BMFS 3373
CNC TECHNOLOGY
Lecture 9
Lecture Objectives
 At the end of the lecture, you will be able to:
 Understand the basic elements comprising the CNC lathe
 Identify the axis of motion for CNC lathes
 State the different types of tooling and cutting operations
performed on the CNC lathe
 Explain the lathe feeds, speeds and depth of cut
Component of CNC Lathes
 The CNC lathe is a machine tool designed to remove material from
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stock that is clamped and rotated around the spindle axis
Single point cutting tool is mostly used
Chucks are used to grip the work while Turrets are used to hold and
index cutting tool called by the word address program.
Two types of turrets: Rear & Front
Two spindle opposed and vertical turret are other features known in
CNC lathe machine.
Component of CNC Lathes
Component of CNC Lathes
 Bed
 Headstock
 Chuck: Jaw/Faceplate – Hard/Soft – Collet
 Turret
 Carriage
 Tailstock
 Slant Bed
 MCU
CNC Lathe Axes of Motion
 Normally two basic axis motion is dealt in a CNC lathe machine: X & Z
 The Z axis is in the direction of the spindle where +Z is motion away
from the spindle and work while –Z is motion towards it
 The X axis is in the direction of the cross-slide movements where +X is
motion away from the spindle centerline and –X is the motion toward it.
 In machines with programmable tailstocks, the W axis is used to
designate the movement for a third axis on these machines.
CNC Lathe Axes of Motion
Basic Lathe Operations
 Facing: flatting the end surface
 Turning: removing the outer layer
Basic Lathe Operations
 Chamfer: smoothing of inner or outer edge
 Grooving
OD & ID Grooving
 Parting
Face Grooving
Basic Lathe Operations
 Drilling; Boring
 Threading
Basic Lathe Tooling
 Insert Materials
 Cemented Carbides: tungsten carbide sintered in a cobalt matrix
 Coated Carbides: cemented carbides coated with wear resistant material-titanium
carbide and aluminum oxide
 Ceramics: material formed without metallic bonding
 Diamonds: Single crystal natural diamond or synthetic diamond crystals
 Insert Shapes
Basic Lathe Tooling
 Advantage of indexable/insert tooling in lathe operation:
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Cutting capabilities at higher speeds
Reduction in tool inventory
Elimination of regrinding time and cost
Inserts are made with a precise tool nose radius for cutting(accurately
determined tool nose center
Cutting Speeds, Feeds & Depth of Cuts
 Cutting speed is defined as the rate at which a point on the
boundary of the material that is cut passes the edge of the
cutting tool
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For drilling, reaming and tapping, the Tool Diameter is used to
calculate the spindle rpm
Spindle rpm = Cutting Speed (mpm)
π × Tool Diameter (m)
(Drilling, reaming and tapping)
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The spindle rpm is input into the CNC program since the spindle
maintains a constant rpm level throughout these machining operation
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The spindle speed is specified by the S code. When programmed with
G97, it indicates the spindle rpm
G97 Sn
(General Syntax)
*n specifies the spindle speed
Cutting Speeds, Feeds & Depth of Cuts
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For turning, boring, facing, grooving and parting, the cut diameter
changes during operations.
The cutting speed is input into the CNC program where the controller
automatically adjusts the spindle rpm up or down in order to maintain
the cutting speed.
The relationship between Cutting Speed and the Cut Diameter and the
Spindle Speed rpm for operation of this matter (turning, etc) is given
approximately:
Cutting Speed (mpm) = Spindle Speed(rpm) × π × Cut Diameter(m)
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Cutting Speeds, Feeds & Depth of Cuts
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The relationship indicates that, for outside operation, constant Cutting
Speed is maintained by increasing the Spindle Speed as the Cut
Diameter decreases and vice versa for an inside cut.
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A G96 code is used to insure constant surface speed control. The S code
no longer specifies the Spindle speed but the Cutting speed.
G96 Sn
*n specifies the cutting speed
(General Syntax)
Cutting Speeds, Feeds & Depth of Cuts
 Tool feed is the rate at which the tool advance into the
work per revolution of the work
 Depth of cut is the thickness of the material machined from
the work or is the distance from the uncut work surface to
the cut surface
Cut Diameter = Uncut Diameter – 2×DOC
Feed Direction & Rake Angles
 Right handed cutting tools have their cutting edge on the
right side and are usually fed from right to left
 Left handed cutting tools have their cutting edge on the left
side and are usually fed from left to right
 Neutral cutting tools have their cutting edge on both the
right and left side and can be fed from either way
Feed Direction & Rake Angles
Feed Direction & Rake Angles
 Tooling Nomencalture
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Tool Nose Radius (TNR) – surface finish & longer tool life
Back Rake Angle (BR) – directing chip away and towards tool holder
Side Rake Angle (SR) – directing chip away and towards side
Side Clearance (SC) – permitting the side of the tool to enter the work
End Clearance (EC) – permitting the end of the tool to enter the work
SCEA – Improving shear cut and producing thinner chips
ECEA – Maintaining clearance between tool and work during boring
or facing operations
End
Chapter 9