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  Clean Cuts

Sharpening tips for your woodworking tools

Router Bits


When you buy a carbide-tipped bit, take a good, close look at the cutting edges. Use a magnifying glass, if necessary. Look for good, clean brazed joint where the tip meets the shank. Tiny, hairline fault bubbles or cracks could indicate a poor quality bit. Be advised, however, that there's no way to forecast disappointment for certain since small gaps might cause no long range problems at all. Still, to be safe, we recommend that you buy a bit that at least looks well-brazed.

Not all carbide-tipped bits are created equal, either. You may find some tagged ?Carbide? while others may be tagged ?Carbide Production?. In most cases, the ?Production? bits have a heavier deposit of Carbide brazed onto the cutting edge, and that allows for more sharpening.

If you're planning to use your router for plywood or particleboard joinery or edging, by all means, invest in top-quality, carbide-tipped bits. If you're trimming high-pressure plastic laminates or rock-like composite countertop materials, ALWAYS use solid carbide or carbide-tipped bits, as high-speed steel bits will dull very rapidly on these materials.

When Carbide bits finally need to have their edges touched-up a bit, you'll have to use a diamond sharpening stone to do the job. When performing this job, be very careful to rub only the flat edge of the Carbide tip against the stone's surface and not, at any time, run the stone across the outer edges of the tips in a fashion that will change the bit's overall diameter.

Sharpening these bits can be a tricky process...especially since carbide bits can easily cost $30, $50, even up to $100 or more for large, specialized shapes. Ruining one of these babies can ?hurt?. If you're not confident in your router bit sharpening abilities, the good news is that virtually every town seems to have at least one, good, professional sharpening service. Even if your local professional lacks the specialized tools for sharpening carbide edges, he probably can recommend someone who has the right tools and the experience to do the job. Qualified sharpeners can even replace broken or chipped carbide cutter edges.

So, how can you tell if your local sharpener has done a good job? Held to the light, a well-sharpened edge should be free of shiny spots and small chips. The final test is simply to use the tool. You'll know right away if it's been sharpened properly by how smoothly and vibration-free it runs and by the finish it leaves on a cut edge. If it doesn't cut at least as well as when it was new, complain.

High-Speed Steel Bits - The workhorses
High-Speed (hardened) Steel bits are the least expensive bits and are the ones found most often in the shops of novice to intermediate level woodworkers. Originally formed from mild steel, these bits are then hardened in a special heat treatment process, usually to within 60 to 65 on the Rockwell ?C-Scale? of hardness.

There's no real secret to sharpening most of these bits. As with their Carbide counterparts, remember to take care in rubbing only the flat edge of the cutter against the stone's surface and not, at any time, run the stone across the outer edges of the tips in a fashion that will change the bit's overall diameter. Use an Aluminum Oxide stone such as ?India? or ?Aloxite? and be sure the stone is well-dressed with sharp, well-defined edges.

Fig. 1. Special purpose Aluminum-oxide honing stones.

A set of triangular or knife-edged Aluminum Oxide stones such as those shown in Figure 1 will make the whole sharpening process a lot easier. Their thinner edges make it easier to sharpen these comparatively tiny tools. Even the smallest of router bits - those used for straight cuts and veining - can be sharpened with a set of these stones. CAUTION: Drop one of these fragile stones on the shop floor and it'll shatter into a thousand pieces!

If you use a larger benchstone, mount it to your work surface with bench dogs or clamps to hold it steady while you rub the bit on it. Use a lubricant to keep the stone clean.


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