Drills & Drilling


Introduction
  • Drilling remains one of the most efficient ways to make a hole in a workpiece.
  • Drills are now made from high speed steel or are carbide tipped.  Drills used to be made of high carbon steel.
  • Drills may be coated or may have a bright or oxide finish.
Types of Drills
  • Spot Drill
  • Spade drill
  • Gun drill
  • Core drill
  • Cast steel, hard steel (Stellite) drills
Drill Sizes
  • Twist drills may be purchased “off the shelf” in diameters from 0.0135” to 2 ¼ inches.
  • Sizes are in fractions, numbers and letters, and metric.
Drill Nomenclature and Geometry
  • Standard Twist drills may have straight or tapered shanks.

     

  • Drilling Brass: Modification of the drill point when drilling brass. (When a straight fluted twist drill is not readily available.)
Drilling Brass

Drilling Brass

  • Drill Point Angles:
    • Use 90º to 140º for aluminum alloys.
    • Use 70º to 80º for magnesium alloys.
    • Use  118º to 135º for high strength steels.
Drill PointAngles

Drill Point Angles

The drill point angle may be modified to cut a variety of materials.

  • Effect of Changing the Drill Point Angle: The rake angle is influenced by the drill point angle.
Effect of Changing the Drill Point Angle

Effect of Changing the Drill Point Angle

  •  Lip Relief (Clearance) Angles:
    • Lip relief angles are normally 10º to 15º
    • Lip relief for high strength or tougher steels is between 7º to 12º (Stronger backing for cutting edge.)
    • Lip relief for softer or free machining materials may be between 12º to 18º
Lip Relief (Clearance) Angles

Lip Relief (Clearance) Angles

Speeds & Feeds for Drilling: Speeds (rpm) may be calculated using

  • RPM = 12 x Cutting Speed / π x Diameter
Holding the Drill & Workpiece
  • Morse taper drill sleeves (Use drift for removal)
  • Jacob’s Chuck (Danger – Flying Chuck Keys)
  • Holding the Workpiece
    • Using a vise
    • Clamping directly to the table. (See next slide)
    • Using a drill jig
  • Clamping Work to a Machine Table
Clamping Work to a Machine Table

Clamping Work to a Machine Table

Locating and Machining a Hole
  • Use one of the following techniques before drilling a hole with a twist drill:
    • Drill a small indentation with a centre drill.  Combined Drill & Countersink.)
    • Make a small indentation using a centre punch.
Drilling Problems
  • Holes out of position
  • Hole wandering
  • Material clogging flutes
  • Drill chatter,  i.e. when drilling brass
Soultion
  • Drilling Through Existing Holes (Drill long holes first when drilling through existing holes)
  • Web Thickening
    • When using an older drill, excessive pressure may be required.  Thin the web
    • The web of the drill becomes thicker as the drill becomes shorter after sharpening.
  • Oversize Holes
Drill lips

Drill lips

  •  Cutting Edges Wearing Prematurely
Speed (rpm) too fast!

Speed (rpm) too fast!

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One Response to Drills & Drilling

  1. drils Online says:

    Your means of telling the whole thing in this paragraph is really pleasant, all be able to without difficulty understand it,
    Thanks a lot.

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