I’m not a safety expert. Use your own judgement. This is just how I think about using a mitre saw:
Problems come when wood touches the side or rear of the moving saw blade. The problems are worse when wood touches both sides of the moving blade at the same time. Our job is to ensure that wood never touches the side of the blade while it’s moving.
Here are some points to consider:
You can counteract this by using a zero clearance fence or table. Alternatively or in addition, you can clamp either or both sides of the workpiece to stop it pivoting.
Note that small pieces are more likely to experience this problem than larger pieces because of mass, friction, and the principle of moments.
You can counteract this potential problem by being conscious of the two sides of the workpiece as individual pieces. Each must be fully supported. Make sure that your workpiece is supported from below at 4 positions with 2 on each side of the blade to counteract the force of gravity for that part of the workpiece.
Make sure when considering each side, that the support positions are on both sides of the centre of gravity of that part of the workpiece.
Clamping can be used to make up for instability, usually if the shape of the separated piece makes it intrinsically unstable. Try not to use clamping as a substitute for 4-point support from below.
Tension can come from two sources. It can be intrinsic to the wood, developed during growth. It can also be put into the wood (or put into equipment that is in contact with the wood) by the saw operator during positioning of the workpiece or during sawing.
In general, not much consideration is given to stresses within the wood that are released by cutting when using a mitre saw (as evidenced by the fact that mitre saws don’t have riving knives). This is because the mitre saw is mainly used for short cross cuts rather than long rip cuts.
Tension put into the system by the operator is a more pressing concern (literally). Pressing the workpiece against a stop block or a clamp can bend or compress the workpiece or the stop block or clamp. The gap opened by cutting the workpiece allows decompression or spring back, releasing the tension and potentially pushing the wood against the side of the blade.
The countermeasures for this issue are things like flip-up or two-piece stop blocks, but also awareness. You need to know that the issue is not specific to stop blocks, you can also put tension into the system by pressing against a clamp put in place for legitimate reasons as described above, or just by pushing the workpiece towards the blade with your hand or a stick.
If your stop block and a single clamp are on the same side of the blade and there’s no work holding (whether clamp, stop block, or hand) on the other side of the blade, you won’t have a problem. Tension could be locked in between the clamp and stop block, but it will never be released during sawing. (Obviously, don’t release the clamp before the saw blade is stationary or out of the way).
But as soon as you put any pressure on the workpiece that acts towards the blade, you could have a problem. It’s important to understand that the pressure can be locked in by clamps or stop blocks or applied during sawing by careless manual holding.
Problems come when wood touches the side or rear of the moving saw blade. The problems are worse when wood touches both sides of the moving blade at the same time. Our job is to ensure that wood never touches the side of the blade while it’s moving.
Here are some points to consider:
- When you advance the blade to make a cut, you exert a force on the wood in that direction. If there is not sufficient support (fence and/or table) behind the wood in the direction you’re advancing, that force can cause the wood to pivot and hit the side of the blade.
You can counteract this by using a zero clearance fence or table. Alternatively or in addition, you can clamp either or both sides of the workpiece to stop it pivoting.
Note that small pieces are more likely to experience this problem than larger pieces because of mass, friction, and the principle of moments.
- When the saw has separated the two sides of the workpiece from each other, gravity (and air currents!) act on each piece individually. If either side of the workpiece considered alone could move or fall towards the blade, you’ve got a problem to address.
You can counteract this potential problem by being conscious of the two sides of the workpiece as individual pieces. Each must be fully supported. Make sure that your workpiece is supported from below at 4 positions with 2 on each side of the blade to counteract the force of gravity for that part of the workpiece.
Make sure when considering each side, that the support positions are on both sides of the centre of gravity of that part of the workpiece.
Clamping can be used to make up for instability, usually if the shape of the separated piece makes it intrinsically unstable. Try not to use clamping as a substitute for 4-point support from below.
- Tension can be released during the cut and cause the wood to move into the blade.
Tension can come from two sources. It can be intrinsic to the wood, developed during growth. It can also be put into the wood (or put into equipment that is in contact with the wood) by the saw operator during positioning of the workpiece or during sawing.
In general, not much consideration is given to stresses within the wood that are released by cutting when using a mitre saw (as evidenced by the fact that mitre saws don’t have riving knives). This is because the mitre saw is mainly used for short cross cuts rather than long rip cuts.
Tension put into the system by the operator is a more pressing concern (literally). Pressing the workpiece against a stop block or a clamp can bend or compress the workpiece or the stop block or clamp. The gap opened by cutting the workpiece allows decompression or spring back, releasing the tension and potentially pushing the wood against the side of the blade.
The countermeasures for this issue are things like flip-up or two-piece stop blocks, but also awareness. You need to know that the issue is not specific to stop blocks, you can also put tension into the system by pressing against a clamp put in place for legitimate reasons as described above, or just by pushing the workpiece towards the blade with your hand or a stick.
If your stop block and a single clamp are on the same side of the blade and there’s no work holding (whether clamp, stop block, or hand) on the other side of the blade, you won’t have a problem. Tension could be locked in between the clamp and stop block, but it will never be released during sawing. (Obviously, don’t release the clamp before the saw blade is stationary or out of the way).
But as soon as you put any pressure on the workpiece that acts towards the blade, you could have a problem. It’s important to understand that the pressure can be locked in by clamps or stop blocks or applied during sawing by careless manual holding.
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