Keith Rucker, of VintageMachinery.org shot the video below at the Georgia Museum of Agriculture in Tifton, Georgia. It’s of a swing saw (also called a pendulum saw) designed for use in a mill. Instead of pivoting like a chop saw or sliding like a slide miter or radial arm saw, it pivots in line with an overhead line shaft—a configuration that allows the blade to be powered by a leather drive belt.
In the days before small electric motors, line shafts made it possible for a single power source to drive all of the machines in a shop. In the early days it would have been done with a steam engine or water wheel. But by the early years of the last century line shafts were more likely to be driven by large electric motors. A single motor would power the line shaft, which in turn powered all the machines in the shop. It was not until many years later that it became practical to put electric motors on individual machines.
If you think about it, this setup is not all that different from a piped dust collection system in a shop. The dust collector creates suction in all of the pipes but does not draw from every machine at once. It only draws from the one you are using—which doesn’t happen until you open the blast gate at that machine. For more on belt-powered machinery see the second video in Three Machine Shop Videos.
Swing saws are still being made, though current models are powered by individual electrical motors.
My comments below:
00:08 You’re looking at three separate wheels. The one on the left is an idler that spins free on the shaft. The one in the center and one on the right are solidly attached to the shaft—when one spins they both spin and the shaft does too.
00:19 The fork-shaped piece of metal is used to shift the powered drive belt (powered by a spinning line shaft that is out of the frame) off of the idler and onto the center wheel—thereby transferring power to the belt that spins the saw blade below.
00:36 A museum worker uses the saw to cross cut a board. Note how the blade swings on a pivot. This is a scary setup because the blade spins in a direction that makes it “want to” pull itself into the work—as is the case with radial arm saws. It the teeth catch the arm and blade can come flying out at the operator, which is why OSHA requires the use of a chain to limit the swing of the arm. This saw appears not to have one. Let’s not even talk about the minimal blade guard.
00:56: To turn the saw “off” the operator moves the lever and shifts the main drive belt back onto the idler wheel. There is no brake so it takes a while for the blade to spin down.