The
indexing head is the operation of splitting the edge of a workpiece into any
number of equal parts.
While
cutting the spur gears, equal spacing of the teeth on the gear blank is
performed by indexing.
The
indexing head can also be used for producing square or hexagonal bolts,
fluting drills, cutting splines on shafts, taps, reamers, etc.
The
indexing can be achieved by using a special attachment known as a dividing head
or index head.
Indexing
Methods.
There
is a total of 4 Indexing Head Methods:
1. Direct Indexing
2. Angular indexing
3. Compound Indexing and
4. Differential indexing
1. Direct Indexing
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· direct indexing is also called rapid indexing, and it is used when a large
number of pieces are indexed with a
small division.
·This
operation can be done in both plain and universal dividing heads. Whenever using
the Universal head, the worm and worm wheel are first disengaged. The required
number of divisions on the work is obtained by means of the rapid index plate
which is fitted at the front end of the spindle nose. The plate has (24)
equally spaced holes.
· The
spring-loaded pin can be pushed into any of the holes to lock the spindle with
the frame.
· For
indexing, the pin is taken out first and then the spindle is rotated by hand, and
after the required position is reached it is again locked by the pin.
· When
the plate is turned through the required part of the revolution, the dividing
head spindle and the work are also turned through the same component of the
revolution. me -2
· With
a Rapid indexing plate of (20) holes, it is possible to divide the work into equal divisions of 2,3,4,6,8,12,14,16, and 24 parts which are all the
factors of (24).
· To
Find the index motion, find the total number of holes in the direct indexing
plate by the number of divisions required in the work, If (N) is the number of
divisions required in the work then,
[Number of holes be removed= 24/N]
2. Simple Indexing Head:
· Simple
indexing is also called (9) indexing. It is more accurate and has a large
range of indexing heads than rapid indexing.
· For
indexing, the dividing head spindle is turned by the indexing crank. The figure
is shown:
· The
worm shaft carried the crank has a single-threaded worm that meshes with worm
gear having (40) teeth, 40 turns of the crank are necessary to rotate the
indexing head spindle through one revolution.
· Therefore,
one completed turn of the indexing crank will cause the worm wheel to make
1/40 of a revolution. To facilitate
indexing to the fraction of a turn, an Indexing plate is used to cover
practically all numbers.
· The
Indexing plate with a circle of holes manufactured by the brown and sharp
company is:
o
Plate No 1- 15,
16, 17,18,19,20
o
Plate No 2- 21,
23, 27,29,31,33
o
Plate No 3- 37,
39, 41,43,47,49
· To
find the index crank movement, divided 40 by the number of divisions required
on the work,
[Index crank movement= 40/N]
Where N is the number of divisions
required on the worked.
3. Angular Indexing Head:
· angular
indexing is the Processed of dividing the periphery of work in angular
measurements.
·
There are (360)
degrees in a circle, and then the index crank is rotated by 40 revolutions,
·
And the spindle rotated
through 1 complete Revolution or by 360 degrees, one completed turn off the
crank will cause the spindle and the work to rotate through 360/40=9 degrees.
·
Therefore in order
to turn work through a required angle, the number of turns required for the index
crank can be calculated by the number ‘9’.
·
Angular
displacement is expressed in a minute then the terms of the index crank can be
calculated by dividing the angle by (540).
·
If it is expressed
in seconds then it is divided by (32400).
· When a result is a
whole number, the index crank is rotated through the full calculated numbers.
If
the result is a fraction and a whole number,
·
the part of the
revolution of the crank after turning the whole number is calculated by
multiplying is suitable for numbers to the numerator and denominator of the
fraction, defecation to make the denominator of the fraction equal to the
number of holes in the index plate circle and the now numerator number for
holes to be moved by the index Crank.
·
The index crank Movements=
Angular displacement of work, in degrees / 9
= in
minutes / 540
= in seconds / 32400
4. Compound Indexing Head:
·
In Compound
indexing, these are two separate movements of the index crank in two different
holes circles of one index plate to get the crank movement.
· The index plate is
held stationary by a Lock pin heed which is engaged with one of the whole circles of
the index placed from the back.
· For indexing
first, the crank pin is rotated by the required number of spaces in one of
the holes of the circle of the index plate and then the pin is engaged with the
plate.
· The second index
movement is done by removing the real lock pin and rotating the plate
together with the index crank forward or backward through the calculated number
of spaces of another hole's circles, and the lock pin is engaged.
The
net movements are the sum of the movement, therefore,
{40/N
= n1 /N1 + n2/N2}
N. is the number of
divisions required
N1.
is the hole circle used by the crankpin
N2. is the hole circle used by
the lock pin
n1.
is space moved by the crankpin in the N1 hole circle
n2.
are the spaces moved by the plate and the crankpin in the N2 hole circle.
The
basic knowledge about indexing, I think now you know.
So
let’s look forward to solving the problem,
Q
1. Find the index movement required to mill a hexagonal Bolt by direct
indexing. The rapid index plate has 24 holes.
Solution:
Number of holes to be moved = {24/N}
= {24/6 = 04}
Therefore
after machining one side of the bolt, the index plate has to move by 4 holes
for the next face to the machine.
Q
2. Set the dividing head to mill 30 teeth on the spur wheel blank by simple
indexing.
Solution:
Index Crank movements = {40/N}
= {40/30}
= {4/3}
= {4/3
* 7/7 =1+ (7/21)
1
Full turn and 7 holes in 21 holes circle of the index plate.
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