to that machine. So the lathe shown in the animation draws it power from the pulley at “e” linked by belt to a shorter shaft at “f” often called a “countershaft” or “jackshaft.” Each machine would have one of these countershafts dedicated to it, and would usually have two pulleys on it as shown at “f” (plus another one or two pulleys we’ll describe under “g”). The important feature of these two pulleys, shown side by side, is that one was fixed to the shaft and the other – an “idler” – was not fixed to it. It would just spin and not carry the shaft around with it.

This was a crucial feature of the whole system, that at each machine there was the opportunity to slide the belt coming from the lineshaft onto an idler, so that the countershaft would not be turned and the machine to which it was dedicated could stop. That is, the machine could stop despite the lineshaft and the horsemill continuing to operate. With the horses driving everything, this was the key to using only those machines needed at any one time, allowing the others to sit idle. By the same token, sliding the belt coming from the lineshaft onto the drive wheel (next to the idler) would engage the counter shaft and “turn on” that particular machine. This was accomplished by a “clutch” pictured below.

Animation: g   Finally, most machines had one last adjustment that could be made, as shown here on the lathe, an adjustment in speed. As before, speed is controlled by belts linking two pulleys of different sizes. If the power is coming from a large wheel to a smaller, the speed goes up (by the ratio of the relative sizes of those pulleys) whereas if it comes from a smaller wheel to a larger, the speed will drop down. In the animation at “g” the option for two speeds is shown, requiring each pulley on the countershaft lining up with a corresponding pulley on the lathe. You might note that the relative difference in the sizes of two corresponding pulleys is matched exactly by the opposite difference in the other two. This ensured that a belt that fit snugly around one corresponding pair of pulleys would also fit snugly around the other pair. Otherwise the belt would have to be shortened or lengthened every time the speed was changed.

That completes our detailing of each step in the power train, but be sure to check out the last image to fill in that one missing feature.
Paul Bogaard
Adèle Hempel, Michael Doan
19-20th Century
© 2007, Tantramar Heritage Trust. All Rights Reserved.

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