Sharpening Wood Cutting Tools
By Stanley Watson

Getting longer life out of your carbide tipped cutting tool portfolio, including router bits, saw blades, planer knives and molding cutters, is more than just keeping them sharp. Keeping them clean is perhaps even more important than worrying about whether they are sharp. In fact, regular cleaning is a proven way to extend the work life between sharpening your tools. I am sure you have noticed the accumulation of wood rosins on the back face of those carbide bits and blades. That is the culprit behind the premature demise of the cutting edges, not the mechanical wear of the actual cutting action.

Carbide cutters are typically comprised of a mechanical mixture of various hard carbides such as tungsten, titanium or vanadium carbides and a suitable metal or alloy as a matrix material. Most commonly found are carbide materials comprised of titanium carbide and cobalt binder ranging from about 2 to 20 percent. Chemical compounds found in the heartwood of many wood species (in varying concentrations depending on the species and whether the wood is dried or wet) such as tropolenes, thujaplicins and polyphenolic lignans will cause chelation of the cobalt binder very similarly as has been shown to occur with iron.(1)

Prolonged exposure to these resin deposits results in metal chelation of the cobalt which releases the previously mechanically entrapped carbides. This dulls or rounds the cutting edge or in extreme cases can micro chip the cutting edge. The amount of cobalt or other alloy binder present in fine grained versus coarse grained carbides is also proportional to the dulling action seen from the chemical attack on the cutter.

Coarse grained carbide cutters actually show a longer service life(2) than the more expensive fine grained carbides that are valued for their superior smooth finish when cutting. Since less matrix binder needs to be removed to release a smaller carbide particle, the finer grained tips will dull more quickly than the larger grained variety.

Excessive heat and creation of a minute electro-chemical reaction while cutting slightly wet wood accelerates this action. So cutters in constant use, even on wood with low moisture, are subject to greatly advanced deterioration. To maximize carbide-tipped tool life, sharpening is important. (Whetstones, such as DMT’s Diamond Whetstones, provide sharpness from one micron to 120 micron.)

Accounting for the importance of sharpening, cleaning the cutting tips of those wood resin deposits when you are finished with the tool is even more crucial. There are many commercially available and environmentally safe cleaners to choose from that are inexpensive as well. Cleaning the tool also affords you the opportunity to inspect the cutter for any damage or wear and will facilitate you keeping your tools in top form. A few extra minutes at the end of the day or the job will extend your cutting tool service life and result in savings you should be able to measure.

Watson is Technical Director of Diamond Machining Technology, Marborough, MA.

1. Kirbach, E., Chow, S., 1976 Chemical Wear of Tungsten Carbide Cutting Tools by Western Red Cedar
2. H. Sugihara, S. Okumura, M. Haoka, T. Ohi and Y. Makino 1978 Wear of tungsten carbide tipped circular saws in cutting particleboard: Effect of carbide grain size on wear characteristics

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