The Indexing or Dividing Head

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
• 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

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Index Head Parts
6
Section view of a dividing head
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Index Head Parts

• Universal chuck
• Threaded onto end of spindle

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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

1. Direct
2. Simple
3. Angular
4. Differential

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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 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
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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 3 _ 5 6 _ _ 10 __
15 __ __ 30 __ 36 2 3 4 _ 6 _ 9 __ 12 __ 18 __ __
36
Never count the hole or slot in which the index
pin is engaged.
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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

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

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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

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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 401)

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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,

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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.
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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

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Finishing Indexing for Seven Flutes
Choose any hole circle that is divisibleby
denominator 7
Index-plate hole circles Brown Sharpe Plate
1 15-16-17-18-19-20 Plate 2 21-23-27-29-31-33 Plat
e 3 37-39-41-43-47-49 Cincinnati Standard
Plate One side 24-25-28-30-34-37-38-39-41-42-43 O
ther side 46-47-49-51-53-54-57-58-59-62-66
5/7 /21
15
So, 5 full turns plus15 holes on 21 holecircle!
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Finishing Indexing for Seven Flutes
Choose any hole circle that is divisibleby
denominator 7
Index-plate hole circles Brown Sharpe Plate
1 15-16-17-18-19-20 Plate 2 21-23-27-29-31-33 Plat
e 3 37-39-41-43-47-49 Cincinnati Standard
Plate One side 24-25-28-30-34-37-38-39-41-42-43 O
ther side 46-47-49-51-53-54-57-58-59-62-66
5/7 /49
35
So, 5 full turns plus35 holes on 49 holecircle!
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Finishing Indexing for Seven Flutes
Choose any hole circle that is divisibleby
denominator 7
Index-plate hole circles Brown Sharpe Plate
1 15-16-17-18-19-20 Plate 2 21-23-27-29-31-33 Plat
e 3 37-39-41-43-47-49 Cincinnati Standard
Plate One side 24-25-28-30-34-37-38-39-41-42-43 O
ther side 46-47-49-51-53-54-57-58-59-62-66
5/7 /28
20
So, 5 full turns plus20 holes on 28 holecircle!
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Finishing Indexing for Seven Flutes
Choose any hole circle that is divisibleby
denominator 7
Index-plate hole circles Brown Sharpe Plate
1 15-16-17-18-19-20 Plate 2 21-23-27-29-31-33 Plat
e 3 37-39-41-43-47-49 Cincinnati Standard
Plate One side 24-25-28-30-34-37-38-39-41-42-43 O
ther side 46-47-49-51-53-54-57-58-59-62-66
5/7 /42
30
So, 5 full turns plus30 holes on 42 holecircle!
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Finishing Indexing for Seven Flutes
Choose any hole circle that is divisibleby
denominator 7
Index-plate hole circles Brown Sharpe Plate
1 15-16-17-18-19-20 Plate 2 21-23-27-29-31-33 Plat
e 3 37-39-41-43-47-49 Cincinnati Standard
Plate One side 24-25-28-30-34-37-38-39-41-42-43 O
ther side 46-47-49-51-53-54-57-58-59-62-66
5/7 /49
35
So, 5 full turns plus35 holes on 49 holecircle!
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Cutting Seven Flutes

1. Mount BS 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

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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

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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

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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

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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

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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

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Angular Indexing

• Calculate indexing for 45º

5 complete turns
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Angular Indexing

• Calculate indexing for 60º

6 full turns plus 12 holes on 18 hole circle
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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.
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Angular Indexing

• Calculate indexing for 24º30'
• First, convert angle into minutes

(24 x 60') 1440' now add 30' 1470 Convert 9
to minutes 9x90 540 Divide 1470'/540'
2 13/18
2 full turns and 13 holes on 18 hole circle
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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

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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

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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.
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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 andthe 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 andindex plate must move
counterclockwise. This negativerotation
required use of two idler gears.
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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

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Example
Calculate the indexing and change gears
requiredfor 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
Choose plate 2 21 holes
5/7 would be 15 holes on 21-hole circle
No 57 hole circle so selectnumber close to 57
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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.
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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

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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
• 401 ratio between worm and dividing head spindle

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D - crank
G gear housing
A large index plate
B - crank
C small index plate
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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 401
• Ratio of small index crank 1001

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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

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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  0 0  0 0
4 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 400000/1250
One hole on 100-holecircle produces 1/4000of a
turn any numberdivides into 4000 areindexed on
large plate
N
20
3
0
Since ratio of large index crank is 401 , 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
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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"

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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 9 holes on small plate
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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

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

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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