Although most people think of the teeth as the most critical part of a circular saw blade, the plate actually is. While the teeth are doing the actual cutting, it is the blade plate which ensures that those teeth are held in proper alignment, not wavering or chattering from side to side. It must remain flat after use in order to run straight and make smooth cuts without creating any noise. A poor quality blade plate will increase the saw kerf, by not holding the teeth in proper alignment.
HSS and Steel Alloys
Blade plates are typically made of high speed steel (HSS) the same material that drill bits are made of. This is a steel alloy, with small percentages of carbon and tungsten, molybdenum, cobalt, vanadium, chromium or manganese added to it. The purpose of these additional metals is to harden the steel, making it less prone to bending and warping. For high speed steel circular saw blades, the blade plate and the teeth are all one piece. However, the vast majority of circular saw blades have carbide coated teeth. For these blades, the plate is always thinner than the teeth, helping to reduce material sticking.
Precision and Flatness
The best blade plates are laser cut to exacting tolerances. Cheaper blades are stamped, with correspondingly lower tolerance levels. The high precision of laser cutting helps insure concentricity of the arbor hole to the position of the teeth, ensuring that all teeth meet the workplace equally. The greatest adverse factors are heat, centrifugal force and kickbacks. These influences cause plate warping, resulting in messy cut, vibrations and noise. Circular blade usually runs at speeds around a hundred revolutions per second. Next to the high temperature, this is enough to bend even a solid blade plate. If teeth meet any obstacle on its path, like knot or metal, kickback could seriously damage the saw blade. Breaking a single tooth will cause saw blade to be and run unbalanced.
An important factor in the manufacture of blade plates is the flatness of the steel used in their manufacture. In the steel mills, the sheet steel being manufactured is formed into huge rolls, weighing many tons. This is then taken to steel distributors and sheet metal manufacturers, who then flatten it and cut it into sheets. Even though it is flattened, there is a slight tendency towards waviness in the sheets. High quality blades are made either from steel which has never been rolled, but rather cut as it comes from the mill and kept flat in sheets, or the blade plates are individually checked and flattened, before and after tempering. Either process is expensive, but is essential to create a blade which has absolutely no wobble. The tensioning ring is occasionally added as a pre-tensioned circumference at 3/4 of the diameter of the blade that keeps long-term flatness. HSS sometimes isn’t enough hard for the part around the spindle called arbor, even if the steel is tensioned or rolled, so the industrial diamond knockout arbor is embedded.
Protecting the Plate
There are many different designs used in the manufacture of blade plates. Many have laser cut holes and lines in them to allow for plate expansion and reduce chatter. They are added not just to make saw blade slightly flexible, but to cool it by dissipating heat by air convection. In some cases these slots and holes are filled with softer metal, such as copper or brass, to help act as a vibration absorber.
Many companies coat their blade plates with other metals or Teflon as it’s the one of the most successful methods to fight plate deformations. This is done to help eliminate the possibility of sawdust sticking to the blade, maintain its hardness and prevent heating. Heat is an enemy of saw blades, in that it dulls the teeth and can cause warping of the blade plate. Coated saw blades have improved performance when cutting composite materials with adhesives like glue, and much better friction and corrosion resistance. Thin carbide, titanium or Teflon coatings barely have an impact on thickness of the kerf, which is actually great. The expansion slots, vibration holes and coating all work together to help eliminate the possibility of plate warping (see: troubleshooting).