vex 1.0 © 2005 carnegie mellon robotics academy inc. tapping a hole introduction in this lesson you...

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.

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


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.


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.


Students will be able to:

• 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


Materials List

• 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


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.


Detailed Procedure List1. Select a machine screw that you would want to tap a hole for.2. 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.3. Identify the pitch of the thread or the number of threads per inch by using a thread pitch gauge.4. 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.

5. 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.

6. Drill a through hole with the selected twist drill using the proper speeds, feeds, clamping devices and following the proper safety procedures.

7. 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.

8. 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.

9. Place the starter tap in the tap wrench making sure that you hold the square part of the tap in the tap wrench.10. 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.11. Turn the tap clockwise for a right hand tap, pushing slightly downward while keeping the tap perpendicular to the top of the

work piece.12. Turn the tap two to three revolutions until the tap is slightly imbedded into the hole. 13. Unscrew the tap wrench from the tap, leaving the tap in the hole. 14. 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.)15. 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. 16. 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. 17. 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.


Machine Screw Assortment

• Several machine screws are pictured at the left

• Machine screws come in various shapes, sizes, and types of metal.


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)


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


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.


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


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

.


Countersink the Hole

• Countersinking the hole helps the tapping process by:– Guiding the tap– Centering the tap– Making it easier to

start the screw


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.


Connect Tap & Tap Wrench

• Place the starter tap in the tap wrench, making sure that the square part of the tap goes in first.


Gather your materials

At this point you will need:• tapping fluid• start and plug tap• tap wrench• square• vice


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.


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.


Turn the Tap

• Turn the tap 2-3 revolutions until it is slightly embedded into the hole.


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.


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.


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.


Questions1. When selecting a twist drill for a tap, why is it very important to

consult a tap and drill chart?2. If you read 3/8-16 on a tap, what does the 3\8 and the 16 stand for?3. While tapping, what might happen if you do not turn the tap out to

break the chip?4. What could be the result of not aligning the tap square to the

material?5. How does countersinking the hole help in both the tapping and

fastening process?6. What is the drill size for a ½-13 tap, 10-32 tap and a ¼-20 tap?7. 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?8. What is the difference between a starter tap and a plug tap?9. What would be the difference between a national course thread

and a national fine thread?10. Explain why the need for standardized threads came about.

vex 1.0 © 2005 carnegie mellon robotics academy inc. tapping a hole introduction in this lesson you...

Documents

tap tap drill chart

hand drill

tap size

hand tap slide

required hole size drill

thread standards

proper drill speeds

chart slide