screw thread measurement by optical profile projector, screw thread terminology, major diameter, minor diameter, pitch, nominal diameter.

1. • What is a screw ?
A screw is a mechanical system that converts rotational motion in to linear motion. ...
Although 'screw' refers to many helical devices, in its simplest form it consists of helical
threads around a cylindrical shaft (male/external thread) and its purpose is to fasten
components together.
• Image of screw thread.

2. • Screw thread terminology.
• Major diameter:-
The major diameter is a diameter that can be measured from two points. It is the
diameter of an imaginary cylinder formed around the crest of an external thread.
• Minor diameter:-
The minor diameter is the diameter of an imaginary cylinder that just touches
the roots of an external thread and (or) the crests of an internal thread. The crest of
a thread is the prominent part of a thread, whether internal or external.
• Pitch diameter:-(effective diameter)
Pitch Diameter is the simple effective diameter of screw thread, approximately
halfway between the major and minor diameters.
• Pitch
Pitch is the distance from a point on the screw thread to a corresponding point on
the next thread measured parallel to the axis .
• Angle thread:-
The thread angle of a screw is the included angle between the thread flanks,
measured in a plane containing the thread axis.

3. How to measure this parameters of screw thread or which
instrument/comparator used to measure this parameters of screw thread
:-
• Optical profile projector:-
• Usage:-
Profile projector is widely used for complex shape stampings, gears, cams,
threads and comparing the measured contour model. It’s easy to use and highly
efficient.
It is a commonly used measurement of optical instruments. Thus, profile
projector is widely used in major machinery manufacturing including
aviation,aerospace industry, watches and clocks, electronics, instrumentation
industry,research institutes and detection metering stations at all levels and etc.
• Working principle:-
The projector magnifies the profile of the specimen, and displays this on the
built-in projection screen. On this screen there is typically a grid that can be
rotated 360 degrees so the X-Y axis of the screen can be aligned with a straight
edge of the machined part to examine or measure. This projection screen
displays the profile of the specimen and is magnified for better ease of
calculating linear measurements.
An edge of the specimen to examine may be lined up with the grid on the screen.
From there, simple measurements may be taken for distances to other points.
This is being done on a magnified profile of the specimen. It can be simpler as
well as reduce errors by measuring on the magnified projection screen of a

4. profile projector.
The typical method for lighting is by diascopic illumination, which is lighting
from behind. This type of lighting is also called transmitted illumination when
the specimen is translucent and light can pass through it. If the specimen is
opaque, then the light will not go through it, but will form a profile of the
specimen. Measuring of the sample can be done on the projection screen. A
profile projector may also have episcopic illumination (which is light shining
from above). This useful in displaying bores or internal areas that may need to
be measured.
• READINGS TAKEN BY OPTICAL PROFILE PROJECTOR OF
VARIOUS SCREW THREADS:-
Sr No. Major Diameter Difference Minor diameter Difference Angle
crest crest root root
1 1.47 6.54 5.07 5.04 1.51 3.51 15
2 1.54 8.54 7 8.15 2.75 5.4 30
3 1.35 9.35 8 9.39 2.35 7 30
4 2.35 12.02 9.67 10.15 2.1 8.05 40
5 2.23 11.41 9.18 9.14 3.01 6.11 30
6 1.1 11.41 10.31 11.35 2.21 9.14 30
7 2.45 12.32 9.87 11.51 4.04 7.47 30
8 9.2 4.17 5.03 8.22 4.15 4.03 25

5. • SUMMARY:-
Optical Profile Projector are widely used due to their ease of use. The profile
projectors are used for measuring several measuring at a time which saves time
and energy, When the components are measured through micrometers and other
instruments, there are indentation marks that may appear on the surface of the
products. The profile projector helps in revealing that indentation on the surface
of the products Unlike the mechanical gauges, which undergo wear and tear due
to prolong uses, measurements by optical projectors are free from wear. Several
people can observe the projected image simultaneously. Thus, projectors are
handy tools when images are to be inspected by a group of people.
• CONCLUSION:-
Optical comparators are used to measure manufactured parts in a wide range of
industries around the world every day. Available with numerous features and
options to suit many applications, comparators can be used throughout a factory,
including incoming inspection areas, R&D labs, machine shops, assembly and
production floors, and final inspection areas. Their versatility, range of
capabilities and return on investment make comparators indispensable and
integral to any quality plan. Optical comparator saves time, ease of use factors and
ergonomic designs reduuce the inspection time retraining costs and operator
fatigue, all while increasing throughout. Custom hard gauges are subjected to
wear and need frequent recertification, which takes them out of service and adds
an additional cost.