1.
Name five important operations that are performed in fitting shop and tools used to perform
those operations
Ans: The basic operations performed in fitting shop are drilling, reaming, boring,
counter sinking, tapping, threading and grinding etc.
2. How do you calculate the drill size for doing internal thread in a job piece?
Ans: Tap-drill diameter equals nominal diameter minus thread pitch. For example,
drill size for a 3/8-16 thread is 0.375 0.0625 (pitch) = 0.312 in. in diameter, and for a 10-
32 thread, the drill diameter is 0.190 0.032 = 0.159 in.
3. Why are three taps used for doing an internal thread by hand?
Ans: Serial taps divide the cutting operation into several passes and thus enable easy but
time-consuming threading; the third tap - due to its short chamfer - is able to almost
completely cut out blind holes.
4. Name the tool used for making an external thread by hand and explain how to make an
external thread by hand using that tool?
Ans: A die cuts an external thread on cylindrical material, such as a rod, which creates a
male threaded piece which functions like a bolt.
5. Draw a typical thread profile and show major diameter, minor diameter, pitch diameter,
depth of thread, angle of thread, crest and root.
Ans:
6. What do the abbreviations mean- BSW stand for in relation to a thread?
Ans: The principal features of the British Standard Whitworth (BSW) thread form are
that the angle between the thread flanks is 55 degrees and the thread has radii at both
the roots and the crests of the thread. The relevant standard for this thread form is the
British Standard BS 84 – 2007.
(I) BSP
Ans: BSP thread form stands for British Standard Pipe and is common in Australia and
the commonwealth countries. It is based on trade size rather than actual diameter which
can lead to some confusion when measuring ports.
(II) TPI
Ans: TPI is a term used to help identify how many threads are in an inch. To
determine treads per inch an inch of the bolt is measured and then the peaks on the
fastener are counted. In the picture you can see there are 5 peaks in the inch
measurement. This means the TPI of this fastener will be 5. When looking at an
example bolt measurement:
1/4″-20 x 2″
The 1/4″ refers to the bolt diameter (in inches), the -20 refers to the threads per inch
meaning that there are 20 threads per inch on this bolt, and the 2″ refers to the
length (also in inches).
