Contractor saw vibration damper
The way I have the motor mounted on my old table saw, if I crank the blade most of the way down, the motor mount "bottoms out" so the motor is no longer hanging off the belt. I noticed that in this state, there is a lot less vibration.
I thought it was because, with the motor mount bottomed out, the motor can't move up and down with the belt anymore. This gave me the idea of mounting a shock absorber between the motor and its mount to prevent it from shaking up and down.
I had seen some very old cars with friction shock absorbers, so I had the idea of making a sort of friction dampener instead. But to get more room for that, I figured I'd make it go from the motor mount down to the bottom of the stand. To accommodate depth and tilt adjustments, I needed a ball and socket joint for each end.
I experimented with carving out a hemisphere, mostly on the belt sander, and drilled an undersized hole, chamfered the edges of it, and tried it out. Though not a captive joint, it worked well enough.
I needed another ball and socket for the bottom. I cut the corners off a piece of wood, then shaped it by spinning it in a drill against a belt sander. This worked well enough without having to worry about how to chuck the piece up on the lathe.
I drilled some large holes into the ends of my friction damper and chamfered the edges to act as the socket part of the ball and socket joints.
With the shallow (not captive) ball and socket joint, I need springs to press the joints together, so for one end, I drilled a hole near either side of the socket and made a wire "clip" to hook a spring onto.
With the wire clip extending beyond the ball and socket, it helps to stabilize the joint. If the spring was hooked directly to the link, the socket would have a tendency to slide off the side of the ball.
Then testing it out, subjectively judging the vibrations by looking at the waves in a small container of water. When I put a small spring clamp on the damper to give it some friction, it made no noticeable difference to the waves in the container. Under some circumstances, it even made it worse!
I figured maybe the reason the vibrations went down when the motor mount bottomed out was because of reduced belt tension. I experimented with using a spring to help pull up the motor to reduce belt tension. This helped, but not hugely so. I experimented with how much belt tension I actually needed and realized that even without the spring, the belt would slip before the motor stalled under heavy load. So I really shouldn't be reducing belt tension.
I tried a different V-belt, and this one produced only about 0.010" of movement. Running it with that V-belt, I got much less vibration.
Comparing the two V-belts. You can see the one on the right has a bit of damage, so you would expect that to result in some vibration. Except, that's the one that causes less vibration. The one on the left causes much more vibration, with no visible signs of damage!
I tried holding a weight against the motor, and that seemed to help a bit. So I decided to mount that to the bottom of the motor mount to help stabilize it and get some of the belt tension back. More weight should reduce vibrations, and the spring helps counter the extra belt tension the weight would add.
Though I previusly gave up up on the friction dampener, on a whim, I tried it again. And this time it worked really well. I guess it just didn't work on the kind of vibrations I got from the other V-belt. So I took the spring and the weight back off the saw.
I made a spring clip to act as a clamp (as opposed to leaving a spring clamp on there)
I then tested the full range of tilt and depth adjustments to make sure the friction damper would not impede the motion. Though, at 45°, the angle is not optimal, and I don't expect it to help much with the saw tilted like that.
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