Machinery's Handbook, 31st Edition
932 Twist Drills Point: The cutting end of a drill made up of the ends of the lands, the web, and the lips. In form, it resembles a cone but departs from a true cone to furnish clearance behind the cutting lips. Point Angle: The angle included between the lips projected upon a plane parallel to the drill axis and parallel to the cutting lips. Shank: The part of the drill by which it is held and driven. Tang: The flattened end of a taper shank, intended to fit into a driving slot in the socket. Tang Drive: Two opposite parallel driving flats on the end of a straight shank. Web: The central portion of the body that joins the end of the lands. The end of the web forms the chisel edge on a two-flute drill. Web Thickness: The thickness of the web at the point unless another specific location is indicated. Web Thinning: The operation of reducing the web thickness at the point to reduce drill ing thrust.
Point Angle
Neck Diam.
Taper Shank
Tang
Drill Diam.
Clearance Diam.
Straight Shank
Lip Relief Angle
Body Diam. Clearance
Rake or Helix Angle
Straight Shank Shank Length Neck Length
Axis
Chisel Edge Angle
Flutes
Shank Diam.
Flute Length
Body Length
Margin
Overall Length
Lip
Web
Land
Chisel Edge
Flute Length
Shank Length
ANSI Standard Twist Drill Nomenclature Types of Drills.— Drills may be classified based on the type of shank, number of flutes or hand of cut. Straight-Shank Drills: Those having cylindrical shanks that may be the same or a differ ent diameter than the body of the drill. The shank may be with or without driving flats, tang, grooves, or threads. Taper-Shank Drills: Those having conical shanks suitable for direct fitting into tapered holes in machine spindles, driving sleeves, or sockets. Tapered shanks generally have a driving tang. Two-Flute Drills: The conventional type of drill used for originating holes. Three-Flute Drills (Core Drills): Drills commonly used for enlarging and finishing drilled, cast or punched holes. They will not produce original holes. Four-Flute Drills (Core Drills): Used interchangeably with three-flute drills. They are of similar construction except for the number of flutes. Right-Hand Cut: When viewed from the cutting point, the counterclockwise rotation of a drill in order to cut. Left-Hand Cut: When viewed from the cutting point, the clockwise rotation of a drill in order to cut. Teat Drill: The cutting edges of a teat drill are at right angles to the axis, and in the center there is a small teat of pyramid shape which leads the drill and holds it in position. This form is used for squaring the bottoms of holes made by ordinary twist drills or for drilling the entire hole, especially if it is not very deep and a square bottom is required. For instance, when drilling holes to form clearance spaces at the end of a keyseat, preparatory to cutting it out by planing or chipping, the teat drill is commonly used.
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