Bosch Riving Knife — No More Excuses for Woodworkers

Posted August 2, 2007

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This year at the AWFS show we saw several new table saws with new guard systems that include riving knives. I wrote about it here on the blog and the other day one of these saws, the Bosch 4100 jobsite saw, arrived on our loading dock. I unpacked the saw this morning, and we’ll have a full review in an upcoming issue of Popular Woodworking. For now, here’s a close look at this innovative guard system.

The guard consists of three components , the riving knife/splitter, the anti-kickback pawls and the blade cover. The best thing about this guard is the engineering that makes it the most user-friendly system I have seen. The reasons many woodworkers don’t regularly use guards are 1) it takes too long to remove, replace and realign the guard, and 2) it gets in the way when you’re setting up for a cut, or when the fence is close to the blade. The two plastic side shields on this guard lift up and out of the way and there is a catch to hold the guard up until you want to lower it.

The blade cover attaches to the riving knife/splitter by clamping into place. The lever in my hand releases the guard and it then is easily removed from the saw. Elapsed time for this operation is about five seconds.

The anti-kickback pawls release in a similar fashion. Squeezing a button disengages a pin and the pawls lift out of the way. This also only takes a few seconds, and you can leave the blade cover in place and remove the pawls independently.

After removing the table insert, another lever releases the riving knife/splitter. This doesn’t come out of the machine, but it slides in an arced slot and locks in one of three positions. The lever clamps the splitter against a flat piece that is part of the arbor assembly, so it is always in line with the blade. In the top position, it comes up above the top of the blade to allow the blade cover and pawls to attach.

The middle position brings the top of the knife just below the top of the saw blade. If you’re making a non-through cut (like a rabbet or a groove) the knife is still acting as a splitter by keeping material against the fence, and by keeping it from binding on the blade. The lowest position drops the knife completely below the blade, out of the way for changing blades.

The riving knife stays in this position when you raise, lower, or tilt the blade. It shields the teeth at the back of the blade to prevent the piece you’re cutting from coming in contact with the saw blade. If you look at the picture, you can see that these teeth are the ones most likely to grab something and throw it up and back.