DRILL: A rotary end cutting tool having one or more cutting lips, and having one or more flutes. The flutes may be helical or straight, and are necessary for the passage of chips and the admission of a cutting fluid.

TYPES OF DRILLS

Beaded Shank Bits: Drills with flat shanks having raised beads parallel to the axis

Composite Drills: Drills having separate cutting portions that are mechanically held in place

Double Margin Drill: A drill whose body diameter clearance is produced to leave more than one margin on each land and is normally made with margins on the leading and trailing edges for increased stability

Flat Drill: A drill whose flutes are produced by two parallel or tapered flats, also called a spade drill

Four-Flute Drills (Core Drills): Similar to three-flute drills in construction

Gun Drill: Special purpose drill used for drilling very deep holes; the depth is typically 10 to 30 times the diameter

Half-Round Drill: A drill with a transverse cross-section of approximately half a circle and having one cutting lip

Indexable Drill: Drill with replaceable inserts for cutting edges

Left-Hand Cut: When viewed from the cutting point, clockwise rotation is required to cut

Right-Hand Cut: When viewed from the cutting point, the counterclockwise rotation of a drill in order to cut; most common

Shell Core Drills: Core drills mountable on arbors specifically designed for the purpose; commonly used with shell reamer arbors

Single-Flute Drills: Drills only one flute, commonly used for originating holes

Solid Drills: Those made of one piece of material, such as high speed steel or carbide

Step Drill: A multiple diameter drill with one set of drill lands which are ground to different diameters

Straight Shank Drills: Drills having cylindrical shanks which may be the same in diameter or different than the body of the drill; the shanks may be made with or without driving flats, tang, grooves or threads

Subland Drill: A type of multiple diameter drill which has independent sets of lands in the same body section for each diameter

Taper Drill: A drill with part or all of its cutting flute length ground with a specific taper to produce tapered holes; they are used for drilling the original hole or enlarging an existing hole

Taper Shank Drills: Drills with conical shanks suitable for direct fitting into tapered holes in machine spindles, driving sleeves or sockets; they generally have a driving tang

Taper Shank Square Drills: Those having tapered shanks with four flat sides for fitting a rachet or brace

Threaded Shank Drills: Drills made with threaded shanks generally used in close center multiple spindle applications or portable angle drilling tools

Three-Flute Drills (Core Drills): Drils commonly used for enlarging and finishing drilled, cast, or punched holes; not used to produce original holes

Tipped Solid Drills: Those having a body of one material with cutting lips made of another material, either brazed or otherwise bonded in place

Two-Flute Drills: Conventional type of drills used for originating holes

GEOMETRY OF DRILLS AND DRILL FEATURES

Axis: An imaginary straight line forming a longitudinal center line of the drill

Back Taper: A slight decrease in diameter from front (point) to back (shank) in the body

Body: Portion of the drill extending from the shank or neck to the outer corners of the cutting lips

Body Diameter Clearance: A portion of the land cut away so it will not rub against the walls of the hole

Cam Relief: The relief from the cutting edge to the back of the land, produced by a cam actuated cutting tool or grinding wheel on a relieving machine; allows for more complexity and consistency

Chip Breaker: Notches or grooves cut in the drill to reduce the size of chips produced while drilling; they may be steps or grooves in the cutting lip or in the leading face of the land at or adjacent to the cutting lips

Chip Packing: The failure of chips to pass through the flute during cutting action; the drill may become clogged with chips

Chipping: The breakdown of a cutting lip or margin by small chips broken away during the cutting action

Chisel Edge: The edge at the end of the web that connects the cutting lips

Chisel Edge Angle: The angle included between the chisel edge and the cutting lip, as viewed from the end of the drill

Clearance: Space designed to eliminate contact between the drill and the workpiece

Clearance Diameter: The diameter over the the cut away portion of the drill lands

Coatings: A thin layer of a different material applied to the surface of the drill to improve performance

Coolant Grooves: Grooves in the shank or lands designed to carry the cutting fluid to the cutting lips

Coolant Holes: Internal holes through the shank and body to pass cutting fluid to the cutting lips

Drift: A flat tapered bar for forcing a taper shank out of its socket

Drift Slot: A slot through a socket at the small end of the tapered hole allowing access to the drift

Drill Diameter: The diameter over the margins of the drill; it is measured at the point

Exposed Length: The distance the large of a shank projects from the drive socket or large end of the taper ring gage

Flutes: Helical or straight grooves in the body of the drill to provide cutting lips, to permit removal of chips, and to allow cutting fluid to reach the cutting lips

Flute Length: The length from the outer corners of the cutting lips to the extreme back end of the flutes

Gage Line: The axial position on a taper used to reference axial lengths

Galling: An adhering deposit of workpiece material on the margin adjacent to the leading edge at and near the point of a drill

Guide: A cylindrical portion, following the cutting portion of the flutes, acting as a guide to keep the drill in proper alignment; the guide portion may be fluted, grooved, or solid

Heel: The trailing edge of the land

Helical Flutes: Flutes which are formed in a helical path around the axis

Helix Angle: The angle made by the leading edge of the land with the axis of the drill

Land: The peripheral portion of the body between adjacent flutes

Land Width: The distance between the leading edge and the heel of the land measured perpendicular to the leading edge

Lead: The axial advance of a leading edge of the land in one rotation of the drill

Lips: The cutting edges of the drill extending from the chisel edge to the periphery

Lip Relief: The axial relief on the drill point

Lip Relief Angle: The axial relief angle at the outer corner of the lip

Margin: The cylindrical portion of the land which is not cut away to provide clearance

Neck: A section of reduced diameter between the body and the shank of some drills

Overall Length: The length from the extreme end of the shank to the outer corners of the cutting lips

Periphery: Outside circumference of a drill

Peripheral Rake Angle: The angle between the leading edge of the land and an axial plane at the drill point

Pilot: A cylindrical portion of the drill body preceding the cutting lips

Point: The cutting end of a drill, made up of the ends of the lands and the web; it resembles a cone, but furnishes clearance behind the cutting lips

Point Angle: The included angle between the cutting lips on a plane parallel to the drill axis

Relative Lip Height: The difference in the lip positions measured perpendicular to the lips

Relief: Removal of tool material behind or adjacent to the cutting lips and leading edge of the land to provide clearance and prevent rubbing or heel drag

Shank: The end of the drill which is held and driven

Sleeve: A tapered shell designed to fit into a specified socket and to receive a taper shank smaller than the socket

Socket: A tapered hole designed to receive, hold, and drive a tapered shank

Straight Flutes: Flutes which form lands lying in an axial plane

Tang: The flattened end of a taper shank, intended to fit into a driving slot in a socket

Tang Drive: Two opposite parallel driving flats on the extreme end of a straight shank

Web: The central portion of the body that joins the lands

Web Thickness: The thickness of the web at the point

Web Thinning: An operation reducing the web thickness at the point to reduce drilling thrust

DRILLING PARAMETERS AND OTHER FACTORS

Built-Up Edge: Material removed from the workpiece that adheres to the cutting lip or the point of the drill

Cutting Fluid: Fluid used to cool the drill and workpiece, lubricate the surfaces, and flush away generated chips

Depth: The depth of the hole generated by the drilling process

Feed: The rate that the drill advances into the material, generally measured in distance per flute

Speed: The cutting speed is usually measured at the periphery of the drill in surface feet or meters per minute

Surface Finish: The roughness of the walls of the drilled hole; a measure of the hole quality

Thrust: The axial force required to drill

Torque: The twisting moment required to drill


Last Modified: 11:52am EDT, October 22, 1996