Tapping A Hole Introduction
• In this lesson you will learn to:
– Produce internal threads for a specific size
machine screw
– Identify and select a tap for a required thread
– Identify and select a drill for the required hole
size
– Drill and tap a hole using a hand tap
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Thread Standards
• Why are thread standards so important and how
did they come about?
– Thread standards allow parts to be interchangeable.
Standards allow parts built in one plant to fit parts
built in another. WWI and WWII played a large role in
the development of standardized thread sizes. Henry
Ford and his assembly line played a significant role in
the development of standards. These standards
enabled Ford’s workers to produce cars at a much
faster rate. This made cars more affordable and made
it easy for a mechanics to replace parts instead of
making them.
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Note to the teacher
• In this lesson the students will learn to:
– Identify the size of a machine screw
– Identify the drill for the tap size by reading a
tap and drill chart
– Tap a hole using a hand tap
• For this lesson, you will need a lab with a
drill press or a hand drill, as well as the
other materials listed on slide 5.
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Students will be able to:
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Reason why threads were standardized
Identify standard thread sizes
Read a tap and drill chart
Identify and select a drill for a tap
Countersink a hole for thread lead-in
Take measurements and apply them to
tapping by using a chart
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Materials List
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Low Carbon Steel or Aluminum Block
Machine Screw
Screw Pitch Gauge
Start and Plug Tap
Tap & Drill Chart
Tap Wrench
Tapping Fluid
Twist Drill and Drill Press
Square
Countersink
Clamping Devices
Micrometer
Bench Vise
Small Cleaning Brush & File
Safety Glasses
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Safety Note
• Remember to follow safety procedures.
Use proper drill speeds and feeds when
working in the lab. If you do not know the
proper drill speed for the material you are
machining, consult your instructor. Make
sure that all equipment is in proper
working order and that all of your cutting
tools are sharp and in good condition.
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Detailed Procedure List
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16.
17.
Select a machine screw that you would want to tap a hole for.
Identify the diameter of the machine screw by using a micrometer or other measuring device that is accurate to within +
or - .003
thousands of an inch.
Identify the pitch of the thread or the number of threads per inch by using a thread pitch gauge.
Identify whether the machine screw is a right hand or left hand screw by looking at the end of the threads. If the threads
turn clockwise, then your threads are right handed. If they turn counter clockwise, then they are left handed threads.
Use a tap and drill chart to identify the proper drill required by lining up both the diameter or decimal size and the pitch or
threads
per inch.
Drill a through hole with the selected twist drill using the proper speeds, feeds, clamping devices and following the
proper safety
procedures.
Countersink the hole to the required depth for the proper lead-in for the thread. Note: The proper lead-in will help you
start the
tap, guide the tap into the center of the hole, help keep the tap from breaking and help start the
machine screw into the hole.
Consult the machinist hand book for the proper depth or countersink the hole a little
bigger than the diameter of the thread.
Place your work piece in a bench vise so that it is level and just above the vice jaws. Note: At this point, you will need
your
tapping fluid, start and plug tap, tap wrench, square and a small cleaning brush.
Place the starter tap in the tap wrench making sure that you hold the square part of the tap in the tap wrench.
Apply a small amount of tapping fluid to the end of the threads on the tap, and place the tap in the pre drilled hole
perpendicular to the top of the work piece.
Turn the tap clockwise for a right hand tap, pushing slightly downward while keeping the tap perpendicular to the top of
the work piece.
Turn the tap two to three revolutions until the tap is slightly imbedded into the hole.
Unscrew the tap wrench from the tap, leaving the tap in the hole.
Check to see if the tap is perpendicular to the top of the material by using a square. ( If it is square, you can continue to
tap. If not,
you need to back the tap out a turn and then realign the tap using a square.)
Continue turning the tap in a clockwise direction for one revolution, or until the tap gets tight. At this point, you no longer
need
downward force- just rotation.
Turn the tap counterclockwise out of the work piece to break the chip. If you do not break the chip, you will break the tap.
Continue following procedures 15 & 16 until the tap breaks through the work piece. Make sure that you have a full thread
the whole way through the part. If the starter tap does not give you a full thread you can use a plug tap.
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Machine Screw Assortment
• Several machine
screws are pictured
at the left
• Machine screws
come in various
shapes, sizes, and
types of metal.
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Identify the Diameter
• Measure the
diameter of the
screw using a
micrometer
• Note the diameter
• The diameter in the
example is .375
• Convert from decimal
to fractional sizes
(.375 converts to 3/8 inch when
converting from decimal to fractional
sizes)
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Identify Thread Pitch
• Use a thread
gauge to
determine the
number of
threads per
inch.
• The example at
the right shows
16 threads per
inch.
Thread gauge
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Combine the diameter and the thread size
.375 or 3/8 inch diameter
16 threads per inch
These two bits of information allow us to
determine that the size of the machine screw
is 3/8-16. Consult the chart on the next slide
to determine the drill size to cut the internal
thread for this bolt.
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Using a Tap & Drill Chart
• Find the 3/8-16
machine screw size
under the column
named tap size
• Read across to the left
to identify the correct
size of the drill you will
use when preparing to
drill the whole before
tapping
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Drill the Hole
• Drill the hole with the bit
that went with the tap
you want to use on the
chart.
Note:
Always use caution when
drilling
• Use safety goggles
• Identify the proper drill
speed for the material you
are drilling
•Secure your work
.
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Countersink the Hole
• Countersinking the
hole helps the
tapping process by:
– Guiding the tap
– Centering the tap
– Making it easier to
start the screw
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Tap Types
• There are various
types of Taps.
• A starter tap is used to
start threading. The
large taper easily
guides the tap into the
hole.
• A Plug Tap has less
taper and has more
threads for going
deeper into holes.
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Connect Tap & Tap Wrench
• Place the starter
tap in the tap
wrench, making
sure that the
square part of the
tap goes in first.
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Gather your materials
At this point you will need:
• tapping fluid
• start and plug tap
• tap wrench
• square
• vice
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Apply Tapping Fluid
• Apply tapping fluid
to threads next to
the hole.
• Place the tap in the
pre-drilled hole,
making sure it is
perpendicular to the
piece of metal.
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Start the Tap
• Push down and
turn the Tap
clockwise for a right
hand tap.
• Twist the tap while
making sure that it
is perpendicular to
the metal piece.
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Turn the Tap
• Turn the tap 2-3
revolutions until it is
slightly embedded
into the hole.
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Examine Tap
• Unscrew the Tap
Wrench from the
Tap and leave it in
the hole.
• Check to see if it is
perpendicular by
using a square.
Note: If tap isn’t perpendicular go back
and re-align the tap before you
continue.
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Continue to Turn Tap
• Continue to turn the
tap.
• Back it out before it
gets tight, so you
don’t break the tap.
• Continue to ease it
through in this
manner until you have
completed threads.
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Check Your Work
• Check your tapped
hole with the correct
size machine screw to
make sure it works.
And here you have the
finished product. This is
what a successfully tapped
hole should look like.
Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.
Questions
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When selecting a twist drill for a tap, why is it very important to
consult a tap and drill chart?
If you read 3/8-16 on a tap, what does the 3\8 and the 16 stand
for?
While tapping, what might happen if you do not turn the tap out to
break the chip?
What could be the result of not aligning the tap square to the
material?
How does countersinking the hole help in both the tapping and
fastening process?
What is the drill size for a ½-13 tap, 10-32 tap and a ¼-20 tap?
Often, through much use, the size of the drill wears off so that you
can not read it. What is another way to check the drill size?
What is the difference between a starter tap and a plug tap?
What would be the difference between a national course thread
and a national fine thread?
Explain why the need for standardized threads came about.
Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.