A circular saw is a useful tool that we can find not only in professional workshops but also in the home. There is a wide variety of circular saws available in different sizes, which can cut many materials such as, among others, wood, metal, plastic, masonry, asphalt or floor coverings.
The cutting element of the circular saws consists of circular blades or blades constructed of various materials and available in a wide range of sizes and types of teeth that affect a particular choice. The price of circular saw blades varies greatly, and many of the most expensive products have characteristics that give them a longer life and better performance. The economic leaves can quickly lose the edge, but they are ideal for those who use them sporadically.
For example, you have a certain idea, specific material and you need to decide which 8″ table saw blade you want. For this reason, it is essential to choose the correct blade for a particular circular saw model. In this article, we will detail the main parameters that we must take into account to choose a circular saw blade.
As always happens when making a purchase, we must first ask ourselves a series of questions that can serve as a guide. For example:
1) What kind of material are we going to cut and what is its thickness? Is it wood? And in that case, soft, hard, chipboard, laminated or plywood? Is it plaster, plastic, granite, concrete or non-ferrous materials? It is important to know that the saw blades are constructed of different materials and have been designed according to what they are going to cut, even if the work surface has nails and screws in the direction of the cut.
2) What type of machine do we have for cutting? A stationary circular saw? A miter? A portable saw with a cable or a wireless one? Some saw blades are designed to be used exclusively on a certain type of saw, so ignoring this detail can produce poor results and can even be dangerous.
3) What type of cut do we want to make and what degree of finish do we intend to achieve? For example, if it is wood, do we want to cut in the direction of the grain (longitudinal) or in the direction transverse to the grain? Or do we prefer to make a dry or wet cut? Again, the availability of saw blades for each of these functions is vast and the finishes vary between regular, good and excellent, where it is always about avoiding the chopping of wood and the formation of burrs in other materials.
In previous articles of Machines and Tools, we provide a series of guidance tables on the type of abrasive discs to be used depending on the material and the type of machine to be used. A large part of this reasoning also applies to the circular saw blades that concern us in this article.
The fundamental difference between the abrasive discs described in these articles and the saw blades lies in their construction. The saw blades are fully metal parts provided almost always of teeth. There are four different types of materials to manufacture the teeth, so in the market, we will find the following varieties of saw blades:
|Saw Blade Material||characteristics||Applications|
|Tool steel||Blades entirely of tempered carbon steel.They are economical and work well for cutting softwood, but they are quickly dull in hardwood.||Softwood.Thick steel tubes.Non-ferrous materials|
|Quick Steel (HSS)||Tempered carbon steel blades with cobalt, chrome, molybdenum and vanadium alloy tips.Good surface finishes are obtained, but they should not be used in abrasive wood or chipboard.||Soft and semi-hardwoodSteel and stainless steel.Ferrous and foundry materials.PipesPlastic.Aluminum.|
|Carbide||Tempered carbon steel blades generally provided with expansion slots to reduce heating and prevent kinks. They can be of two types:With sintered metal carbide teeth (tungsten carbide powder + cobalt carbide).With teeth that have HM hard metal inserts (widia): they allow optimal finishes and excellent durability.||Soft, semi-hard and hardwood.Agglomerates.Melamine.PlasticsAluminum, steel, copper and non-ferrous metals.|
|Diamond||Tempered carbon steel blades with a continuous or segmented edge of a poly crystalline diamond (PCD).They usually do not contain teeth.Exceptional hardnessPerformance far superior to carbide inserts.Ideal for highly abrasive materials.Excellent performance in solid wood without knots.||Hard and abrasive woods.Chipboard and plywood.PlasticsAluminum.Non-ferrous materialsCeramics.Glass.Concrete.Asphalt.|
In view of its own design characteristics, the performance of a saw blade is determined, in part, by the following parameters.
- Cutting width
- Number and pitch of teeth
- Throat size
- The angle of attack of the teeth
- Tooth geometry
It depends on the thickness of the material to be cut and in the market, we can find saw blades whose diameters vary from approximately 85 mm to 650 mm. It is important to achieve the maximum stability of the machine and the smallest possible stroke of the saw blade, and this is achieved with a small diameter, although, in this respect, the decision will be given by the characteristics of the machine and by the diameter and the rotation speed of the rod that carries the saw blade. Usually, the most common diameter is 184 mm. However, table saws and miter saws. They may require larger diameter sheets, for example, 250 or 300 mm. The type of material to be cut and the type of cut to be made must also be considered: if it is solid and moist wood, it is advisable to use large diameter blades and few teeth. For cross-cuts, blades of intermediate diameter and number of teeth (more than 40 teeth) are used with which a better cut finish is obtained.
Number and pitch of teeth
Although there is a wide selection in the number of teeth that contain the circular saw blades, the general rule is that fewer teeth cut faster. The number of teeth is usually measured by the size of a particular sheet, and most products are identified by their number of teeth per unit length (centimeter or inch). The saw blades having fewer teeth create larger cuts and are ideal for longitudinal cuts parallel to the longest edge. The blades that have more teeth are better for coarse cuts of transverse type.
The distance between each tooth is called a step. To obtain a good quality cut it is essential that a certain number of teeth penetrate the work piece at the same time. Generally, the thinner the material, the smaller the pitch of the tooth (and the greater the number of teeth), so that a finer finish is obtained. The thicker the material, the greater the pitch of the teeth (and the smaller the number of teeth), which generates a more coarse sawing. The amount of teeth on a disc is also adjusted according to the feed rate of the sawn material.
It is the thickness of the sheet and therefore represents the groove that produces this when penetrating the work piece. Some sheets are thicker, while others are thinner. Blades that have a greater cutting width are usually more expensive, but usually, last longer, extract more material, produce a slow cut that requires more force and are ideal for cutting through nails and screws.
Blades with smaller cutting widths are ideal for carpentry finishing because they remove less material during cutting, are faster, sharper and softer, but are less stable than wide cuts and can be quickly deflected.
The throat is the space in front of each tooth to allow the evacuation of shavings. In a longitudinal cutting operation, the feed rate is faster and the chip size is larger, so the throat has to be deep enough for a large amount of material to be handled. In a cross-sectional blade, the chip is smaller and smaller per tooth, so the throat is much smaller. Combined saw blades can be purchased commercially (see figure below) that are designed to handle longitudinal and transverse cuts. These leaves have large and small throats between the groups of teeth: the large ones help to clean the greater amounts of material that are generated in the longitudinal cut, while the small throats inhibit a speed of advance too fast in the transverse cut.
The angle of attack of the teeth
On most saw blades, the faces of the teeth are tilted forward or backward, rather than perfectly aligned with the center of the blade. This is called the angle of attack. On a blade with a positive angle of att 0° ack, the teeth are tilted forward, toward the direction of the blade’s rotation. A negative angle of attack means that the teeth are tilted in the opposite direction to the rotation, and an angle of attack of 0° means that the teeth are aligned with the center of the blade.
The degree of penetration is given by the angle of attack and the best finish of the piece is obtained with large angles, although if the material is especially hard or abrasive, this will shorten the life of the tool. Generally, soft materials should be worked with tools that have a large angle of attack, and hard materials, with a smaller angle of attack. As a rule, it can be said that the angles of attack are inversely proportional to the hardness of the material to work.
The different shapes of the teeth of a circular saw blade are more or less suitable for different work materials and cutting conditions. Generally, the saws contain only one type of tooth or two different types of alternately. In the following table, we detail the most common geometries, with the acronym in English in parentheses.
|Flator Straight(FTG)||It is a single type of flat top tooth.Optimal for quick and rough longitudinal cuts in solid wood and uncoated boards.Easy maintenance|
|BeveledAlternateor Variable(ATB)||The tips of the teeth are beveled alternately to the right and left, tearing the fiber from the material to produce a clean cut.Suitable for universal application in soft and hard wood, pressed chip boards, composite materials, sensitive or thin-coated board materials, multi-sheet boards, plywood, fiber composite materials and MDF.Ideal for longitudinal and transverse cuts.|
|FlatorTrapezoidal(TCG)||A slightly higher trapezoidal tooth is followed by a flat tooth.The trapezoidal tooth cuts a groove through the material followed by a flat tooth that cleans the cut.Suitable for universal application in profiles and solid materials: table of pressed shavings, soft and hard wood, board materials (coated on one side or both), plastics, non-ferrous metals, copper, brass, aluminum, laminates, chipboard and other wood-derived materials.Deliver an optimal finish.|
|A tooth with the pointed top is followed by a rectified tooth with a concave shape.Suitable for board materials coated on one side or both.Ideal for cutting laminated boards and highly abrasive materials without using an incisor saw blade, with a very clean cutting result and long service life.|
By way of synthesis of what we have just seen, the following guidelines are generalizations that can help us achieve the successful purchase of a circular saw blade.
- The more teeth the saw blade has, its useful life will be less, its cost will be greater, we will have a low feed rate, it will require a tool of greater power, and we will obtain a smoother, more uniform and delicate finish.
- The fewer teeth the saw has, its useful life will be longer, its cost will be lowered, we will have a high feed rate, it will require a lower power tool, and we will obtain a less uniform and more coarse finish.
- The fine pitch of teeth is ideal for shortcuts and hard materials.
- The wide pitch of teeth is ideal for long cuts and soft materials.
- Teeth with a positive angle of attack confer more aggressiveness to the cut.
- The teeth with an angle of attack 0 reduce the possibility of the saw jumping bacfewerkwards, avoiding the risk of harming the saw, the operator and the material to be cut.
- The teeth with a negative angle of attack are designed to improve cuts in materials such as non-ferrous metals.
- Taking into account the thickness of the material, to determine the correct number and pitch of teeth there must be a minimum of 3, but no more than 4 teeth that penetrate at the same time the material to be cut.
- Finally, the following table details some additional recommendations according to the material to be cut.