Drill Bits and Sizes
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Questions and Answers

What is the primary function of drill bits?

  • To create circular holes in materials (correct)
  • To polish metal surfaces
  • To shape irregular objects
  • To mix materials together
  • What is the common increment size for metric drill bits?

  • 2 mm
  • 0.1 mm
  • 1 mm (correct)
  • 0.5 mm
  • Where can you find drill bit sets in 0.5-mm increments?

  • At a specialized tool shop
  • At an engineers' store
  • At a market stall
  • At any hardware store (correct)
  • What is the purpose of attaching a drill bit to a drill?

    <p>To power the drill bit to cut through materials</p> Signup and view all the answers

    In which country is the use of fractional inch and gauge drill bit sizes more common?

    <p>United States</p> Signup and view all the answers

    When were the British standards for replacing gauge size drill bits with metric sizes first published?

    <p>1959</p> Signup and view all the answers

    What is the primary purpose of centre drills?

    <p>Drilling lathe centres</p> Signup and view all the answers

    What is the included angle of the standard centre drill bit?

    <p>60°</p> Signup and view all the answers

    Why are close-tolerance bolts not cad plated?

    <p>Due to the tight specs, cad plating is not possible</p> Signup and view all the answers

    What is the typical way machinists think about decimal places for 0.25, 0.5, and 0.75?

    <p>Expressing them to thousandths</p> Signup and view all the answers

    What is the tolerance range for standard-tolerance bolts?

    <p>+0.000 to -0.0055 in.</p> Signup and view all the answers

    What is the definition of a light drive fit?

    <p>An interference fit with approximately 0.0006 in. interference</p> Signup and view all the answers

    What is the typical length of the flutes of a jobber-length drill in relation to the drill's diameter?

    <p>Nine to fourteen times the diameter</p> Signup and view all the answers

    How deep can a 1/2-in.(12.7-mm) diameter drill drill a hole?

    <p>4 1/2 in.</p> Signup and view all the answers

    What is the general rule for selecting a drill size for a bolt hole?

    <p>Use the first lettered drill size larger than the nominal bolt diameter</p> Signup and view all the answers

    What is the main difference between jobber-length drills and aircraft length drills?

    <p>Fixed lengths available for thicker drills</p> Signup and view all the answers

    What is the minimum diameter for which aircraft length drills are available in fixed lengths?

    <p>1/8 in.</p> Signup and view all the answers

    What is the typical length of an aircraft length drill?

    <p>6, 8, 12, or 18 in.</p> Signup and view all the answers

    What type of tolerance allows variation in only one direction from the specified dimension?

    <p>Unilateral</p> Signup and view all the answers

    What is the largest size permitted by a toleranced dimension?

    <p>Upper limit of size</p> Signup and view all the answers

    What is the term for the extremes of size allowed for a dimension?

    <p>Limits of size</p> Signup and view all the answers

    What is the term for the size about which the limits of a particular fit are fixed?

    <p>Basic size</p> Signup and view all the answers

    What is the total amount of variation permitted by the limits of the dimension?

    <p>Tolerance</p> Signup and view all the answers

    What type of tolerance allows variation in both directions from the specified dimension?

    <p>Bilateral</p> Signup and view all the answers

    What is the primary purpose of drawing upper and lower limits on mating parts?

    <p>To establish the basic size and tolerance of the components</p> Signup and view all the answers

    Which of the following is NOT a method of expressing tolerance on dimensions?

    <p>Calibration method</p> Signup and view all the answers

    What is the result of calculating the clearance between the smallest shaft and the largest hole?

    <p>Slackest fit</p> Signup and view all the answers

    What is the minimum clearance calculated in the worked example?

    <p>0.040 in.</p> Signup and view all the answers

    What is the purpose of determining the acceptable component limits during maintenance?

    <p>To determine if the components are suitable for further service</p> Signup and view all the answers

    What is the result of calculating the clearance between the largest shaft and the smallest hole?

    <p>Tightest fit</p> Signup and view all the answers

    Study Notes

    Drill Bits and Sizes

    • Drill bits are cutting tools used to create holes of circular cross-section in various materials.
    • They come in many sizes and shapes, and can be attached to a drill to cut through a workpiece by rotation.
    • Standard sizes are available, and a comprehensive drill bit and tap size chart lists metric and imperial-sized drill bits alongside required screw tap sizes.

    Metric Sizing

    • Drill bits in metric sizes are most commonly used in nearly all countries except the United States.
    • Drill bits are available in increments of 1 mm, 0.5 mm, and 0.1 mm.
    • Sets of bits in 1-mm increments can be found in a market stall, in 0.5-mm increments at a hardware store, and in 0.1-mm increments at an engineer's store.

    Centre Drill Bit Sizes

    • Centre drills are available with two different included angles: 60° (standard for drilling centre holes) and 90° (used for locating holes prior to drilling with twist drills).
    • Centre drills are made specifically for drilling lathe centres, but are often incorrectly used as spotting drills.

    Bolt Tolerance

    • Close-tolerance bolts can be placed in a freezer prior to fitment to eliminate friction.
    • Standard-tolerance bolts are manufactured to +0.000 to -0.0055 in. of the diameter's nominal size.
    • Close-tolerance bolts are manufactured to +0.000 to -0.0005 in. of the diameter's nominal size.

    Bolt Holes

    • Bolt holes of primary connecting elements have close tolerances.
    • For general application, it is generally permissible to use the first lettered drill size larger than the nominal bolt diameter.

    Decimal Fraction Equivalents

    • Decimal places for 0.25, 0.5, and 0.75 are shown to thousandths (0.250, 0.500, 0.750).
    • Machinists usually think about decimal fractions in terms of 'two-fifty', 'five hundred', and 'seven-fifty'.

    Jobber-Length Drill

    • Jobber-length drills are the most common type of drill.
    • The length of the flutes is between 9 and 14 times the diameter of the drill, depending on the drill size.

    Aircraft Length Drill

    • Aircraft length drills are commonly used for manufacturing riveted aluminum aircraft.
    • They are available in fixed lengths, such as 6, 8, 12, or 18 inches, rather than the progressive lengths of jobber drills.

    Unilateral and Bilateral Tolerances

    • Unilateral tolerance means variation is permitted only in one direction from the specified dimension.
    • Bilateral tolerance means variation is permitted in both directions from the specified dimension.

    Limits of Size and Fit

    • Limits of size are the extremes of size allowed for a dimension.
    • Basic size is the size about which the limits of a particular fit are fixed.
    • Upper limit of size (ULS) is the largest size permitted by a toleranced dimension.
    • Lower limit of size (LLS) is the smallest size permitted by a toleranced dimension.
    • Tolerance is the total amount of variation permitted by the limits of the dimension.

    Calculating Clearances

    • The amount of clearance is found by calculating the upper and lower limits of both the male and female components.
    • The smallest shaft is subtracted from the largest hole to calculate the slackest fit.
    • The largest shaft is subtracted from the smallest hole to calculate the tightest fit.
    • The tolerances of the individual items will produce a minimum clearance and a maximum clearance.

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    Drill Bits and Sizes PDF

    Description

    Learn about drill bits, their uses, and various sizes. Understand how they are attached to a drill and create holes in different materials. Explore the different types of drill bits and their applications.

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