Tip #21
Choosing A Router Bit (continued)
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High Speed Steel Bits: the workhorses

High speed hardened steel bits are less expensive and found more often in the typical homeshop. Formed as mild steel, these bits are hardened in a special heat treatment, usually to within 60 to 65 on the Rockwell “C” Scale.

There's no real mystery to sharpening most of these bits: the steel in them is hard, but if you own a common bench-stone, you can hone the larger varieties and put a keen edge back on them. The stone you use should be well-dressed, with sharp, well-defined edges. An aluminum-oxide stone works well (“India” or “Aloxite”).

Figure 1. Special purpose Aluminum-oxide honing stones

You can make the whole process a lot easier if you purchase a set of aluminum-oxide triangular or knife-edge stones. (See Figure 1) Their thinner edges make it easier to sharpen these comparatively tiny tools. Even the tiniest of router bits -those used for straight cuts and veining - can be sharpened with a set of these stones. (But watch out! Drop one of these fragile stones and it'll shatter to pieces.)

Figure 2. Honing face of router bit on benchstone

If you use a benchstone, mount it on your worktable with bench dogs or clamps to hold it steady while you rub the bit on it. Use a lubricant to keep the stone clean. Honing almost all router bits is based on the principle that the whole face of the cutting flute is on one plane. If that flat plane is large enough, you can find and hone it. Touchup sharpening is always done on the face of the flute, never on the contoured profile. (See Fig. 2.)

Unlike honing large chisels on a bench-stone, the action of the stone on these small tools is limited to very, very small movements: 1/4" total back and forth movement, or even less.

Figure 3. Drill chuck mounted on tailstock chuck arbor to hold router bits while sharpening.

You might choose to mount the bit securely in a vise and move the stone. You can put together a handy vise to hold router bits by mounting the drill chuck on the tailstock chuck arbor in the lathe tail-stock of the Mark V. (See Fig. 3.) Squirt a drop or two of oil on the bit itself and position the stone on the major portion of the flat. Avoid rubbing the pilot as you hone - this will ruin the bit. When the oil on the bit darkens with swarf (little flakes of metal) you'll know that you're on the way to a keen edge.

If you're having trouble getting the feel of the flat, you can check just how well you're doing by using a dark color felt-tipped marker to coat the bit's face. By checking to see how much of the color is removed, you can tell whether you're honing the entire surface. It helps to use a good, concentrated light and a magnifying glass.

If a burr forms on the profile of the bit, remove it carefully with a Hard Arkansas stone. To check for sharpness, run the cutting edge over your thumbnail: it should “grab” the nail and leave a light “track” rather than slip over it easily.

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