If you own a band saw, you probably wish the blades would last longer. After all, once you have invested in a band saw, blades become the single biggest cost of operating it. What happens to the blade in the cutting process? Does it get dull — or worse, break? Heat is the biggest enemy of a band saw blade. As the metal blade gets hotter, cutting ability is diminished. The first signs of excessive heat normally are the teeth. Most blades used today have set teeth. In other words, each tooth is set or bent in a pattern — typically right, left, then straight. The overall set or outside dimension is usually between 0.06-inch and 0.08-inch. As the blade heats up, the set or bent teeth tend to move back toward the center, reducing overall kerf and clearance of the blade. As side clearance decreases, more of the body of the blade rubs against the wood, increasing blade temperature further and contributing to blade failure. A blade that has lost its set leaves tell-tale black marks on the wood being cut. Without proper set to the teeth, the blade rubs the wood, causing so much friction that it actually burns the wood — resulting in the black marks. At this point we call it a dull blade. Although it probably is ‘dull’ to some extent, the main reason that cutting ability has been diminished is because the blade has lost its set. The tips of the teeth get ‘dull’ from the same build-up of heat, but if you could maintain the set, the blade would continue to cut much longer. Heat also causes blades to break. When the temperature of the metal increases, the blade suffers fatigue, which leads to cracks. A crack eventually will widen until — boom! The blade breaks. What causes heat? There are three things that can cause the blade to become excessively hot. 1. The number one generator of heat is the friction caused by the blade cutting the wood. Feeding wood to the saw too fast can contribute to excessive blade heat. It is important to match feed speed to the ability of the blade. Other than that, there is not much you can do about the friction that results from the normal cutting process. 2. Another big contributor to blade heat is wheel diameter. The smaller the wheel, the more times the blade bends at a given blade speed. Also, the smaller the wheel, the sharper the bend the blade must make. These two factors work together to compound the problem on small wheels. 3. The last — and most easily corrected — cause of excessive heat is poor guide set-up. If the guides contact the blade, friction will occur, and friction causes heat. The trick to proper guide set-up is to get the guides so close that they appear to touch the blade but actually do not. About .005-inch clearance per side is correct. If the blade squeaks when you turn the wheel by hand, it will absolutely generate excessive friction and heat. Blade heat can be reduced by adding a coolant system to your saw. A liquid is applied to the blade by a drip or wick system throughout the cutting process. This helps cool the blade and also reduces sap build-up on the wheels. It may be messy if the saw does not have a good blower attached to it, but it is well worth while. Blades are the single largest cost of operating a band saw. Heat impairs the blade and eventually leads to blade failure. Reducing heat will improve cutting ability, extend blade life, and reduce your blade costs. (Editor’s Note: Sam Baker is the owner of Samuel Kent Baker Inc., which supplies machinery and equipment to the pallet and sawmill industries. He may be contacted at (866) 544-0538.)
