It is assumed that general purpose blades will be used.
Blunt saws are known to contribute to many accidents. Instead of cutting efficiently and smoothly they require excessive effort from the sawyer, which combined with erratic cutting caused by variations in the material, can induce a dangerous situation. Modern carbide tipped blades have done much to reduce risk from this cause.
Using undersized blades increases the risk of accident because of the inefficient cutting which results from the low peripheral speed of such a blade. Such blades are more inclined to flutter, create a poor finish and/or deflect to one side. It is contrary to the UK factory regulations to use a blade of a diameter less than 60% of the of the sawbench's design size. (The drive of a saw bench is normally designed to give a speed of 3,000 metres/minute (10,000ft/min) with the intended blade).
Deposits of gum or resin near the teeth tend to cause a saw to stall or the timber to stick and so increase the risk of a throwback. Since the cleaning implement is liable to be caught up with the sawyer's hands drawn onto the teeth, it is dangerous to clean a running blade by pressing anything against the side of a running blade. There seem to be many recipes for soaking solutions, but it appears that in time almost any liquid, including water, will serve to loosen the gum. Oven cleaner is frequently recommended but it has been shown to slightly impair carbide teeth.
Do not use a saw with two or more missing teeth.
When sawing very thin stuff, the work can be fed too far into a gullet. Snatching occurs.
An appropriate height for setting the crown of the blade can be difficult to resolve. Please consider the following points:
Minimum Practicable Height
The gullets must be able to readily release their charge of dust. The minimum height needs to be set so that the gullet roots clear the upper surface of the workpiece.
When the bade is in this state, more teeth are engaged with the wood, hence there is less load on each tooth, and thus longer tooth life is obtained.
The blade makes the cut at an oblique angle. This can help to reduce breakout on the underside of plywoods and suchlike.
The sawyer-facing thrust is greater.
Some self-adjusting guards might raise themselves more efficiently when the blade is set low down.
As the workpiece approaches the blade, it sees what is more or less a curved ramp. If the wood is very hard, or the blade somewhat blunt, the work will tend to climb the ramp. Hurriedly then pressing down on the workpiece has been the cause of injuries.
Maximum Height
If the blade is set to the maximum height, the cut becomes more of a chopping rather than a slicing action. (At least one tooth must be in contact with the wood at any time).
The teeth exert less sawyer-facing thrust.
The action presses the workpiece more firmly against the surface of the table.
More gullets are exposed, hence better chip clearance is obtained.
Indirectly, the hazard is increased. When work on material of a variety of sizes is undertaken, the high position can be more convenient since there will be less need to stop to make adjustments to blade height. However, it takes considerable self-discipline to adjust some guards for each different cut (ie, so that its lower edge is not less than 12mm (1/2in) above the top surface of the workpiece). This points to the need for an easily but safely-adjustable guard.
Deep Cutting
This is work undertaken when re-sawing stuff that cannot be parted in one cut, ie it is too deep for the saw. The work is sawn from one side and then turned over for a second cut.
Where the height of the riving knife is greater than the crown of the saw, it has to be removed thus losing its protection. Riving Knives. This can mean that the crown guard also has to be removed.
The gullets cannot adequately clear themselves of chippings. There is a risk of overheating when the saw loses its tension, becomes drunk and binds in the cut, leading to a kickback. In UK factories it is illegal. (A bandsaw is more suitable).
Since the travel of each tooth is relatively long, the gullets are unlikely to effectively clear their load of chips. The teeth will not be cutting effectively. The work will tend to ride up the saw so the sawyer will need to press down very firmly and quite likely his/her hands will be too near to the blade. If control is lost, especially likely with small workpieces, the hands are likely to follow through onto the unprotected blade. (See below).
Friction can cause the saw to overheat, especially if the teeth are blunt or have inadequate set. The distortion resulting from the overheating will give rise to additional friction and the timber will have to be drawn back to ease the load. As the saw regains speed the horizontal thrust resulting from contact with the saw plate tends to fling the wood out of the worker's hands.
Quite probably the wood becomes burnt.
Bevelled Work
If a blade is canted to make an oblique cut, ensure that the workpiece is not trapped between the blade and the fence. In the event of the job being caught by the uprunning teeth, in being lifted this can generate a kickback of great force. For a blade that is canted to the right, transfer the fence to the left of the blade.
Table Saw Inserts
Loose inserts (finger plates) are usually supplied with a saw aperture wide enough to allow the saw to be canted, or sometimes to take dado cutters. Unfortunately when making some normal cuts the wide gap can allow thin wedge-shaped offcuts to become lodged in the aperture. To use a hand to try to remove them while the blade is moving is, of course, just asking for trouble.
Making a wooden insert with minimum clearance is a good idea. The usual tactic is to fit the insert while the saw is below table level and create the gap by raising the saw.
This can mean that workers have to bend down to operate the control wheel. Unfortunately there have been reports of people being hit as the insert is lifted and then ejected by the crown teeth of the saw.
