Circular saw blades may look simple, but they are surprisingly complex tools. If a blade is chosen correctly for both machine and application, the result will be cleaner cuts, less waste and longer blade life. But mismatching blades to work or machine can be disastrous. The best way to avoid that is to know more about blades.
No matter how good a blade is, it will not compensate for an underpowered or inadequate machine, says Jim Forrest Jr., of Forrest Manufacturing. Everything affects the performance of a blade, from the type of machine and model it's used in to the feed rate and spindle rpm of the machine.
Where to begin
"Typically the saw came with a blade approved by the machine manufacturer, which is always a reasonable place to start," says Greg Neer, director of sales for Leuco Tool Corp. But when it comes time to replace or upgrade an original blade, manufacturers agree that not all blades are made equally.
"A plate's stiffness is matched to its use," says Glenn Mihalovic, marketing manager, Gladu Tools. "Some manufacturers use better-quality steels; others provide better heat treatment." Bargain blades will likely not stand up to industrial use.
John Schulz of Super Thin Saws adds, "Tolerances are important, even critical to overall quality, especially in heat treating, surface grinding, straightening, flattening, tensioning and side grinding."
Mike Staudacher of Guhdo-USA Inc. suggests that it might be a good idea to determine the manufacturer's niche in the market and what market demands the blade meets - trade, shop, industrial or production. Staudacher also says you should make sure that you have a dense steel plate for longevity and that the plate is tensioned, or pre-stressed, so it will perform effectively.
Size, shape and quality of the carbide tips are other important factors. "Tips should be made of a C-4 micro-grain material to give long-lasting cutting life," says Gene Veening of Royce Ayr.
"What it boils down to is what tool will give you the cut you desire," says Fred Hoffman of AH Industries. And it's not just what you're cutting, but how thick the material is and how many pieces you're cutting at one time.
"If the customer is in a high-speed single-sheet or minimal-sheet application where we want the best possible finish, we would begin in a different geometry than a customer who wants to cut at a large book height with the large machines," says Neer. "Each specific grind and angle on a saw blade is designed for a particular performance aspect, whether it is speed, quality, longevity or durability."
Consider the teeth
"A one-tooth saw will do anything a 120-tooth saw does," says Hoffman. Although this is an exaggeration, he is making the point that the number of teeth the blade has must be considered in relation to spindle rpm, feed rate and the thickness of stock being cut. He recommends using as few teeth as possible to produce a quality cut and prevent burning.
What, then, is ideal? "For proper blade operation (at least) one tooth needs to be in the cut of the workpiece (at all times)," says Staudacher. To know how many teeth are ideal, consider the tooth pitch, he says. "Tooth pitch is the distance from any point on the face of the tooth to the corresponding point on the next tooth." The general rule of thumb is that narrow tooth pitch (less than 15mm) or spacing is better for hard or thin materials, while wide tooth pitch (26 to 70mm) is appropriate for soft or thick materials.
The most common mistake in selecting the number of teeth is in selecting too many, says Mark Leavens, saw blade products specialist at Leitz Tooling. "This causes premature dulling, finish quality problems and, in some cases, safety concerns."
One way to determine whether you're using the correct number of teeth is to analyze the chips produced by the blade, says Schultz. "Check your sawdust. If the chips are just powder, you will dull the blade very quickly and can burnish the surfaces of the wood. You need to feed faster or use a saw blade with fewer teeth. If the individual chips are too thick, they will have too much structural integrity and will damage the surfaces produced by sawing, especially the corners and ends."
Everything depends on the material, says Forrest. He says that he doesn't really think that the gullet between the teeth has to be big to effectively remove chips. He says that with so many teeth on a blade and the rpm and feed rate at a correct speed, each tip of the blade removes only a very small amount of material at one time.
The geometry of the blade
Different terms are often used to describe the same angle on saw teeth. Veening says, "The hook angle and cutting angle denote the same angle, which is the attack angle of the tooth. The smaller the pitch size of the blade, the higher the hook angle." For ripping, he says this would be 20 to 30 degrees, for cross cutting 10 to 15 degrees, for fine saw blades as little as 5 degrees and for melamine and non-ferrous metals 0 to -6 degrees is ideal.
Besides the angle of the teeth, there is also the shape of the teeth to consider. The five most widely used tooth profiles are flat top, alternate top bevel, hollow ground, triple chip and inverted V. There are also different combinations of these profiles.
"Flat type cuts you most always see in standard linear ripping applications, grooving or hogging. The advantage to the more straight flat cut is that you are in more control of the finish on the side without the broken cut, but often cannot control the exit cut," says Neer.
ATB teeth are often used in non-scoring applications. "We typically use this grind where we want a good clean top cut and a minimized chipping on the exit cut," says Neer.
Hollow-ground teeth have extremely precise upper points that give an optimum finish, and are considered ideal for double-sided coated boards, says Neer. However, this tooth configuration is fragile and prone to breakage, and sharpening is more critical, say manufacturers.
"Triple chip is best for manmade materials, which are typically hard or brittle," says Leavens, but is not good for cross cutting in solid woods.
"The blade (triple chip) has an excellent finish characteristic, but because of the flat raker tooth you cannot control the exit so you must use scoring," says Neer. "Triple chip blades are generally known as the 'standard' when it comes to horizontal beam saws," he adds.
The inverted V is often used in conjunction with other teeth configurations or a scoring blade. "It is a very good tracking saw, which is used in a lot of diamond saw blade applications," says Neer.
Whatever blade you use to get the finish you want, adjustments to the blade height can also improve the finish. "For example, proper blade height is essential to chip-free cuts," says Freud Tools. "If you experience chipping on the bottom of the material, lower the blade slightly. If there is chipping in the top of the material, the blade height should be increased slightly."
Thin versus thick
Tiny Coffin of L.S. Starrett says that with the price of lumber climbing ever higher, more companies are considering thinner blades, which produce less waste.
Thickness of the blade affects yield, the quality of the cut, how much power is required and the rigidity of the blade. "The wider the cut is, the more horsepower is needed. Some of the cheaper table saws and miter saws do not have the power to run an industrial blade," says Veening.
The disadvantage of thinner blades is primarily less durability. "The blades are more delicate and expensive to maintain, typically needing more adjustments in tension and strengthening, and a high level of calibration in the machinery running the blades," says Neer.
"A blade for ripping is normally made with a heavier plate than a fine trim saw simply because it has to work harder and still remain stable in the cut," says Veening. With a thinner blade there's less stability and it has a tendency to wander through the cut, giving a bad finish, he says.
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