Deciding on Feed Rates

A wide range of variables -- such as the router RPM's, the depth of cut, the diameter of the router bit, the material you are routing, et cetera -- affect the required feed rate. When any of these factors change, your feed rate may need to be adjusted.

There are some basic guidelines to keep in mind when figuring your feed rate. A greater depth of cut requires a slower feed rate. The deeper the cut the more material removed and the more heat and side pressure generated. When heat and pressure reach the critical point the cutter will break off.

Smaller diameter cutters should be fed at a slower rate than larger diameter cutters -- although smaller diameter cutters require faster RPM's. This is a point of confusion for many because, when using the same diameter tooling, the rule of thumb is a slower feed rate for slower RPM's and a faster feed rate for faster RPM's.

The material being routed affects the required feed rate. Balsa wood, for instance, will machine much easier than rock maple or other hard woods. Real woods need a slower feed rate than engineered woods. Plastic materials require even slower speeds due to the risk of melting.

For maximum life, start at a "safe" feed rate, say 400" per minute, and then increase until you determine an upper limit where you are still getting a good cut. If the feed rate is too fast, the tooling can break. If the feed rate is too slow, the tooling can burn. Usually, the faster a bit is fed, the longer the cutting edges will last. Moving the cutter into cool material helps to keep the cutting edge from overheating; if you stop, the cutter will burn. When plunging use a slower feed rate.

Don't get attached to a magic number. Each combination of factors gives rise to a unique situation. When it comes to determining feed rate, nothing can substitute for the intuitive know-how of an experienced woodworker.