Plywood, MDF, Laminate, Melamine, Particleboards
Cutting engineered wood sheet goods is a special challenge. Circular saw blades used for sheet goods are applied for cutting a wide variety of wooden materials. This category includes anything that can be considered a plywood. The main parts of a sheet product are face and back veneer, and a core. Under the term “sheet goods” the following composite materials are considered: medium-density fiberboard (MDF), particleboard or chipboard, oriented strandboard (OSB), medium density overlay (MDO) and high density overboard (HDO), luan plywood, melamine and laminates, such as countertops, and other dense woods differing by the core type. These engineered products can be divided into two main categories: veneered and reconstituted panels.
Veneered and Reconstituted Panels
Veneered panels are made from layers of veneers, with the grain running in alternating directions, each 90 degrees from the previous layer. While the number of layers of veneer and the type of wood used for the veneer may vary, all layers of the panel will be made of veneers. Veneer core products made from sheets of thin layers are glued together in thick plies. The thickness of a veneer is less than 0.118″ or 3mm, and adhesive type depends on the type of use.
Reconstituted panels include all engineered panels which use chips, sawdust or particles of wood fibers. These are pressed together and heated, adhered with a glue or resin to compose a material, forming them into sheets. The outer surface of these panels is generally some sort of veneer or laminate. The vast majority of these sheet goods use some sort of an outer veneer layer, which can be highly susceptible to chipping, especially when crosscutting to the grain of the veneer. Laminated materials used for floorings or kitchen countertops consist of layers of paper or cardboard, high-pressured and adhered with resin glue. If laminate sheet was treated with low pressure, and melamine resin is used for bounding, the material may refer to “melamine board”. The lower the moisture content of the sheet goods panels, the greater the probability of chipping and splintering when sawing. This also increases on panels where the exterior veneer is extremely thin, such as luan plywood. Although mentioned sheet goods look so different, saw blades used to cut them have similar properties, considering the parameters such as teeth type and number, hook angle, kerf and diameter.
Chipping
Sawing panels is very risky and requires an appropriate circular saw blade since many of sheets have plastic veneers, like laminate, while the others like chip-prone plywood floorings demand a perfect precision. Saw blade selection is critical to reduce the possibility of chipping. Although there are several types of circular saw blades designed for dealing with these materials, some which work better with some sheet goods and others which are preferable to other sheet goods, they all have certain design characteristics in common. Mostly in the grind of the teeth. Creating the cleanest cut is possible only if the best saw blade for the sheet you are working with is chosen. Otherwise the circular saw could chip valuable plywood or double-sided laminate, which can represent a huge expense.
Teeth Shape: HiATB and TCG
Alternate top bevel (ATB) ground blades, which were developed for crosscutting, are generally good saw blades for cutting sheet goods. Saw blade with an alternating “left-right” composition of the tooth create an amazing effect on the paneling. The alternately ground teeth score the surface veneer of the panel, before cutting it, reducing the chance for splintering. However, its original purpose is crosscutting. The rougher finish just won’t look nice on boards prone to chipping like laminate or plywood. A modification of this design, HiATB blades, increases the angle of the top bevel (hence the prefix “Hi” in the name) increasing the amount of scoring which is accomplished by the blade and creating a cleaner cutoff. It’s a regular ATB circular saw blade with higher bevels angle, up to 38°, as the only difference. These blades have been specifically designed for cutting engineered wood panels, with the intent of reducing the amount of splintering.
If a HiATB blade is mounted on the circular saw, it will leave the smoothest cut for softer woods, but harder sheet materials like melamine, MDF and hardboards, or any other dense material can wear-out the saw blade teeth easily. It is common for blade manufacturers to use a combination of different type of teeth on a circular saw blade designed for cutting sheet goods. A perfect example of this is the triple-tooth style. TCG or “Triple chip grind” configuration is a suitable replacement for HiATB tooth design. This blade style combines cornerless “trapeze” teeth with a shorter flat-top raker tooth to clean out wood debris in the center of the kerf. Trapeze tooth is designed with the corners relieved to make the smooth, chip-less finish, allowing the FTG tooth to cut out the sides of the kerf, dealing only with the points of the cut. Industrial TCG saw blades are too abrasive and not recommended for softwoods because they chip the wood very likely. The main types of laminate saw blades, according to the teeth design are HiATB and TCG. The total tooth number ranges about 80, from 64 up to 150.
In case you don’t care how will laminate or plywood look after sawing, you don’t need to care about the type of your plywood circular saw blade. For rough cuts, even a planer blade with specific, so-called ATBR tooth pattern can be used. This blade has a standard ATB configuration with small but consequential modification: every fifth tooth is a flat raking tooth.
Hollow Ground and Thin-kerf Blades
Another tooth style which has been developed specifically for dealing with sheet goods is the “hollow ground tooth.” This is the most common category of circular blades used for composite materials and sheets. Hollow ground teeth present a sharer edge at both the top and sides of the tooth (sharper than 90 degrees), slicing the material more than chopping through it.
Some circular saw blades, which are designed for use with hardwood plywood, are thin-kerf blades. This is primarily done to reduce materials waste, due to the high cost of these hardwood plywoods. If you choose to use a thin-kerf blade, please keep in mind that these blades are more susceptible to flexing than standard blades. They measure 0.091″ or less, while normal full-kerf have 0.110″, 0.126″ or 0.150″ thicknesses of tooth. If the panel being cut twists slightly as it is being cut, the blade will probably follow, damaging the panel and possibly even damaging the blade.
Negative Hook Angle
Most blades which are specially designed for use with these sheet goods will have a slight negative tooth hook angle, of -3° to -6 degrees. This reduces the feed rate and simultaneously the aggressiveness of the cut, showing the blade’s travel through the material and helping the woodworker maintain better control over the cut. Hook angle can be neutral, 0 degrees.
Coatings and Expansion Slots
Laminate floorings and plywood should be cut with circular saw blades made of stainless steel, or even better, HSS (high speed steel) coated with tungsten or C4 micro grain carbide. It has a bit higher cost but much better efficiency and durability. This means cutting high density composite materials without wearing-out. Carbide coated teeth provide professional quality, excellent performance and long-term sharpness. The perma-shield coating helps to resist heat by reducing the friction. This can be useful when cutting the plywood with thin veneers glued in the plies, since saw blade melts the glue connecting the layers of plywood.
The saw blade expansion under the influence of heat must be compensated somehow. Additional improvements to blade’s plate include laser cut reeds like expansion slots. Laser cut slot begins in the gullet, finishing at the middle of the blade plate towards the arbor. If it ends with a copper plug, saw blade has anti-vibration/noise reduction properties offering a much better working experience.
Cutting Sheets
Sheet goods most commonly come in 4’ x 8’ sheets, although other sizes are available from specialty lumberyards. Sheets as wide as five feet and as long as twelve feet are manufactured, but due to their rarity, typically cost more. Table saws or hand-held circular saws are generally better for cutting sheet goods than radial arm saws are. Unless the pieces are pre-cut to approximate dimensions on a table saw or with a hand-held circular saw, they are normally too large to fit into a radial arm saw. Beside the selection of the right type of blade, there are some other precautions which the woodworker should make, in order to avoid damages of sheet. First of all, set the blade depth of cut to only about 1/4” higher than the thickness of the sheet. Permitting an excessive amount of saw blade to extend through the sheet increases the chance of the sides of teeth catching in the sides of the kerf, causing splintering. It is essentially to keep the sheet as straight as possible during the cut, avoiding it twisting and the sides of the blade scoring the sides of the kerf. For this reason, it is always recommended to work with an assistant as the individual panels can be a bit unwieldy for a single person. This problem is usually increased by the inability to use a fence, due to the size of the sheet.
When cutting sheet goods which have very thin veneer coatings, such as luan, chipping and splitting can be reduced by first scoring the cut line through the outer veneer coating with a sharp utility knife and a straight edge. The cut can then be made immediately adjacent to the scored line, totally eliminating any splintering on that side. Quality blade will make chip-free cuts even without pre-scoring. However, the panel may still splinter on the other side of the blade. Plywood has perpendicular grains between plies. This means cutting it will be both rip and crosscutting. Sheet goods should always be cut on a table saw with the face side (good side) up. This will eliminate the possibility of scoring or marking the face side on the panel on the saw’s table. It will also keep splintering of the face side to a minimum, as the greater amount of splintering will happen on the bottom side of the panel. If the saw blade is unacceptably grinding the face or bottom veneer, try to adjust the angle under which the saw is operating.
Conclusion
Finally, when selecting a circular saw blade for use in cutting sheet goods, pay attention to the manufacturer’s recommendations on the blade package. Although all these blades are similar in design and manufacture, there are slight differences and they cannot be put under the single category as the shops classified them. The saw blade will be designed with a particular type or group of paneling in mind. By selecting a sheet goods saw blade which best matches your material choice, you will receive the best possible cut and superior performance. When cutting, always remember that the side having an advantage when looking at the overall finish should face the saw blade.