Regarding tapping and drilling...

2. MODULE OBJECTIVES
After the completion of this module, student should be able to:
 Explain the tapping process
 Identify the tap types.
 Explain the tapping.
 Use the tapping tools to create a tap.

3. INTRODUCTION
One of the most effective ways to fasten two or more components is
through the use of screws or bolts, secured in properly threaded
holes. This method of fastening is more robust then other fastening
methods, allowing repeated assembly and dismantling via simple
screwing and unscrewing of the screw.
Screw
Bolts
Nut

4. TAPPING
Tapping is the process of producing threads in a metal using certain
tools.
Tapping
Threading

5. HAND THREADING SAFETY
 Chips produced by hand threading are sharp and should be cleaned
by using a brush or piece of cloth.
 Do not use compressed air to remove the metal chips.
 Newly-cut external threads are very sharp. Again use a brush or
cloth to clean them.
 Wash your hands after using cutting fluids or oils.
 Have cuts treated by a qualified person.
 Be sure the die is clamped firmly in the die stock. If not, it can fall
from the holder and cause injury.
 Broken tap have very sharp edges and are very dangerous. An extra
care should be taken in dealing with broken taps.

6. THREADS STANDARDS
There are many types of threads used in different applications. The most
frequently used standard is the ISO standard that is shown in the
figure
F: Crest
D: Thread Depth
P: Thread Pich

7. Tolerance: Is the
acceptable
difference
between
theoretical and
manufactured
pieces.

8. TAPS TYPES
A set of standard hand taps is
made of a taper, plug and
bottoming tapers
A: Taper for starting thread.
B: Plug tap for continuing thread
after taper tap has cut into hole
C: Bottoming for continuing
threads to bottom of a blind
hole.

9. TAP TYPES
Threads are started with a taper tap.
Then the plug tap is used after the taper tap has cut threads as far into
the hole as possible.
Finally threads are cut to the bottom of a blind hole (one that does not
go through the part) with a bottoming tap. It is necessary to use the
full set of taps, only when a blind hole is to be made.
A: Open or through hole.
B: Blind hole that is drilled deeper than desired threads
C: Blind hole with threads tapped to bottom.

10. TAP DRILL
The drill used to make the hole prior to tapping is called a tap drill.
Theoretically, it should be equal in diameter to the minor diameter of
the screw that will be fitted into the tapped hole.
Table (1) below shoes the relationship between the thread normal size
(diameter) and the its proper tap drill diameter.

12. Table (1): Thread and tap drill
chart for metric threads.
Tap Drill = Normal size –
thread pitch

13. TAP WRENCH
Two types of tap wrenches are available.
The selection of tap wrench depends on the tap size.
A T-handle tap wrench is used with all small taps while the Hand Tap
Wrench is used with large taps.
Hand tap wrench
T-handle tap wrench

14. CARE IN TAPPING
 Use the correct size tap drill
 Use a sharp tap and apply sufficient quantities of cutting fluids.
 Start the taper tap square with the work.
 Do not force the tap to cut.
 Avoid running a tap to the bottom of a blind hole and continuing
to apply pressure.
 Remove burrs on a tapped hole with a smooth file.

15. DRILLING
Drilling is the operation of producing circular hole in the work-piece by
using a rotating cutter called DRILL.
The machine used for drilling is called drilling machine.
The drilling operation can also be accomplished in lathe, in which the
drill is held in tailstock and the work is held by the chuck.
The most common drill used is the twist drill.

16. DRILL MATERIALS
The two most common types are
1. HSS drill
- Low cost
2. Carbide- tipped drills
- high production and in CNC machines
Other types are
Solid Carbide drill, TiN coated drills, carbide coated masonry drills,
parabolic drills, split point drill

17. TOOL HOLDING DEVICES
The different methods used for holding drill in a drill spindle are
 By directly fitting in the spindle hole.
 By using drill sleeve
 By using drill socket
 By using drill chuck
Drilling operations:-Operations that can be performed in a drilling machine
are
 Drilling
 Reaming
 Boring
 Counter boring
 Countersinking
 Tapping