Tech Talk
What is "Thin Kerf Sawing"?
Thin Kerf Sawing is the principle of reducing the thickness of the saw tooth., which reduces the width of the cut. This reduction in kerf can have a significant effect on waste reduction. For example, a standard 12 inch diameter Rip Saw has a kerf of approximately 0.155". A Thin Kerf Saw at 0.095" would reduce waste by almost 40%. This would also create an increase in either finished size or, quantity of pieces produced.
Thin Kerf Sawing is primarily used in Multi-Rip applications, because the gains are more predominant. Ripping 6 inch wide material to a finish of 3/4's of an inch would produce one full extra piece, if using the example above. At 50 ft. / min. this translates to 3000 lineal ft. per hour that you are getting paid for, with no increase in material or labour cost. Unless your goal is to increase finished size there may be little to gain in single or even double line ripping, or for that matter in cross-cutting, or trimming applications.The upside to thin kerf sawing is quite simple and obvious, so why isn't it an accepted normal practice? This is where it can get complex and why in some applications it just won't work. Every application for thin kerf sawing is unique, in that there is such a large number of questions and specifics to be considered, there is always some variations.The kerf you are trying to achieve is probably the first thing to consider. The finish size and the raw board size will determine the ideal kerf. In the example above, reducing the kerf further would not improve yield, and since the kerf required is inversely proportional to the degree of difficulty, there is little benefit to asking for 0.070" kerf, and a whole lot more to be addressed. The biggest obstacle to overcome is dealing with the body weakness of extra thin saw blades. The tooth is not the problem. It's the saw plate supporting the tooth that fails if the correct conditions for cutting are not maintained. Whatever the kerf is, the saw body has to be even thinner, to provide adequate side clearance (how much thinner depends on the material being cut) . Without side clearance, friction would occur between the saw plate and the wood, causing heat generation. Heat is your worst enemy. If heat is created in the body, expansion and warpage will follow, creating even more heat, by friction and cutting resistance. In heavy kerf saws a limited amount of heat can be absorbed and dissipated by the heavy body, but with thin bodies the heat builds faster, has no place to dissipate, and will do more damage because the blade is more fragile..It is well known that different materials have different machining properties. Also, different materials have differing affects on the on the cutting tool. Harder woods have more cutting resistance and require a stronger blade. All other conditions being equal, you could reduce kerf a little more when ripping softwood. Factor in moisture content here. Dry wood machines better (unless, of course, it is too dry) and is a lot easier on the blades than wet wood. The higher the moisture content the more side clearance is required (therefore higher kerf) to keep the material from rubbing on the plate. Wetter wood also greatly increases the wear on the teeth, again increasing the cutting resistance. Dressing is critical before thin ripping. Rough material will not go smoothly through the feed system and the material needs to be fed into the blade(s) firmly and securely, without any movement or vibration, therefore it must be D4S before ripping. How thick is the cut? This can affect how the blade is designed and how it is mounted. If, for example, the depth is 3/4", the blade could be designed to be thin only on the outer 1 to 1 1/4 inch of the rim, giving it greater strength and a bit better at heat dissipation. In lieu of this stepped body, or in conjunction with it, the spacers or saw collars could be made larger, strengthening the saw and absorbing some heat.Feed and Speed. The feed rate is dependant on several factors. Higher blade speeds allow higher feed rates, but, particularly with thin kerf sawing, material dimensions have a significant affect on the rate of cutting. Over-loading the blades will damage them - often irreparably - and under-feeding can cause substantial increased wear on the teeth. The last thing we need to know is the type of machine and blade diameter. Thin kerf ripping can be done on a Multi-Rip or a Moulder. Moulders have certain advantages over Rip Saws in that they usually run at higher RPM. This allows for either increases in feed and/or using smaller diameter saws. The smaller the diameter, the more stable the blade is.Although thinner blades offer less cutting resistance a gang of them can require a lot of power to drive them. Inadequate horse power will result in too much load on the blade. The blade will bog down, and heat up. Heavier blades, again, may be able to absorb a certain amount of increased cutting pressure, but not extra thin blades, and depending on the job, a standard machine may not have enough power to achieve the desired productivity from thin kerf saws.Thin Kerf Sawing can be a frustrating and costly experience if every detail is not addressed and all required conditions are not met. As a follow up to this we will look into set-up, maintenance and problems that can occur. by: Doug Reid, President, B.C. Saw
