Virtually nowhere are you more at the mercy of a vendor than with router bits. So much is hidden and so little is visible that you have to rely upon the reputation and guarantee of the vendor. It is no longer even possible to use country of origin as a reliable indicator of quality.

For example, we have bits made in Israel, Italy, the United States, and Taiwan. All of these bits have carbide inserts that have been made either in Germany or the United States, their bearings come from Japan, and they were probably all ground on machines that came from Germany. Even the steel bodies might have come from a specialist supplier.

What an individual firm brings to the manufacturing process is bit design, knowledge of the type of carbide to use, fineness of finish (both in the sharpening process and in shank preparation) and the care with which the inserts are brazed onto the steel bodies. The same components are available to all; it is the method of combining them and finishing them that is unique to individual manufacturers.

It is exactly for these differences among firms that we buy bits from four different countries. American companies are generally the best in high-speed steel router bits. This seems to go hand-in-hand with the fact that the best high-speed steel twist bits are still made in the United States.

Solid carbide bits are common in fairly small sizes. Rather than brazing pieces of carbide on a steel body, it is more economical to grind a carbide rod to the shape required. But again, this is a specialty. There are very few firms (one of which is in Italy), that can do this economically to a high standard. Finally, for carbide insert router bits, there are good manufacturers in a number of countries and it boils down to price at the quality level you want. In our experience, we have found that the best price/quality combinations come from Israel, Taiwan, and the United States.

This is a fluid situation. It was not that many years ago that the Taiwanese could not make a decent router bit. It may only be a few years until this widely disseminated technology raises China or North Korea or Thailand to a quality level that makes them a world competitive supplier. Meanwhile, we watch, we analyze, we test, we decide, and we catalog the results.

It is nearly impossible for you as a buyer to determine anything about the quality of carbide or the quality of steel in a router bit by visual inspection. You are limited to inspecting the sharpness, the overall finish, and the brazing.


Sharpness

The sharpness of a router bit depends upon the grit of the diamond wheel used to form the cutting edge. 400x diamond is routinely used. A few manufacturers use 600x on the insert face and 400x on the profile. Both the profile and the insert face of our router bits have been ground with a 600x wheel. This gives an exceptionally keen edge. Much as you would with a chisel, you test the edge on a router bit by sliding it along your thumbnail. It should slide along smoothly and if the bit is rotated it should take a small shaving from the thumbnail. You should never accept a router bit that has a chip in the edge even if it is a very small chip.

Because router bits are sharpened in a jig that controls the relationship of the router bit to the diamond sharpening wheel, they are sharpened to a condition called "spark-out". This means that the sharpening wheel is moved over the router bit surface several times until it no longer cuts at all. This gives a much finer finish than a single pass. So, when you sharpen your bit, you should use at least a 1200x diamond hone if you want to replicate the finish that comes from a 600x wheel when ground to "spark-out". Because you will not be filing to "spark-out", you will leave a more highly serrated surface for a given grit size than a jigged grinding device would.


Body Quality and Finish

Router bit bodies should never be out of balance and the only time you should ever experience a bent router bit is when you have misused a bit. A bit should always be seated as deeply as possible in the collet. The only qualification on this is that the bit should be allowed to bottom out in the collet and then be raised 1/32" to prevent heat transfer between the bit and the motor. Bits should not be gripped half way out of the collet. The farther a bit is from being fully seated in the collet, the more likely the bit will be damaged.

The size and finish of the router bit shank are important. Size should always be within 1/1000" of the stated size and the shank should have a smooth finish so that it will be gripped securely by the collet.


Brazing

Carbide inserts should be brazed to the steel body of a router bit without gaps and without porosity in the brazing. A brazing gap means that the insert will be unsupported and subject to fracture in use. A single pin hole in the brazing is nothing to worry about, but if the brazing has several of these and looks generally spongy, you can be fairly sure that this is a bit that you do not want spinning at 18,000 rpm in your router.


The Carbide in Router Bits

There is currently a substantial flurry in the marketplace about the micro-grain carbides. The carbide particles in a true micro-grain carbide are all less than one micron in diameter. Very small carbide particles produce a harder material; they pack closer together and less cobalt is needed as a binder. This gives maximum hardness and wear resistance, but unfortunately, it also reduces the toughness. The micro-grain carbides are most suitable for cutting abrasive materials of fairly consistent hardness. A number of man-made materials fall into this category. Wood, however, can be quite inconsistent in hardness; knots, for instance, are several times harder than the wood that surrounds them. A tough bit is required in such conditions. Our main line of router bits has no carbide particles larger than four microns and 80% of the particles are three microns or smaller.

It is sometimes said that micrograin carbides give you a sharper cutting edge. But because a 600x diamond wheel has particle sizes that average 16 microns in diameter, and since there is no porosity in good carbide, the particle size of the diamond sharpening wheel will dictate the fineness of the edge, not the carbide particle size. However, this should not be of major concern to you, since most manufacturers claiming micro-grain carbides do not supply them anyway.


Chip Limitation Bits

Virtually all of our bits are of the chip limiting style. These are very safe to use, but may require some adjustment in feed rates, since this type of bit is designed to limit the size of chip taken, in order to prevent kickbacks. For most routers at 15,000 rpm or higher, this is not a major consideration, but at lower speeds you may have to reduce your feed rate correspondingly.


Trouble-Free Finishes

Our carbide insert bits are coated with a type of polytetrafluoroethylene, a non-stick finish also used on cooking utensils. Unfortunately, this only keeps the bodies clear, so you should regularly remove any resin build-up that you find on the carbide insert. This can be done with resin remover or another cleaner. If you put a bit of machinery wax on it after cleaning, it will stay clean longer. (LGL)

 
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