From DIYinfo.org
A router is one of the most useful tools a workshop can have. Few tools can rival a router for its versatility. With the proper jigs and a little creativity you can use a router to cut out circles, edge-join wood and veneer, plane wood, cut mortise and tenons, rout a dado groove, make copies from a pattern, and an almost unlimited number of other things.
The most common use for a router is to add shapes and profiles to the edge of a project. Before the router was invented, early woodworkers had to use special planes fitted with custom blades to create these patterns. With a router and a pilot bit, you can create the same shapes in a matter of minutes. Few tools are as accurate as a router; many woodworkers use a router to straighten and smooth joints that must be cut to the highest tolerances.
[edit] Bit Terminology
Solid Bit – A router bit machined from a solid piece of steel. In some cases a screw is mounted on the top for the bearing.
Pilot Bit – A router bit fitted with a bearing or less commonly, a steel pin coming from it’s top. The bearing rubs the edge of the workpiece and limits the cut of the bit. The bearing spins at the rate the router is moved while the bit spins at the speed of the router. Different size bearings can be used to achieve different depth of cuts.
Arbor – The arbor is the shaft of a router bit that typically fits into the collet.
Collet - In a router, the collet is the sleeve that grips the shank on a router bit.
Shank - The part of the router bit that is inserted into the collet.
HSS – High Speed Steel – A heat resistant form of steel used to make some router bits, saw blade, and drill bits.
Carbide – A very hard and brittle metal made from tungsten-carbon particles fused with
Cobalt - Carbide is harder and more heat resistant that steel but it is also more expensive.
Titanium Nitride – Titanium Nitride is a surface coating that is often added to HSS router and drill bits. It improves surface hardness and increases lubricity, Bits coated in titanium nitride have a golden tint to them.
Hook or Rake – The degree to which the cutter leans into the cut.
[edit] Bits
The bit is arguably the most important element in ensuring a quality finish and a good clean cut. You are probably wondering, "What about the router or woodworker? Aren’t they just as important?" While both the router and the woodworker are important, neither are as critical as a good quality bit. The router simply turns the bit; the woodworker can learn to improve his techniques, but even an experienced woodworker will have trouble getting good results from a poor quality bit. There are a wide variety of router bits available today. The number of bits is limited only by the imagination of the companies that make them. You should be able to find them at your local hardware store.
[edit] Carbide vs. HSS Bits
The vast majority of bits on the market today are carbide tipped. Carbide is an extremely hard material. Its density actually rivals that of a diamond! Carbide has a number of advantages; it’s very resistant to heat, and it keeps an edge (stays sharp) longer than steel. It does have a number of drawbacks; it’s very brittle, prone to chipping, and it’s very expensive. This is why most bits are carbide tipped and not made from solid carbide.
HSS bits (High Speed Steel) were the only type available for a number of years. They are still available from a number of hardware stores and catalogs. HSS bits are best suited for occasional work. A HSS bit is considerably less expensive than a comparable carbide bit. HSS bits tend to dull relatively quickly and need to be re-sharpened to keep from burning the wood’s surface. Some manufacturers coat their HSS bits with Titanium Nitride to help them stay sharper longer. Unfortunately, this coating eventually wears off. It will disappear quicker if you work with hardwoods. A carbide bit can last up to 20 times longer that a HSS bit - making it far cheaper in the long run.
[edit] Pilot vs. Non-Pilot
There are two different types of bits; Pilot and Non-Pilot. Pilot bits are fitted with a ball bearing that keeps them a fixed cutting distance from the edge of the wood. They are used most commonly to rout a profile on the edge of a workpiece or as a flush trim bit. Non-pilot bits do not have a bearing and are used in conjunction with a fence or jig of some sort to control their cutting paths.
[edit] Chip Limiting Bits – "Safety Bits"
Chip limiting bits are a relatively new arrival in the world of woodworking. Spawned from German legislation that mandates increased safety, many bit manufacturers are now offering their own chip limiting bits. The bits are designed with an extra body mass that extends further back on the bit. This extra mass reduces the amount of material that can be fed into the bit’s cutters. Reducing the amount of material that can be fed reduces the chance of over-feeding the bit. This, in turn, reduces the chance of the bit kicking back or splintering the wood. The picture to the right shows the difference between a chip limiting and normal router bit.
[edit] Does size really matter?
Router bits are most commonly available in two sizes; ¼" and ½". This size refers to the diameter of the shank; the part of the bit that is inserted into the router. Larger routers are supplied with two collets that will allow them to accept either size shank. Most small routers are limited to ¼" bits because of their smaller motors. Is there an advantage to one size over the other? Yes and no; it depends on your use. 1/2" bits have a couple of advantages. First, the thicker diameter of the shank reduces vibration and is more resistant to bending or breaking. Second, the larger shank allows you to use a larger diameter bit. If your router will accept ½" bits it is best to use them. The price difference between a ½" and a ¼" inch bit is negligible; many are the same price. The only place you are likely to see an increased price is in the router itself. Most lower priced routers only support ¼" bits or larger, more expensive routers support both bit sizes.
[edit] For You?
Which bit is better for you? Again, it depends on what you plan to do with it. If you need a router for basic routing, small edge profiles, and rounding over, then a ¼" router is probably sufficient. However, if you plan to eventually do more advanced routing; cabinetmaking for example, you should consider investing in a ½" router.
[edit] Selecting The Right Bit
In the interest of safety, you should always select the right bit for the job. If the job you are working on requires a 3/8" straight bit (for a dado) don’t use a 1.5" straight bit. Longer bits tend to generate more vibration and this vibration causes wear on your router and bit. Vibrations also result in a less accurate cut. Try to select a bit with the largest diameter shank possible.
[edit] Using a Pilot Bit
If you are using a pilot bit make sure the bearing rotates freely. A frozen bearing can burn the edge of your workpiece. There are two things to remember when using a pilot bit. First, don’t push too hard or you risk denting softwoods with the bearing. Second, be sure to apply enough pressure to keep the bearing pressed against the wood. If it is allowed to spin on its own, it may burn the wood. Confused? With time you will learn the right amount of pressure for the job.
[edit] Pitch And Tar
When working with some woods, pine in particular, it is inevitable that pitch and tar will build up on your bit. This pitch can force the bit and router to work harder. This generates excessive heat, which reduces bit life. Pitch and tar can also collect on the surface of the bearing. This can force the bit to roll unevenly and "bounce" on the surface, leaving a rough finish. Pitch and tar can often be scraped off with a scrap of wood or removed with a commercial bit cleaner.
[edit] Bit And Collet Condition
The condition of your bit and collet are important to the quality of your work and your personal safety. Inspect your collet regularly for signs of wear; replace immediately if you suspect any damage. Rust and corrosion on either the bit or the collet reduce the collet’s holding power. Keep the collet and bit free of lubricants that might loosen this bond.
Always insert your bit all of the way into the collet and then back it out a little (1/16"). This will help insure it is properly seated. Make sure the collet is free from sawdust, shavings, or any other foreign bodies. As a safety precaution, you can mark a vertical line on your bit’s shank and a matching line on your collet. Line the two lines up. After you finish using your router check the lines. If they are not lined up any more, your bit is slipping in your collet. This is a sign that it might be time to replace the collet.
Before buying a bit you should inspect it thoroughly to make sure the brazing that holds the carbide on is done properly. If it looks sloppy, or has open voids or pits, don’t buy the bit. The surface of the bit’s body should be free of rust or pitting. It should be ground well and smooth to the touch. A rough finish will tend to collect sap and pitch and will slow the bit down. Inspect the cutting edge of the bit to make sure the carbide is free of grinding marks or chips.