cutting fluid helps ensure a smooth and accurate hole while preventing the metal from grabbing the drill bit in the process of drilling the hole. When cutting brass, and other soft metals that can grab the drill bit and causes "chatter", a face of approx. 1-2 millimeters can be ground on the cutting edge to create an obtuse angle of 91 to 93 degrees. This prevents "chatter" during which the drill tears rather than cuts the metal. However, with that shape of bit cutting edge, the drill is pushing the metal away, rather than grabbing the metal. This creates high friction and very hot swarf. For heavy feeds and comparatively deep holes oil-hole drills are used in the drill bit, with a lubricant pumped to the drill head through a small hole in the bit and flowing out along the fluting. A conventional drill press arrangement can be used in oil-hole drilling, but it is more commonly seen in automatic drilling machinery in which it is the workpiece that rotates rather than the drill bit. In computer numerical control (CNC) machine tools a process called , or interrupted cut drilling, is used to keep swarf from detrimentally building up when drilling deep holes (approximately when the depth of the hole is three times greater than the drill diameter). Peck drilling involves plunging the drill part way through the workpiece, no more than five times the diameter of the drill, and then retracting it to the surface. This is repeated until the hole is finished. A modified form of this process, called high speed peck drilling or chip breaking, only retracts the drill slightly. This process is faster, but is only used in moderately long holes, otherwise it will overheat the drill bit. It is also used when drilling stringy material to break the chips. When it is not possible to bring the material to the СNС machine, a Magnetic Base Drilling Machine may be used. The base allows drilling in a horizontal position and even on a ceiling. Usually, for these machines, it is better to use cutters because they can drill much faster with less speed. Cutter sizes vary from 12mm to 200mm DIA and from 30mm to 200mm DOC(depth of cut). These machines are widely used in construction, fabrication, marine, and oil & gas industries. In the oil and gas industry, pneumatic magnetic drilling machines are used to