Common Drill Bit Terms

Common Drill Bit terms

From A to Z, a short glossary of common Drill Bit terms and their meanings.  If you are around people who have been in a specific industry for a while you may notice that they use specific jargon or certain words that are pretty industry specific. For someone that is still pretty new to the tool industry, a lot of those terms may leave one a little puzzled. I took a short glossary of Drill Bit terms and their meanings from the Triumph Twist Drills catalog. You can view Triumph Twist Drill’s full catalog online by clicking on the link.

Drill Bit Axis– The imaginary line that forms the lengthwise Center of a drill bit.

Drill Body– The section of a drill-bit from the shank to the outer edges of the cutting edge.

Body Clearance Diameter– The portion of the land that has been cut away so it will not bind against the walls of the hole.

Chip Removal– The ability of a drill bit to pull material that has been cut away from the point, up the flutes of the drill, and out of the hole.

Chisel Edge– The edge at the end of the web that connects the cutting tip

Chisel Edge Angle– The angle between the chisel edge and cutting tip, as viewed from the end of the drill-bit

Cobalt Steel– A heat-resistant steel that increases the life of the drill bit

Drill Diameter– The diameter over the margins of a drill bit, measured at the point. It is a common drill bit term used by many.

Feeds– Feed rates for drilling are determined by the drill diameter, machinability of the material, and depth of the desired hole.  Small drills, harder materials, and deeper holes require additional considerations in selecting proper feed rates.

Flute– Groove cut in the body of the drill bit to provide cutting surfaces, permit removal of chips and allow cutting fluid to reach cutting surfaces.

Flute Length– The distance from the outer edges of the cutting tip to the extreme back of the flutes.

Helix Angle– The angle formed between the leading edge of the land and the axis of the drill-bit.Helix Angle

High-Speed Steel– The high-quality steel used in drill bits for most maintenance and industrial applications

IPM– Feed rate in Inches Per Minute.  IPS (Inches per Revolution) x RPM (Revolutions per Minute)= IPM

IPR– Inches per second (The feed rate)

Land– The outer portion of the body of the drill bit between two adjacent flutes.

Lip– The cutting edge of a two-flute drill bit extends from the chisel edge to the outer edge.

Neck– The section of reduced diameter between the body and the shank of all the common drill bit.

Overall Length– The length from the end of the shank to the outer corners of the cutting lip.

Point– The cone-shaped cutting end of a drill bit, made from the ends of the lands and the web.

Point Angle– The angle of the cutting surfaces on a drill point, commonly 118 deg or 135 deg.

RPM– Revolutions Per Minute.  RPM= (SFM(Surface Feet per Minute) / Dia) x 3.82

SFM– Surface Feet Per Minute.  SFM= RPM x Dia x .26

Shank– The part of the drill bit that is held driven.

Size– Measurement reference for the diameter size of a drill bit.  Drill bit size is usually expressed as either fractional, wire, letter, or metric.

Speed– The speed of a drill is determined by the rate at which the outer edge of the tool rotates about the material being cut.  In general, the SFM is within a range based upon the work-piece material, its condition, hardness, and depth of the hole.  The deeper the hole, the greater tendency for more heat to be generated.  Speed reduction is often recommended to minimize the amount of heat.  It is usually best to start drilling at a slower speed and increase till you reach your optimum Feed speed.

Split Point– A split point drill has a special point configuration that eliminates “walking” so holes stay center.


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