8. INTRODUCTION
• Threads are of prime importance, they are used as
fasteners.
• It is a helical groove, used to transmit force and
motion.
• In plain shaft, the hole assembly, the object of
dimensional control is to ensure a certain
consistency of fit.
• The performance of screw threads during their
assembly with nut depends upon a number of
parameters such as the condition of the machine
tool used for screw cutting, work material and
tool.
9. GEOMETRICAL FEATURES
• The measurement of
• Straightness
• Flatness
• Squareness
• Parallelism
• Roundness
• Circularity
• Cylindricity
11. STRAIGHTNESS MEASUREMENT
• A line is said to be straight over a given length,
if the variation of the distance of its from two
planes perpendicular to each other and
parallel to the general direction of the line
remains within the specified tolerance limits.
• The tolerance on the straightness of a line is
defined as the maximum deviation in relation
to the reference straight line joining the two
extremities of the line to be checked.
12. • Important geometrical parameter of machines
• Example: shaping machine-guideways
• Shortest distance between the two lines –
straight line
• Ray of light, liquid level
• It is a qualitative measure of a surface
• Straightness measuring system should be in
line with functional point – called Bryan’s
principle
14. METHODS OF STRAIGHTNESS
SPIRIT LEVEL:
• Inspecting the horizontal surfaces
• Finding direction and magnitude of minor
deviation from nominal condition
• The bubble will move from its position along
the radius of the angle of tilt.
• Ether, alcohol, benzol- low viscosity fluid
• Having graduated scale
18. STRAIGHT EDGES:
• With the help of surface plates and sprit
levels straight edges are used for checking
straightness and flatness
• Flat – sectioned measuring instrument
• Made up of steels
• Straight edges are used for testing large areas
of surface
• Painted surfaces are used to measure
straightness
LASER MEASURING SYSTEM:
20. FLATNESS MEASUREMENT
• Minimum distance between the two planes,
which will cover all irregularities of the
surface to be tested
• Best-fit plane between two standard
reference plane one above and one below
the plane surface to be tested
• Deviation of the surface from the best fitting
plane
23. METHODS
• Beam comparator is used for flatness testing
• Flatness measuring by using
interferometry(NPL)
• Using laser interferometer
• Using electromechanical gauges.
• Autocollimator
29. ROUNDNESS MEASUREMENT
• Measure of how closely
the shape of an object
approaches the circle.
• All points of cross
sections are equal
distant to a common
surface.
40. THREAD MEASUREMENT
• Helical structure
• To convert rotational movement into linear
movement
• Helical ridge produced by forming a
continuous helical groove of uniform section
• To transmit power and motion
45. NOMENCLATURE
• Major diameter of nominal diameter (d)
• Minor diameter or core diameter or root
diameter (dc)
• Pitch diameter or effective diameter (dp)
• Pitch(p)
• Lead: lead=pitch
• Crest
• root
46. • Depth of thread
• Flank
• Angle of thread
• Screw thread:
• Flank angle
• Helix angle
• Addendum
• Deddendum
tan α= p/π d
47. TYPES OF THREAD
• British association thread
• Whitworth (bsw) threads
• Metric thread
• It is necessary to measure the following
– Major diameter
– Minor diameter
– Effective diameter
– Pitch
56. MEASUREMENT OF EFFECTIVE
DIAMETER
• Effective diameter measurement is carried out
by following methods.
1. One wire,
2. Two wires, or
3. Three wires method.
4. Micrometer method
72. SURFACE FINISH MEASUREMENT
• Surface texture
• Primary texture or roughness
• Secondary texture or waviness
• The factors to be affected
cutting speed
feed
depth of cut
73. • Properties of the work piece
• Tool materials
• Types of machine tool
• Quality of the machine tool
74. ANALYSIS OF SURFACE FINISH
• For determining the surface tecture
• Peak to valley height method
• The average roughness method
• Form factor or bearing curve