Here is my best effort to describe what happens to the gears in relation to wood and metal cutting.
In the picture below, imagine the pulley on the drive shaft. The geared pulley is essentially held in place by being bookended between the drive shaft gear and the pulley hub. The pulley hub is that painted cast iron disc seen in the second picture adjacent to the short side of the pulley.
The pulley hub is affixed to the drive shaft with two large set screws set against two corresponding flat spots milled towards the end of the drive shaft (not visible in picture).
When the lever is out, meaning the gears are not touching each other, and the plunger is in, meaning the pulley hub has now engaged the pulley, upon the rotation of the motor, the pulley is now essentially attached to the drive shaft as if it had a keyway/key. In this configuration it is one to one drive. The motor is turning the pulley which is turning the drive shaft/wheel.
When the lever is in, the pulley gears are in mesh with the reduction gear, which turns the small reduction gear, which turns the drive reduction gear. Through these lathe like gears, the drive is reduced to roughly 10 to 1. Obviously in this configuration the plunger needs to be out, so the pulley would be free floating on the drive shaft and the gears themselves are turning the reduction drive gear. The drive gear is held onto the shaft with a key way and so is permanently affixed. With the plunger in as you have described the owner doing, the pulley is now affixed to the drive shaft and the gears are in mesh. So what is happening is the gears are trying to slow it down, the pulley is trying to speed it up, and over time I imagine some if not all of the teeth have been sheared off.
Sometimes a visual aid helps, I have an Instagram page with a brief video I made a year ago or so that could help describe this relationship. You don't need Instagram to view it.
80 likes, 12 comments - oldamericantools on July 7, 2023: "Inching closer to finishing this 1940 Walker Turner band saw. Want to show inside the gearbox before it's all greased up and closed how the gears operate. Just an outstanding, well thought out and engineered example from the Golden age...
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