CNC MILLINGCNC MILLING

SUBJEKSUBJEK: AMALAN : AMALAN KEJURUTERAAN MEKANIKAL IIIKEJURUTERAAN MEKANIKAL III

KOD SUBJEKKOD SUBJEK : BDA 2801 : BDA 2801

1.11.1 Learning OutcomeLearning Outcome

At the end of this module, the student should be At the end of this module, the student should be able to:able to:

Apply and practice workshop safety Apply and practice workshop safety regulations during working in CNC workshop. regulations during working in CNC workshop.

Apply the concept of CNC metal cutting Apply the concept of CNC metal cutting operation correctly in milling process.operation correctly in milling process.

Carry out CNC mill machining procedures Carry out CNC mill machining procedures systematically.systematically.

Utilize the important parameters in CNC Utilize the important parameters in CNC millmill machining operation effectively according to machining operation effectively according to a given task a given task

1.2 Introduction1.2 Introduction

Milling is a cutting operation with a geometrically Milling is a cutting operation with a geometrically specified cutting edge in which the tool makes the specified cutting edge in which the tool makes the rotating main movement, and the feed as well as the rotating main movement, and the feed as well as the infeed movement are generally made by the work part.infeed movement are generally made by the work part.

Milling operations are classified according to the Milling operations are classified according to the position of the milling axis towards the work part, i.e. position of the milling axis towards the work part, i.e. between face milling and peripheral milling. In case of between face milling and peripheral milling. In case of face milling, the milling axis is located vertically to the face milling, the milling axis is located vertically to the machining. machining.

The work part surface is machined by the main cutting The work part surface is machined by the main cutting edges. Also, the work part surface is further finished edges. Also, the work part surface is further finished with auxiliary cutting edges with auxiliary cutting edges

Figure 1.1 : Milling Cutting OperationFigure 1.1 : Milling Cutting Operation

Figure 1.2 : End Milling Figure 1.3 : Plain MillingFigure 1.2 : End Milling Figure 1.3 : Plain Milling

synchronous and conventional milling (Figure 1.4 synchronous and conventional milling (Figure 1.4 and 1.5) are differentiated. and 1.5) are differentiated.

In case of conventional millingIn case of conventional milling the rotation the rotation direction of the milling tool is opposite to the feed direction of the milling tool is opposite to the feed direction of the work part. direction of the work part.

The milling tool chamfer edge starts with chip The milling tool chamfer edge starts with chip thickness zero. thickness zero.

The milling tool cutting edge slides in front of the The milling tool cutting edge slides in front of the chip chamfer edge until the required minimum chip chamfer edge until the required minimum chip thickness has been achieved for chip chip thickness has been achieved for chip building.building.

Figure 1.4 : Conventional MillingFigure 1.4 : Conventional Milling

For synchronous millingFor synchronous milling the rotation the rotation direction of the milling tool and the feed direction of the milling tool and the feed movement of the work part are parallel. movement of the work part are parallel.

The tooth of the milling cutter immediately The tooth of the milling cutter immediately penetrates into the work part. penetrates into the work part.

Since the milling tool cutting edge is exposed to Since the milling tool cutting edge is exposed to impact forces the feed drive needs to be play impact forces the feed drive needs to be play free. Several cutters should always be in free. Several cutters should always be in operation. operation.

The surface quality is flatter and duller when The surface quality is flatter and duller when synchronous milling is used. synchronous milling is used.

Compared with conventional milling higher feed Compared with conventional milling higher feed movements and cutting speeds within the same movements and cutting speeds within the same cutting edge life can be achieved. cutting edge life can be achieved.

Figure 1.5 : Synchronous MillingFigure 1.5 : Synchronous Milling

Due to the cutting path comma-form chips are Due to the cutting path comma-form chips are cut with a changing chip thicknesscut with a changing chip thickness

Figure 2.6 : Milling Plan

1.3 Theory of CNC Milling 1.3 Theory of CNC Milling MachineMachine

1.3.1 Characteristics of CNC Milling 1.3.1 Characteristics of CNC Milling Machine ToolsMachine Tools

Work part machining on CNC machine Work part machining on CNC machine tools requires controllable and adjustable tools requires controllable and adjustable infeed axes which are run by the servo infeed axes which are run by the servo motors independent of each other. motors independent of each other.

CNC- milling machines (Figure 1.7) on the CNC- milling machines (Figure 1.7) on the other hand have at least 3 controllable or other hand have at least 3 controllable or adjustable feed axes marked as X, Y, Z. adjustable feed axes marked as X, Y, Z.

Figure 2.7 : Controllable NC Axes on a Milling MachineFigure 2.7 : Controllable NC Axes on a Milling Machine

1.3.2 Basic Geometry for CNC 1.3.2 Basic Geometry for CNC MillingMilling

a)a) Coordinate Systems On CNC Coordinate Systems On CNC Machine ToolsMachine Tools

Coordinate systems enable the exact Coordinate systems enable the exact description of all points on a work description of all points on a work plane or room. Basically there are plane or room. Basically there are two types of coordinate systemstwo types of coordinate systems

•Cartesian coordinate systemCartesian coordinate system

A Cartesian coordinate system, also A Cartesian coordinate system, also called rectangular coordinate system called rectangular coordinate system includes for the exact description of the includes for the exact description of the pointspoints Two coordinate axes (two-dimensional Two coordinate axes (two-dimensional

Cartesian coordinate system) or also.Cartesian coordinate system) or also. Three coordinate axes (three-dimensional Three coordinate axes (three-dimensional

Cartesian coordinate system), located Cartesian coordinate system), located vertically to each other vertically to each other

Figure 1.8 : Cartesian Coordinate SystemFigure 1.8 : Cartesian Coordinate System

•Polar Coordinate SystemPolar Coordinate System

In the Cartesian coordinate system a point is In the Cartesian coordinate system a point is described, for instance, by its X and Y coordinates. For described, for instance, by its X and Y coordinates. For rotation symmetrical contours, such as circular boring rotation symmetrical contours, such as circular boring patterns, calculating the needed coordinates requires patterns, calculating the needed coordinates requires extensive computing. extensive computing.

In the polar coordinate system a point is specified by its In the polar coordinate system a point is specified by its distance (radius r) to the point of origin and its angle (α) distance (radius r) to the point of origin and its angle (α) to a specified axis. The angle (α) refers to the X axis in to a specified axis. The angle (α) refers to the X axis in the X,Y coordinate system. the X,Y coordinate system.

The angle is positive, if it is measured The angle is positive, if it is measured counterclockwise starting from the positive X axis counterclockwise starting from the positive X axis (Figure 1.9)(Figure 1.9)

Figure 1.9 : Polar Coordinate System (Positive Angle α)Figure 1.9 : Polar Coordinate System (Positive Angle α)

The specifications of the three axes as well as the three coordinates The specifications of the three axes as well as the three coordinates are done as a so-called clockwise-rotating system and follow the right-are done as a so-called clockwise-rotating system and follow the right-hand-rule (Figure 1.10). The fingers of the right hand always show to hand-rule (Figure 1.10). The fingers of the right hand always show to the positive direction of each axis. This system is also called the the positive direction of each axis. This system is also called the clockwise-rotating coordinate system. clockwise-rotating coordinate system.

Figure 1.10 : Right-Hand-Rule

b) CNC Milling Machine Coordinate b) CNC Milling Machine Coordinate SystemSystem

Machine Coordinate SystemMachine Coordinate System The machine coordinate system of the CNC machine tool is The machine coordinate system of the CNC machine tool is

defined by the manufacturer and cannot be changed. defined by the manufacturer and cannot be changed. The point of origin for this machine coordinate system, also The point of origin for this machine coordinate system, also

called machine zero point M, cannot be shifted in its location.called machine zero point M, cannot be shifted in its location. Work Part Coordinate SystemWork Part Coordinate System

The work part coordinate system is defined by the programmer The work part coordinate system is defined by the programmer and can be changed. The location of the point of origin for the and can be changed. The location of the point of origin for the work part coordinate system, also called work part zero point work part coordinate system, also called work part zero point W, can be specified as desired.W, can be specified as desired.

Figure 2.11 : Machine Coordinate SystemFigure 2.11 : Machine Coordinate System Figure 2.12 : Work Part Coordinate SystemFigure 2.12 : Work Part Coordinate System

The design of the CNC machine specifies the The design of the CNC machine specifies the definition of the respective coordinate system. definition of the respective coordinate system.

Correspondingly, the Z axis is specified as the Correspondingly, the Z axis is specified as the working spindle (tool carrier) in CNC milling working spindle (tool carrier) in CNC milling machines (Figure 1.13), whereby the positive Z machines (Figure 1.13), whereby the positive Z direction runs from the work part upwards to the direction runs from the work part upwards to the tool.tool.

The X axis and the Y axis are usually parallel to The X axis and the Y axis are usually parallel to the clamping plane of the work part. When the clamping plane of the work part. When standing in front of the machine, the positive X standing in front of the machine, the positive X direction runs to the right and the Y axis is away direction runs to the right and the Y axis is away from the viewer. from the viewer.

The zero point of the coordinate system is The zero point of the coordinate system is recommended to be placed on the outer edge of recommended to be placed on the outer edge of the work part.the work part.

Figure 1.13 : Milling Part In Three-Dimensional Cartesian Figure 1.13 : Milling Part In Three-Dimensional Cartesian Coordinate SystemCoordinate System

1.3.3 Zero And Reference Points On 1.3.3 Zero And Reference Points On CNC Machine ToolsCNC Machine Tools

a) Types Of Zero And Reference Pointsa) Types Of Zero And Reference PointsTable 1.1 : Types of zero and references pointsTable 1.1 : Types of zero and references points

b) Machine Zero Point Mb) Machine Zero Point M

Each numerically controlled machine tool works Each numerically controlled machine tool works with a machine coordinate system. with a machine coordinate system.

The machine zero point is the origin of the The machine zero point is the origin of the machine-referenced coordinate system. machine-referenced coordinate system.

It is specified by the machine manufacturer and its It is specified by the machine manufacturer and its position cannot be changed. position cannot be changed.

In general, the machine zero point M is located in In general, the machine zero point M is located in the center of the work spindle nose for CNC lathes the center of the work spindle nose for CNC lathes and above the left corner edge of the work part and above the left corner edge of the work part carrier for CNC vertical milling machines. carrier for CNC vertical milling machines.

c) Reference Point Rc) Reference Point R

A machine tool with an incremental travel path A machine tool with an incremental travel path measuring system needs a calibration point measuring system needs a calibration point which also serves for controlling the tool and which also serves for controlling the tool and work part movements. work part movements.

This calibration point is called the reference point This calibration point is called the reference point R. Its location is set exactly by a limit switch on R. Its location is set exactly by a limit switch on each travel axis. each travel axis.

The coordinates of the reference point, with The coordinates of the reference point, with reference to the machine zero point, always have reference to the machine zero point, always have the same value. This value has a set adjustment the same value. This value has a set adjustment in the CNC control. in the CNC control.

Figure 1.14 : Location Of The Zero And Reference Point For Figure 1.14 : Location Of The Zero And Reference Point For MillingMilling

1.3.4 Structure of a NC Milling 1.3.4 Structure of a NC Milling ProgrammingProgramming

a) Structure of an NC-Block (Format)a) Structure of an NC-Block (Format) Unlike the conventional milling machine, a Unlike the conventional milling machine, a

modern machine tool will be equipped with a modern machine tool will be equipped with a numerical control system. The machining of a numerical control system. The machining of a work part can be executed automatically, work part can be executed automatically, provided that each machining cycle has been provided that each machining cycle has been described in a "language" (code) which can be described in a "language" (code) which can be read by the control system. read by the control system.

The total of coded descriptions relating to a The total of coded descriptions relating to a work part is called an NC-program.work part is called an NC-program.

* * BlocksBlocks Each NC-program consists of a number of so-called Each NC-program consists of a number of so-called

blocks, which contain the commands to be executed. The blocks, which contain the commands to be executed. The blocks are consecutively numbered; each block number blocks are consecutively numbered; each block number consisting of a letter "N" plus a (e.g. three-digit) numeral. consisting of a letter "N" plus a (e.g. three-digit) numeral. Block numbers appear at the beginning of each program Block numbers appear at the beginning of each program line line

* * Words Address, ValueWords Address, Value As a rule an NC block is comprised of several words. As a rule an NC block is comprised of several words.

Each word consists of an address (letter) and a value or Each word consists of an address (letter) and a value or code (numerals).code (numerals).

A numeral can either represent a code (e.g. G01: A numeral can either represent a code (e.g. G01: Linear feed motion) or a real value (e.g. X+60 : Linear feed motion) or a real value (e.g. X+60 :

Approaching the target coordinate X=60).Approaching the target coordinate X=60). Example of part program:Example of part program:

N110 F95 S850 M03N110 F95 S850 M03

N115 G00 X+25 Y+30N115 G00 X+25 Y+30

N120 G01 Z-8N120 G01 Z-8

N125 X+105N125 X+105

N130 Y+80N130 Y+80

Explanation:Explanation:

Block-No.Block-No.

N110 N110 A feed rate of 95 mm/min and a spindle speed of A feed rate of 95 mm/min and a spindle speed of 850 U/min is850 U/min is programmed.programmed.

N115 N115 The tool is moved in the rapid traverse motion The tool is moved in the rapid traverse motion from its current position to the starting point from its current position to the starting point

(X+25 Y+30)t(X+25 Y+30)tN120 N120 Infeed in the Z-axis at the programmed feed rate Infeed in the Z-axis at the programmed feed rate

(G01)(G01)N125 N125 Because G01 is a modal command, the tool will Because G01 is a modal command, the tool will

continue to move at the programmed feed rate on a continue to move at the programmed feed rate on a straight line to the target position X=105straight line to the target position X=105

N130 N130 The tool moves in the Y-axis to the target position The tool moves in the Y-axis to the target position Y=80. Y=80.

The technology data programmed in block N110 (feed rate, The technology data programmed in block N110 (feed rate, speed and sense of cutter rotation) will be retentive and speed and sense of cutter rotation) will be retentive and take effect through blocks N120 to N130.take effect through blocks N120 to N130.

Figure 1.15 : Tool motions effected by modal commands Figure 1.15 : Tool motions effected by modal commands (G01) (G01)

b) List Of G Codesb) List Of G Codes G00 Rapid move G0 X# Y# Z# up to 6 axis or G0 Z# X#G00 Rapid move G0 X# Y# Z# up to 6 axis or G0 Z# X#

G01 Linear feedrate move G1 X# Y# Z# up to 6 axis or G1 G01 Linear feedrate move G1 X# Y# Z# up to 6 axis or G1 Z# X#Z# X#G02 Clockwise moveG02 Clockwise moveG03 Counter clockwise moveG03 Counter clockwise moveG04 Dwell timeG04 Dwell timeG08 Spline smoothing on, optional L# number of blocks to G08 Spline smoothing on, optional L# number of blocks to bufferbufferG09 Exact stop check, spline smoothing OffG09 Exact stop check, spline smoothing OffG10 Linear feedrate move with decelerated stopG10 Linear feedrate move with decelerated stopG11 Controlled Decel stopG11 Controlled Decel stopG17 X Y PlaneG17 X Y PlaneG18 X Z PlaneG18 X Z PlaneG19 Y Z PlaneG19 Y Z PlaneG28 move to position relative to machine zeroG28 move to position relative to machine zeroG53 Cancel fixture coordinate offsetsG53 Cancel fixture coordinate offsetsG54-G59 fixture coordinate offsets 1 through 6G54-G59 fixture coordinate offsets 1 through 6

Cont…Cont… G70 Inch modeG70 Inch mode

G71 Millimeter modeG71 Millimeter modeG80 Cancels canned cycles and modal cyclesG80 Cancels canned cycles and modal cyclesG81 Drill cycleG81 Drill cycleG82 Dwell cycleG82 Dwell cycleG83 Peck cycleG83 Peck cycleG84 Tapping cycleG84 Tapping cycleG85 Boring cycle 1 bore down, feed outG85 Boring cycle 1 bore down, feed outG86 Boring cycle 2 bore down, dwell, feed outG86 Boring cycle 2 bore down, dwell, feed outG88 Boring cycle 3 bore down, spindle stop, dwell, feed outG88 Boring cycle 3 bore down, spindle stop, dwell, feed outG89 Boring cycle 4 bore down, spindle stop, dwell, rapid G89 Boring cycle 4 bore down, spindle stop, dwell, rapid

out outG90 Absolute modeG90 Absolute modeG91 Incremental modeG91 Incremental modeG92 Home coordinate resetG92 Home coordinate resetG93 cancel home offsetsG93 cancel home offsetsG98 - G199 User-definable G codes G98 - G199 User-definable G codes

c) Additional Functions (M-Functions)c) Additional Functions (M-Functions) With each NC-block a number of additional functions (M-Functions) With each NC-block a number of additional functions (M-Functions)

can be programmed, such as machine functions and switches, e.g. can be programmed, such as machine functions and switches, e.g. to specify the feed rate, the spindle speed and the tool change.to specify the feed rate, the spindle speed and the tool change.

List of M CodesList of M Codes

Feed Rate, FFeed Rate, FThe feed rate is programmed in millimeters per minute The feed rate is programmed in millimeters per minute (mm/min). Example: (mm/min). Example: F080.000F080.000; Here the programmed ; Here the programmed feed rate is 80 millimeters per minute.feed rate is 80 millimeters per minute.

Spindle Speed, SSpindle Speed, SThe spindle speed is programmed in revolutions per The spindle speed is programmed in revolutions per minute (RPM). Example: minute (RPM). Example: S500S500; Here the programmed ; Here the programmed spindle speed is 500 revolutions per minute.spindle speed is 500 revolutions per minute.

Tool Change, TTool Change, TA tool change is programmed by a four-digit number at A tool change is programmed by a four-digit number at the address T. The first two positions of that number the address T. The first two positions of that number indicate the tool position in the magazine; the last two indicate the tool position in the magazine; the last two positions indicate the tool compensation storage.positions indicate the tool compensation storage.Example:Example: T0808 T0808; This command effect the loading of the ; This command effect the loading of the tool to position No.8 of the current tool magazine and the tool to position No.8 of the current tool magazine and the reading-in of the corresponding compensation value reading-in of the corresponding compensation value storage No.8.storage No.8.

Cont…Cont…

In the CNC Simulator there is a maximum In the CNC Simulator there is a maximum of 99 magazine positions available, as well of 99 magazine positions available, as well as 99 compensation value registers. This as 99 compensation value registers. This provides the opportunity, for example, to provides the opportunity, for example, to assign the compensation value register No. assign the compensation value register No. 36 to the tool in the magazine position No. 36 to the tool in the magazine position No. 12). The applicable NC-command would 12). The applicable NC-command would then be programmed as follows: T1236then be programmed as follows: T1236

1.3.5 Clamping Devices For Milling1.3.5 Clamping Devices For Milling

The following clamping variations can be distinguished for The following clamping variations can be distinguished for milling machine.milling machine. Jaw ChuckingJaw Chucking Magnetic ChuckingMagnetic Chucking Modular ChuckingModular Chucking

The milling cutter machine table with its T-slots is the basis The milling cutter machine table with its T-slots is the basis for work part clamping. Depending on how the work part is for work part clamping. Depending on how the work part is to be clamped, the following clamping devices can be to be clamped, the following clamping devices can be distinguished:  distinguished:   Mechanical clamping devicesMechanical clamping devices Hydraulic clamping devicesHydraulic clamping devices Pneumatic clamping devicesPneumatic clamping devices Electric clamping devicesElectric clamping devices

Figure 1.16 : Clamping DevicesFigure 1.16 : Clamping Devices

Mechanical Clamping DevicesMechanical Clamping Devices

Figure 1.17 : Clamping Iron And Clamping BardFigure 1.17 : Clamping Iron And Clamping Bard

Shallow clamps are used for flat work parts whose surfaces need to Shallow clamps are used for flat work parts whose surfaces need to be kept free for machining.be kept free for machining.

Figure 2.18 : Shallow ClampFigure 2.18 : Shallow Clamp

Machine VisesMachine Vises

Machine vises are easy to use and reliable. Machine vises are easy to use and reliable. They are used for clamping smaller work They are used for clamping smaller work parts. Alignment is achieved with a measuring parts. Alignment is achieved with a measuring gauge.gauge.

Figure 1.19 : Machine ViseFigure 1.19 : Machine Vise

Figure 2.20 : Power TransmissionFigure 2.20 : Power Transmission

Universal machine vises can be horizontally as well as Universal machine vises can be horizontally as well as vertically turned. Furthermore, there are also vises that vertically turned. Furthermore, there are also vises that pneumatically generate clamping power.pneumatically generate clamping power.

Figure 2.21 : Precision Sine ViseFigure 2.21 : Precision Sine Vise

Magnetic Clamping DevicesMagnetic Clamping Devices

Work parts made of iron can be clamped with Work parts made of iron can be clamped with electromagnetic devices. The work part is drawn to the electromagnetic devices. The work part is drawn to the clamping plate after a current is switched on. It can be clamping plate after a current is switched on. It can be easily removed after the current is switched off.easily removed after the current is switched off.

Figure 1.22 : Electromagnetic Clamping PlateFigure 1.22 : Electromagnetic Clamping Plate

1.3.6 Cutting Values1.3.6 Cutting Values

Milling is a cutting operation with a rotating tool, Milling is a cutting operation with a rotating tool, whereby the cutting edges are not in operation all whereby the cutting edges are not in operation all the time. The cutting movement is caused by the the time. The cutting movement is caused by the rotation of the tool. Feed direction and cutting rotation of the tool. Feed direction and cutting direction do not depend on each other. It is realized direction do not depend on each other. It is realized either by the tool or by the work part or by both of either by the tool or by the work part or by both of them (Figure 2.23).them (Figure 2.23).

The Cutting Speed (VThe Cutting Speed (Vcc) and the Feed Speed (V) and the Feed Speed (Vff) is ) is

overlap to each other and results in a continuous overlap to each other and results in a continuous cutting operation.cutting operation.

Cutting Speed (Vc)Cutting Speed (Vc) The cutting movement is the movement between the tool The cutting movement is the movement between the tool

and the work part, generating only one nonrecurrent chip and the work part, generating only one nonrecurrent chip cut during one rotation without a feed movement. Cutting cut during one rotation without a feed movement. Cutting speed corresponds to circumferential speed of the milling speed corresponds to circumferential speed of the milling tool on the current cutting edge. It is expressed as Vc and tool on the current cutting edge. It is expressed as Vc and m/min. Under consideration of the number of rotations of m/min. Under consideration of the number of rotations of the spindle n the following formula is receivedthe spindle n the following formula is received

  

Vc = π * d * n in m/minVc = π * d * n in m/min

   The cutting speed of a cutting tool depends on the number The cutting speed of a cutting tool depends on the number

of the rotations. The direction constantly changes however of the rotations. The direction constantly changes however during cutting operation.during cutting operation.

Figure 1.23 : Cutting Values For MillingFigure 1.23 : Cutting Values For Milling

Feed Speed (VFeed Speed (Vff))

The feed movement together with the cutting The feed movement together with the cutting movement enables a constant chip removal movement enables a constant chip removal during several rotations. In milling, the feed during several rotations. In milling, the feed can be indicated in three ways:can be indicated in three ways:

Feed speed (VFeed speed (Vff) in mm / min) in mm / min

Feed per tooth (fFeed per tooth (fzz) in mm) in mm

Feed per milling rotation (f ) in mmFeed per milling rotation (f ) in mm

The calculation of the feed speed VThe calculation of the feed speed Vff is based on the feed is based on the feed

ffzz , i.e. the feed path per milling tooth. Under consideration , i.e. the feed path per milling tooth. Under consideration

on the number of rotations n and the number or teeth z the on the number of rotations n and the number or teeth z the formula is as follows:formula is as follows: VVff= f= fzz * n * z in mm / min * n * z in mm / min

   The feed speed can be expressed with the following The feed speed can be expressed with the following

formula as well with reference to the feed per milling formula as well with reference to the feed per milling rotation.rotation. VVf f = f * n in mm / min= f * n in mm / min

   Consequently, the following equivalence is valid:Consequently, the following equivalence is valid:

VVff = f * n = f = f * n = fzz * n* z in mm / min * n* z in mm / min

Calculation ExamplesCalculation Examples

Example 1.1Example 1.1Calculate the cutting speed for milling if the Calculate the cutting speed for milling if the milling tool diameter, d = 50 mm and the milling tool diameter, d = 50 mm and the number of rotations, n = 520 1/minnumber of rotations, n = 520 1/min

Example 1.2Example 1.2Calculate the number of rotations, n of an end Calculate the number of rotations, n of an end mill with a diameter of d = 12 mm and cutting mill with a diameter of d = 12 mm and cutting speed of Vc = 120m/min.speed of Vc = 120m/min.

Example 1.3Example 1.3In plain milling with a face milling cutter a cutting In plain milling with a face milling cutter a cutting speed of Vc = 180 m/min has been scheduled speed of Vc = 180 m/min has been scheduled and the number of rotations should not exceed and the number of rotations should not exceed 400 1/min. What is the maximum diameter, d of 400 1/min. What is the maximum diameter, d of the face milling cutter so that these values are the face milling cutter so that these values are not exceeded?not exceeded?