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About Sharpening
	1. How sharp are new tools? 2. Tool sharpening in general 3. What causes wear on carbide? 4. How many times can a tool be sharpened? 5. side clearance 6. sharpening ForrestTM sawblades 7. diamond abrasives
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	New Tooling The design and production quality of modern industrial-duty cutting tools have evolved to a very high level of consistency and workmanship. Sophisticated engineering, manufacturing methods and quality control procedures result in optimized tool performance. Unlike earlier tooling of iron or steel, which was, and still is, frequently distributed with their cutting edges coarsely ground and in need of expert sharpening before they were ready for service, today's carbide tooling is ready for immediate service as shipped from the factory. When new, carbide tooling can be thought of as in its ideal condition, and should perform at its best. All dimensions, balance, surface finishes and coatings should be within the tolerances set by the engineers.
	General Note about tool service It is the goal of a service shop to restore damaged or worn tools to a condition where its performance is returned, as close as possible, to that of the tool when it was new. However, there are changes that accumulate over repeated use cycles that will ultimately require the replacement of the tool. The focus of the sharpening shop is on re-establishing the geometry and surface finish of the cutting edges, while maintaining the profile, concentricity, and balance of the tool. Re-sharpening, in all cases, requires removal of some material from the cutting edges. This is ordinarily done as a grinding process. Dimensional changes are inevitable. Cutting tips are made slightly smaller with each sharpening, slightly reducing the cutting diameter, and sometimes the kerf, of the tool. Wear, stress, vibration, and corrosion from use can also cause changes in the tool over time. Used tools, and re-sharpened tools are not identical to new tools. With each use and re-sharpening cycle the difference is increased, until the tool no longer meets the dimensional requirements of the application, or has become uneconomical or unsafe to use.
	What causes wear on carbide edges? When carbide edges wear, it is usually a combination of abrasion, fracturing and corrosion of the binder material. Abrasion occurs when the workpiece contains fine mineral particles. Some wood species, such as teak, are naturally abrasive and rapidly erode the edges of cutting tools. Fracturing occurs when pressure on the carbide exceeds its transverse rupture strength. This typically happens when the cutting edge suddenly strikes a particle or object of high density, such as embedded fasterners, or particles of sand or stone. In this event the cutting edge or face can chip or break. The chipping can be microscopic or quite large and easily visible. Corrosion occurs when the carbide binder material, mostly cobalt, is exposed to moisture and acidity which are naturally present in wood. The process is accelerated at the high temperatures that normally occur near the edges of high RPM cutting tools.
	How many times can a tool be resharpened? The number of times a cutting tool can be resharpened is a function of the size of the cutting tips and the amount of wear or damage that has to be removed in order to restore the correct cutting angles. For example, a sawblade, with tips measuring 1/8" thick and 3/8" tall could be expected to take between 10 and 15 re-sharpenings, assuming normal wear. Eventually the performance of the blade will deteriorate if the tips become too small. The side clearance (see illustration below) may become too little to prevent friction between the saw plate and the workpiece, the gullets may become too small to effectively clear chips out of the cut, or the tip seat becomes too small to support the carbide tips which can potentially break off, posing a safety hazard. A typical router bit will not yield as many re-sharpenings - perhaps 5-6 on average. Router bit tips are normally thinner than saw tips, so there is less stock available to remove. Router bits are also only ground on the face of the carbide, as opposed to both face and OD or "profile" grinding which would extend the number of sharpenings, but is not practical or cost justified in most cases.
	Side Clearance Side clearance, also known as "tip-to-body" clearance is what keeps a sawblade from binding in the workpiece. Traditional steel sawblades for wood-cutting achieved the same thing by having "set". Their tips are bent slightly, alternating one side to the other. When steel blades are re-sharpened, the teeth can be re-set. Carbide-tipped blades, on the other hand, cannot have their side clearance restored without a complete re-tip of the blade, which is not economical in most cases. Even though the sides of the tips are not normally ground in re-sharpening, the side clearance diminshes due to the clearance angles. Saw tips almost always have a slight taper from top to bottom and from front to back. Without it they would work with much greater friction, easily burning the wood and accelerating the wear on the cutting edges. As a result of having clearance angles, the kerf of a sawblade is gradually reduced with repeated sharpening. As the kerf is reduced, so is the side clearance. Wood cutting blades should have at least .010" of side clearance on each side. Teflon coated blades and some special application blades work with somewhat less clearance, but without at least some side clearnce, any blade would perform poorly.
	Sharpening ForrestTM Sawblades A well equipped, industrial sawshop is capable of re-sharpening the highest quality sawblades with accuracy and finish quality equal to that of the original factory grind. CNC grinding machines, such as our Walter systems, are the same machines used in the manufacture of new blades. Forrest sawblades are of exceptionally high quality, particularly in the flatness of the saw plate or "body". The close tolerance for plate runout allow them to use minimal radial and tangental clearance angles on the sides of the saw tips. That is primarily why Forrest blades leave such a smooth surface on cut edges. There is nothing unusual in the Forrest carbide tips themselves, in terms of their composition, grinding tolerances or finish quality, that can't be routinely reproduced by a qualified sawblade service facility. Forrest sawblades are expensive and must be carefully sharpened to close tolerances for proper performance. The manufacturer gives good advice when it recommends against having just any sawshop service their blades, and it is surely good business for the company to urge their customers to return the blades to the factory for service. No doubt they do an excellent job re-sharpening their own blades and , but it is definitely not the only place where they can be reliably sharpened. We have sharpened Forrest sawblades for many years for satisfied customers who enjoy the faster turn-around time and lower priced service we provide.
	Diamond Abrasives Virtually all precision grinding of tungsten carbide is done with diamond abrasives. Industrial diamond particles are bonded to aluminum or steel bodies in a wide variety of composition, shapes, sizes and grits. Machine shops traditionally used "green wheels" made of silicon carbide for free-hand grinding of single point tools such as lathe bits or boring bars. However, the erosion of silicon carbide wheels is far too rapid for saw shops to use on multi-fluted or multi-pointed tools where concentricity is of great importance. Diamond wheels also wear from grinding carbide. The consumption of diamond abrasives is, in fact, for many grinding shops, the largest expense after labor. Yet diamond wheels are sufficiently durable that, for example, under the right conditions a 120-tooth sawblade can be ground with only a couple ten-thousandths ("tenths") of an inch of wear on the face of the grinding wheel. This allows for excellent repeatability and thus the fine precision of modern automatic grinding machines. There is perhaps too much attention paid to the grit of a diamond wheel used in sharpening. The proper selection of grit is very important, but there are several other equally important considerations. Feed rate, stock removal, wheel concentricity, vibration, and coolant quality and pressure all have an effect on finish quality and precision. It is possible to achieve better results with a 240 grit wheel than a 600 grit wheel depending on the interactions of these various factors.