NIMS Core CNC Turning Skills 142

NIMS Core CNC Turning Skills covers the skills necessary for CNC turning-related job roles within the NIMS Level 1 Machining standard. This course introduces the components and functions of the CNC lathe, as well as its offsets.

Taking this course in conjunction with the other listed requirements for the NIMS Machining Level 1 standards will prepare users for certification in CNC Turning: Operations and CNC Turning: Programming, Setup, and Operations.

  • Difficulty Beginner

  • Format Online

  • Number of Lessons 19

  • Language English


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Course Outline
  • Types of CNC Lathes
  • Common Components of the CNC Lathe
  • CNC Lathe Movement
  • Lathe Components
  • Outer Diameter Operations
  • Toolholders for the CNC Lathe
  • CNC Lathe Turrets
  • The Turret and Cutting Operations
  • CNC Lathe Workholding
  • Machine Coordinates for the Lathe
  • Homing a CNC Lathe
  • Offset Types
  • Workshift Offset
  • Reference Tools
  • Geometry Offsets
  • Offsets and Reference Tools
  • Wear Offsets
  • Wear Offsets in Action
  • Tool Nose Radius Compensation
  • Contrast different types of CNC lathes.
  • Identify the components of the CNC lathe.
  • Explain how CNC lathe components move during cutting operations.
  • Describe common outer diameter operations.
  • Describe toolholders used on the CNC lathe.
  • Describe the functions of a CNC lathe turret.
  • Describe workholding tools used on the CNC lathe.
  • Describe the Cartesian coordinate system.
  • Describe how to perform a homing procedure on a CNC lathe.
  • Describe the three different types of CNC lathe offsets.
  • Describe the workshift offset.
  • Describe reference tools for CNC lathe offsets.
  • Describe geometry offsets.
  • Describe how the reference tool, workshift offset, and geometry offset work together.
  • Describe wear offsets.
  • Describe wear offsets.
  • Describe tool nose radius compensation.
Vocabulary Term


Imaginary lines that pass through the center of a point or object. Axes are used to describe the positions of objects in the Cartesian coordinate system.


An imaginary straight line or circle used to describe the location or movement of an object in three-dimensional space. Horizontal lathes spin along a horizontal axis of rotation.


A long, threaded device that rotates to move the worktable or cutting tool of a CNC machine. Ballscrews are powered by a servomotor.

bar machine

A lathe that continuously cuts a number of parts from a piece of bar stock. Bar machines use collets to hold the bar stock during cutting operations.

bar stock

Raw material sold in the form of long bars. Bar stock can be round, square, or hexagonal.


The main supporting structure upon which the operating parts of the machine are mounted and guided. Both the headstock and tailstock rest upon the bed of the lathe.


The process of enlarging or smoothing an existing hole with a single-point tool. Boring is an inner diameter operation.

boring bar

A long bar used to position a single-point tool for boring operations. Boring bars are usually a round shank.


A compound developed by the combination of carbon with other elements such as chromium, tungsten, or titanium. Carbide is often used to make metal cutting tools.

carbide insert

A replaceable cutting bit made out of carbide that has multiple cutting edges. Carbide inserts can be indexed to another cutting edge once one is excessively worn.


The section of the lathe that slides back and forth along the ways. Carriages support the cross slide and turret.

Cartesian coordinate system

The system that describes the position of any point or object in three-dimensional space by numerically expressing its distance from a fixed position along three linear axes. The Cartesian coordinate system is used to describe measurements in CNC milling and turning.


A workpiece formed by melting various raw materials, pouring them into a mold or cavity, and removing the workpiece once the materials have cooled and solidified. Metal castings are machined in a chucker.


The device in a lathe or turning center that supports the end of a cylindrical workpiece opposite the spindle. Centers are located in the tailstock.


A lathe cutting operation that creates an angled edge around the end of a cylindrical workpiece or the entrance of a hole. Chamfering can be an inner or outer diameter operation.


The occasional vibration between a workpiece and a cutting tool. Chatter decreases machining productivity, negatively impacts surface quality, and increases tool wear.


A device that holds a workpiece in place as it rotates on a lathe or other machine tool. Chucks commonly have three or four jaws that can be adjusted to fit various workpieces.


A lathe that requires an operator to load one workpiece at a time. The workholding device used for a chucker is called a chuck.

CNC lathe

A machine that uses computerized numerical data to control workpiece rotation and cutting tool movements for the machining of cylindrical parts. CNC lathes are precise and versatile.


A slitted device that holds a workpiece or cutting tool in place as it rotates. A collet has a hole through which the bar stock passes and is designed to hold specific diameter or shape dimensions.

computer numerical control

CNC. A self-contained system of computers and precision motors that executes program instructions to guide machine tool components and manufacture parts. CNC machines can be either open-loop or closed-loop systems.

contour turning

A lathe cutting operation that creates curved or complex shapes on the workpiece surface. Contour turning is an outer diameter operation.

cross slide

The toolholding component of a lathe that allows tools to approach a workpiece centerline. Cross slides are supported by the carriage and position the turret toward and away from the workpiece.


A slicing operation performed on a lathe that uses a cutting tool to separate a finished part from the rest of the stock. A cutoff operation is an outer diameter operation.

cutoff tool

A cutting tool that separates a part from the rest of the stock. Cutoff tools establish the final length of a part.

cutting forces

Force generated by the motion of the cutting tool and the resistance of the workpiece. Cutting forces eventually cause tool wear, which degrades the accuracy and precision of a tool.

depth of cut

The distance that a cutting tool penetrates the surface of a workpiece. Depth of cut is determined by the cross slide on a lathe.


The workpiece surface that corresponds with the X axis on the lathe. The diametrical portion is the circular end or cross-section of a cylindrical workpiece.


A metal cutting tool used to penetrate the surface of a workpiece and make a round hole equal to the drill diameter. Drills on CNC turning centers are powered by a small motor in the turret.


A lathe cutting operation that feeds a cutting tool across an end of a cylindrical workpiece to create a flat surface and shorten its length. Facing is an outer diameter operation.

facing cut

A cut on the end of a cylindrical workpiece that removes material to leave a flat surface. A facing cut is usually the first step in a part program for a CNC lathe.


A defining characteristic. Features include shapes, lines, and other elements machined into a workpiece.


A workpiece formed by compressing or hammering hot metal to achieve a specific shape. Forgings are machined in a chucker.

G codes

A CNC programming code that determines the type of operation performed on the machine. G codes are one of a variety of CNC programming codes.

geometry offset table

A table holding geometry offsets that is stored in the machine control unit. The geometry offset table is used to store tool nose radius compensation, among other offsets.

geometry offsets

An offset used to account for the orientation and dimensions of a specific tool held in the turret. A geometry offset is required for each individual tool.


A lathe cutting operation that cuts a narrow channel into a rotating cylindrical workpiece. Grooving can be an inner or outer diameter operation.


The end of a lathe that holds the spindle and the spindle drive that rotates the workpiece. Headstocks hold the workpiece in place on the spindle end of the lathe.

high-speed steel

HSS. A category of tool steels used for cutting tool applications. Drills and other multi-point tools are often made of high-speed steel.

home mode

The control mode that allows for the operator to find the location of the home position after complete machine shutdown and restart. Home mode only occurs on those machines that do not store the location of machine zero when powered down.

home position

The location of machine zero on a CNC machine. Home position must be referenced during machine warm up after a full shut down unless the machine has a reference return button.

homing procedure

A method for locating a CNC machine’s home position. The homing procedure must be completed upon starting up a CNC machine that has been fully shut down unless that machine has a reference return button.


A system that uses the force of flowing liquids to transmit power. Hydraulics can be used to power a chuck.

inner diameter

ID. The interior surface of a workpiece. Inner diameter cutting operations include drilling, reaming, and boring.


A replaceable cutting tool with a geometric shape that has multiple cutting surfaces. Some inserts can be used as reference tools.

jog controls

Buttons on a CNC control interface that move the machine components along the axes. The jog controls move machine components in steady movements.

jog mode

The control mode that allows for the manual operation of steady axis movement using the jog control buttons. Some machines have a combined handle/jog mode.


A machine tool used to create cylindrical parts. Lathes hold a cylindrical workpiece on one or both ends while moving a single-point cutting tool along the surface of the rotating part.

live tooling

A feature that equips the turret with power-driven tools such as end mills and drills. Live tooling can perform cutting operations off-center while the workpiece is held still in the spindle.


The workpiece surface that is parallel to the Z axis on the lathe. The longitudinal portion is the long, non-circular portion of a cylindrical workpiece.

machine control unit

MCU. A small, powerful computer that controls and operates a CNC machine. Machine control units can be used to store offsets.

machine zero

The default origin position on a CNC machine. Machine zero is set by the machine manufacturer.


Machine control unit. A small, powerful computer that controls and operates a CNC machine. MCUs can be used to store offsets.


A multi-point cutting tool that has teeth around its cutting surface. Mills are often used to create flat or contoured surfaces.

nose radius

The dimensions of the rounded tip of an insert. Tools with rounded tips usually require tool nose radius compensation.


Outer diameter. The external surface of a workpiece. OD cutting operations on the lathe include turning, facing, and cutoff.


A numerical value that repositions machine components. Offsets are used to adjust for variations in tool geometry, part size, and other factors.


A fixed, central point in the Cartesian coordinate system where the three X, Y, and Z axes intersect. The origin has a numerical value of zero.

outer diameter

OD. The external surface of a workpiece. Outer diameter cutting operations on the lathe include turning, facing, and cutoff.

part face

The flat, circular end of a cylindrical part. The part face is used as a reference point to calculate program zero.

parts catcher

A device used to catch a part once it is separated from the stock. A parts catcher is one component in a bar machine.


A system that uses the force of flowing gases to transmit power. Pneumatics can be used to power a chuck.

program zero

The position that acts as the origin for a specific part program. Program zero is unique to each part design and is selected by the part programmer.


A direction that radiates outward from a common center. The cross slide determines the radial depth of cut on a CNC lathe.


A curved feature of a tool or part. A radius may be present at the tip of some cutting tools.


A multi-point cutting tool with straight cutting edges used to enlarge or smooth holes that have been previously drilled. On a lathe, reamers are held in place by a collet.

reference tool

A tool to which all other tools in the turret are compared when setting geometry offsets. The reference tool does not require a geometry offset because its exact location is already stored as the workshift offset.


A motor in a CNC machine that powers movement of the machine tool. Servomotors rotate the ballscrew on a CNC machine, causing the table of a mill or the slides of a lathe to move.


All the necessary preparation of tooling and fixturing that occurs on the machine before a part program can be executed. Every part setup requires the calculation of new offsets.


The part of the machine tool that rotates. On the lathe, the spindle holds the workpiece.

spindle drive

The main device that powers the rotation of the lathe spindle. Drives are located in the headstock.

stick tool

The most common tool style on a lathe on which the tools are mounted in a turret that indexes the tools. A stick tool is a long square shank that clamps a carbide insert in a pocket on one end.


Raw material that is used to make manufactured parts. Stock is available in standard shapes, such as long bars, plates, or sheets.

stock stand

The component of a bar machine that supports the bar stock. Stock stands feed bar stock through the machine one workpiece length at a time.

surface finish

The smoothness of a surface after it has been machined. Surface finish is the complete, desired surface as per the part specifications.


The part of a lathe located opposite the headstock. Tailstocks can hold a center to support longer workpieces or an internal diameter cutting tool.

taper turning

A lathe cutting operation that gradually increases or decreases the diameter along the workpiece length to create a conical shape. Taper turning is an outer diameter operation.


A multi-point cutting tool used to create internal threads. On a CNC lathe, taps are held by the turret.

theoretical tool tip

TTT. The location from which the CNC lathe calculates the position of the tool. The theoretical tool tip may or may not be located at the actual tip of the tool.

thermal expansion

An increase in a material's dimensions that occurs as temperature increases. Thermal expansion of machine components is undesirable and can lead to misalignment.


The process of cutting a long, spiraling groove into a cylindrical workpiece with a single-point tool. Threading can be an inner or outer diameter operation.


A long, spiral ridge around the exterior or interior of a cylindrically shaped object. Threads are used to fasten or provide motion.

tool nose radius compensation

TNRC. An offset feature that slightly shifts the toolpath to accommodate the rounded tip of an insert during machining operations. Tool nose radius compensation is required for contouring and chamfering.

tool wear

The erosion of tool material as a result of friction. Tool wear degrades the accuracy and precision of a tool.


A device used to rigidly hold a cutting insert in place during machining. Toolholders generally hold an indexable insert.

touch off

To determine the exact location of a tool tip by touching it against an object with a known measurement. Touching off is used to set geometry offsets.


A machining operation that rotates a cylindrical workpiece while a single-point tool is guided along the length of the part. Turning is performed on a lathe.

turning center

A sophisticated CNC lathe that can perform a variety of drilling and milling operations all at the same location. Turning centers usually use live tooling.

turning tools

An insert designed for turning operations on a CNC lathe. A turning insert will usually require a unique geometry offset.


A lathe component that holds a number of cutting tools. Turrets rotate or index to place tools in cutting position.

vertical lathe

A lathe with a spindle axis that is perpendicular to the ground. Veritcal lathes are ideal for turning excessively large and heavy workpieces.


Two precisely measured, parallel tracks that support and guide the movement of the carriage and cross slide of the lathe. Ways are located along the bed of the lathe.

wear offsets

An offset that allows for the slight adjustment of tool tip location. Wear offsets compensate for part deflection and tool wear.


The process of securely supporting, locating, and clamping a workpiece for a manufacturing operation. Chucks and collets are both workholding devices.


A part that is in the process of being manufactured. A workpiece may be a complete product in itself or one component of a product consisting of many parts.

workshift offsets

An offset used to adjust the location of every tool loaded in the machine. Workshift offsets change the position of the entire turret.

X axis

An axis in the Cartesian coordinate system that is perpendicular to the Z and Y axes. On the CNC lathe, the X axis describes turret motion towards and away from the spindle centerline and controls workpiece diameter.

Y axis

An axis in the Cartesian coordinate system that is perpendicular to the Z and X axes. On most basic CNC lathes, the Y axis is not programmable.

Z axis

An axis in the Cartesian coordinate system that represents motions and positions perpendicular to the X axis and parallel to the machine spindle. On a CNC lathe, the Z axis is parallel to the workpiece.