It’s no secret that the circular saw is one of the most versatile saws you can own, but using this power saw certainly doesn’t come without its own set of hazards. These tools are powerful and virtually untethered. As such, the user must always use the utmost caution when operating a handheld circular saw, especially when considering the potential for circular saw “kickback” in woodworking.
What is Kickback?
Kickback, in general terms, is defined as a sudden forceful recoil. If you’ve ever fired a gun and felt the firearm lurch backwards after pulling the trigger or had your table saw bind up on some plywood and kick the wood back towards you, you’ve experienced the concept of kickback.
In the case of circular saws, kickback not only causes your heart to skip a beat, but it can also be extremely dangerous causing serious injuries, and it is not a rare occurrence.
Thankfully, though, it is also generally avoidable, and precautions can be taken so that if kickback does happen while operating a circular saw, its effect is minimized.
Fans of physics might recognize Newton’s third law at play here: every action has an equal and opposite reaction. In other words, forward momentum is met with an equal and opposite backward force.
But how does this apply to the use of circular saws and result in kickback?
What Causes Kickback and How to Prevent It?
In short, as you manually move the saw forward, the pushing motion you are using and the power applied by the saw’s motor to rotate the blade provide the saw with a specific amount of forward momentum. If there is forward momentum, then there must also be backward resistance that creates a balanced system.
This physics lesson is easier to see in the gun example because kickback is almost always experienced when firing a gun, regardless of technique.
However, it is a bit less obvious in the world of power tools because, though not at all uncommon, circular saw or table saw kickback is usually only noticeable when something has gone a bit awry during a cut. The reason typically is that the saw’s forward movement is hindered in some way or another while the forces acting on the saw either stay the same or increase as the operator tries to overcome the resistance they are experiencing. The result can be a noticeable (and dangerous) kickback.
So what conditions can hinder the movement of the blade and cause kickback when operating a circular saw?
1. Improper Support
This is especially common when working with large pieces, like 4’x8’ sheets of plywood. Rather than simply thinking about support as something that helps hold the wood level and make the cut easier to make, think about the supports as something that prevents compression or tension in the wood.
If there are large portions of the sheet that are left unsupported, especially near your cut-line, the wood will bow inwards as a result of its own weight, the weight of your saw, and the pressure you are placing on it. This compresses and binds the blade as it cuts, which creates a lot of friction on the blade and increases the force required to push the blade forward along the cut-line. In turn, this increases the opposing force as well, thereby greatly increasing the potential for kickback.
Not only will ensuring proper support balance both of these forces and make for a safer cut, but it will also make for a cleaner and easier cuts as you and your blade won’t have to work any harder than necessary to glide through your cut-line.
2. Twisting the Saw
Have I mentioned yet, that binding, pinching, or hindering your blade’s strictly forward-designed motion is a terrible idea if you want to avoid kickback? Well, twisting your saw during a cut is another reason why binding occurs. You probably didn’t grab your circular saw out of your collection to cut a curve, so what kind of twisting am I talking about?
Some might notice that their cut-line is trending a bit wonky while making a cut and think that they can correct and straighten out their cut-line by just twisting their saw slightly in one direction or another and proceeding as usual. The assumption is that the now-different angle of the blade will compensate for a badly aimed start to the cut, even if the kerf (the channel cut by your saw) is less than consistent. This is a bad idea. Please stop this kind of thought process in its tracks before it drives you into Kickback City.
Other times, someone’s blade may just be warped and twisted itself, and it may not even be the operator’s choice to twist the blade during a cut, but the result will be the same and the blade should simply be marked and discarded as no longer usable.
Whatever the reason for twisting occurring during a cut, one thing is certain: it will cause excessive friction on the sides of your blade as you push harder to get your blade through the cut until the blade completely binds up and leaps backward quickly.
3. Using a Dull Blade or Using the Wrong Blade Type
The importance of a sharp blade cannot be understated for a number of reasons, but particularly for preventing circular saw kickback. A dull blade not only increases the amount of force needed to move the saw through the cut-line, thereby increasing the force with which the saw will recoil if it is to do so, but it also increases the chances of the blade binding up when it is unable to cut through the wood fibers due to its dull nature. When the saw is unable to cut through what it is attempting to cut through, the saw’s motor and the operator will attempt to keep cutting, and this will cause the saw to jump out of its cut-line, resulting in kickback.
Similarly, if you are using a blade meant to cut a different kind of material than that of what you’re actually cutting, your blade may not be able to cut through the material efficiently, and this will result in kickback and likely many other issues. In other words, don’t attempt to use a circular saw blade meant for wood to try and cut through metal. There are a million and one reasons not to do this (and one of them includes ruining a perfectly good blade), but the most important reason is that it’s dangerous and can cause your circular saw to recoil.
4. Absence of a Riving Knife
Riving knives are not commonly installed on circular saws sold in the US, but they are more common in similar-use tools like track saws and table saws, as well as in circular saws sold in other countries. A riving knife’s purpose is to follow the blade within the kerf relative to the blade’s cutting depth which maintains an even gap between each side of the wood being cut. The riving knife (and the gap it maintains) is wider than the width of the saw blade and helps to prevent binding, pinching, or jamming of the blade, thereby preventing kickback. Having a riving knife installed on your circular saw is a great solution for reducing the potential of kickback.
5. Setting the Cut Depth of the Blade Too Deep
Having your saw depth set too far below your cut piece can cause instability in your blade. It allows for greater torsion or twisting of your blade and, as we learned above, this can quickly result in kickback. Additionally, setting your blade’s cut depth too deep provides more surface area than necessary, which in turn provides more opportunity for your blade to catch, pinch, jam, or bind. It’s best to limit your blade’s depth to extend no more than ¼-inch below the bottom of the wood you’re cutting.
6. Adjusting ANY Part of the Saw or the Saw’s Direction While Cutting
Apart from it being incredibly dangerous to move your hand around in order to touch any part of your saw while a blade is spinning (because.. well, spinning blades and loosey-goosey fingers don’t go together very well), changing the depth of your blade or angle of the shoe while the blade is spinning can also cause the wood you’re cutting to catch on the blade, resulting in kickback. We spoke earlier about trying to adjust your cutting direction in an already established kerf and why this is a dangerous idea, but doing so while the blade is in motion is even more dangerous. Absolutely all adjustments to the circular saw or the cut-line should be made prior to beginning your cut.
7. Pulling the Saw from the Cut-Line Before the Blade Stops Spinning
When ending a cut or withdrawing your saw from a kerf, it is important to ensure that the blade on your circular saw comes to a complete stop before pulling the tool away from the cut. This is because twisting of the blade can occur when pulling your circular saw away from the piece you’ve just cut, and if the blade is still in motion, it can both damage the edge of the cut you just made and cause the blade to bind, resulting in kickback.
8. Powering Up the Saw While It’s in Contact with the Piece You’re Cutting
If you’ve ever used a circular saw and hadn’t read this article or learned from anyone other than the school of hard knocks, you probably know that it’s not a good idea to try and start a cut with a circular saw by first touching your blade to your workpiece and then trying to power the blade. Most saws available on the market today have safety features that prevent the saw from even starting in this instance. The blade must already be in motion before coming into contact with the edge of the piece you’re cutting. This is because starting a saw while it’s in contact with the edge of your wood increases the chances of the wood catching on the teeth of the blade, resulting in kickback.
Why Do Circular Saws Kickback at the End of a Cut?
This happens due to binding. Adequately supporting the wood as you cut is important to consider when considering how the fall-away or waste piece is being supported.
When the cut is completed, will the piece just fall to the ground? If so, you will want to consider that this action can also pinch the blade of your circular saw, especially toward the end of the cut. That’s because the upper surface of the wood is in a state of tension, while the undersurface of the wood is in a state of compression (this is where the pinching comes from), much like that of bowing wood, just reversed.
At the end of the cut, you introduce yet another source of compression: as the piece is cut, gravity pulls the fall-away piece downward beginning at the start of the cut; the closer you get to the end of the cut, the more downward force is acting on the wood which pinches the wood together tighter. This is especially apparent if your supports are straddling your cut-line so that your fall-away piece falls inward toward the saw (please say it ain’t so).
Please remember that any amount of blade binding can result in kickback, and supporting your wood properly can be hugely beneficial in reducing the chances of binding your blade.
Back to Contents
- What is Kickback?
- What Causes Kickback and How to Prevent It?
- 1. Improper Support
- 2. Twisting the Saw
- 3. Using a Dull Blade or Using the Wrong Blade Type
- 4. Absence of a Riving Knife
- 5. Setting the Cut Depth of the Blade Too Deep
- 6. Adjusting ANY Part of the Saw or the Saw’s Direction While Cutting
- 7. Pulling the Saw from the Cut-Line Before the Blade Stops Spinning
- 8. Powering Up the Saw While It’s in Contact with the Piece You’re Cutting
- Why Do Circular Saws Kickback at the End of a Cut?