What is the definition of "length-to-diameter ratio"?
A numerical value describing the length of a cylindrical tool or workpiece compared to its diameter. Higher length-to-diameter ratios offer less rigidity.

Learn more about length-to-diameter ratio in the class Drill Geometry 247 below.


Metal Cutting Training


Class Information
Metal Cutting Training Tooling U-SME classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and will take approximately one hour to complete.
Class Name:Drill Geometry 247
Description:This class identifies the major drill components and angles that impact drilling operations. Includes an Interactive Lab.
Prerequisites: 200120  200140 
Difficulty:Intermediate
Number of Lessons:17
Language:English, Spanish
 
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Class Outline
  • Objectives
  • The Importance of Drill Geometry
  • The Drill Body
  • The Drill Point
  • What Happens During Drilling?
  • Web Size
  • Point Angle
  • Helix Angle
  • Rigidity and Deflection
  • L/D Ratio
  • Drilling Speed and Feed
  • The Importance of Workpiece Material
  • Regrinding
  • Spade Drills
  • Indexable Carbide Insert Drills
  • Modular Drills
  • Summary
  
Class Objectives
  • Describe the importance of drill geometry.
  • Identify components of the drill body.
  • Identify components of the drill point.
  • Describe the action that occurs during drilling.
  • Describe web size.
  • Describe how the point angle affects the drilling process.
  • Define the helix angle.
  • Describe rigidity and deflection.
  • Determine the L/D ratio of a drill.
  • Define speed and feed.
  • Describe the impact of workpiece material on the drilling process.
  • Describe regrinding.
  • Describe a spade drill.
  • Describe an indexable carbide insert drill.
  • Describe a modular drill.

Class Vocabulary

Vocabulary TermDefinition
axial force A force that exists parallel to the drill centerline.
bearing surface The portion of the drill that makes contact with the sides of a hole. On a drill, the bearing surface is along the margins.
body The area at one end of a drill opposite the shank. Drill flutes are located on the body.
boring The process of enlarging an existing hole with a single-point tool.
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.
chuck A clamping workholding device that grips the shank of a mounted drill.
clearance diameter The drill diameter measured from the cut away portion of the lands.
collet A workholding device that grips the shank of a mounted drill.
deflection The unintended movement or repositioning of a drill due to mechanical force. Deflection of a drill can cause poor hole location and inaccurate hole dimensions.
dial indicator A device that measures the angles at the drill point to assure the drill point is symmetrical and "on center."
drill A metal cutting tool used to penetrate the surface of a workpiece and make a round hole equal to the drill diameter.
drill geometry The angles formed by the dimensions of a drilling tool that make it suited for a particular job.
drilling The process of producing an original hole with a multi-point tool.
extended length The length that a drill extends from the toolholder.
fast-spiral drill A drill with compact flutes. Also called high helix angle drills, fast-spiral drills have excellent chip evacuation for drilling deep holes.
feed The rate at which the drill moves into the workpiece. Drilling feed is measured in either inches per minute (IPM) or inch per revolution (IPR).
finishing Metal cutting processes that emphasize tight tolerances and smooth surface finish. Finishing operations often require faster speeds and a lighter depth of cut.
flute A helical recess that winds up the length of a drill body. Flutes enable the evacuation of chips from the cutting area during drilling.
general-purpose drill A standard web-sized drill that is used in high-production applications on cast iron, steel, and nonferrous metals.
grinding The use of an abrasive to wear away the diameter of a drilled hole to achieve highly accurate measurements.
heavy-duty drill A larger web-sized drill that is used for drilling steel forgings, hard castings, and high-hardness ferrous alloys.
helix angle The angle formed by the edge of a flute and a line parallel to the drill centerline.
high helix angle drill A drill with compact flutes. Also called fast-spiral drills, high helix angle drills have excellent chip evacuation for drilling deep holes.
inch per revolution A unit of measurement for feed that indicates how many linear inches a drill travels in one workpiece revolution.
inches per minute A unit of measurement for feed that indicates how many linear inches a drill travels in one minute.
indexable carbide insert drill A drill with carbide inserts clamped to a steel body. Indexable carbide drills are among the most cost-effective drills.
land The area of a drill between flutes.
lead angle The approach angle of the cutting edge as it enters the workpiece. The lead angle controls the direction of the radial and axial cutting forces.
left-hand twist drill A drill that rotates counterclockwise.
length-to-diameter ratio A numerical value describing the length of a cylindrical tool or workpiece compared to its diameter. Higher length-to-diameter ratios offer less rigidity.
lip The cutting edges of a drill that extend from the chisel edge to the periphery.
lip relief angle The angle measured from behind the cutting lip to a line perpendicular to the axis of the drill at the heel of the face of the land. The lip relief angle measures the clearance behind the cutting lip.
low helix angle drill A drill with elongated flutes. Also called slow-spiral drills, low helix angle drills have high rigidity and withstand great force.
machinability The ability of a metal to be cut and shaped by machine processes such as cutting, grinding, turning, or drilling.
major diameter The diameter of a drill measured between the outermost surfaces of the land.
margin A portion of the land that is not cut away to provide clearance. Margins guide the drill in the hole and maintain the drill diameter.
minor diameter The diameter of a drill measured between the innermost surfaces of the land.
modular drill A drill consisting of an interchangeable and disposable tip mechanically attached to a drill body.
point The tip of a drill body that contains the cutting edges.
point angle The angle formed by the cutting edges of the drill. The point angle performs the same function as the lead angle for all other cutting tools.
radial force A force that exists perpendicular to the drill centerline.
reaming The use of a multi-point cutting tool to smooth or enlarge a previously drilled hole.
relief Clearance behind the lip and leading edge of the land. Relief prevents rubbing.
revolutions per minute RPM. A unit of measurement that indicates the number of revolutions a drill makes in one minute.
right-hand twist drill A drill that rotates clockwise.
rigidity The ability of a drill to resist bending.
shank The area at one end of a drill that allows the drill to be held and driven.
slow-spiral drill A drill with elongated flutes. Also called low helix angle drills, slow-spiral drills have high rigidity and withstand great force.
spade drill A drill with a wide blade at the tip. The width of the blade often exceeds the diameter of the drill.
speed The rate at which the drill rotates in relation to the workpiece. Drilling speed is usually expressed in surface feet per minute (SFPM).
surface feet per minute SFPM. A measurement of speed that accounts for the number of linear feet that a particular location on the drill periphery travels in one minute.
tang The flattened end of some drill shanks that locks into the machine head and allows the drill to be rotated and driven securely.
taper shank drill A drill with a tapered shank.
torque The amount of force exerted to rotate a drill and cut a hole in a workpiece.
torsion strength The ability of a rotating drill to handle the forces of workpiece resistance.
twist drill A common drill characterized by helical flutes along its length and two cutting edges at the drill point.
walk The tendency of a rotating drill to deviate from its intended path upon contact with a stationary workpiece.
wear land The worn portion of the drill near the cutting edges. Wear lands appear gradually due to abrasion and other harsh conditions.
web The central portion of the drill body that joins the lands. The extreme end of the web forms the chisel edge on a two-flute drill.
web thinning The grinding of the web and chisel point to bring a drill back to its original specifications. Grinding a drill point without thinning the web may cause suboptimal drilling conditions.
workhead The component of a drilling machine that houses the spindle mechanism that rotates the drill.