the indexing or dividing head

The Indexing or Dividing Head Session 14

Indexing (Dividing) HeadOnce one of the more important attachments for milling machineUsed to divide circumference of workpiece into equally spaced divisions when milling gear teeth, squares, hexagons, and octagonsAlso used to rotate workpiece at predetermined ratio to table feed rate

Index Head PartsHeadstock with index platesHeadstock change gearsQuadrantUniversal chuckFootstockCenter rest

Index Head PartsSwiveling blockMounted in base enables headstock to be tilted from 5 below horizontal to 10 beyond verticalSpindleMounted in swiveling block with 40-tooth worm wheel, meshes with wormWormRight angle to spindle, connected to index crankDirect indexing plateEngaged by pin and attached to front of spindle

Index Head Parts

Section view of a dividing head

Index Head PartsUniversal chuckThreaded onto end of spindle

Index Head PartsFootstockUsed in conjunction with headstock to support work held between centers or in chuckMay be adjusted longitudinally, raised or lowered off center, and tilted out of parallel

Index Head PartsAdjustable center restHolds long, slender work between centers

Methods of IndexingDirectSimpleAngularDifferential

Direct IndexingSimplest form of indexingPerformed by disengaging worm shaft from worm wheel by means of eccentric device in dividing headSpring-loaded tongue lock engages numbered slots in index plateUsed for quick indexing of workpiece when cutting flutes, hexagons, squares, etc.

Direct Indexing DivisionsDirect indexing plate usually contains three sets of hole circles or slots: 24, 30, and 36Number of divisions possible to index limited to numbers that are factors of 24, 30, 36Slots Direct indexing divisions242 3 4 _ 6 8 _ __ 12 __ __ 24 __ __302 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __362 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 36

Example: Direct IndexingWhat direct indexing is necessary to mill eight flutes on a reamer blank?Slots Direct indexing divisions242 3 4 _ 6 8 _ __ 12 __ __ 24 __ __302 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __362 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 36Since 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.Never count the hole or slot in which the index pin is engaged.

Milling a Square with Direct IndexingDisengage worm and worm shaft by turning worm disengaging shaft lever if dividing head is so equippedAdjust plunger behind index plate into the 24-hole circle or slotMount workpiece in dividing head chuck or between centersAdjust cutter height and cut first side

Milling a Square with Direct IndexingRemove plunger pin using plunger pin leverTurn plate attached to dividing head spindle one-half turn and engage plunger pinTake second cut

Milling a Square with Direct IndexingMeasure work across flats and adjust work height if requiredCut remaining sides by indexing every six holes until all surfaces cutCheck for finish size

Simple IndexingWork positioned by means of crank, index plate, and sector armsWorm attached to crank must be engaged with worm wheel on dividing head spindle40 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)

Simple IndexingCalculating the indexing or number of turns of crank for most divisions, simply divide 40 by number of divisions to be cut or,

Simple IndexingThe 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.

Index Plate and Sector ArmsIndex plateCircular plate provided with series of equally spaced holes into which index crank pin engagesSector armsFit on front of plate and may be set to any portion of a complete turn

Finishing Indexing for Seven FlutesIndex-plate hole circlesBrown & SharpePlate 115-16-17-18-19-20Plate 221-23-27-29-31-33Plate 337-39-41-43-47-49Cincinnati Standard PlateOne side 24-25-28-30-34-37-38-39-41-42-43Other side 46-47-49-51-53-54-57-58-59-62-66Choose any hole circle that is divisible by denominator 75/7 = /21So, 5 full turns plus 15 holes on 21 hole circle!15

Cutting Seven FlutesMount B&S Plate 2 index plate on dividing headLoosen index crank nut and set index pin into hole on 21-hole circleTighten index crank nut and check to see that the pin enters hole easilyLoosen setscrew on sector armPlace narrow edge of left arm against index pin

Cutting Seven FlutesCount 15 holes on 21-hole circleDo not include hole in which index crank pin is engaged.Move right sector arm slightly beyond fifteenth hole and tighten sector arm setscrewAlign cutter with work pieceStart machine and set cutter to top of work by using paper feeler

Cutting Seven FlutesMove table so cutter clears end of workTighten friction lock on dividing head before making each cut and loosen lock when indexing for spacesSet depth of cut and take first cutAfter first flute has been cut, return table to original starting position

Cutting Seven FlutesWithdraw index pin and turn crank clockwise five full turns plus the 15 holes indicated right sector armRelease index pin between 14th and 15th holes and gently tap until it drops into 15th holeTurn sector arm farthest from pin clockwise until it is against index pin

Cutting Seven FlutesLock dividing head; continue machining and indexing for remaining 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.

Angular IndexingSetup for simple indexing may be usedMust calculate indexing with angular distance between divisions instead number of divisionsOne complete turn of index crank turns work 1/40 of a turn1/40 of 360 equals 9 degrees

Angular IndexingCalculate indexing for 455 complete turns

Angular IndexingCalculate indexing for 606 full turns plus 12 holes on 18 hole circle

Angular IndexingCalculate indexing for 24'Divide 24'/540' = 4/90 4/90 = 1/22.5 1 hole on a 22.5 hole circleThe 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.

Angular IndexingCalculate indexing for 2430'First, convert angle into minutes(24 x 60') = 1440' now add 30' = 1470Convert 9 to minutes 9x90 = 540Divide 1470'/540' = 2 13/182 full turns and 13 holes on 18 hole circle

Differential IndexingUsed when 40/N cannot be reduced to a factor of one of the available hole circlesIndex 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

Differential MethodNumber chosen close to required divisions that can be indexed by simple indexingExample: Assume index crank has to be rotated 1/9th of a turn and only 8-hole circleCrank moved 1/9th, index pin contacts plate at spot before first holeExact position would be the difference between 1/8th and 1/9th of a revolution of the crank

Differential Method cont.one-seventy-second of a turn short of first holeSince 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.

Method of Calculating the Change GearsA = approximate number of divisionsN = required number of divisionsIf 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.

GearingSimpleOne idler for positive rotation of index plate and two idlers for negative rotationCompoundOne idler for negative rotation of index plate and two idlers for positive rotation

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, 86The available index plate hole circles are as follows:Plate 1: 15, 16, 17, 18, 19, 20Plate 2: 21, 23, 27, 29, 31, 33Plate 3: 37, 39, 41, 43, 47, 49No 57 hole circle so select number close to 575/7 would be 15 holes on 21-hole circleChoose plate 2: 21 holes

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

Example: continuedFor 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 twoAfter proper gears installed, the simple indexing for 56 divisions should be followed

Wide-Range Dividing HeadPossible for 2 to 400,000 divisionsLarge index plate contains 11 hole circles on each sideSmall index plate mounted in front of large, contains a 54 hole and a 100-hole circle40:1 ratio between worm and dividing head spindle

A large index plate B - crankC small index plateD - crank G gear housing

Indexing for DivisionsOne turn of small crank drives index head spindle 1/100 of 1/40, or 1/4000 of a turnRatio of large index crank to dividing head 40:1Ratio of small index crank 100:1

Indexing for DivisionsOne hole on 100-hole circle of small index plate C = 1/100 x 1/4000 1/400,000 of a turnFormula for indexing divisions = 400,000/N

Indexing for DivisionsNo. of turns of large index crankNo. of holes on 100-hole circle of large plateNo. of holes on 100-hole circle of small plate4000 00404000NNumber of Divisionsxx

Indexing for DivisionsFor 1250 divisions 400000/1250Since ratio of large index crank is 40:1 , any number that divides into 40 (first two numbers) represents full turns of large index crankOne hole on 100-hole circle produces 1/4000 of a turn; any number divides into 4000 are indexed on large plate204000 00404000N30Zero turns of large crank, 3 turns of 100-hole large plate and 20 holes on 100-hole small plate

Angular Indexing with the Wide-Range DividerIndexing in degrees, minutes, and seconds easily accomplishedBoth large and small index cranks set on 54-hole circle of each plateEach 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"

Angular Indexing: cont.Example: Index for an angle of 1736'18" One full turn + 48 holes on large plate3 holes on large plateOne full turn + 9 holes on small plate

Linear GraduatingOperation of producing accurate spaces on piece of flat or round stockAlign workpiece parallel with table travelDividing head spindle geared to lead screw of milling machine for accurate longitudinal movement of table1 revolution of index crank = 1/40th revolution of spindle and lead screw

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 inchExample: Movement of table .001 in4 holes on 25-hole circle

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 mmPoint of toolbit used for graduating generally ground to V-shape

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

the indexing or dividing head

Documents

dividing head chuck

dividing head session

index pin

indexing dividing headonce

direct indexingdisengage

dividing head spindle40

worm shaft

index plateused