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Router Bit Basics

Shank Diameter

Router bits are most often available in 1/4" and 1/2" shank diameters. When available, it is best to select 1/2" shank bits.  A 1/2" shank diameter bit has four times the cross-sectional surface area of a 1/4" shank, and is therefore much more rigid than a 1/4" shank bit. The extra rigidity and support for the cutting edge translates into a smoother cut with less chatter. Most better quality router bits are available in either a 1/4" or 1/2" shank.

Router Bit Speed

Better routers are equipped with a speed adjustment that allows for speed adjustment typically ranging from around 8,000 to 24,000 rpm (revolutions per minute). The reason is that not all router bits can be safely or optimally run at the same speed. Larger router bits have more mass and therefore a potential to create forceful vibration at higher speeds.

It's important understand what router speed actually measures. "Revolutions per minute" is simply a measure of the number of times that the bit makes a complete revolution in a given period of time, and not a measure of the speed at which the body and cutting surfaces of the bit are actually traveling. The outer perimeter of a 3-1/2" diameter bit is actually traveling significantly faster at 24,000 rpm (and much faster than it should be!) than a 1/2" straight bit's cutting surface would be at the same shaft speed.

Manufacturers often supply maximum free-running speeds for the router bits they sell. The maximum speed for a given bit is the maximum speed at which it can be safely operated, and may not be the best speed for the task. There are other factors to consider: router horsepower (a less powerful router will slow down when it's driving a large bit through a cut), feed rate, quality and condition of the bit, and the cutting properties of the material. It is impractical to give a list of specific speeds that will work well in every situation.

In general, a faster speed is more desirable than a slower one, for the simple reason that a faster speed provides more cuts per inch, and more cuts per inch normally yield a smoother cut. Using sharp, high quality bits and using the correct feed rate go hand in hand with bit speed in making a clean cut. Make practice cuts with a new bit until you are able to produce a smooth, even feed rate that is neither too fast and produces a rough cut or too slow and results in burnishing and burn marks. 

The chart below offers speed guidelines for the maximum safe free running speed of bits of various diameters. This is supplied for general reference - manufacturer’s guidelines should be consulted:

 

Router Bit Diameter Maximum Speed
Up to 1" 22,000 - 24,000 rpm
1" to 2" 18,000 - 22,000 rpm
2" to 2-1/2" 12,000 - 16,000 rpm
2-1/2" to 3-1/2" 8,000 - 12,000 rpm

Anti-Kickback Design

rockler drawer lock router bitMany better-quality bits offer the additional safety feature of an anti-kickback design. The enlarged body of anti-kickback an anti-kickback bit prevents the bit from biting in too deeply and catching on the material. Bits of this design have more body mass than other carbide bits, which helps to dissipate heat and keep the bit sharp for longer service between regrindings. Pictured on the left is an example of a bit with this safety design: Rockler's Drawer Lock Router Bit

Router Bit Quality

A number of qualities distinguish better quality router bits from "bargain" bits. Good quality router bits are sharp, and stay sharp for a long time (with proper use). Good bits are well balanced and therefore create minimal vibration. They are designed for good cutting geometry and have excellent chip ejection properties.

Currently, most woodworkers prefer carbide tipped router bits. Carbide cutters can hold their edge between ten and twenty-five times as long as hss (high speed steel) bits. Better carbide bits are ground to a finer edge and have thick cutters to allow for numerous regrindings. They are also made of high quality, fine grained carbide, which allows for a sharper cutting edge.

Rockler offers high quality router bits from respected manufacturers including Freud and Amana. Rockler also offers it's own line of router bits designed for the serious woodworker. Rockler router bits are made using high quality ISO K10 and K20 carbide, are finish sharpened with 600-800 diamond abrasives, and are precision balanced and are geometrically designed for superior chip ejection. Rockler, we're confident that the router bits we sell will provide long-lived, safe and smooth cutting - but to make you their ultimate judge, Rockler Router Bits are also unconditionally guaranteed.


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