Some of my router bits have the new "full body" design. I find this annoying as I can't hold the bit against the wood to check the profile before I make the cut. Is there any advantage to this design?
This type of design is being advertised by some manufacturers as a safety feature, as it will limit the depth of cut that each tooth may take per revolution. This feature has more merit when used on larger diameter bits, such as panel raisers. Another advantage is that these bits should be more forgiving against kickback. Woodworkers, however, should not use this as an excuse to relax safe work practices.
On the down side, tools with the "full body" design can not be sharpened with a normal diamond cup wheel. A special diamond dish wheel is required, which sometimes "flexes", and may cause the tooth to take on a convex or concave shape. These full bodied bits are more expensive to maintain. Some say the extra mass at the top increases the chances of bending or breaking the bit. Also, if the body is limiting the amount of cut, then it must be rubbing the steel against the wood, creating heat, which is the primary cause of carbide losing its edge.
Frank Finan is owner of Top Shelf Tools