From Wikipedia, the free encyclopedia
Important things to remember when using a table saw are:
- Read all warning labels and
the owners manual carefully before using the saw.
- When the saw is not in use,
it is a good habit to lower the blade below the table.
- Be sure to disconnect the
power when performing maintenance or changing blades.
- Use a push stick or other such
safety device when making cuts that would otherwise require fingers to be
close to the blade.
- Never use the saw in a way
that your fingers advance into the path of the blade. Always be fully
present and alert, as this piece of equipment causes more serious injuries
than anything else in the shop. Many experienced woodworkers know someone
who may have lost a finger.
- Keep the blade guard in
place whenever possible. If you do not like the guard that came with the
saw, it is possible to purchase and use an aftermarket guard of various
configurations. Note that one main function of a typical blade guard is to
act as a splitter, which helps prevent the cut in the wood from closing
and pinching the back of the blade and kicking back. Sometimes the blade
guard is more of a danger than a safety feature, most commonly during
smaller cuts (less than 3 inches), and cuts with a push stick, and should
be removed.
- Wood being cut can be
violently kicked back. This is due to advancing the wood in a sinuous line
or because natural stresses in the wood cause the cut to pinch the back of
the saw blade. This can be strong enough to cause the material to jolt
backwards and result in serious injury to the operator. The use of the
splitter or a riving knife can reduce or eliminate this
problem. See Avoiding
Kickback
- Wear eye protection. Eye
protection is paramount while operating all power tools. When
operating a table saw, it is particularly important. The rotational mass
of a spinning saw blade combined with a large electric motor can
contribute to the violent and unexpected ejection of material. Safety
glasses should fully encompass the eye area, including the front and sides
of the eye. Good safety glasses should be comfortable so they are always
worn when needed.
- Wear ear protection. Wear
ear protection to prevent the steady loss of hearing that occurs when
using power equipment without protection.
- Wear clothing that is not
excessively loose-fitting and tie back long hair. Loose-fitting clothing
and long hair can be extremely dangerous if it comes in contact with the blade.
This not only applies to table saws, but all power tools, especially a jointer and
a drill
press. Cuffs should always be buttoned if wearing a long-sleeved
shirt.
- The table saw must be
adjusted so the blade is perfectly parallel with the fence and the miter
slots. If it is not parallel, the workpiece can easily become pinched
between the blade and the fence, inducing violent kickback and causing
injury. The manufacturer of the table saw will very likely send a manual
free of charge.
- Always push the material
past the saw when finishing a cut. Pieces not pushed far enough past the
blade can get caught and violently drawn into the blade, resulting in
kickback.
- Use the saw defensively.
This could be the most dangerous piece of equipment that a woodworker
would ever use. The nature of wood includes variations in structure and
internal forces. It is not uncommon for natural stresses in a piece of
wood to cause the blade to be pinched and thrown violently. Do not work in
a way that such an event could result in injury. It is paramount to THINK
carefully and operate cautiously.
Avoiding kickback
Kickback happens when the blade catches the workpiece and violently throws
it back to the front of the saw, towards the operator. It can be thrown very
hard and can injure the operator. It is not uncommon for the object to have
high enough velocity to become embedded in a wall or to cause other damage or
injury. Never stand in a direct line between the blade and the fence when
ripping narrow stock. A kickback can be fatal.
Kickback happens when ripping if:
1. The wood pinches the blade because of internal stresses. This is
difficult to predict and can be impossible to control when using fingers to
hold the wood down. Many times the board pinches the blade and is thrown back
before the wood reaches a splitter. This type of kickback never happens when a
board is not cut all the way through (dado). By starting a cut with a dado and
then raising the blade to leave a splitter tab of uncut wood, this type of
kickback can be avoided, but raising the blade during a cut cannot be done
unless anti-kickback hold downs are used, so it is safe to raise the blade with
a free hand.
2. The wood is allowed to raise up or moved sideways during a cut, then
pushed back down, taking too big a bite at the top of the blade. This can be
prevented by using feeder wheels very close to the start of the blade and hold
downs after the blade to control the wood all the way through the cut. The
right feeder wheels are very effective for both dados in plywood and for rip
cuts on boards as narrow as 1/8". Feeder wheels can be powered or
unpowered, clamped or held magnetically, and replace fingers near the blade so
a hand can be free to turn off the saw during a cut.
3. The board is pinched between the rear of the blade and the fence. The
fence should be parallel with the blade, for the best cut on both sides of the
blade. The fence can be set with the rear farther from the fence for safety,
but at the expense of upcut marks on the "waste" piece. Never allow
the fence to be closer to the rear of the blade than the front.
Kickback can also happen when crosscutting boards with internal stresses. A
chop saw or circular saw is the best preference for cutting poor lumber.
- Blade must be sharp and
clean. Novices often may not recognize the importance of using a clean and
sharp blade. Pitch buildup on a blade greatly increases friction and
decreases the quality of the cut, causing it to burn. Pitch also increases
the probability of kickback.
- Saw must be aligned. The
blade must be adjusted so that it is parallel with the miter grooves but
the rip fence should angle minutely. If the blade is parallel with the
fence you will notice the marks made by the back of the blade on the wood.
It is possible for the workpiece to be pinched between the blade and the
rip fence, which will cause violent kickback if the fence is closer at the
back of the blade. The correct relationship for the fence is minutely
spread which means that the angle is different depending on the side of
the blade the fence is set.
- Use the blade guard when
possible. The blade guard on typical American market saws incorporates a
spreader called a riving knife, which helps prevent the cut from closing
on the back of the saw blade. Natural tension can exist in wood that
causes the cut to close. Some blade guards have anti-kickback devices that
allow only forward travel past the blade.
- Push the workpiece past the
blade. Do not release a workpiece until it is past the blade and removed
from the saw. Turn the saw off before removing small cut off pieces.
- Always maintain control. Do
not execute a cut where you do not have complete control of the situation.
Make sure there are no obstructions. Do not cut a workpiece that is too
large to handle.
- Do not use the rip fence as
a guide during crosscuts. If you need to make a series of equal length
crosscuts, use a stop block in front of the blade so the workpiece
is not in contact with the rip fence during the cut. It is easy for the
workpiece to twist out of perpendicular at the end of the cut and thus get
caught by the blade and thrown.
- Check for flaws in the
wood. Cutting through a loose knot can be dangerous. Cutting a warped or
twisted board along the rip fence is dangerous because it can get pinched
between the fence and blade.
New safety technologies
In recent years, new technology has been developed which can dramatically
reduce the risk of serious injury caused by table saws.
One way to prevent fingers from being severed is to use springs or feeder
wheels to apply pressure on the side and top of the lumber when ripping. These
feather boards and push sticks are substitutes for fingers. Traditionally they
are clamped to a saw top.
The new version, developed in 1990 to speed setup time is the magnetic
featherboard, which is held to a cast iron table top or steel fence plate by
high strength magnets. The fence mounted feeder has roller wheels which pull
wood to the fence. These roller guides are used both before and after the cut
and allow cuts with no fingers near the blade.
Power feeders are a motorized version with rubber wheels which take the
place of hands and assure constant pressure.
One new type of table saw, made by SawStop, incorporates a mechanism that
applies a small amount of electrical current to the blade of the saw. This
current is continuously monitored. If the saw detects a change in this current
(as would occur if a hand or other body part came into contact with the blade)
an automatic braking system is activated, forcing an aluminum brake block into
the blade. The saw stops within 5 milliseconds, and angular momentum lowers the
blade into the table. The operator suffers a small nick rather than a potential
amputation. This does ruin the blade, however. [2] Due to
the structural changes necessary to incorporate this technology into older
table saws, it is currently impractical to retrofit older units with this
system.
Blade height
There are two competing schools of thought when it comes to properly setting
the height of the blade for sawing. The first is commonly expressed thus:
"Only allow the blade to rise above the work by the amount of finger you
wish to lose." That is, the blade should protrude above the piece as
little as possible, to prevent the loss of a finger in case of a sawing accident.
Another competing view is that the saw functions at its best when the angle
of the blade teeth arc relative to the top surface of the workpiece is as
extreme as possible, facilitating chip rejection and shortening the overall
distance through which the teeth act on the part, reducing power consumption
and heat generation.
Each of these philosophies about setting proper blade height is true for
some cutting situations, but not all. When working on a piece that is thick and
short, such as a board in crosscut, the blade should be set high, but when
working on panel or sheet stock, the blade should be set as low as possible
while cutting completely through the piece.
