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Questions and Answers
What is the primary function of drill bits?
What is the primary function of drill bits?
What is the common increment size for metric drill bits?
What is the common increment size for metric drill bits?
Where can you find drill bit sets in 0.5-mm increments?
Where can you find drill bit sets in 0.5-mm increments?
What is the purpose of attaching a drill bit to a drill?
What is the purpose of attaching a drill bit to a drill?
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In which country is the use of fractional inch and gauge drill bit sizes more common?
In which country is the use of fractional inch and gauge drill bit sizes more common?
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When were the British standards for replacing gauge size drill bits with metric sizes first published?
When were the British standards for replacing gauge size drill bits with metric sizes first published?
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What is the primary purpose of centre drills?
What is the primary purpose of centre drills?
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What is the included angle of the standard centre drill bit?
What is the included angle of the standard centre drill bit?
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Why are close-tolerance bolts not cad plated?
Why are close-tolerance bolts not cad plated?
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What is the typical way machinists think about decimal places for 0.25, 0.5, and 0.75?
What is the typical way machinists think about decimal places for 0.25, 0.5, and 0.75?
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What is the tolerance range for standard-tolerance bolts?
What is the tolerance range for standard-tolerance bolts?
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What is the definition of a light drive fit?
What is the definition of a light drive fit?
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What is the typical length of the flutes of a jobber-length drill in relation to the drill's diameter?
What is the typical length of the flutes of a jobber-length drill in relation to the drill's diameter?
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How deep can a 1/2-in.(12.7-mm) diameter drill drill a hole?
How deep can a 1/2-in.(12.7-mm) diameter drill drill a hole?
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What is the general rule for selecting a drill size for a bolt hole?
What is the general rule for selecting a drill size for a bolt hole?
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What is the main difference between jobber-length drills and aircraft length drills?
What is the main difference between jobber-length drills and aircraft length drills?
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What is the minimum diameter for which aircraft length drills are available in fixed lengths?
What is the minimum diameter for which aircraft length drills are available in fixed lengths?
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What is the typical length of an aircraft length drill?
What is the typical length of an aircraft length drill?
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What type of tolerance allows variation in only one direction from the specified dimension?
What type of tolerance allows variation in only one direction from the specified dimension?
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What is the largest size permitted by a toleranced dimension?
What is the largest size permitted by a toleranced dimension?
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What is the term for the extremes of size allowed for a dimension?
What is the term for the extremes of size allowed for a dimension?
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What is the term for the size about which the limits of a particular fit are fixed?
What is the term for the size about which the limits of a particular fit are fixed?
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What is the total amount of variation permitted by the limits of the dimension?
What is the total amount of variation permitted by the limits of the dimension?
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What type of tolerance allows variation in both directions from the specified dimension?
What type of tolerance allows variation in both directions from the specified dimension?
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What is the primary purpose of drawing upper and lower limits on mating parts?
What is the primary purpose of drawing upper and lower limits on mating parts?
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Which of the following is NOT a method of expressing tolerance on dimensions?
Which of the following is NOT a method of expressing tolerance on dimensions?
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What is the result of calculating the clearance between the smallest shaft and the largest hole?
What is the result of calculating the clearance between the smallest shaft and the largest hole?
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What is the minimum clearance calculated in the worked example?
What is the minimum clearance calculated in the worked example?
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What is the purpose of determining the acceptable component limits during maintenance?
What is the purpose of determining the acceptable component limits during maintenance?
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What is the result of calculating the clearance between the largest shaft and the smallest hole?
What is the result of calculating the clearance between the largest shaft and the smallest hole?
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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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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.