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  Riving Knife Conversion  

This article DOES NOT advocate the modification of a manufactured tool. ANYTIME YOU MODIFY A MANUFACTURER'S PRODUCT YOU ASSUME ALL LIABILITY FOR THAT PRODUCT. However, a lot of carpenters use their jobsite table saws WITHOUT guards--which is a major modification. If you or your employees suffer an injury while using the tool without a guard, you will be liable for all consequences!
You many not know it, but a portable table saw guard is really a combination of three separate safety devices: a splitter, anti-kickback pawls, and a clear plastic cover. The reason you may not know it is because you never took a good look at your guard before sticking it in some dark corner of your shop, or more likely, sending it on a short trip to the landfill. Portable table saw guards aren’t known for their ease of use, so most carpenters don’t use them. In a recent poll of professional carpenters, 99% of those who responded said they never use a guard on their portable table saw. Why? Because most guards are hard to remove; they’re even harder to re-install. And you have to remove them frequently: they interfere when making thin rips, rabbets, blind kerf cuts, dadoes, steep bevels—just about anything difficult (and nothing is easy on a jobsite). The anti-kickback pawls are nearly always in the way, they jamb when you’re making thin rips, and if you need to back off a touch or change your mind and want to stop in mid-rip…good luck. The splitters are another sore point for carpenters. Being on a portable tool, the splitters take a beating. They’re rarely aligned with the blade. Ask any carpenter and they’ll tell you—with at least one expletive—that splitters cause more binding and kick back then they prevent. But universally carpenters hate the plastic covers most. After spending years developing a “good eye,” it’s tough trusting a saw to cut something you can’t see.
European saw guards and some cabinet saws are different. There’s more room—and more budget—for guards that don’t combine all three elements. Besides, after market guards are available for cabinet saws—overhead guards with integral dust collection, splitters with anti-kickback pawls that are easy to remove, and covers that can be lifted neatly out of the way. Best of all, some cabinet saws, and many European saws, come with a riving knife, not a splitter.
Because so many carpenters use their portable saws without guards, exploring alternative safety measures is important.
A riving knife travels with the blade, it’s always just a bit below the teeth, so it’s never in the way of a rabbet cut or a blind kerf. And a riving knife follows the blade tilt, too; without pawls or a cover that binds against the saw table, a riving knife is never in the way of a bevel cut.
One of the nice things I’ve discovered about my Bosch portable table saw—besides the one-wrench blade change, the smooth low-vibration cut, and the low-decibel motor—is that the blade guard attaches to the saw carriage and travels up, down, and sideways with the saw. I also discovered that it’s easy to remove the pawls and the plastic cover. I pried the keepers off the cover bracket with a screw driver and needle-nose pliers. I drilled out the large rivet running through the pawls, then drove the pin through with a nail set.  
All in all, I spent only a few minutes more than it takes to throw the guard away, but that extra time was well worth the effort. Fortunately, the front of the splitter was already cut neatly to follow the saw blade. To turn my splitter into a riving knife I only had to cut the back a bit, and grind a chamfer on both edges of the front. I used a jig saw with a metal cutting blade to cut the back. I made sure that the top of the riving knife would be about 1/4 in. below the saw blade (recommended height varies from 1/4 in. to 7/16 in. below the saw blade). The splitter that came with the saw was also the perfect thickness, just over the width of the saw-blade body, but thinner than the kerf.
Installing the knife (and removing it) is easy on my saw if you raise the motor all the way and tilt it to a 45 degree bevel. The riving knife is secured by two studs and a plate. Loosen the plate, lift it out of the way a little, then slide the knife under and onto the studs.  
The plate is secured with only one Allen bolt, which makes the riving knife easy to remove, but I only need to remove it when I put on a smaller dado blade set, or make a plunge cut, which I don't do every day.
Adjusting the knife so that it's perfectly aligned with the blade isn't difficult at all. I loosened the top two Allen bolts and eyeballed the knife into alignment with the blade, then tightened the bolts real good. Because the knife descends with the blade, it doesn't stick up above the table when I carry and store the saw in my truck. That saves the riving knife from the beating most saw guards take during transportation, which is the main reason saw guards require frequent re-alignment.
A riving knife is a splitter that never interferes with the cut. A large percentage of table-saw accidents are the result of kick back. Kick back can be caused by several things: a misaligned rip fence, a badly twisted or warped board, or stress built up in lumber that’s sometimes released during a cut and closes the saw kerf. When the kerf closes and pinches the saw teeth at the back of the blade, the work piece can shoot right at you. A narrow strip becomes a spear; a wide board becomes a battering ram. Even worse, if you’re using your hand as a featherboard near the blade and pushing the board against the fence, when the work piece shoots out of the saw, your hand won’t be pressing on anything but air—at least not until it hits the blade. A riving knife helps eliminate kick back from most causes.
A riving knife adds another degree of protection from two other common table-saw accidents: projectiles and tired hands. Small cut offs often vibrate on the table and walk themselves right into the back of the blade. That’s when the saw teeth pick them up and shoot them at you like a bullet. But a riving knife will help prevent more then just cutoffs from contacting the back of the blade. One of the most common table-saw accidents doesn’t happen near the front of the blade but at the back of the saw. Too many tired carpenters have reached around behind a table saw blade and missed the safety zone by a fingertip—or more. A riving knife helps protect your hands from the back of a saw blade, too. Of course, if you used the guard that came with your saw, you'd have even better protection. But who does?


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