Screw-on Router Bits and Threaded Arbors

A feature of most Her-Saf router bits is the screw-on style. The arbors are a separate item, available in several diameters and lengths, purchased individually. All Her-Saf arbors are threaded ¼"-28 as are most Her-Saf router bits. (A few Her-Saf cutters are solid-shank and are specifically identified as such. Another notable exception are the drill end cutters, which were specifically designed for the Kval "Edge" machine and are threaded 3/8"-24 to fit that machine.)

A common fear of those unfamiliar with screw-on tooling is that the router bit will work loose when the router turns. Of course, the arbors are threaded so that the action of the router tightens the bit onto the arbor even more. (Left-hand cutters and left-hand arbors are available for routers that run in the opposite direction.)

A cutter wrench is available which can be used to remove the router bit from the arbor. The aluminum cutter wrench (similar in shape to a tongue depressor) is placed in the open throat of the cutters (sizes .437" through 1.500") and turned to loosen them. Avoid using steel tools for this purpose as contact with steel will cause fractures and chips in the carbide cutting edge.

The advantage of screw-on tooling is faster speed in changing cutters, something woodworkers who need to change router bits often should appreciate. You can leave the arbor in the chuck and simply screw off one cutter and screw on another. If you are using the same size cutter, your depth doesn't need to be reset. It is important that the router bit be firmly seated (make sure there is no dirt or grit on the threads or between the cutter and arbor) but it is not necessary for the router bit to be any more than "finger tight".