General Purpose Twist Drills

Jobber Drill

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, 135º Split Point Twist Drill

Heavy duty type with 135º 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

Silver & Deming Reduced Shank Drill with flats

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.

Parabolic Drill

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.

Morse Taper Drill

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.