The good metal drill is capable to drill set of openings in the most solid materials before the expiration of the life cycle, at the same time it should not become blunted and, especially, break. Such functional performance from drill can achieve only if it is picked correctly up under the drilled material, is ground in a necessary way and qualitatively made.
Drill material
Make sure that the drill is made of special quick cutting steel, only the drill from this material can keep the properties at very high temperatures arising in the place of drilling. Quick cutting steel without fail contains molybdenum and tungsten which provide it the highest wear resistance.
Metal drills carry to class spiral as they have spiral grooves on all length, on them when drilling shaving is taken away.
Color of drill
When choosing metal drill pay attention to its color. Gray drills will be the cheapest, they are made of normal steel, such drills are very short-lived, and with some grades there were they just will not cope. Black drills receive the color thanks to additional treatment superheated steam, they are much stronger than normal. Drills with covering of saturated gold color will be the best metal drills, such color of drill means that it is covered with nitride of the titan that provides it the highest wear resistance. Will drill such tool much more simply and quicker, but also the price of it will be higher.
Marking
When choosing drill you have to know, you need to drill size what opening. On drill its diameter, so, and diameter of the opening received with its help will be surely specified. Make sure that marking begins with letter P - it will mean that the drill is made of quick cutting steel. As metal drills are usually made of titanic, cobalt or tungsten alloys, it surely is reflected in marking.
Angle of sharpening
The quality and speed of drilling are affected not only by material of which the drill, but also quality of its sharpening is made. Only well ground drill is capable to cope with metal, low-quality drills are rebated very quickly, the cheapest - after the first drilling.
The dull drill can be ground independently on normal sandpaper, but independently not to achieve factory sharpening.
From that what sheet of material needs to be drilled, the necessary angle of sharpening of drill depends, so, drilling of structural steel requires drill with the angle of sharpening in 116 degrees, to stainless steel - 120 degrees, bronze - 130-140 degrees, cast iron - 118 degrees.
Shaft
You have to know what type of shaft is necessary to you that the drill has approached your tool. Drills with tapered shank insert directly into the machine, with cylindrical - into special cartridge which then is inserted into the tool.