Basic Drill Tooling Information for Metalworking
General Purpose Twist Drills
The Jobber Drill is designed for general purpose drilling with a wide variety of drilling applications. It can drill many materials such as cast iron, steel, and brass forgings. Surface treatments prevents chip welding, improves chip flow and improves abrasion resistance. They are available in a bright polished finish or a black oxide finish. Black oxide is the most common finish. The bright polished finish reduces loading when drilling soft materials like brass or aluminum.
There are three standard lengths of common twist drills. They are: Jobber length, Screw Machine length and Taper length. The the most common length is the Jobber length and is usually considered the standard length unless otherwise specified.
Heavy Duty, 135Âº Split Point Twist Drill
Heavy duty type with 135Âº split point for use in cast iron,steel alloys, stainless steels, titanium, etc. This style is available in the three common lengths, jobber, screw machine and taper.
Jobber Length Drills
Jobber Drill - Reduced Shank
Reduced shank drills are used for drilling holes larger than the capacity of a 1/4, 3/8, or 1/2 drill chuck. Reduced shank drills should only be used for light to medium duty drilling applications as they do not have the torque strength of a straight shank drill.
For drill sizes above 1/2" the Silver & Deming (S&D) drills are available for use with 1/2" capacity drill chucks. They have a 1/2" diameter shank, either round or with three equally spaced flats, for drill sizes up to about 1-1/2". These drills are not made for higher precision holes but serve the purpose for many common large hole requirements where only 1/2" capacity chucks are available.
Jobber Drill - Parabolic Flute
For deep hole drilling in a wide range of materials especially aluminum and mild steel. Parabolic flutes ease chip ejection.
Cobalt Jobber Length - Straight Shank - Heavy Duty
Heavier construction than General Purpose Twist Drills for use in the harder, tougher alloy steels of the stainless and manganese types; castings; forgings; and chilled cast iron. These drills can be run approximately 25% faster than those of High Speed Steel, because of Cobalt steel's ability to withstand high cutting temperatures.
Common Drill Types
Jobber Length Drills
The most common drill type is the jobber type drill. Jobber actually refers to the drill overall length. It is one of three lengths commonly available for snall diameter, less than 3/4", drills. The other two lengths are Screw Machine and Taper.
Screw Machine length drills
These are shorter than Jobber and are used when the depth to be drilled is shallow and when the hole tolerance is important. Since they are shorter than Jobber length they will have less tendency to flex. This may minimize any tendency to move from the intended location. This is important when the surface to be drilled is not exactly perpendicular to the tool. The drill may also have less tendency to drill an oversized bell-mouth hole in the entrance area.
Taper length drills
These are longer than Jobber and are used when the extra length is necessary for the application.
Taper Shank Drills
These are available for larger cutting sizes. The shank taper is usually a Morse Taper. These drills must be used with spindles specifically made to accept the taper. Most drills presses have a Morse Taper spindle. Morse tapers are specified as MT1 to MT5.