On the level (Kickback, part 2) - Woodshop News

On the level (Kickback, part 2)

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Last time I opined that my kickback incident might have been caused by vibration that allowed a piece of offcut to move into the blade. I’ve confirmed it.

After the kickback incident, I took a serious look at my table saw. Do I have too much vibration? And, if so, what do I do about it? I’ve used several table saws over the years, and always thought my table saw was pretty smooth, with a lot less vibration than most. Still, all table saws vibrate to a degree so the real culprit in my kickback incident is what made that piece of offcut move into the blade?

You older guys may remember a toy we all had as kids. It was a really lame plug-in tabletop football game. When you turned it on, the tin football field buzzed and vibrated, sending these metal football players slowly skittering willy-nilly across the surface. In reality, game play didn’t resemble football so much as it did scattering 22 drugged mice onto a hotplate. It was silly, but we played it. The thing of it was, was that if the football field wasn’t perfectly level, once it set to vibrating all the little men would eventually cluster on the lowest edge or corner.

There it was: My saw’s table wasn’t level. I pulled out my bubble level and checked, but it looked good. Of course, bubble levels aren’t precision instruments; you can be off a degree or fraction thereof and that bubble looks like it’s in the middle.

Lacking a digital level, I tried something else. I placed a large ball bearing on the saw. Sure enough it started to roll to the right. Not fast, but it was definitely going downhill. I tried this in several places on the table, and each time the bearing would roll to the right. Again, this roll was very slow, so I couldn’t have been off by much. But, obviously, it was just enough.

Offcuts aren’t ball bearings, but when you keep your saw table as smooth and clean as mine, then add that thin layer of ultra-fine dust you get with each cut, it makes for a pretty frictionless surface. Combine that with a bit of vibration, and even a small offcut can begin to slide downhill just like those little football players. Considering where an offcut remains after the cut, that downhill direction leads right to the blade.

I spent a half hour or so readjusting the supports on the cabinet base, then testing with the ball bearing until I was satisfied the table was as level as I can get it. I can’t confirm this will prevent a similar vibration-related kickback, but I feel confident I’ve removed at least one potential cause.

The rest of preventing kickback is up to my own diligence.

Till next time,

A.J.

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