User:Prototype Engineer/sandbox

Safety practices

The use of a push stick reduces the risk of injury.

Avoiding personal injury

One way to prevent injury is to use push sticks on medium-small pieces that would require the pieces to be held close to the blade.

When cutting small pieces that are shorter than the diameter of the blade, special attention is required. These pieces should not be cut "free-hand" using push sticks. Rather, a sliding-clamping jig is used to securely clamp the piece, then the jig is moved past the blade making the cut. This is particularly true when cutting very thin, very smooth pieces such as sheet aluminum or sheet plastic. Even when using a well designed push-tool, these small, smooth pieces have a tendency to rotate once the cut is being made, producing a poor cut at best.

Using a Sliding-Clamping Jig to cut small pieces.

Another way to prevent injury is to use springs, feeder wheels or featherboards to apply pressure on the side and top of the lumber when ripping. Traditionally they are clamped to the saw's table top to apply side pressure and to the fence to apply top pressure.

These featherboards and push sticks are substitutes for fingers.

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. For safety, the operator should 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.

The risk of kickback is reduced by certain practices:

• The blade must be kept sharp and clean, something novice users may not recognize. The buildup of pitch on a blade greatly increases friction and increases the probability of kickback. It also decreases the quality of the cut, causing the edges to burn and turn black.
• The saw must be aligned, adjusted so that it is parallel to the miter grooves, with the rip fence should angled 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.
• The blade guard should be used whenever possible. Typical table saws incorporate a riving knife, a spreader 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 called anti-kickback pawls.
• 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.
• When making beveled rip cuts on narrow workpieces, the workpiece should be above the angled blade and the fence. NOT below the angled blade and the fence. When the workpiece is below the angled blade, it is confined between table top, fence and blade. It can be shot out of the saw at a high velocity like a pitching machine. When the workpiece is above the angled blade, and a bad spot in the workpiece is encountered, the workpiece is not confined and may just "pop-up" into the air.

Optional safety features

In recent years, new technology has been developed which can dramatically reduce the risk of serious injury caused by table saws.

Dust extractor

A dust extractor should be fitted if sawdust is prone to build up under the cutting blade. Through friction the spinning blade will quickly ignite the accumulated dust, and the smoke can be mistaken for an overheated blade. The extractor also reduces the risk of a dust explosion and facilitates a healthier working environment.

Materials cut on table saws

Although the majority of table saws are used for cutting wood, table saws can also be used for cutting sheet plastic and sheet aluminum.

Cutting plastic sheet

When cutting sheet plastic, a new or recently re-sharpened carbide blade that has never been used to cut any other type of material (such as wood) should be used. For best results, the blade should be of a "Triple-Chip" design.

When cutting acrylic sheet (or other brittle plastic), the preferred rake angle (or hook angle) of the blades cutting edges should be 0°. These blades have cutting edges that "scrape" the plastic instead of "scooping" the material like most other blades which help prevent cracking of the cut edge. These type of blades should NOT be used to cut any other type of materials.

Special mention is in order, regarding the cutting of polycarbonate sheet (or other "tough" plastics). Polycarbonate sheet, used in bulletproof glass and safety shields, has the tendency to stretch instead of cut. When cutting polycarbonate sheet, it is absolutely essential to have a new or recently re-sharpened carbide blade. Using a dull blade can lead to very dangerous kickbacks and destruction of the workpiece. The preferred rake angle (or hook angle) of the blades cutting edges should be 10°-15°. Although, when cutting very thin material (less than 1/16 inch), a negative rake is preferred for the best cuts. When using these type of blades on the very thin material, the cutting edge breaks out (or knocks out) the material instead of cutting it, producing a cleaner cut. Using a normal blade that cuts, causes excessive vibration in the thin material, producing a very rough cut. In this case, a plain steel, fine tooth panel cutting blade (also known as a OSB/plywood blade), can be mounted in reverse (providing a negative rake) and used to cut the very thin material.

Cutting aluminum sheet

When cutting sheet aluminum a new or recently re-sharpened carbide blade be used. The preferred rake angle (or hook angle) of the blades cutting edges should be 5°-10°. Care should be taken when handling the aluminum, since the cut edges can be extremely sharp.

Cutting small pieces of aluminum and plastic sheet

When cutting small pieces of aluminum and plastic sheet (pieces that would be normally require push sticks to be used), push sticks should NOT be used. The pieces are too thin and smooth to maintain full control of them, likely resulting in a severe kickback. Small pieces should be securely clamped in a sliding-clamping jig (mentioned above).

Mini and micro table saws

A 1-inch (25 mm) micro table saw.

Mini and micro table saws are table saws that have a blade diameter of 4 inches (100 mm) and under. Mini table saws are typically 4 inch, while micro table saws are less than 4 inch. Although, the naming of the saws is not well defined.

Mini and micro table saws are generally used by hobbyists and model builders. Although, the mini table saws (4 inch) have gained some popularity with building contractors that only need a small saw to cut small pieces (such as wood trim). Being a fraction of the size (and weight) of a normal table saw, they much easier to carry and transport.

Being much smaller than a normal table saw, they are substantially safer to use when cutting very small pieces (but, don't under-estimate them, they can still cause severe injury). Using blades that have a smaller kerf (cutting width) than normal blades, there is less material lost and the possibility of kickback is reduced as well.

Miter Gauge

A Simple Miter Gauge

A miter gauge is a device used for holding workpieces at a set angle while being cut on table saws, band saws and sanded on stationary disk sanders. The miter gauge slides in a slot on the worktable (known as a miter slot) on the machine being used. Typically, the Miter Gauge and the workpiece are held together by hand and moved across the worktable making the cut (or sanded edge). Although, there are more sophisticated miter gauges that have the ability to clamp the workpiece or have adjustable stops for repetitive machining of workpieces.