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A table saw takes the center stage in many woodworking shops. Equally, it poses more safety risks than any other tool. In fact, table saw accidents account for most of the occupational accidents in a woodshop. In the U.S. emergency departments, for instance, table saw injuries such as finger and thumb cuts, vascular damage, and amputation are commonplace. According to biomedical research, over 30 thousand table saw injuries occur every year in the United States and table saw kickbacks are among the causes.
What is table saw kickback?
Table saw kickback is any material kicked back by the saw during operation. It occurs when the spinning circular blade of a table saw grabs and propels stock or offcuts back at you violently during operation. Because of the high RPM of the cutting blade, kickbacks travel at a very high speed and momentum.
To understand how fast a table saw kickback can travel, take for instance a 10-inch circular saw blade spinning at speed of 4000 RPM. If we convert this angular speed into linear speed or velocity, we get:
Velocity (v) = r x RPM x 0.10472 = 0.127 x 4000 x 0.10472 = 53.19 m/s or about 118 miles per hour.
This means that a saw blade spinning at 4000 rpm can potentially hurl an object from its circumference at a speed of 118 miles per hour. So, if the object weighs just a few tens of grams, it can have high momentum which can be dangerous. This is why kickbacks from a table saw are dangerous and sometimes fatal.
What causes kickback on a table saw?
The key to preventing kickbacks in the workshop is to understand how they occur. There are many reasons why workpieces can fly back to you when operating a table saw. These reasons range from a misaligned blade to simply an offcut just coming into contact with the spinning blade unknowingly. The following are the most common causes of table saw kickbacks.
1. When a workpiece turns towards the blade when cutting
Sometimes when making a cut, a workpiece can turn inwards towards the blade. This can pull your hands on top of the blade as well, resulting in a serious hand injury. This is how most finger injuries occur on a table saw.
2. When the kerf closes in on the back of the blade
Sometimes when making a rip cut, the kerf on the workpiece may start to close in on the back of the blade. This happens particularly if you are cutting reactionary wood and/or your table saw does not have a splitter. If you do not sort out this problem, your workpiece may eventually shoot back at you or flip upon you. The closing up of the kerf also happens mostly when rip cutting hardwood.
3. When workpiece binds between saw blade and rip fence
When making cross cuts, an offcut may bind between the fence and the blade. This may result in a violent kickback, especially if you are standing in the path of the projectile. This problem is usually caused by a misaligned fence or blade.
4. Not pushing a workpiece past the blade
Pushing a work piece through the cutting blade helps overcome the cutting resistance. If you do not push the workpiece completely through the cut, it will be propelled in the opposite direction and might find you in the way. So, it is necessary that you push your stock completely through the blade to reduce the possibility of kickback.
5. Applying force towards the side of the blade
A table saw cannot cut without you pushing the workpiece through the blade. This is known as table saw feeding. However, the direction you push the workpiece is as important as the force you apply. The direction of the force you apply on a table saw workpiece must be parallel to the saw blade. Otherwise, the blade can protest by ejecting the workpiece and pulling your hand towards it. This can result in hand amputation and other serious injuries.
How to prevent tablesaw kickbacks
It is difficult to stop table saw kickbacks completely from happening but there are things you can do to reduce their occurrence. The following are measure you can take to prevent some of the most common table saw kickbacks.
1. Steer clear of the kickback path
The most important safety precaution when it comes to kickbacks is to avoid being on their path. Materials coming from the spinning saw blade often fly in the direction of rotation of the blade. So, when using the table saw, always stand on the side to prevent the accidental projectiles from landing on you. Ensure you also put on the necessary safety gear such as a pair of gloves and a face shield.
2. Install a wood splitter or riving knife on your blade
A splitter is an important safety part of a table saw assembly. It prevents the kerf from closing in at the back of the blade. A table saw splitter is simply a small stationary blade of the same thickness as the saw blade mounted at the back of the blade. It aligns vertically with the blade so that the stock can slide through seamlessly after coming out at the back of the blade, effectively keeping the kerf open to prevent pinch back. A metallic splitter also holds the stock tight against the fence to prevent misalignment that may cause kickback to occur.
A wood splitter on a table saw has two main disadvantages. First, it does not tilt, raise, or lower with the blade. This means that you must remove it when making angle cuts. It is also less effective on thick stock unless you replace the short splitter with a taller one. Second, there is a fairly large gap between the saw blade and the splitter. This gap may cause the kerf of some wood types to start closing in before reaching the splitter, potentially causing kickback. Nonetheless, a splitter is better than nothing. You can also add one to your custom zero clearance throat plates. Most old table saws come with a splitter while newer ones have a riving knife as the primary anti-kickback accessory.
A riving knife mounts onto the trunnion. In other words, it mounts on the same mechanism the saw blade mounts on. This allows the riving knife to raise, lower, or tilt with the blade while maintaining a fixed gap with the blade. This fixed gap allows the riving knife to enter the kerf as soon as the workpiece leaves the back of the blade thereby eliminating the pinching back of the stock that otherwise may cause dangerous kickback. For that reason, a riving knife is more effective than a splitter in preventing kickback. However, having one of them on your table saw is safe enough.
Before you begin cutting, you should always make sure that a splitter or a riving knife is properly installed and aligned with the saw blade. They increase the table saw safety significantly particularly when making rip cuts on long workpieces.
3. Use dry wood for rip cuts
Lumber that is not well dried is prone to the kerf closing up. This is because wet wood has a high moisture content which causes the grains to pull back together after a cut. Such wood is dangerous because it can even close up on the splitter and cause a lot of friction that may result in dangerous kickback. So, you should always avoid ripping wet lumber. However, if you have to do it, keep them short enough by precutting them the desired application lengths.
4. Align table saw fences perfectly
Align the fences of the table saw perfectly to prevent workpieces from binding and potentially resulting in violent kickbacks. Use the miter slots to align the rip fence parallel with the saw blade. You can also adjust the fence further away from the trailing edge of the blade by a few thousandths of an inch without a problem. This is also known as fence toe-out. Toeing out the fence prevents the binding of the offcut and keeps the kerf open. What you should avoid by all means is narrowing the gap between the fence and the rear of the blade, otherwise known as toeing in. A slight toe-in of the fence can cause burn marks on cuts at the minimum and dangerous workpiece kickbacks when the fence is severely toed in.
Use the same miter slots and a square to align the miter gauge fence. Align the fence for two angles. First, align it perpendicular to the saw blade using the square tool’s right angle. Second, adjust the miter gauge to 45 degrees and measure it against the blade using the square’s 45 degrees to ensure that the angle is dead-on accurate. These are the most common crosscut angles on a table saw.
5. Align the saw blade
A misaligned blade may cause a workpiece to get stuck between it and the fence and result in dangerous kickback. So, as you adjust the fence, also pay attention to the alignment of the blade. A misaligned blade can also cause inaccurate cuts and/or burnt cuts.
6. Keep the saw blade sharp and the tabletop smooth
A blunt saw blade and a rough tabletop can cause control problems on the workpiece, which may easily result in kickbacks. To prevent this scenario from happening, always make sure your cutting blade is sharp and your table saw top as smooth as a mirror. You can apply wax on the tabletop to reduce friction. This will help improve your control of workpieces. As far as keeping the blade sharp is concerned, check out how to tell when to sharpen or replace a circular saw blade.
Reference
Chung, K. C., & Shauver, M. J. (2013). Table saw injuries: epidemiology and a proposal for preventive measures. Plastic and reconstructive surgery, 132(5), 777e–783e. https://doi.org/10.1097/PRS.0b013e3182a3bfb1
