The shape of individual saw blade teeth are specific design elements directed at dealing with the physical properties of a vast range of materials seen in the woodworking industry. Our most common solid wood species vary greatly in density and strength. Most weigh from as little as 24 pounds per cubic foot to more than 70 pounds. Man-made wood fiber panels usually range from 30 to 60 pounds per cubic foot. We cut plastic materials that may weigh more than 100 pounds per cubic foot, as well as nonferrous metals weighing more than 200 pounds per cubic foot, with the same tools and machine processes. Tooth shape, cutting angle, tooth spacing and peripheral speed are the basis of all saw blade performance study, and have to be examined together.
Circular saw blades, like all cutting tools, have evolved as other related technologies have advanced. The introduction of new materials into the woodworking industry over the past half century have driven most of the changes that are now commonplace. The basic machining process, though faster in every way and more refined, largely has not changed.
Initially, circular saw blades were made of basic tool steel alloys having teeth that were bent, shaped and ground into forms that could provide a good cutting edge and lateral clearance and be easily maintained. The introduction of man-made panels and lamination materials created the need for hard metal teeth to provide a reasonable sharpening life.
Braze-attached saw blade teeth are a fairly recent technology that was developed more fully with the creation and mass marketing of particleboard/MDF and the onset of plastic laminate materials into the furniture industries during the late 1940s.
The basic circular saw blade plate, that is, the body of the tool, has not changed dramatically in appearance nor basic composition for several decades. The steel alloys are still produced and heat-treated in much the same manner. Strength properties regarding performance characteristics, such as horsepower, rim speeds and feed loads, have in most instances remained fairly constant, because these features have been studied for so many years at great depth. What has changed and been improved upon is the accuracy of the manufacturing process in steel making. Steel producers have all made excellent use of computer technology, too.
The many saw blade tooth shapes/forms that have been developed over the years were all the result of seeking a solution to a unique application or machining a particular material. Each special shape provides a different contact surface pressure in the cutting process. The first shapes to be developed were the flat top knife and alternate top bevel. Both were concerned with cutting solid woods - though admittedly both will work well in other materials under the proper conditions. These two tooth/knife forms are still practical, efficient and less costly to produce and maintain than most others, given their unique and simple shape.
A saw circular blade is an interesting tool to examine with regard to how the material is actually cut and the subsequent waste chips formed and removed. What is difficult to visualize and understand is the enormous speed involved in the cutting process.
Imagine first a blade having only 24 teeth, for instance, and being turned at 4,000 rpm. By crunching a couple of numbers, we discover that 1,600 times each second one of the 24 teeth is making contact with the workpiece and passing through it.
For a 48-tooth saw it would be 3,200 times per second. For a 60-tooth saw, it would be 4,000 times a second. For a 96-tooth saw it would be 6,400.
The purpose of this exercise is to illustrate that the cutting process for a circular saw blade takes place at an enormous rate of speed. There are few manufacturing processes that we could describe that involve such an ongoing stream of events, and we have to consider each cutting knife entering the process as a single event. In this manner it becomes clear that even small changes of tool geometry and cutting knife shape can and do have a dramatic effect.
The tooth/knife forms for saw blades that have evolved over the years have been shown to be highly effective. Some are costly to manufacture and maintain, others less so. Today, there are a vast selection of tools being produced and marketed, each having a well defined and prescribed set of operational conditions.
There is no all-purpose saw blade - one that does everything well, costs nothing and lasts forever. Of all tooth forms, a saw blade having alternate-top-beveled teeth probably has the broadest range of applications, but it will not cut all types of materials well. The cost of manufacturing and maintaining the most popular and widely used tooth forms has leveled out considerably. Just a few years ago, for instance, maintaining a triple-chip saw blade tooth required as many as four complete sharpening machine cycles, a cycle for each of the peripheral angles on the top of the tooth and another to grind the face if needed or desired. Today, a computer-controlled grinding machine does all of it in a single pass, with maybe a second pass to face grind. Other tooth forms are as easily sharpened with the current level of sharpening machine technology. s
Saw blade tooth forms
The most common saw blade tooth form for lengthwise cutting of solid woods works well because of the pre-splitting force of the contact surface pressure being directed forward. The beneficial effect is diminished when the rim speed and feed speeds are reduced.
The triple-chip or trapezoid tooth form produces three sets of contact surface pressure which has been shown to be successful for cutting a wide range of composite panels and laminated materials. This has been widely used for many years.
The hollow-ground tooth creates a contact surface pressure nearly identical to the effects of shear, even with the tooth impacting the material at 90 degrees. Hollow-ground teeth are very good at cutting expensive hardwoods and veneers, but are not widely used because of their cost and relative frailty.
Alternate top bevel
The most widely used tooth form is an alternate top bevel. The contact surface pressure simply moves from left to right as each tooth enters the cutting process. The mechanical effect is similar to providing a shear angle on each following tooth.
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