I have read many posts in several forums regarding kickback and how to prevent it. I read them because I want to get others impressions of why kickbacks happen in the first place. In my 50+ years working with power tools, including saws of all types, I have never regarded kickbacks as a very pressing problem. I get the impression that those who are worried about kickbacks have a basic fear of whirling blades. They can be and are intimidating, but they don’t have to be feared, though they must be respected. Saw blades can be compared with firearms. They both have to be respected for what they can do.
I have used all types of saws; table saws, swing saws, radial arm saws, miter saws and band saws. I have never been cut by a saw blade and can’t remember when I have had a kickback. I don’t have an anti-kickback device (except on the radial arm saw), a reeving knife, blade guard or hold-downs on my saws. I have ripped 4×8 sheet goods on radial arm saws (the most feared operation by most) with nary a blink of an eye. I do use a push stick on my table saw, but have no fear pushing a piece of wood past the blade with my fingers within an inch of the blade. I have analyzed the causes of kickback and trace it back to basic fear and unfamiliarity with power tools and saws in particular. Those who scream safety first and “never get your fingers closer than 6” from the blade” may be a little over cautious to the point of making us paranoid around dangerous machines. Off course, I’m not advocating “throw caution-to-the-wind”; I don’t even want to suggest that you do anything that you are uncomfortable with. I can’t convert anyone nor am I trying to convert anyone over to my way of thinking. That is not my task which is to teach others about the dangers of working with power tools and how to work safely. On safe working, I must emphasize your reliance on working safely without depending on safety devices designed to keep you safe. The most blatant safety device to hit the market as everyone has heard of is the “Sawstop” . It does what it claims, but doesn’t make you a safer woodworker. It only capitalizes on your making a mistake. That mistake, happening on a non Sawstop machine would probably result in serious injury and even loss of some digits. There are two schools of thought when you discuss Sawstop. One school says it creates a false sense of security and the other; it is an insurance policy against injury; either way, any safety device can only do so much. Ultimately the responsibility for your well-being lies with you, not reliance on safety devices or government decrees. I got a little ahead of myself and return to my initial topic, which is kickback.
What is kickback? A piece of wood is pushed into a whirling blade and all of a sudden, without warning, the blade, instead of cutting, decides to grab the wood and hurl it backwards towards the operator. If you are standing directly in-line with the blade, the wood can be kicked back with enough force to inflict damage to person. Most people say, “never stand directly in-line with the blade, but stand to one side” This may be good advice to some, but actually this can be bad advice because if you are standing to one side, you are now pushing the wood at a slight angle. Standing in direct line is the most efficient position for pushing the wood, but more on this later. So what are the reasons for kickback in the first place?
What causes kickback? There are several reasons for kickback and they are enumerated below:
• Saw blade too low: When the blade is set too low (not recommended), the attack angle of the tooth is in a straight back direction, which means all the cutting force of the teeth is directed towards the rear. When the blade is set high (recommended), the cutting force is directed downward toward the table surface. When the blade is set low, the teeth have to cut through more wood than when it is set high. Think: swinging a hammer at the edge of a table and swinging the hammer down at an angle to the top. Which creates more movement of the table?
• Wood not under control: The most important tip is to always keep the wood you are cutting under positive control at all times. When you relax your grip on the wood, that’s when kickback can occur. Don’t be timid about holding the wood. Grip it well and hold it down to the table. I’ve seen people pushing the wood with their thumb without holding it down. (instant kickback)
• Dull blade: When the blade is dull, the teeth tend to “rub” rather than slice or sever the wood grain. A sharp blade severs the grain cleanly. Rubbing causes the blade to slow down and build up pitch especially in the case of resinous woods.
• Pitch and resin build-up: This creates friction, which causes heat to build up, slowing down the motor.
• Fence not parallel to the blade: A fence must be perfectly aligned and parallel to the blade. If it is not, the wood becomes wedged and as the wood tries to follow the fence, the wood burns, friction increases and kickback can occur.
• Lack of power: Most contractor type saws have 1-3/4 hp motors, which is usually adequate for the building trades as they deal mostly with construction grade lumber (softwoods), but when used in the home shops, more demand may be asked of them, such as cutting hardwoods, 2 or more inches thick and cutting sheet goods on smallish size tables. They usually lack the sturdiness of the cabinet saw which has a minimum of 3 hp. The greater power afforded by the cabinet saw enables the user to cut harder and thicker woods without slowing down. The slowing down of the blade which results in burned wood and increased friction which causes kickback is mostly eliminated in cabinet saws, as long as the other points are followed; namely sharpness of blade, parallelism of the fence and height of the blade.
• Wrong type of blade: The wrong type of blade can also cause kickback. A blade intended for a miter saw or radial arm saw with a negative rack can easily cause kickback if used in a saw with the blade below the table. That type of saw requires a blade with a positive rake. The number of teeth is also important. In a rip operation, you want to use fewer teeth. Fewer teeth means there is more open gullet room to hold sawdust. A blade with lots of teeth would clog up quickly while ripping and cause burning. Crosscutting severs the grain and expels the sawdust, although feeding the wood into the blade rapidly can also clog the gullets which are much smaller than in rip blades.
Now that we know what kickback is and what causes it, how can we prevent it? First I doubt that it can ever be completely prevented. There are too many factors to consider. I feel though that developing an understanding of the tool goes a long way. Anyone who has served in the army knows that his rifle is his friend and must respect it. That same respect when applied to dangerous tools will help keep you safe. I’m far from being an expert on saws, or anything else for that matter, but I feel my relationship with dangerous machines is a good one. I hope whoever reads this will see some of the points raised. Safety is our responsibility, not the responsibility of makers of after market devices.
Disclaimer: Because this blog concerns safety, the opinions and statements made are solely the responsibility of the author and not Lumber Jocks.