Tech Talk
What are "Carbide Tipped Saw Blades"?
The request is usually the same - "Just give me a blade that will cut everything." The response is just as simple - "there's no such thing!" Carbide tipped saw blades are used to cut almost everything from asbestos to Zirconium, including paper, plastics, rubber, steel, insulation, aluminum, and even food, as well as every kind of wood in the world and all the wood composites. Sure, almost any of the dozens of blade styles will actually cut all of these materials, but when you consider accuracy, finish, tool life and safety, there is no blade that will do everything.
The variety of machines carbide blades run on is just as diverse as the materials they cut. On a table saw, for example, the material is pushed through the blade and the cutting action is downward, whereas the radial arm saw is just the opposite - the blade moves into the material and the cut is upward. It only makes sense that the same style blade will not work equally on both. Because of this wide variety of materials and machines - with new ones being developed all the time - the saw blade industry is constantly updating and modifying blade designs. For our purposes here we will consider blades for cutting wood and wood composites. The first consideration in a carbide saw blade is quite simple - diameter. Use the saw diameter the machine was designed for. Cutting the cost by going to a smaller blade is not saving anything. Even if the material being cut doesn't require the depth of cut you will get from the proper size blade, you want the rim speed attained by a full diameter blade. The reduction in blade life and the likely decrease in cut quality will more than outweigh the initial saving. Next consider tooth count. The basic rule is the more teeth the finer the cut, but you also have to consider the thickness of the cut and the cutting feed rate. The fine tooth saws do tend to leave a smoother finish, because each tooth takes a smaller bite. However, if the material is too thick (remember, it's the overall thickness when it's stacked that's important), or if it is being fed at a high rate, the gullet capacity of fine tooth blades is too small. The gullet is the open space between the teeth and inadequate gullet capacity will cause burning, poor quality cut, and possibly heat damage to the blade. Conversely, not enough teeth will cut aggressively, at lower feed, or on thinner materials and leave a rougher finish.If you are cutting material that is finished on two sides, the tooth count may have to be higher and/or the feed rate lower, unless there is a scoring blade. Pre-scoring will allow a coarser tooth count and therefore a higher feed. So. if you make any changes to the material thickness, feed rate, or finish requirements,you may want to adjust tooth count accordingly.The last consideration is the tooth style. Blade manufacturers usually have specific brand names or numbers for the various tooth styles they offer. Generally, however, they fall into one of three categories: Square Top style - rip saw, for downgrain cutting of solid wood; Alternate Top Bevel (ATB) style - cut-off saw, for cross grain cutting; and Triple Chip style - designed primarily for composite board cutting. In addition to these basic designs there are specialty blades for specific applications that represent a small percentage of the saw blade market. These are often overlooked, yet can be very useful for solving specific problems, improving the product, or even eliminating a manufacturing step. The following is a few of the more common specialty blades available at most saw blade suppliers.
Thin Kerf/Thin Rim Saws - These blades come in all tooth styles, depending on the application. Thin rim saws have a thick body core, but the plate is thinner at the outer rim. On thin kerf saws the entire plate is thin. Thin rim blades have a maximum cutting depth limited by the depth of the rim. They can be used with standard saw collars. Thin kerf saws have no preset depth of cut limitations, but usually should be used with larger and very accurate saw collars or stabilizers for strength and accuracy. Neither of these blades is recommended for deep cutting. Thin Kerf/ Thin Rim blades are very popular in the plastic display business, but can also be very useful in fine woodworking, thin material cutting, and even cutting melamine and other laminates. The advantages are low resistance cutting, low waste, and generally an excellent finish. Overheating, running them too dull, pushing them too hard, or running them on poorly maintained equipment and/or collars will take away all the advantages of thin kerf sawing and could cause permanent damage to the blade. Attention must be paid to setting the blade height correctly, and they should never be used on unstable or green material. Sharpening is also critical, as the tooth geometry must be maintained. Thin blades should only be used for finish cutting.Chip Limiter Rip Saws - These blades are more widely used in Europe than North America. Between each tooth there is a hump-like shape, designed to limit the amount that the tooth following the hump will bite. The primary purpose of this is safety in hand feed ripping applications. The chip limiting hump will resist over-feeding, jamming and possible kick-back by controlling the in-feed rate of the material.Double End Tenon Saws - The tooth style on these is usually 3 or 4 teeth all top beveled one way, and one tooth beveled the opposite way. The purpose is so that 75 to 80% of the teeth are giving a clean finish on one side of the material, because the other side is waste. For obvious reasons, these blades come in left and right hand for each side of the tenoner. This style is also used on edge banders for trimming, and has also been used on other types of machines when one side is always waste.Negative Hook Saws - These blades are available in Alternate Top Bevel and Triple Chip tooth styles. There are two primary applications for this type of blade - the first being on overhead machines, particularly miter saws ( they are absolutely necessary on sliding miter saws) and often on radial arm saws. On these machines the negative angle of the tooth prevents the material from lifting and jamming the blade, plus the surface finish is usually better than the standard positive hook blades. The other application for negative hook blades is on table saws cutting double sided melamine board where there is no pre-scoring. In this application, when the blade is set at the correct height, a satisfactory surface finish can usually be achieved, as well as a reasonable life to the blade's cutting edge.Hollow Ground or Hollow Face Saws - These are specifically used for cutting double sided composite board, usually melamine. By design, the edges are very sharp and they do an excellent job of leaving a chip-free finish, top and bottom. The downside is that they tend to wear faster than some other styles and are little more expensive to sharpen. When conventional blades designed for this purpose will not work satisfactorily on a particular machine, usually the hollow ground blade will solve the problem.High ATB (Alternate Top Bevel) and Alternate Face Bevel Blades - These are used in composite board applications where surface chipping is a problem. Each tooth is ground to a very sharp and fragile point for cutting the surface fibres as cleanly as possible. They should never be used for solid wood sawing as the intermittent cutting resistance can cause tooth breakage.These are just a few of the many designs of carbide saw blades. Combinations of these tooth styles and others, along with variations in hook, kerf, clearance angles, carbide grades, and tooth pitch, make it possible to solve most sawing problems in wood and other machinable materials. by: Doug Reid, President, B.C. Saw
