A riving knife is a variation of what most US woodworkers know as a splitter. Its stationary blade of metal or plastic that holds the kerf open behind the blade. This prevents the wood from closing in and pinching the back of the blade and prevents the stock from getting pinched between the blade and the fence, both of which will cause kickback.
A riving knife differs from a simple splitter in some important ways:
- Since it doesn’t extend beyond the height of the blade, there is no need to remove it for non-through cuts like dados and grooves.
- It sits closer to the back edge of the blade, making it much more effective at preventing kickback.
- It can be used in conjunction with a variety of overhead blade guards.
The way it achieves all of this is that is mounted on the same mechanism that mounts the blade, allowing it to move with the saw blade as it’s raised, lowered and tilted. To work properly, the knife should be just slightly less than the width of the blade, and is just slightly shorter than the blade.
In 2009, Underwriters Laboratories (UL) will require that all new table saw designs include a riving knife.