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3.0 - CNC tools

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Lesson overview

• 3.1 End Mills• 3.2 Face Mill• 3.3 Corner Radius Tool• 3.4 Slot Mill/Slotting Saw• 3.5 Hole Making Tools• 3.6 Cutting Tool Fundamentals• 3.7 Cutting Speeds & Feeds Formulas• 3.8 Speed/Feed Examples• 3.9 Cutting Data & Best Practice Parameters

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objectives

• List most commonly used CNC tools.• Determine spindle rotational direction.• Interpret a chip formation diagram.• Define chip load.• Distinguish between Climb and Conventional milling.• Compute cutting speeds and feeds for a specified tool, material and

operation.

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Overview

• Many cutting tool types/shapes/sizes.• Few types needed for most CNC

parts.• Most often used listed to right.

Tools Used in this Course• End Mill• Face Mill• Corner Round• Slot Mill• Spot/Center Drill• Twist Drill• Tap• Reamer

Tip: If possible acquire a tool catalog from a supplier.

Other good sources:

Company Web Address

McMaster-Carr www.mcmaster.com

MSC Industrial Supply www.mscdirect.com

Sandvik www.sandvik.com

Valenite www.valenite.com

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3.1 - End mills

• End Mills are the primary cutting tool used in CNC milling.• Many different:

• Shapes• Sizes• Geometric configurations• Materials

End Mill

RoughingEnd Mill Lollipop

Carbide InsertFace Mill

TaperedEnd Mill

ConvexRadius

Ball NoseEnd Mill

CornerRounding

ConcaveRadius

ChamferMill

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3.1 - End mills: Nose types

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End mills: Nose Types/applications

• Flat Nose:• 2D contours and pockets.

• Bull Nose:• Fillets and 3D roughing.

• Ball Nose:• 3D rough and finishing.

• Chamfer• De-burr or chamfer edges.

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End mill: number of cutting flutes

• Four flutes.• Rigid.• Higher feed rates than 2 or 3 flute (see Feed Formula).

• Two flutes.• More chip clearance (room for chip to be ejected).

• Three flutes.• Less common, but good compromise.

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End mills: center cutting

• Center cutting: Cutting edges extend across center of tool (see cutting end view below).

• Non-center cutting: Relief hole in center.

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End mills: center cutting

• Only center cutting end mills can plunge straight down through material.

• Non-center cutting must be ramp, spiral, or drop through existing hole.

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3.2 - Face mill

• Very high material removal rate.• High initial cost (tool body).

• Carbide inserts can be replaced when worn.• Do not use coolant:

• Environmental. Cleaner. Lower maintenance.

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3.3 - Corner round

• Use to machine fillet on outside corners of part.

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3.4 - Slot mill

• Includes:• Side milling cutters.• Slitting saws.• Woodruff keyset cutters.

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3.5 Hole making Tools

• Center drills• Countersink Drills• Drill Point Countersink• Twist Drills (Jobber Length)• Stub-Length Drill• Taps-Spiral Point (Gun Tap)• Taps-Bottoming• Reamer• Counterbore

CenterDrill

Stub LengthDrill

Drill PointCountersink

Spiral Point Tap

(Gun Tap)

Twist Drill(Jobber Length)

BottomingTap

CountersinkDrill

Reamer

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3.5 - Center & Countersink Drills

• Center drills:• Short, very rigid.• Used to put conic on part.• Prevents subsequent twist drill wobble.• Ensures hole will be located precisely.

• Countersink drills:• Create conical face for flush machine screws.

• Drill Point Countersink (Combined Spotting + Countersink):• Create both screw clearance hole and C’sink.

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Center & Countersink Drills

• Many different sizes and tip angles:• C’sink tip angle = machine screw tip angle (60, 82, 100, 110, 120

degrees).• C’sink body diameter > screw head diameter.

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Twist drill

• Tip angle usually 118 degrees.• Long drills will wobble before piercing part surface.

• Spot drill first to create conic.

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Taps

• Cutting: • Create thread by removing material.

• Form tap:• Create thread by displacing material.• Preferred, especially for plastics and aluminum.

• Bottoming:• For blind (not through) holes.

• Spiral Point.• Best for through holes.

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Rigid Tapping

• Rigid tapping: • CNC Machine can grip tap in rigid (not floating) holder.• Spindle reverses to retract tap.

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Reamer

• Used to finish holes that require precise size.• Examples: ground pins and bushings (+/- .0002 typical).

• Machining parameters must be correct to achieve high precision, including:• Cutting speed.• Cutting feed.• Material to remove (Stock allowance).• See Cutting Data and Best Practices, Chapter 4.

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Reamer

• Chamfer on end of reamer helps it get started and centered in hole.

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Counterbore (About)

• Looks like an end mill with “pilot” in center.• Used to spot face holes for cap screws.• Centers spot face on hole.

• Not often used on CNC machines.• Use End Mill and either Drill or Circular Pocket instead.

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3.6 Cutting Tool fundamentals

• Rotational direction.• Chip formation diagram.• Chip load.• Climb vs. Conventional Milling.

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Rotational direction

• Most CNC Tools cut when rotating Clockwise (view looking down from machine spindle).

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Chip formation

• Tools cut using a shearing action.• Cutting flute produces a chip that is ejected away from part.

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Chip load

• The (max) thickness of material removed by each sweep of each cutting flute across the part (typically: .001-.020in).

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Climb vs. conventional milling

• Climb Milling: Tool begins at max chip thickness and ends with minimum.

• Conventional Milling: Tool begins at min chip thickness and ends with max.

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conventional milling

• Creates excessive heat increasing tool wear.• Rakes chips across surface leaving poor finish.• Not used often on CNC (mostly on Manual mills).

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Climb milling

• Reduces heat and tool wear.• Reduces horsepower used.• Better surface finish.• Use unless material requires otherwise.

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Tips

• Never use a cutting tool to machine plastic that has cut any metal.• Machining metal compromises the sharp edge of the tool and will

produce poor results in plastic.• A good practice is to keep 2 sets of tools, one for plastic and the

other for metal.• High speed steel cutter work best for plastic.• Carbide cutters work best for metals.

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3.7 cutting speeds and Feeds

• Speeds and feed definition.• Resources.• Speed formula.• Feed formula.• Tapping feed rate calculation.

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Speeds and feeds definitions

• Speed = Rotational velocity of tool.• Revolutions per minute (RPM).

• Feed = How fast tool moves through material.• Inches per minute (IPM) or• Millimeters per minute (mm/min)

• Selection based primarily on tool, material, and machining operation.

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Speeds and feeds resources

• Tool supplier/salesman.• Tool maker web site.• Tooling catalogs.• CAD/CAM software.

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Speeds and feeds resources

• Based on many variables including:• Setup rigidity.• Quality of CNC machine.• Capabilities of CNC machine.• Material variation.

• Even the best speeds and feeds data is a “scientific guess”. • Often adjusted at machine based on actual conditions (chip

formation, sound, etc).

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Speed formula–where it comes from

• Derived from a formula that relates rotational velocity of tool with flute speed for a given tool diameter.

• Do not memorize this formula. It is there so you can see how the simpler formula is derived. The complete step-by-step derivation is in the reading assignment.

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Speed formula – derived version

• Dia = Tool Diameter (in)• 3.82 = Constant• SFM = Speed (ft/min) at which material moves past cutting edge

• Get from reference tables, CAD/CAM or other resources.

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Feed formula

• Feed (in/min) = rate tool advances through material.• CL (in) = Chip Load: Amount of material removed by each pass of a

cutting flute.• NumFlutes = Number of cutting flutes of tool (for drill, use 1).

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Tap feed formula

• Feed = Linear (plunge) feed rate of tap.• Speed = Cutting speed (from Speed formula).• TPI = Threads Per Inch

• Based on cutting speed and Threads Per Inch (TPI) of tap.• Example: ¼-20 tap = 20 TPI

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3.8 Milling speed/feed examples

• Calculate the cutting speed and feed for a milling operation given the following parameters.

Parameter ValueTool Diameter .500inNumFlutes 4SFM 600ft/minIPR .005in

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Milling speed/feed example – step 1

• Calculate Speed (RPM).

Note: Always round off Speeds to the nearest integer.

Where: Speed (rev/min)SFM (ft/min) = 6003.82 = ConstantDia (in) = .500

Solution:a. Speed = [(SFM x 3.82) / Dia]

b. Speed (rev/min) = [(600 x 3.82) / .500]

c. Speed (rev/min) = 4584 RPM

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Milling speed/feed example – step 2

• Use Speed from previous formula to help calculate Feed.

Note: Round off milling feeds to nearest integer value.

Where: Speed = 4584 (rev/min)Chip Load = .005inNumFlutes = 4

Solution:a. Feed = Speed x Chip Load x NumFlutes

b. Feed = 4584 x .005 x 4

c. Feed = 91 in/min

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Drilling speed/feed example

• Calculate the cutting speed and feed for a drilling operation given the following parameters.

Parameter ValueTool Diameter .201inSFM 250ft/minIPR .002in

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Drilling speed/feed example – step 1

• Calculate Speed (RPM).• Same formula as mill but different data.

Where: SFM = 250 (ft/min)3.82 = ConstantDia = .201 (#7 Drill)


b. Speed (rev/min) = [(250 x 3.82) / .201]


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Drilling speed/feed example – step 2

• Use Speed from previous formula to help calculate Feed.

Note: Round off milling feeds to first decimal point.

Where: Speed = 4751 (rev/min)Chip Load = .002in/revNumFlutes = 9.5

Solution:a. Feed = Speed x Chip Load x NumFlutes

b. Feed = 4751 x .002 x 1

c. Feed = 9.5 in/min

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Tap speed/feed example

• Calculate the cutting speed and feed for a tapping operation given the following parameters (1/4 – 20 tap).

Parameter ValueTool Diameter .25inSFM 100ft/minTPI (Threads per Inch) 24

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Tap speed/feed example – step 1

• Calculate Speed (RPM).

Where: SFM = 100 (ft/min)3.82 = ConstantDia = .250 )


b. Speed (rev/min) = [(100 x 3.82) / .250]


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Tap speed/feed example – step 2

• Calculate Feed (IPM.

Note: Round off tapping feeds to three decimal points.

Where: Speed = 1528 (rev/min)TPI = 24 (threads/in)

Solution:a. Feed = Speed / TPI

b. Feed = 1528 / 24

c. Feed = 63.667 in/min

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What if speed exceeds max spindle rpm?

• In cases were the calculated RPM exceeds the maximum spindle speed capability of the machine:• Substitute max spindle speed for Speed value.• Use max spindle speed in Feed calculation.

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3.9 Cutting data

Mill Cutting Speeds (SFM) surface ft/min

Material HSS CarbideAluminum 600 800Brass 175 175Delrin 400 800Polycarbonate 300 500Stainless Steel 303) 80 300Steel (4140) 70 350

Drill Cutting Speeds (SFM) surface ft/min

Material Drilling C-Sink Reamer TapAluminum 300 200 150 100Brass 120 90 66 100Delrin 150 100 75 100Polycarbonate 240 160 120 100Stainless Steel 303) 50 35 25 35Steel (4140) 90 60 45 35

Cutting Feeds (IPR) in/rev

Operation Tool Diameter Range (in)<.125 .125-.25 .25-.5 .5-1. >1.

MillingAluminum .002 .002 .005 .006 .007Brass .001 .002 .002 .004 .005Delrin .002 .002 .005 .006 .007Polycarbonate .001 .003 .006 .008 .009Stainless Steel (303) .0005 .001 .002 .003 .004Steel (4140) .0005 .0005 .001 .002 .003

Drilling .002 .004 .005 .010 .015

Reaming .005 .007 .009 .012 .015

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Cutting data – parameters/allowances

Stock Finish Allowances (Inches)

Operation Tool Diameter Range (in)

<.125 .125-.25 .25-.5 .5-1. >1.Milling (XY) .001 .005 .015 .020 .020Milling (Z) .001 .002 .005 .005 .005Reaming .005 .010 .012 .020 .030

Recommended Machining ParametersOperation Parameter ValueAll Clearance Height 1.0 inchesAll Feed Height .1 inchesAll Rapid Height As needed to clear clamps and fixturesMill (Roughing)

Stepover (XY) 50-80% of tool dia.

Mill (Roughing)

Stepdown (Z) 25-50% of tool dia.

Drill Peck Increment .05 inchesSpot Drill Dwell .5 seconds

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Troubleshooting speeds/feeds

• Be methodical.• Analyze what is happening and draw on resources.• Don’t make the mistake of thinking the best solution is always to

reduce cutting speeds and feeds: sometimes increasing is better.• Machinery’s Handbook has detailed troubleshooting information.

autodesk fundcnc pwrpnt3 coordinate systems

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