Drill Bits

Drills and drill bits are used in many industrial applications for machining of metals, plastics, and other materials, construction, woodworking, and specialty applications and crafts such as gemology and medical surgery.  Many of the cutting edge features and specifications are application-dependent, as are the optimal feed rates and cutting speeds.

Drill bits can be supplied in one of four standard size units.  These include English or fractional, metric, wire gauge, and letter size.  An English drill bit is designed with base units of inches or fractions of an inch.  A metric drill bit is designed with metric base units such as millimeters or centimeters.  A wire gauge drill bit is designed in standard wire gauge sizes, designated 1 to 80.  A letter size drill bit is designed in standard letter designation sizes from A to Z.  The full tool-cutting diameter is an important specification when considering drill bits.

Drill bits are available for different drill types.  These include standard or twist drills, jobber length drills, taper length drills, extension or extra length drills, screw machine drills, spotting drills, center drills, microdrills, gundrills, core drills, spade drills, step drills, silver and Deming drills, forstner drills, taper drills, high helix drills, masonry drills, surgical or dental drills, hole saw, wood bit, combination drill and countersink, combination drill and counter bore, combination drill and tap, and drill blank.

Rotation on drill bits can be either right hand or left hand.  Right hand drill bits are the most common.  They are designed to cut while turning clockwise.  Left hand drill bits are designed to cut while turning counterclockwise.  Drill bits may have NAS specifications stating that they are manufactured in accordance with National Aerospace Standards (NAS).  Some drill bits are coolant fed; they have a hole or channel for directed coolant feed at or near the cutting edges.  Split point drill heads are used for chip clearance and for good centering, avoiding "walking" on the workpiece on initial contact.

Drill bits can be of solid construction or a holder and inserts.  In a solid construction the drill is manufactured from a solid piece of material.  In a holder and inserts construction the drill is constructed with a holder with attachable inserts; these inserts typically bolt onto the holder are replaceable when the cutting edges are worn.  Common materials of construction include high-speed steel, cobalt, carbide, and diamond PCD.  Drill bits may be coated to assist in cutting lubricity and/or add abrasion resistance for longer tool life.  Shank types include straight, tapered, reduced, hex, square, and threaded.

Cutting applications for drill bits include general-purpose, aluminum, brass, bronze, and copper, ceramic, hard or hardened materials, plastic, steel, stainless steel, titanium and other exotic materials, and wood.

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  Melting holes is sometimes a better option than drilling them. Thermal drilling relies on friction from a carbide bit to melt and extrude metal and form a hole. The process leaves a thicker lip around...
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• Drill Hole Specifications
  QA Technology highly recommends that holes initially drilled in fixture plates be verified using pin gauge tools (PG Tools) due to the tolerances of purchased drill bits which can be undersized by as...
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• Cryogenic Tool Conditioning Extends Useful Life
  Cryogenic Tool Conditioning: Fact or Frostbite? Exposure to extreme cold can cut wear so tools last longer. � Soaking parts at -300°F or less relieves internal stresses by "squeezing"...
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Part Numbers for Drill Bits