1. The Indexing or Dividing Head
Session 14

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

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

4. Index Head Parts Swiveling block Spindle Worm Direct indexing plate
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

5. Index Head Parts

6. Section view of a dividing head

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

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

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

10. Methods of Indexing
Direct
Simple
Angular
Differential

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.

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
_ 6 8 _ __ 12 __ __ 24 __ __
_ 5 6 _ _ 10 __ 15 __ __ 30 __
_ 6 _ 9 __ 12 __ 18 __ __ 36

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
_ 6 8 _ __ 12 __ __ 24 __ __
_ 5 6 _ _ 10 __ 15 __ __ 30 __
_ 6 _ 9 __ 12 __ 18 __ __ 36
Never count the hole or slot in which the index pin is engaged.

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

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

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

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)

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,

19. Simple Indexing The indexing required to cut eight flutes:
The indexing required to cut seven flutes:
The five-sevenths turn involves use of an index plate and sector arms.

20. Index Plate and Sector Arms
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

21. Finishing Indexing for Seven Flutes
Choose any hole circle that is divisible by denominator 7
Index-plate hole circles
Brown & Sharpe
Plate
Plate
Plate
Cincinnati Standard Plate
One side
Other side
5/7 = /21 15
So, 5 full turns plus 15 holes on 21 hole circle!

22. Finishing Indexing for Seven Flutes
Choose any hole circle that is divisible by denominator 7
Index-plate hole circles
Brown & Sharpe
Plate
Plate
Plate
Cincinnati Standard Plate
One side
Other side
5/7 = /49 35
So, 5 full turns plus 35 holes on 49 hole circle!

23. Finishing Indexing for Seven Flutes
Choose any hole circle that is divisible by denominator 7
Index-plate hole circles
Brown & Sharpe
Plate
Plate
Plate
Cincinnati Standard Plate
One side
Other side
5/7 = /28 20
So, 5 full turns plus 20 holes on 28 hole circle!

24. Finishing Indexing for Seven Flutes
Choose any hole circle that is divisible by denominator 7
Index-plate hole circles
Brown & Sharpe
Plate
Plate
Plate
Cincinnati Standard Plate
One side
Other side
5/7 = /42 30
So, 5 full turns plus 30 holes on 42 hole circle!

25. Finishing Indexing for Seven Flutes
Choose any hole circle that is divisible by denominator 7
Index-plate hole circles
Brown & Sharpe
Plate
Plate
Plate
Cincinnati Standard Plate
One side
Other side
5/7 = /49 35
So, 5 full turns plus 35 holes on 49 hole circle!

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

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

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

29. Cutting Seven Flutes
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

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.
Lock dividing head; continue machining and indexing for remaining flutes

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

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

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

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.

35. Convert 9° to minutes 9°x60 = 540'
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 '/540' = 2 13/18
2 full turns and 13 holes on 18 hole circle

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

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

38. Differential Method cont.
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.

39. Method of Calculating the Change Gears
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.

40. Gearing Simple Compound
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

41. No 57 hole circle so select number close to 57
Example:
Calculate the indexing and change gears required for 57 divisions. The change gears supplied with the dividing head are as follows: , 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
Choose plate 2: 21 holes
5/7 would be 15 holes
on 21-hole circle
No 57 hole circle so select number close to 57

42. Example: continued
The fraction is negative and simple gearing is to be used, the index plate rotation is counterclockwise and two idlers must be used.

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

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

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

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

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

48. Indexing for Divisions
No. of turns of large index crank
No. of holes on 100-hole circle of large plate
No. of holes on 100-hole circle of small plate x x
4 0
4 0  0 0  0 0
4 0  0 0
Number of Divisions N

49. Indexing for Divisions
4 0  0 0  0 0
4 0
4 0  0 0
For 1250 divisions /1250
One hole on 100-hole circle produces 1/4000 of a turn; any number divides into 4000 are indexed on large plate N
No. of turns of large Index
Crank = 3 20
40|00|00
1250
No. turns 100-hole=
Large plate 3
20 holes on the 100-hole circle small plate
Since ratio of large index crank is 40:1 , any number that divides into 40 (first two numbers) represents full turns of large index crank
Zero turns of large crank, 3 turns of 100-hole large plate and 20 holes on 100-hole small plate

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"

51. Angular Indexing: cont.
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

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

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 = in.
Formula for calculating indexing for linear graduations in thousandths of an inch
Example: Movement of table .001 in
4 holes on 25-hole circle

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 mm
Point of toolbit used for graduating generally ground to V-shape

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