Experiment No 5 Measurement of thread parameters using floating carriage diameter measuring machine.

 

EXPERIMENT NO 4

TITLE: Determine Parameters of screw thread using floating carriage micrometer

 

 APPARATUS: 

Floating carriage micrometer with all accessories and specimens.

THEORY:

The measurement of minor diameter is carried out on a floating carriage diameter measuring machine in which threaded work piece is mounted between centers. Such micrometer is constrained to move at right angles to axis of centers by v ball side. If reading on setting cylinder with u-pipe in position R1 and reading R2 and diameter D=Dm+ (R2-R1) reading may be taken at various positions in order to determine the tapers variety.
The machine consists of parts:-
1.Base: base casting carries a pair of centre’s on which threaded work piece is mounted
2.Another carriage is mounted on it and exactly 90° to it on this provided carriage is capable of moving towards centre.
3.On this carriage one head having a large thimble enabling reading up to 0.002 mm is provided.

Procedure: 

TWO WIRE METHOD:

The effective diameter of the screw may be as certain by planning two wires or rods at identical diameter between the flanks of thread and measuring the effective diameter ‘E’ is then calculated as:
E=T+d Where D=diameter under wire
T=m-2d m=dimension over the wire d=diameter of wire’
The wires used are made up of hardened steel to sustain wear and tear in use. Diameter ‘T’ can also be determined by placing wires over standard cylinder greater than the diameter under wire and note the reading R1 and take with other gauge say R2,
T=S-(R1-R2)
D= It is the value which depends upon the diameter of wire and pitch on thread. P=0.8P-d(for metric thread)
In figure line BD on the effective diameter, 

BC=0.5pithch=0.5P
OP=dxcosec(x/2) X 0.5 

PA=a(cosec(x/2-1))/2 

PQ=2cosec(x/2)=0.25Pcot(x/2)
AQ=PQ-AP=0.25Pcot(x/2)=0.5dcosec(x/2-1) 

AQ is half value of P.
P=2AQ=0.5cos(x/2)-dcosec(x/2-1)

Two wire method cannot be carried out on diameter measuring because alignment is not possible by two wires.

OBSERVATIONS: 

Best wire diameter=1.333 mm 

Master cylinder diameter=19.995 mm 

Reading over specimen=4.3076 mm
Reading over master cylinder=3.7658 mm

[1]

Use of floating Carriage micrometer for effective diameter measurement of screw thread

 Please see the video for working of floating carriage micrometer

CALCULATIONS:

R1=Standard specimen reading,

 R2=reading over the wire with specimen 

R1=4+0.306+0.0001X6,    (R1=4.3076    mm),(R2=3.7658    mm),    Master    cylinder diameter, D=19.995 mm, M=D+(R2-R1),    =19,995+(3.7658-4.3076),    =19.4577 Now,T=M-2.7,(T=16.7577 mm),E=T+P, M-3w+0.8666P, =19.4577- 3(0.577P)+0.866P,Where P=2.49, (E=17.30385 mm)

RESULT:

Diameter over wire M=19.4577 mm Major diameter D=18.92 mm Effective diameter E=17.3035 mm
T=16.7577 mm D=15.46 mm

CONCLUSION: Hence we have studied the floating carriage micrometer and found out effective diameter of given threaded specimen.

Reference:- 

1. https://5.imimg.com/data5/FG/CV/EY/IOS-25020678/product-jpeg-500x500.png