Offsets on the CNC Lathe 261

"Offsets on the CNC Lathe" provides explanations of the concept, purpose, and use of offsets on a CNC lathe or turning center. The workshift, geometry, and wear offsets are essential components of any part program. The class first introduces the concepts of offsets, referencing, machine zero, and program zero and then details the axis movements of and programming involved for each type of offset. Additionally, it introduces other offset features, including automatic toolset probes and tool nose radius compensation.

Offsets are used in all CNC processes. Since offsets are the most foundational machine tool movements in any part program, a complete understanding of CNC operations requires an equally complete understanding of CNC offsets. After taking this class, users should be able to understand CNC lathe offsets and how to use them.

Class Details

Class Name:
Offsets on the CNC Lathe 261
Description:
"Offsets on the CNC Lathe" provides explanations of the concept, purpose, and use of offsets on a CNC lathe or turning center. The workshift, geometry, and wear offsets are essential components of any part program. The class first introduces the concepts of offsets, referencing, machine zero, and program zero and then details the axis movements of and programming involved for each type of offset. Additionally, it introduces other offset features, including automatic toolset probes and tool nose radius compensation.

Offsets are used in all CNC processes. Since offsets are the most foundational machine tool movements in any part program, a complete understanding of CNC operations requires an equally complete understanding of CNC offsets. After taking this class, users should be able to understand CNC lathe offsets and how to use them.
Version:
2.0
Difficulty:
Intermediate
Number of Lessons:
14
Related 1.0 Class:
CNC Offsets 210

Class Outline

  • Introduction to Offsets
  • Machine Coordinates for the Lathe
  • Machine Zero and Program Zero
  • Offset Types
  • Offset Basics
  • Workshift Offset
  • Reference Tools
  • Workshift Offset and Reference Tools
  • Geometry Offsets
  • Offsets and Reference Tools
  • Wear Offsets
  • Wear Offsets in Action
  • Tool Nose Radius Compensation
  • Final Review

Objectives

  • Define offsets.
  • Describe the Cartesian coordinate system.
  • Identify machine zero and program zero.
  • 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 tool nose radius compensation.

Job Roles

Certifications

NIMS
  • CNC Lathe Operations
  • CNC Turning Programming, Setup, & Operation

Glossary

Vocabulary Term Definition
accuracy The exactness of a measurement compared to the desired result. CNC lathes are highly accurate.
axes 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.
boring bars A toolholder that holds a cutting insert in order to remove material from the inner surface of a drilled hole. Boring bars will typically require a unique geometry offset.
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.
chamfering Cutting an angled edge around the end of a cylindrical workpiece. Chamfering removes sharp corners.
chatter The occasional vibration between a workpiece and a cutting tool. Chatter decreases machining productivity, negatively impacts surface quality, and increases tool wear.
CNC lathes A computer numerically controlled machine that performs cutting operations on cylindrical parts. CNC lathes, also called turning centers, are much more precise and perform work much more quickly than their manual counterparts.
computer numerical control CNC. A programmable control system for a machine tool, which uses microcomputers to carry out various machining operations. Computer numerical control is much quicker and more precise than its manual counterpart.
contouring Tool movement along two or more axes at the same time to create a curved surface. Contouring can require tool nose radius compensation.
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.
diametrical 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.
drills A cutting tool used to create holes in workpieces. Drills usually require a unique geometry offset.
facing cut A cut on the end of a cylindrical workpiece which removes material to leave a flat surface. A facing cut is usually the first step in a part program for a CNC lathe.
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 and 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.
insert A replaceable cutting tool with a geometric shape that has multiple cutting surfaces. Some inserts can be used as reference tools.
longitudinal 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 specific CNC machine. Machine control units read part programs and translate them to machine movement.
machine zero The default origin position on a CNC machine. Machine zero is set by the machine manufacturer.
MCU Machine control unit. A small, powerful computer that controls and operates a specific CNC machine. MCUs read part programs and translate them to machine movement.
nose radius The dimensions of the rounded tip of an insert. Tools with rounded tips usually require tool nose radius compensation.
offsets A numerical value that repositions machine components. Offsets are used to adjust for variations in tool geometry, part size, and other factors.
origin 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.
part face The flat, circular end of a cylindrical part. The part face is used as a reference point to calculate program zero.
part zero The position that acts as the origin for a specific part program. Part zero is more commonly referred to as program zero.
precision The ability of a process to repeat the same accurate measurement over time. CNC lathes are very precise.
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.
radius A curved feature of a tool or part. A radius may be present at the tip of some cutting tools.
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.
referencing Locating a tool, workpiece, or machine component in a known position. Referencing accurately positions a tool relative to a workpiece and workholding for a given cutting operation.
setup 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.
spindle centerline An imaginary line on the Z axis precisely in the center of the spindle. Program zero is usually set along the spindle centerline.
surface finish The smoothness of a surface after it has been machined. Surface finish is the complete, desired surface as per the part specifications.
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.
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.
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.
turning centers A computer numerically controlled machine that performs cutting operations on cylindrical parts. Turning centers, also called CNC lathes, are much more precise and perform work much more quickly than their manual counterparts.
turning tools An insert designed for turning operations on a CNC lathe. A turning insert will usually require a unique geometry offset.
turret The component of a lathe that holds a number of cutting tools. The turret rotates to place tools in the cutting position.
wear offsets An offset that allows for the slight adjustment of tool tip location. Wear offsets account for part deflection and tool wear.
wear offsets An offset that allows for the slight adjustment of tool tip location. Wear offsets compensate for part deflection and tool wear.
work zero The position that acts as the origin for a specific part program. Work zero is more commonly referred to as program zero.
workpiece A part or component that is being worked on. Workpieces in CNC machines are the raw materials that are shaped by the machine.
workshift offset 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.