Drill bit shank

The shank is the end of a drill bit grasped by the chuck of a drill. The cutting edges of the drill bit contact the workpiece, and are connected via the shaft with the shank, which fits into the chuck. In many cases a general-purpose arrangement is used, such as a bit with cylindrical shaft and shank in a three-jaw chuck which grips a cylindrical shank tightly. Different shank and chuck combination can deliver improved performance, such as allowing higher torque, greater centering accuracy, or moving the bit independently of the chuck, with a hammer action.

Brace shank

Brace drill bit shank

This shank was common before 1850, and is still in production. At first, the tapered shank was just rammed into a square hole in the end of the drill. Over time, various chuck designs have been invented, and modern chucks can grasp and drive this shank effectively.

It has been difficult to find a reference to the included angle of the taper, but 7 different bits were measured, and they all had an included angle of 8 ± 0.25 degrees.

• Easy to make in a forge
• Very wide tolerances allowable (not very precise)
• Moderate torque transmission but without the slipping possible with round shanks
• Appropriate chuck required

Straight shank

Straight drill bit shank

The straight shank is the most usual style on modern drill bits, by number manufactured. The whole of the drill bit, shaft and shank, is usually of the same diameter. It is held usually in a three-jaw drill chuck. Bits of diameter too small to grip firmly can have straight shanks of larger diameter than the drill, which can be held firmly in a standard size collet or chuck. Large drill bits can have straight shanks narrower than the drill diameter so that they can be fitted in chucks not able to chuck the full diameter. Such a drill bit is called a reduced-shank or blacksmith's drill. For example, this allows a 1⁄2-inch (13 mm) bit to be used in a pistol-grip drill's 3⁄8-inch (9.5 mm) chuck. One particular type of reduced-shank drill bits are Silver & Deming (S&D) bits, whose sets run from 9⁄16-inch (14 mm) to 1+1⁄2-inch (38 mm) drill body diameter with a standard 1⁄2-inch (13 mm) reduced shank for all. This allows drill presses with 1⁄2-inch (13 mm) chucks to run the larger drills. S&D bits are 6 inches (150 mm) long with a 3-inch (76 mm) flute length. The name comes from a company in Salem, Ohio that broke up into other companies circa 1890; bits of this design were popularized by that company.

• Easy to centerless grind or turn on a lathe
• Minimum of turning or grinding needed if the drill bit is made from appropriately sized round bar stock
• Can be held in a standard drill chuck, which must be tightened—only friction prevents slipping
• Can also be held in a collet chuck (which must be tightened), particularly for smaller sizes
• Very accurate centering
• Torque transmission limited by slipping of cylindrical shank

Hex shank

Hex drill bit shank

The flats of a hex shank can either be machined on a round shank, as in the photograph, or be the natural flats of hex bar stock. A hex shank can be grasped by a 3-jaw drill chuck or held in a chuck specifically for hex shanks. Quarter-inch hex shanks are common for machine screwdriver bits and have spread from that application to be used for drill bits that are compatible with screwdriver machinery.

• Zero manufacturing if the drill bit is made from hex bar stock
• Can be held in a drill chuck made for cylindrical shanks
• Can be held in a hex screwdriver bit chuck
• High torque transmission, limited only by strength
• No need to tighten, shape does not allow slipping
• Moderately accurate centering
• Cannot be held in a regular round collet

• A special 3c or 5c HEX collet must be used.

SDS shank

See also: Chuck (engineering) § Special_Direct_System_(SDS)

The SDS system is a standardized method for attaching drill bits and chisels to rotary hammers used for masonry and concrete work. The SDS shank fits into a spring-loaded chuck without tightening. The bit can move slightly back and forth in the chuck, allowing efficient hammer impact transfer. Its non-circular cross-section prevents slipping during rotation. The hammer mechanism strikes only the bit, not the heavier chuck, which improves drilling efficiency.

The chuck keys engage the shank slots to transfer rotation and hold the bit securely. The hammer strikes the flat end of the shank.

Four standardized SDS sizes are used:

• SDS-Quick – for small drills and light-duty applications
• SDS-plus – the most common; 4–30 mm drills, 110–1500 mm lengths
• SDS-Top – 14 mm shank, now obsolete
• SDS-max – for large rotary hammers; 12–45 mm drills, 300–530 mm lengths

Hilti’s TE-S system is similar but designed for chiselling only in larger demolition tools.

The SDS system was developed by Bosch in 1975, based on the TE system introduced by Hilti in 1960. Later Hilti TE designs became compatible with SDS systems. The name SDS comes from the German phrase Steck – Dreh – Sitzt! (“Insert – Turn – Seated!”). Bosch uses “Special Direct System” internationally, and alternate interpretations exist in German-language sources.^[1][2]

• 
  SDS-plus
• 
  SDS-Top
• 
  SDS-max
• 
  TE-S

• Higher hammer-drilling efficiency than solid-gripped bits
• Compatible with chiselling bits in rotation-stop drills
• Allows quick one-hand insertion
• Requires SDS-compatible chuck
• Limited centering accuracy
• Transmits torque effectively

SDS-plus drill bit shanks

SDS-max drill bit shanks

Triangle shank

Triangle drill bit shank

The triangle shank is almost always made by machining three flats on round bar stock. It is intended as a minor modification of a straight shank, still allowing it to be held in a 3-jaw drill chuck, but allowing higher torque transmission and limited slipping.

• Can be held in a drill chuck
• High torque transmission
• Moderately accurate centering
• Cannot be held in a collet

Morse taper shank

Morse taper drills, from 13.5mm (with the No. 1 Morse taper shank) through to a 30mm drill (No. 4 morse taper shank)

Morse Taper Drill Bit Shank

The Morse taper twist drill bits pictured right are used in metalworking. The full range of tapers is from 0 to 7.

The Morse taper allows the bit to be mounted directly into the spindle of a drill, lathe tailstock, or (with the use of adapters) into the spindle of milling machines. It is a self-locking (or self holding) taper of approximately 5/8" per foot^[3] that allows the torque to be transferred to the drill bit by the friction between the taper shank and the socket. The tang at the end of the taper provides a positive drive of the drill when the taper fails to grip.^[4] Many believe that the tang is there for the purpose of ejecting the tool from the taper but as not all tools have a tang (e.g. a centre lathe centre) these can still be ejected despite not having the tang.

The arbor of a drill chuck is often a Morse taper and this allows the chuck assembly to be removed and directly replaced with the shank of a Morse taper drill bit. A range of sleeves may be used to bring the size of the smaller Morse tapers up to the size of the drive spindle's larger taper. Sockets are also available to extend the effective length of the drill as well as offering a variety of taper combinations.

The detail image shows a Morse taper shank on a 16 mm diameter drill bit.

• Simple to manufacture on a lathe
• Cannot be held in a chuck or collet
• High torque transmission provided the bit is driven hard into the workpiece
• Very accurate centering

Square shank

Square taper drills were also used for large ratchet drills, for drilling large holes, or in thick plate. These bits would fit straight into a ratchet drill, and the ratchet drill would be used against a strong arm, for pressure to push the drill into the work piece.

Threaded shank

Some drills, wire wheels, etc. use a threaded shank. One example is cylindrical wire wheels meant to be pushed into a pipe of some sort to clean the inside of the pipe, but some ordinary, but mostly rather large, wood drills have threaded shanks as well.

Small (about 1⁄4 in or 6.35 mm diameter) threaded drill bits and countersinks are common in aircraft metal work. Threaded drill bits may be held in drills meant to reach into very tight spaces, and threaded countersink cutters are widely used (along with finely adjustable depth stops) to create holes which put a matching rivet directly flush with the surface.