Hi Everyone There is also a Really Good Article on Our Blind Handy Man Files Area explaining Kick Back with Circular and Chain Saws . What causes circular saw kickback?
kickbackKickback is when a saw suddenly impacts and the wood is shot toward the front with a bang. When operating a table saw, stand to the side. The kickback zone is adjacent to the blade, and risk increases near the end of the cut. As wood exits the back, it is caught on the heel of the blade. The wood pulls into the blade and bounces away from the fence. The piece turns as it lifts off the table and rides back up and over the blade in the general direction of rotation. Use a long handled push stick with a notched tip to hold down stock against the table. Feed stock against rotation, entirely past the blade all the way to the rear. Don't let flexible panels lift off the table as they exit. If a piece is ever left adjacent to the blade, first switch off and let it come to a full stop before retrieving it. Don't pull back the scrap to the front with the motor running. Rotation direction more or less predicts where stock will go if it flies out. A table saw is aimed at your torso, with its target anywhere from your waist up to your head. When the blade is raised, it aims lower. A bandsaw aims downward. Bent teeth After a startling kickback, even without injury, for a few minutes adrenaline flows and the heart pounds. This could temporarily distract you, so it is a wise time to take a short break to look for the cause of impact. After an incident the suspect blade deserves methodical scrutiny. Investigate all around the rim for a chipped, bent or missing tooth and mark the plate near it. Carbide teeth are not supposed to be set or bent for side clearance like steel teeth. Sometimes a tooth was bent during the incident, but if it was already bent, it may have contributed to the kickback. A likely place to discover a bent tooth is next to an expansion slot. When mounting a blade, as the nut is tightened, some people put a screwdriver in the narrow opening to keep the blade from turning. This can bend a tooth several thousandths of an inch; enough to cause kickback or at best a very ragged cut. When you mount a clean, sharp blade, jam a scrap of softwood like a doorstop head on into the teeth to hold it still, and tighten the arbor nut. Anti-kickback blades prevent grabbing Anti-kickback blades are a wise choice when the teeth might impact those surprises encountered in gutting or tear-down. This type of blade has few teeth and carbide that won't fracture easily. Grabbing happens when a tooth bites too deep. To limit grabbing a high shoulder behind each tooth can be elevated almost as high as the tip. Shoulders running almost continuously around the periphery are also less likely to get bent. An anti-kickback blade can cut all the way through, but only at a measured rate. A blade with numerous teeth spaced close together naturally self-limits the rate of cutting so kickback risk is less, but it lacks efficiency. On an overhead saw, don't use a blade with grabby, forward rake that is overly eager to feed. Anti-kickback fingers on a saw blade are extra bumps on the shoulders behind teeth. Since rip blades have coarse teeth and big gullets, some rip saws have a hump back fin between each tooth. This safety bump looks like a dull tooth that leans back and can't cut at all but it limits grabbing. Take a second look when you mount one of these blades to be sure it isn't on backwards. Rotation speed and stalling The risk of kickback is greater for a lightweight portable saw with a weak motor that bogs down or stalls in heavy cutting, than it is for a big table saw with capable horsepower. Powerful momentum is safer. If you are using an underpowered saw you may need to raise the blade higher to reduce drag. Slow rim speed (Peripheral Feet Per Minute or Surface Feet) could also be caused by undersized blade diameter. Suppose your table saw held a 12 inch blade. If you put on a 6 inch blade, rim speed would be too sluggish. It is unsafe to use a diameter less than 60% of full size. Avoid binding Eliminate practices that could risk kickback due to binding or friction. On a table saw, behind the blade align the fence just a bit away. To cut bevels, position the fence so the blade slants away from it. Don't use a circular saw to cut freehand or curves; a bandsaw is an appropriate alternative. Don't let small pieces bind between blade and fence. When you use a miter gauge the fence is unnecessary. Using a table saw to trim a small piece off the end of a long board may risk kickback even with extended support, because it would be difficult to keep square. When you prepare to cut a large panel, arrange full support under all the parts so that as you cut them apart they will not shift, droop, pinch or bind and kick back. On a table saw keep all parts of the panel flat against the surface. Don't set a plywood blade too low. When it gets dull, wood may try to climb up and ride on it. When this happens don't force the panel down or it could jam or seize. Instead, stop pushing then slowly ease back and finally turn it off to raise the blade. A sharp blade is less likely to seize. Friction can cause binding. Fresh cut timber has a high moisture content. Green wood is springy and binds, so the wetter the lumber, the coarser the saw and the wider the kerf should be to reduce kickback. Warp could cause rubbing or binding. A warped plate is not perfectly flat. With a blade standing still, warp isn't immediately apparent, but you might detect a telltale scorched high spot that has been rubbing. Inspect both sides of the plate for anything else that could rub, such as lumps of gummy pitch, wrinkled labels or heavy rust. Spreader When ripping, wood may close back up and pinch as it exits the back. Warped lumber could twist as it is cut. Don't let the heel of the blade lift the stock. Prevent this kind of kickback by installing a spreader, splitter or riving knife just behind the blade. It is thicker than the plate but thinner than the kerf. A table saw is suited to ripping. Do not rip with a radial arm saw unless you lock the head parallel to the fence and feed against rotation. Featherboard Use a featherboard to put the brakes on backward motion. A featherboard has many narrow, springy anti-kickback fingers angled forward. It is often homemade of wood. One featherboard can be clamped to the fence to hold stock down against the table. Another can be clamped to the table near the front to hold stock against the fence. Strange Tales Of Woe Steadied a board to be cut on a swivel chair. What goes around, comes around. Left the chuck key where it could be found: in the chuck. It was even easier to find after it flew out and stuck in the wall at eye-level. Put a new blade on a portable table saw but it hardly cut anything. The boss said to turn the saw around. I pushed the table saw around the other way but it still couldn't cut butter. Got a snakebite due to reaching into a woodpile. Ran a dip-sealed saw through scrap wood to strip it. Some of the plastic went in the dust collector. The rest splattered all over. Put on a bigger saw blade, but forgot to adjust saw depth before cutting the workbench in half. Driving up a hill, the portable table saw fell off the truck and collided with a car. Fell off a portable belt sander during a race. They don't make those extension cords as long as they used to. Measured twice, cut once, and then stoked the wood stove with the finished piece instead of the cut-off. 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