59-*Milling MachinesUsed to produce one or more machined surfaces accurately on workpieceOne or more rotary milling cuttersWorkpiece held on work table or holding device (machine vise) and brought into contact with cutter(tool).Vertical milling machine most commonHorizontal milling machine handles operations normally performed by other tools

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The Vertical Milling Machine

59-*Vertical Milling MachineDeveloped in 1860'sCombines vertical spindle of drill press with longitudinal and traverse movements of milling machine.Milling process may be vertical, horizontal, angular, or helical.Can be used for milling, drilling, boring, and reamingCan machine in one, two, or three planes (axes) X, Y, Z

59-*Variety of OperationsFace millingEnd millingKeyway cuttingDovetail cuttingT-slot and circular slot cuttingGear cuttingDrillingBoringJig boringMany facing operations done with fly cutter (cost reduction).

59-*Ram-Type Vertical Milling Machine

59-*Parts of Ram-Type Vertical MillBase made of ribbed cast ironMay contain coolant reservoirColumn often cast with baseMachined face provides ways for vertical movement of kneeUpper part machines to receive turret where overarm mounted

59-*Parts of Ram-Type Vertical MillOverarm round and may be adjusted toward or away from columnHead attached to end of ramMade to swivel head in one planeUniversal-type machines allow swivel in 2 planesMotor mounted on top of headprovides drive to spindle through V-belts

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Cutting Speed, Feed, and Depth of Cut

60-*Factors Affecting the Efficiency of a Milling OperationCutting speed (n)Too slow, time wastedToo fast, time lost in replacing/regrinding cuttersFeed (f) Too slow, time wasted and cutter chatterToo fast, cutter teeth can be brokenDepth of cut (a)Several shallow cuts wastes time

60-*Cutting SpeedSpeed, in surface feet per minute (sf/min) or meters per minute (m/min) at which metal may be machined efficientlyWork machined in a lathe, speed in specific number of revolutions per min (r/min) depending on its diameter to achieve proper cutting speedIn milling machine, cutter revolves r/min depending on diameter for cutting speed

60-*Important Factors in Determining Cutting SpeedType of work materialCutter materialDiameter of cutterSurface finish requiredDepth of cut takenRigidity of machine and work setup

CUTTING VELOCITY AND SPEEDSThe mean value Vc = 115 m/min is selectedThis cutting velocity and the known tool diameter is used to compute the speed n.The formula

60-*Milling Machine Cutting SpeedsHigh-Speed Steel CutterCarbide CutterMaterialft/min m/minft/minm/minAlloy steel4070 12201502504575Aluminum5001000 15030010002000300600Bronze65120 203520040060120Cast iron5080 15251252004060Free m steel100150 3045400600120180Machine steel70100 21301502504575Stainless steel3080 10251003003090Tool steel6070 18201252004060

60-*Cutting Speed Rules for Best ResultsFor longer cutter life, use lower CS in recommended range.Know hardness of material to be machinedWhen starting, use lower range of CS and gradually increase to higher rangeReduce feed instead of increase cutter speed for fine finishUse of coolant will generally produce better finish and lengthen life of cutter

60-*Milling Machine FeedDefined as distance in inches (or mm) per minute that work moves into cutterIndependent of spindle speedFeed: rate work moves into revolving cutterMeasured in in/min or mm/minMilling feed: determined by multiplying chip size (chip per tooth) desired, number of teeth in cutter, and r/min of cutterChip, or feed, per tooth (CPT or (FPT): amount of material that should be removed by each tooth of the cutter

60-*Factors in Feed RateDepth and width of cutDesign or type of cutterSharpness of cutterWorkpiece materialStrength and uniformity of workpieceType of finish and accuracy requiredPower and rigidity of machine, holding device and tooling setup

60-*Recommended Feed Per Tooth(High-speed Cutters)Slotting Face Helicaland Side Mills MillsMillsMaterial in. mm in.mmin.mmAlloy steel .006 0.15 .0050.12.0040.1Aluminum .022 0.55 .0180.45.0130.33Brass and bronze (medium) .014 0.35 .0110.28.0080.2Cast iron (medium) .013 0.33 .0100.25.0070.18Sample TableSee Table 60.2 in TextTable shows feed per tooth for roughing cuts for finishing cut, the feed per tooth would be reduced to1/2 or even 1/3 of value shown

60-*Ideal Rate of FeedWork advances into cutter, each successive tooth advances into work equal amountProduces chips of equal thicknessFeed per toothFeed = no. of cutter teeth x feed/tooth x cutter rev(r/min)Feed (in./min) = Z(no of tooth) x CPT x N(r/min)

60-*Examples: Feed CalculationsCalculationsFind the feed in mm per minute using a 10 mm. diameter, 4 tooth helical cutter to cut machine steel (CS80)

TOOL MOVEMENTUP-MILLING The cutting action occurs either by conventional milling or climb milling.In conventional milling, also called up milling, the maximum chip thickness is at the end of the cut. The feed movement is opposite to the tool rotation

60-*Direction of Feed: ConventionalMost common method is to feed work against rotation direction of cutter

TOOL MOVEMENT (cont.)CLIMB MILLINGIn climb milling, also called down milling, cutting starts with the chip at its thickest location. The feed movement and the tool rotation have the same direction.

60-*Direction of Feed: ClimbingWhen cutter and workpiece going in same directionCutting machine equipped with backlash eliminatorCan increase cutter life up to 50%

60-*Advantages of Climb MillingIncreased tool life (up to 50%) Chips pile up behind or to left of cutterLess costly fixtures requiredForces workpiece down so simpler holding devices requiredImproved surface finishesChips less likely to be carried into workpiece

60-*Advantages of Climb MillingLess edge breakoutThickness of chip tends to get smaller as nears edge of workpiece, less chance of breakingEasier chip removalChips fall behind cutterLower power requirementsCutter with higher rake angle can be used so approximately 20% less power required

60-*Disadvantages of Climb MillingMethod cannot be used unless machine has backlash eliminator and table gibs tightenedCannot be used for machining castings or hot-rolled steelHard outer scale will damage cutter

60-*Depth of CutRoughing cuts should be deepFeed heavy as the work and machine will permitMay be taken with helical cutters having fewer teethFinishing cuts should be light with finer feedDepth of cut at least .015 in.Feed should be reduced rather than cutter speeded up

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End Mills

61-*End MillsGreatly improved since days of carbon-steel cutting toolsHigh-speed steel (HSS) cutting tools maintain very important place in metal-cutting industryVariables influencing cutter decisionPart shape, work material, wear resistance of tool, red hardness, machine condition

61-*High-Speed End MillsRelatively inexpensive, easy to get and do jobs quite wellCapable of machining with close tolerancesSingle most versatile rotary tools used on conventional and CNC machinesIf need harder tool, frequent solution is cobalt end millLess expensive than carbide, long tool life

61-*Carbide End MillsCarbide properties vs. HSS tool materialsHigher hardnessGreater rigidityCan withstand higher cutting temperaturesCan run at higher speeds and feedsIncreasing production ratesProviding long tool lifeHigh-performance tool material

61-*Common Machining OperationsOpen and closed pocketsFacing operations for small areasCounterboringPeripheral end millingMilling of slots and keywaysChannel groves, face grooves and recessesChamfering 30/9/14Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Performed with HSS, cobalt, solid carbide, or indexable insert type end mill

61-*End Mill FormsGround into required shapesFlat bottom end mill (most common)Used for all operations requiring flat bottom and sharp corner between wall and bottomEnd mill with full radium (ball nose end mill)Used for 3D machining of various surfacesEnd mill with corner radium (bull nose end mill)Used for either 3D work or for flat surfaces that require corner radius between wall and bottomCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

61-*Three common types and the relationship of the radius to the tool diameter.

61-*Common Types of End MillsTwo-Flute End MillHave large, open flutes that provide excellent chip flowRecommended for general-purpose millingAlways select shortest end mill possible for job to obtain maximum tool rigidityCan have different length lips on endMill slots, keyways, plunge cut and drill shallow holes

61-*Common Types of End MillsThree-Flute End MillWith end teethUsed to plunge into workpieceUsed to mill slots, pockets and keywaysMinimize chatter and better chip removalRoughing End MillDesigned to provide best performance while machining broad range of materialsAllows deeper cuts at faster feed rates

61-*Direction of Cut: ClimbCutter rotation and table feed going in same directionVertical milling: cutter tendency to pull work into cutting flutesHorizontal milling: cutter pushes work against tableMaximum thickness of chip occurs at beginning of cut and exits when thinResult chip absorbs heat generatedCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

61-*Direction of Cut: ConventionalWhen cutter rotation and table feed are moving in opposite directionsHas tendency to pull or lift workpiece up from tableImportant that work be held securely

61-*Direction of Cut

61-*Milling Cutter FailureExcessive heatOne of main causes of total cutting edge failureCaused by cutting edges rubbing on workpiece and chips sliding along faces of teethEver-expanding cycleMinimized by correct speeds, feeds, and coolantAbrasionWearing-away action caused by metallurgy of workpiecedulls cutting edges and cause "wear lands"

61-*Chipping or Crumbling of Cutting EdgesSmall fractures occur and small areas of cutting edges chip out when cutting forces impose greater load on cutting edgesMaterial left uncut imposes greater cutting loadCondition progressiveOnce started will lead to total cutter failureDull edges increase friction, heat, and horsepower requirements

61-*CloggingSome workpiece materials have "gummy" compositionChips long, stringy and compressibleChips clog or jam into flute areaMinimize by reducing depth or width of cut, reducing FPT, using tools with fewer teeth, creating more chip space and coolantCoolant applied under pressure to flush out flute area

61-*Work Hardening of WorkpieceCan cause milling cutter failureResult of action of cutting edges deforming or compressing surface of workpiece, causing change in work material structure that increases its hardnessImportant to use sharp tools at generous power feeds and use coolantCauses glaze break by vapor honing or abrading surface with coarse emery cloth

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Vertical Mill Operations

62-*Objectives Align the vertical head and vise to within .001 in. (0.02 mm)Insert and remove end mills from spring colletsAccurately machine a block square and parallelDrill holes to an accurate location

62-*Vertical Milling MachineVersatile and easy setupPerforms wide variety of operationsEnd milling, face millingKeyway and dovetail cuttingT-slot and circular slot cuttingGear cutting, drilling, boring, reamingCutting tools used relatively small so cost lower

62-*Aligning the Vertical headHead must be square to table (90)Procedure to check spindle alignmentMount dial indicator on suitable rod, bent at 90 and held in spindlePosition indicator over front Y axis of tableCarefully lower spindle until indicator button touches table and dial indicator registers no more than revolution; set bezel to zero; Lock spindle in place

62-*Carefully rotate spindle 180 by hand until button bears on opposite side of table; Compare readingsIf differences, loosen locking nuts on swivel mounting and adjust head until indicator registers approximately difference between two readings; Tighten locking nutsRecheck accuracy of alignmentRotate vertical mill spindle 90 and set dial indicator as in step 3

62-*Rotate machine spindle 180, check reading at other end of tableIf two readings do not coincide, repeat step 5 until readings are sameTighten locking nuts on swivel mountRecheck readings and adjust if necessary

62-*Aligning the ViseWhen vise aligned on vertical milling machine, dial indicator may be attached to quill or head by clamps or magnetic baseSame method of alignment followed as outlined for aligning vise on horizontal milling machine

62-*ColletsHold end mills, cutting tools and accessories in machine spindleSpring colletPulled into spindle by draw-bar that closes on cutter shankDriven by means of friction between collet and cutter Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Solid colletMore rigidPulled into spindle by draw-barDriven by setscrews that bear against flats of cutter shank

62-*To Mount a Cutter in a Spring ColletShut off electric power to machinePlace proper cutter, collet, and wrench on piece of masonite, wood, or soft plastic on tableCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

62-*Clean taper in machine spindlePlace draw-bar into hole in spindle topClean taper and keyway on colletInsert collet into spindle bottom, press up, and turn until keyway aligns with key in spindleHold collet up with one hand and with other, thread draw-bar clockwise into colletHold cutting tool with cloth and insert it into collet for full length of shankTighten draw-bar into collet (clockwise) by handHold spindle brake lever and tighten draw-bar tightly as possible with wrench

62-*Procedure to Remove Cutter from a ColletOperation for removing cutting tools similar to mounting, but in reverse orderShut off electric power to machinePlace piece of masonite, wood, or soft plastic on machine table to hold necessary toolsPull on spindle brake lever to lock spindle, loosen draw-bar with wrench (counterclockwise)

62-*Loosen draw-bar, by hand, only about three full turnsHold cutter with clothWith soft-faced hammer, strike down sharply on head of draw-bar to break taper contact between collet and spindleRemove cutter from colletClean cutter and replace it in its proper storage place where it will not be damaged by other tools

62-*Machining a Block Square and ParallelImportant that each side be machined in definite orderMachining Side 1Clean vise thoroughly and remove all burrs from workpiece, vise and parallelsSet work on parallels in center of vise with largest surface (side 1) facing up

59-*

62-*Procedure to Machine an Angular SurfaceLay out angular surfaceClean viseAlign vise with direction of feedUtmost importanceMount work on parallels in the viseCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

62-*Swivel vertical head to required angleTighten quill clampStart machine and raise table until cutter touches workRaise table until cut desired depthTake trial cut for about .50 in.Check angle with protractorIf angle correct, continue cutMachine to required depth, taking several cuts if necessary

62-*With center drill spot each hole to be tapped to slightly larger than tap diameterDrill hole to correct tap drill size for size of tap to be usedMount stub center in drill chuckCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

62-*Slots and KeyseatsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.May be cut in shafts more easily on vertical milling machine, using a two- or three-fluted end millProcedure for CuttingLayout position of keyseat on shaft, and scribe reference lines on end of shaft

62-*Lower table until cutter clears workpieceMove table over amount equal to half diameter of shaft plus half diameter of cutter plus thickness of paperCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

62-*Woodruff KeysUsed when keying shafts and mating partsWoodruff keyseats can be cut more quickly than square keyseatsSemicircular in shape and can be purchased in standard sizes designated by E numbersCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

62-*Woodruff Keyseat CuttersHave shank diameters of in. for cutters up to 1 in. in diameterCutters over 2 in. in diameter mounted on arborSize stamped on shankLast two digits indicate nominal diameter in eighths of inchPreceding numbers nominal width of cutter in thirty-seconds of an inchCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Horizontal Milling Machines and Accessories

64-*Objectives Recognize and explain the purposes of four milling machinesKnow the purposes of the main operational parts of a horizontal and a vertical milling machineRecognize and state the purposes of four milling machine accessories and attachments

64-*Classification of Horizontal Milling MachinesManufacturing-typeCutter height is controlled by vertical movement of headstockSpecial-typeDesigned for specific milling operationsKnee-and-column-typeRelationship between cutter height and work controlled by vertical movement of table

64-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Plain Manufacturing Type Milling Machine

64-*Cross section of a Cincinnati Machine Backlash EliminatorCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

64-*Arbors, Collets, and AdaptersCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

64-*VisesCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

64-*FixturingSystemsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

64-*Indexing, or Dividing, HeadPermits cutting of bolt heads, gear teeth, ratchetsRevolve work as required to cut helical gears and flutes in drills, reamers, and other toolsWhen connected to lead screw of milling machine

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Milling Cutters

65-*Plain Milling CuttersMost widely used Cylinder of high-speed steel with teeth cut on peripheryUsed to produce flat surfaceSeveral typesLight-dutyLight-duty helicalHeavy-dutyHigh-helixCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Light-Duty Plain Milling CutterLess than in. wide, straight teethUsed for light milling operationsThose over in have helix angle of 25Too many teeth to permit chip clearanceCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Heavy-Duty Plain Milling CuttersHave fewer teeth than light-duty typeProvide for better chip clearanceHelix angle varies up to 45Produces smoother surface because of shearing action and reduced chatterLess power requiredCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*High-Helix Plain Milling CuttersHave helix angles from 45 to over 60Suited to milling of wide and intermittent surfaces on contour and profile millingUsually mounted on milling machine arborSometimes shank-mounted with pilot on end and used for milling elongated slotsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Standard Shank-Type Helical Milling CuttersCalled arbor-type cuttersUsed for Milling forms from solid metalRemoving inner sections from solidsInserted through previously drilled hole and supported at outer end with type A arbor supportCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Side Milling CuttersComparatively narrow cylindrical milling cutters with teeth on each side and on peripheryUsed for cutting slots and for face and straddle milling operationsFree cutting action at high speeds and feedsSuited for milling deep, narrow slotsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.StraightStaggered

65-*Half-Side Milling CuttersUsed when only one side of cutter requiredAlso make with interlocking faces so two cutter may be placed side by side for slot millingHave considerable rakeAble to take heavy cutsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Face Milling CuttersGenerally over 6 in. in diameterHave inserted teeth made of high-speed steel held in place by wedging deviceMost cutting action occurs at beveled corners and periphery of cutterMakes roughing and finishing cuts in one passCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Shell End MillsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Face milling cutters under 6 in.Solid, multiple-tooth cutters with teeth on face and peripheryHeld on stub arborMay be threaded or use key in shank to drive cutter

65-*Angular CuttersSingle-angleTeeth on angular surfaceMay or may not have teeth on flat45 or 60Double-angleTwo intersecting angular surfaces with cutting teeth on bothEqual angles on both side of line at right angle to axisCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Types of Formed Cutters Concave Convex Gear ToothCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Metal-Slitting SawsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*T-Slot CutterUsed to cut wide horizontal groove at bottom of T-slot After narrow vertical groove machined with end mill or side milling cutterConsists of small side milling cutter with teeth on both sides and integral shank for mountingCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Dovetail CutterSimilar to single-angle milling cutter with integral shankUsed to form sides of dovetail after tongue or groove machinedObtained with 45, 50, 55, or 60 anglesCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

65-*Woodruff Keyseat CutterCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Similar in design to plain and side milling cuttersSmall (up to 2 in) solid shank, straight teethLarge mounted on arbor with staggered teethUsed for milling semicylindrical keyseats in shaftsDesignated by number system

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Milling Machine Setups Unit 66

66-*Objectives Mount and remove a milling machine arborMount and remove a milling cutterAlign the milling machine table and vise

66-*Milling Machine SafetyBe sure work and cutter are mounted securely before taking cutAlways wear safety glassesWhen mounting or removing milling cutters, always hold them with cloth to avoid being cutWhen setting up work, move table as far as possible from cutter to avoid cutting your hands

66-*Be sure cutter and machine parts clear workNever attempt to mount, measure, or adjust work until cutter completely stoppedKeep hands, brushes, and rags away from revolving milling cutter at all timesDo not use an excessively heavy cut or feedCause cutter to break and fly apart

66-*Always use brush, not rag, to remove cuttings after cutter has stopped revolvingNever reach over or near revolving cutterKeep hands at least 12 in from revolving cutterKeep floor around machine free from chips, oil, and cutting fluid

66-*Milling Machine SetupsCheck if machine surface and accessory free from dirt and chips prior to mountingDo not place tools, cutters, or parts on milling machine tableUse keys on all but slitting saws when mounting cutters

66-*Check that arbor spacers and bushings clean and free from burrsWhen tightening arbor nut, take care to only hand tightenHammer or wrench will strip threads and bend or damage accessory or partWhen mounting work in vise, tighten vise securely by hand and tap into place with lead or soft-faced hammer

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The Indexing, or Dividing, Head

68-*Indexing (Dividing) HeadOne of most important attachments for milling machineUsed to divide circumference of workpiece into equally spaced divisions when milling gears, splines, squares and hexagonsAlso used to rotate workpiece at predetermined ratio to table feed rate

68-*Index Head PartsHeadstock with index platesHeadstock change gearsQuadrantUniversal chuckFootstockCenter restCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

68-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.A large index plate B - crankC small index plateD - crank G gear housing

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