Gun drill
A gun drill is a tool of the machining , with the cylindrically-fitting holes are made. It allows very deep bores (depth to diameter ratio up to greater than 250) to be made with very little migration of the hole axis and high surface quality - requirements such as those encountered in particular in the manufacture of barrels for firearms - hence the name.
It is a special form of deep hole drilling (see deep hole drilling , drill ).
It has only one cutting edge that runs perpendicularly outwards from the axis, i.e. H. exactly along the radius of the cross-section circle. Because of this asymmetrical position of the cutting edge, part of the cutting force must be absorbed by the borehole wall. Therefore you have to pre-drill some diameters with another drill. The hole is cut across the entire cross-section - there is no central area in which the material is butt displaced, as is the case with the twist drill.
In the simplest case, the cannon drill is a cylinder, the front two to three diameters milled to a semicircular cross-section; half of the face is ground back, the other half beveled so that the radius becomes a cutting edge. Drilling with it has to be interrupted more often to rinse out the chips.
Gun drills can have spiral or central channels to supply coolant and remove chips.
Like other drills, they can have cutting edges made of special steel or cutting ceramics that give them a longer service life.
The cannon drill is used in dental implantology to bore the bearing for the dental implant . He gives the drilling the final "fine-tuning" after the bone cavity has been prepared with pilot and pilot drills.