In my September 24 entry I discussed the importance of an accurate rip fence in preventing table saw kickback. Having an effective method of keeping the saw kerf open during rip cuts is equally critical if not more so. Stresses within the wood can cause the saw cut to either open up or pinch shut as it passes over the saw blade. If the kerf springs open so that it presses against the rip fence, the wood may be pushed against the trailing edge of the saw blade causing kickback. If the kerf pinches shut, it may grab the rear of the blade with the same result. The traditional solution has been to install a splitter behind the blade.
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| Traditional Splitter |
The photo at right shows the type of splitter traditionally supplied with American table saws. These often come equipped with clear plastic guards. Both are generally removed and lost because they are so inconvenient to use.
The splitter does have some good features. The metal blade that makes up the body of the splitter is effective at keeping the saw kerf open. The toothed blade visible on the side of the unit, actually one of a pair that straddle the splitter, is a pawl that can grab the piece of wood if it starts to be thrown back at the operator, thus preventing kickback.
There are several drawbacks to this design. The gap between saw blade and splitter, clearly visible in the photo, is one of the most serious. This gap makes it possible for the wood to contact the rear of the blade before it even reaches the splitter, causing kickback. Many splitters of this type are also made of soft metal that is easily bent and difficult to realign. The height of the splitter is also fixed, rather than raising or lowering along with the blade, so that it must be removed when making grooves or buried cuts, as in tenoning, etc. Once removed, the splitter is rarely replaced.
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| Riving Knife |
The riving knife, long in use in Europe but only recently required here, addresses many of these issues. The riving knife is attached to the saw arbor so that it raises, lowers, and tilts along with the saw blade. As long as the correct size blade is installed, the gap between the riving knife and blade is constant and quite small. Finally, because the knife is slightly shorter than the saw blade, it can be left in place when making buried cuts. The riving knife must be removed when using a dado set or molding head but, at least in the case of the saw I own, this is easily done without tools.
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| Modern Splitter With Guard |
The riving knife is especially useful for cuts where the operator needs to be able to see the blade clearly, as when cutting to a pencil mark. It lacks anti-kickback pawls and a plastic shield, both of which would make ripping long boards or cutting sheet goods much safer. On my saw, the riving knife is easily exchanged for a splitter of this type. Unlike the traditional design, this guard rides up and down with the blade, preserving many of the advantages of the riving knife. Presently, riving knives are only required on new saw designs, existing designs being grandfathered in under the new safety rules. I am convinced the new designs are worth the added cost.
The other anti-kickback device that has been receiving a lot of press is an electronically activated brake that instantly stops the blade if it contacts flesh. The action is so fast that no injury to the operator results. While this is an extremely important development, it is currently available only on one brand of saw. I suspect it will become more widely available in future, but for now most woodworkers will have to rely on accurate rip fences, splitters or riving knives, and their own vigilance to avoid kickback injuries.
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