The measurement of how fast a circular saw blade goes through the wood you are cutting is referred to as the feed rate. The feed rate depends on a number of factors, both from blade design and other. Some of the factors which have nothing to do with the blade design are motor speed, pressure applied towards moving the saw through the material, the density of the wood you are cutting and whether you are ripping or crosscutting.
Design and Feed Rate
There are a wide range of factors in the blade design itself which can affect the feed rate. The tooth number, design and geometry affecting the clearance and hook angles of the teeth are all major contributing factors. If the hook is positively angled but under the smaller values, from 0° to 10°, the circ blade has a lower feed rate and it is suitable for MDF, plywood, particleboard or chipboard. A neutral or negative hook angle gives a better control over the sheet due to lower speed. Such saw blades are good for double-sided laminate and melamine. Number of teeth and teeth shape is crucial for cutting speed. Less teeth means less times the saw blade will hit the surface being cut. Additionally, the gullet depth, kerf thickness and clearance can all affect the feed rate as well. The gullet depth in particular is a major factor in determining the feed rate. A deeper gullet will store more chips without binding, and has enough time to draw it from a cutting line. This allows a faster feed rate and the corresponding larger chips that occur. Otherwise the circular blade gets clogged and feed speed decreases.
Another thing which can contribute to the feed rate is moisture in the wood. High moisture content essentially makes the wet wood more dense, increasing the amount of power needed to push the blade through the wood. At the same time, the damp sawdust is much more likely to stick in the gullet and to the sides of the saw blade plate, increasing friction and temperature. Blades with coated plates reduce the possibility of sticking, countering this problem.
High or Low Rate
Generally speaking, the higher the feed rate, the faster you’ll finish the job. But this causes the poorer finish on the cut and the more pronounced the tooling marks. A high rate may be useful for some types of cuts, but too high rate can represent a potential damage to the sheet you are processing. A slow feet rate, especially with a high tooth-count blade, will provide a far superior finish with the tooling marks reduced. However, the slower the rate, the longer the cut will take and the more the saw blade will heat up.
Rip Cutting and Crosscutting
Rip cutting requires an aggressive approach to the lumber that’s cut in order to decrease the cutting time and avoid overheating of a saw blade. Ripping can generally handle higher feed rates than crosscutting, due to the ease in which the saw blade can remove the chips of material. By cutting with the grain, less pressure is necessary to push the blade tooth through the material. The tooth hook angle is, of course, positive. When crosscutting, the blade has to break every fiber in the wood as it passes through it. Feed rate can also affect the amount of power a saw needs, especially when crosscutting. High feed rate requires more horsepower to prevent the saw from bogging down in the wood. This bogging down affects the saw’s efficiency (in use of electrical power) and can cause the motor to overheat, tripping circuit breakers and thermal breakers.
The following formula describes the feed speed:
Feed rate = RPM x teeth number x chip load
RPM stands for “revolutions per minute” and “chip load” is feed rate per tooth. The rate is expressed in feet (or inch) of distance cut per minute.