1. The Indexing or
Dividing Head
Session 14
1

2. Indexing (Dividing) Head
• Once one of the more important
attachments for milling machine
• Used to divide circumference of
workpiece into equally spaced
divisions when milling gear teeth,
squares, hexagons, and octagons
• Also used to rotate workpiece at
predetermined ratio to table feed rate
2

3. Index Head Parts
• Headstock with index plates • Universal chuck
• Headstock change gears • Footstock
• Quadrant • Center rest
3

4. Index Head Parts
• Swiveling block
• Mounted in base enables headstock to be
tilted from 5º below horizontal to 10º beyond
vertical
• Spindle
• Mounted in swiveling block with 40-tooth
worm wheel, meshes with worm
• Worm
• Right angle to spindle, connected to index
crank
• Direct indexing plate
• Engaged by pin and attached to front of
spindle 4

5. Index Head Parts
5

6. Section view
of a dividing
head
6

7. Index Head Parts
• Universal chuck
• Threaded onto end of spindle
7

8. Index Head Parts
• Footstock
• Used in conjunction with headstock to
support work held between centers or in
chuck
• May be adjusted longitudinally, raised or
lowered off center, and tilted out of parallel
8

9. Index Head Parts
Adjustable center rest
• Holds long, slender work between centers
9

10. Methods of Indexing
1. Direct
2. Simple
3. Angular
4. Differential
10

11. Direct Indexing
• Simplest form of indexing
• Performed by disengaging worm shaft
from worm wheel by means of
eccentric device in dividing head
• Spring-loaded tongue lock engages
numbered slots in index plate
• Used for quick indexing of workpiece
when cutting flutes, hexagons,
squares, etc.
11

12. Direct Indexing Divisions
• Direct indexing plate usually contains
three sets of hole circles or slots: 24,
30, and 36
• Number of divisions possible to index
limited to numbers that are factors of 24,
30, 36
Slots Direct indexing divisions
24 2 3 4 _ 6 8 _ __ 12 __ __ 24 __ __
30 2 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __
36 2 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 36
12

13. Example: Direct Indexing
• What direct indexing is necessary to mill eight
flutes on a reamer blank?
Since the 24-hole circle is the only one divisible
by 8 (the required number of divisions), it is the
only circle that can be used in this case.
Slots Direct indexing divisions
24 2 3 4 _ 6 8 _ __ 12 __ __ 24 __ __
30 2 Never count _ 10 __ or slot in which__
3 _ 5 6 _ the hole 15 __ __ 30
36 2 the index _ 9 is engaged. 18 __ __ 36
3 4 _ 6 pin __ 12 __
13

14. Milling a Square with
Direct Indexing
1. Disengage worm and worm shaft by
turning worm disengaging shaft lever
if dividing head is so equipped
2. Adjust plunger behind index plate
into the 24-hole circle or slot
3. Mount workpiece in dividing head
chuck or between centers
4. Adjust cutter height and cut first side
14

15. Milling a Square with
Direct Indexing
1. Remove plunger pin using plunger pin
lever
2. Turn plate attached to dividing head
spindle one-half turn and engage
plunger pin
3. Take second cut
15

16. Milling a Square with
Direct Indexing
1. Measure work across flats and adjust
work height if required
2. Cut remaining sides by indexing every
six holes until all surfaces cut
3. Check for finish size
16

17. Simple Indexing
• Work positioned by means of crank,
index plate, and sector arms
• Worm attached to crank must be
engaged with worm wheel on dividing
head spindle
• 40 teeth on worm wheel
• One complete turn on index crank cause
spindle and work to rotate one-fortieth of a
turn (ratio of 40:1)
17

18. Simple Indexing
• Calculating the indexing or number of
turns of crank for most divisions, simply
divide 40 by number of divisions to be
cut or,
40
Indexing =
N
18

19. Simple Indexing
• The indexing required to cut eight
flutes:
40
= 5 full turns of index crank
8
• The indexing required to cut seven flutes:
40 5
= 5 turns of index crank
7 7
The five-sevenths turn involves use of
an index plate and sector arms. 19

20. Index Plate and Sector
Arms
• Index plate
• Circular plate provided with series of
equally spaced holes into which index
crank pin engages
• Sector arms
• Fit on front of plate and may be set to any
portion of a complete turn
20

21. Finishing Indexing for
Seven Flutes
Choose any hole
Index-plate hole circles circle that is divisible
Brown & Sharpe by denominator 7
Plate 1 15-16-17-18-19-20 5/7 = 15 /21
Plate 2 21-23-27-29-31-33 So, 5 full turns plus
Plate 3 37-39-41-43-47-49 15 holes on 21 hole
Cincinnati Standard Plate circle!
One side 24-25-28-30-34-37-38-39-41-42-43
Other side 46-47-49-51-53-54-57-58-59-62-66
21

22. Finishing Indexing for
Seven Flutes
Choose any hole
Index-plate hole circles circle that is divisible
Brown & Sharpe by denominator 7
Plate 1 15-16-17-18-19-20 5/7 = 35/49
Plate 2 21-23-27-29-31-33 So, 5 full turns plus
Plate 3 37-39-41-43-47-49 35 holes on 49 hole
Cincinnati Standard Plate circle!
One side 24-25-28-30-34-37-38-39-41-42-43
Other side 46-47-49-51-53-54-57-58-59-62-66
22

23. Finishing Indexing for
Seven Flutes
Choose any hole
Index-plate hole circles circle that is divisible
Brown & Sharpe by denominator 7
Plate 1 15-16-17-18-19-20 5/7 = 20/28
Plate 2 21-23-27-29-31-33 So, 5 full turns plus
Plate 3 37-39-41-43-47-49 20 holes on 28 hole
Cincinnati Standard Plate circle!
One side 24-25-28-30-34-37-38-39-41-42-43
Other side 46-47-49-51-53-54-57-58-59-62-66
23

24. Finishing Indexing for
Seven Flutes
Choose any hole
Index-plate hole circles circle that is divisible
Brown & Sharpe by denominator 7
Plate 1 15-16-17-18-19-20 5/7 = 30/42
Plate 2 21-23-27-29-31-33 So, 5 full turns plus
Plate 3 37-39-41-43-47-49 30 holes on 42 hole
Cincinnati Standard Plate circle!
One side 24-25-28-30-34-37-38-39-41-42-43
Other side 46-47-49-51-53-54-57-58-59-62-66
24

25. Finishing Indexing for
Seven Flutes
Choose any hole
Index-plate hole circles circle that is divisible
Brown & Sharpe by denominator 7
Plate 1 15-16-17-18-19-20 5/7 = 35/49
Plate 2 21-23-27-29-31-33 So, 5 full turns plus
Plate 3 37-39-41-43-47-49 35 holes on 49 hole
Cincinnati Standard Plate circle!
One side 24-25-28-30-34-37-38-39-41-42-43
Other side 46-47-49-51-53-54-57-58-59-62-66
25

26. Cutting Seven Flutes
1. Mount B&S Plate 2 index plate on
dividing head
2. Loosen index crank nut and set index
pin into hole on 21-hole circle
3. Tighten index crank nut and check to
see that the pin enters hole easily
4. Loosen setscrew on sector arm
5. Place narrow edge of left arm against
index pin
26

27. Cutting Seven Flutes
1. Count 15 holes on 21-hole circle
• Do not include hole in which index crank
pin is engaged.
2. Move right sector arm slightly beyond
fifteenth hole and tighten sector arm
setscrew
3. Align cutter with work piece
4. Start machine and set cutter to top of
work by using paper feeler
27

28. Cutting Seven Flutes
1. Move table so cutter clears end of work
2. Tighten friction lock on dividing head
before making each cut and loosen
lock when indexing for spaces
3. Set depth of cut and take first cut
4. After first flute has been cut, return
table to original starting position
28

29. Cutting Seven Flutes
1. Withdraw index pin and turn crank
clockwise five full turns plus the 15
holes indicated right sector arm
• Release index pin between 14th and 15th
holes and gently tap until it drops into
15th hole
• Turn sector arm farthest from pin
clockwise until it is against index pin
29

30. Cutting Seven Flutes
The arm farthest from the pin is held and
turned. If the arm next to the pin were held
and turned, the spacing between both
sector arms could be increased when the
other arm hits the pin. This could result in
an indexing error not noticeable until the
work was completed.
1. Lock dividing head; continue machining
and indexing for remaining flutes
30

31. Angular Indexing
• Setup for simple indexing may be
used
• Must calculate indexing with angular
distance between divisions instead
number of divisions
• One complete turn of index crank
turns work 1/40 of a turn
• 1/40 of 360º equals 9 degrees
no. of degrees required
Indexing in degrees =
9 31

32. Angular Indexing
Calculate indexing for 45º
45
Indexing = =5
9
5 complete turns
32

33. Angular Indexing
Calculate indexing for 60º
60 2
Indexing = =6
9 3
6 full turns plus 12 holes on 18 hole
circle
33

34. Angular Indexing
Calculate indexing for 24'
Divide 24'/540' = 4/90
4/90 = 1/22.5
1 hole on a 22.5 hole circle
The nearest is a 23 hole circle. Indexing
would be 1 hole on a 23 hole circle with
a slight error (approximately 1/2 minute).
A need for higher accuracy requires
differential indexing.
34

35. Angular Indexing
Calculate indexing for 24º30'
• First, convert angle into minutes
(24 x 60') = 1440' now add 30' = 1470'
Convert 9° to minutes 9°x60 = 540'
Divide 1470'/540' = 2 13/18
2 full turns and 13 holes on 18
hole circle
35

36. Differential Indexing
• Used when 40/N cannot be reduced to a
factor of one of the available hole circles
• Index plate must be revolved either
forward or backward part of a turn while
index crank turned to attain proper
spacing (indexing)
• Change of rotation effected by idler gear or
gears in gear train
36

37. Differential Method
• Number chosen close to required
divisions that can be indexed by simple
indexing
• Example: Assume index crank has to
be rotated 1/9th of a turn and only 8-hole
circle
• Crank moved 1/9th, index pin contacts plate
at spot before first hole
• Exact position would be the difference
between 1/8th and 1/9th of a revolution of
the crank 37

38. Differential Method cont.
1 1 9 8 1
− = − =
8 9 72 72 72
one-seventy-second of a turn short of
first hole
Since there is no hole at this point, it is
necessary to cause plate to rotate backward
by means of change gears one-seventy-
second of a turn of pin will engage in hole.
38

39. Method of Calculating the Change
Gears
40
Change gear ratio = (A - N) x
A
driver (spindle) gear
=
driven (worm) gear
A = approximate number of divisions
N = required number of divisions
If A is greater than N, resulting fraction is positive and
the index plate must move in same direction as crank
(clockwise). This positive rotation uses an idler gear.
If N is greater than A, resulting fraction is negative and
index plate must move counterclockwise. This negative
rotation required use of two idler gears.
39

40. Gearing
• Simple
• One idler for positive rotation of index
plate and two idlers for negative
rotation
• Compound
• One idler for negative rotation of index
plate and two idlers for positive rotation
40

41. Example:
Calculate the indexing and change gears required
for 57 divisions. The change gears supplied with
the dividing head are as follows:
24, 24, 28, 32, 40, 44, 48, 56, 64, 72, 86
The available index plate hole circles are as follows:
Plate 1: 15, 16, 17, 18, 19, 20
Plate 2: 21, 23, 27, 29, 31, 33
Plate 3: 37, 39, 41, 43, 47, 49
40 40 40 5 Choose plate 2: 21 holes
Indexing = = =
N 57 56 7 5/7 would be 15 holes
No 57 hole circle so select on 21-hole circle
number close to 57 41

42. Example: continued
40
Gear ratio = (A - N) x
A
40 40 5
= (56 - 57) x = −1 x =−
56 56 7
5 8 40 (spindle gear)
Change gears = - x = −
7 8 56 (worm gear)
The fraction is negative and simple gearing is to be
used, the index plate rotation is counterclockwise
and two idlers must be used.
42

43. Example: continued
• For indexing 57 divisions, a 40-tooth
gear is mounted on the dividing head
spindle and a 56-tooth gear is mounted
on the worm shaft.
• Index idlers must be used. plate rotation
is negative and two
• After proper gears installed, the simple
indexing for 56 divisions should be
followed
43

44. Wide-Range Dividing Head
• Possible for 2 to 400,000 divisions
• Large index plate contains 11 hole
circles on each side
• Small index plate mounted in front of
large, contains a 54 hole and a 100-
hole circle
• 40:1 ratio between worm and dividing
head spindle
44

45. G – gear housing D - crank A–
large
index
plate
B - crank
C–
small
index
plate
45

46. Indexing for Divisions
• One turn of small crank drives index
head spindle 1/100 of 1/40, or 1/4000 of
a turn
• Ratio of large index crank to dividing head
40:1
• Ratio of small index crank 100:1
46

47. Indexing for Divisions
• One hole on 100-hole circle of small
index plate C = 1/100 x 1/4000
• 1/400,000 of a turn
• Formula for indexing divisions =
400,000/N
47

48. Indexing for Divisions
No. of turns No. of holes on No. of holes on
of large x 100-hole circle x 100-hole circle
index crank of large plate of small plate
40 00 00
Number of
N Divisions
48

49. Indexing for Divisions
40 00 00 For 1250 divisions
400000/1250 One hole on 100-hole
N
circle produces 1/4000
No. of turns
0 3 20 of a turn; any number
of large Index
40|00|00 divides into 4000 are
Crank = 0 indexed on large plate
1250
No. turns
100-hole= 3 20 holes on the
Large plate 100-hole circle
small plate
Since ratio of large index crank is 40:1 ,
Zero turns that divides into 40 (first two 100-hole
any number of large crank, 3 turns of
numbers) represents holes on large
large plate and 20 full turns of100-hole small plate49
index crank

50. Angular Indexing with the
Wide-Range Divider
• Indexing in degrees, minutes, and
seconds easily accomplished
• Both large and small index cranks set
on 54-hole circle of each plate
• Each space on 54-hole large plate will
cause dividing head spindle to rotate 10'
• Each space on 54-hole small plate will
cause work to rotate 6"
50

51. Angular Indexing: cont.
N
Degrees = (indexed on large plate) = 17 = 1 8 turns
9 9 9
N 36
Minutes = (indexed on large plate) = = 3 with r of 6'
10 10
N (6' x60) + 18 378
Seconds = (indexed on small plate) = = = 63
6 6 6
Example: Index for an angle of 17º36'18"
One full turn + 48 holes on large plate
3 holes on large plate
One full turn + 51 holes on large plate
One full turn + 9 holes on small plate
51

52. Linear Graduating
• Operation of producing accurate
spaces on piece of flat or round stock
• Align workpiece parallel with table
travel
• Dividing head spindle geared to lead
screw of milling machine for accurate
longitudinal movement of table
• 1 revolution of index crank = 1/40th
revolution of spindle and lead screw
52

53. Linear Graduating: cont.
• Rotation of lead screw (4 threads per
inch) would cause table to move 1/40th x
1/4th or 1/160th = .0025 in.
• Formula for calculating indexing for
linear graduations in thousandths of an
inch
Example: Movement of table .001 in
N
.001 1
.00625 = turns
.00625 6 1
4
4 holes on 25-hole circle
53

54. Linear Graduating: cont.
• If lead screw of metric milling
machine has pitch of 5mm, 1 turn of
index crank would move table 1/40th
of 5 mm or 0.125 mm
• Point of toolbit used for graduating
generally ground to V-shape
54

55. Linear Graduating: cont.
• Uniformity of line length controlled by
accurate movement of crossfeed
handwheel
• Uniformity of line width maintained if
work held absolutely flat and table
height never adjusted
55