Forstner bits are superior bits for drilling wood because they are guided by the rim and not a centre point. Hence they are not deflected easily by the natural differences in hardness found in timber such as knots or strong grain patterns. They can be used to be bore in any direction and are extremely useful for boring holes on an angle or to true up and increase the size of an existing hole or timber imperfection.
The design permits large chip clearance easily and this combined with their ability to track truly makes them especially suited for drilling deep or extra large diameter holes. Extension bars are available for this purpose.
All the bits up to 7/8in with all bits 1in and larger having a sawtooth design. A sawtooth design makes them able to cut more easily when drilling with the grain (such as through end-grain). They still retain clean cutting characteristics when used drilling across the grain but just not as clean as a true forstner bit - although acceptable for virtually all wood boring.
All forstner & sawtooth bits up to 2 1/8in size are 90mm long and all sawtooth bits 2 1/4in or larger are 160mm long. Shaft installation in a chuck is recommended at 25mm meaning that you can achieve a depth of cut of 65mm up to 2 1/8in and 135mm for bits 2 1/4in or larger. You can increase this by purchasing the forstner bit extension (sold separately).
Sharpen by running a small flat diamond plate along the horizontal scraper cutter keeping the angle constant. The rim needs less frequent sharpening but can be touched up using a round file or diamond stone on the inside. Never grind or touch up the outside of the bit.