Offsets on the CNC Mill 262

"Offsets on the CNC Mill" provides an explanation of the concept, purpose, and use of offsets on the CNC mill or machining center and details the movements and programming involved with each type of offset. The workshift, tool length, and cutter radius compensation (CRC) offsets are essential components of any part program. CNC milling may also use additional offset features, including wear offsets and semi-automatic tool compensation.

Programming and operating CNC machines requires an understanding of offsets, since offsets form the foundation of all other tool movements. All CNC processes use offsets.

Class Details

Class Name:
Offsets on the CNC Mill 262
Description:
"Offsets on the CNC Mill" provides an explanation of the concept, purpose, and use of offsets on the CNC mill or machining center and details the movements and programming involved with each type of offset. The workshift, tool length, and cutter radius compensation (CRC) offsets are essential components of any part program. CNC milling may also use additional offset features, including wear offsets and semi-automatic tool compensation.

Programming and operating CNC machines requires an understanding of offsets, since offsets form the foundation of all other tool movements. All CNC processes use offsets.
Version:
2.0
Difficulty:
Intermediate
Number of Lessons:
14
Related 1.0 Class:
CNC Offsets 210

Class Outline

  • Introduction to Offsets
  • Machine Zero and Program Zero
  • Offset Types
  • Offset Basics
  • Workshift Offsets
  • Tool Length Offsets
  • Setting Tool Length Offsets
  • Workshift and Tool Length Offsets
  • Workshift and Tool Length Offset
  • Cutter Radius Compensation
  • Cutter Radius Compensation in Action
  • Tool Wear Adjustments
  • Offset Features
  • Final Review

Objectives

  • Describe offsets.
  • Identify machine zero and program zero.
  • Describe the three different types of CNC milling offsets.
  • Describe workshift offset.
  • Describe tool length offset.
  • Describe how to set tool length offset.
  • Describe workshift offset. Describe tool length offset.
  • Describe how cutter radius compensation adjusts for cutter size.
  • Describe tool wear adjustments.
  • Describe automatic tool compensation and machine tool probes.

Certifications

Glossary

Vocabulary Term Definition
1-2-3 block A precise metal block with dimensions measuring 1 in. (25.4 mm), 2 in. (50.8 mm), and 3 in. (76.2 mm) long, respectively. A 1-2-3 block can be used to touch off a tool during calculation of tool length offset.
axes An imaginary line that passes through the center of an object. Axes are used to measure the distances of objects in the Cartesian coordinate system.
Cartesian coordinate system A positioning system that uses three perpendicular linear axes to locate positions in three-dimensional space. The Cartesian coordinate system's axes are the X axis, Y axis, and Z axis.
computer numerical control CNC. A sophisticated machining device that uses a computer to carry out machining operations. CNC machine tools are much more sophisticated than their manual counterparts.
contour A curved surface or dimension that is cut into a workpiece. Contours can be affected by the dimensions of the cutting tool if CRC is not used.
CRC Cutter radius compensation. An offset that accounts for variations in tool diameter. CRC is only necessary for tools that continuously cut along a horizontal plane.
cutter radius compensation CRC. An offset that accounts for variations in tool diameter. Cutter radius compensation is only necessary for tools that continuously cut along a horizontal plane.
diameters The distance from one edge of a circle to the opposite edge across its widest point. Tool diameters must be accounted for with cutter radius compensation.
drills A multi-point cutting tool used to make round holes. Drills are usually made from high-speed steel and cemented carbides.
edge finder A device used to locate the exact position of a part edge along the X axis or Y axis. Edge finders determine workshift offsets.
end mill A milling cutter that cuts with its bottom and side edges. End mills can be used to machine grooves, slots, circular slots, and pockets, among other features.
fixture A customized device that is used to position and hold a workpiece in place. Fixtures are normally used to machine flat surfaces parallel to the table on a CNC mill.
fixture offset An offset that adjusts the location of every tool loaded in a machine by changing the position of the spindle. Fixture offsets may also be called workshift offsets.
flange A ring or collar surrounding the toolholder. The flange allows the tool to be grasped by the toolchanger.
G codes A CNC programming code that determines the type of operation the machine performs. G codes are one of a variety of CNC programming codes.
gage line An imaginary line marking the toolholder along the bottom edge of the machine spindle. The gage line on the toolholder taper matches up with the machine tool spindle when fitted together.
horizontal mill A mill in which the spindle is oriented horizontally. On a horizontal mill, the Z axis describes left-to-right movement, the X axis describes towards-and-away movement, and the Y axis describes up-and-down movement.
horsepower hp. A unit of power used to describe machine strength. Increased horsepower can be a sign that a cutting tool insert needs to be changed.
insert A cutting bit that has multiple cutting edges. Inserts which are worn excessively can be indexed to another edge, or the insert can be replaced.
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 tool probe A device that acts as a point for touching off tools to quickly calculate offsets. Machine tool probes can be used to measure parts and may reduce setup time.
machine zero The built-in origin on a CNC machine. Machine zero is set by the machine manufacturer during assembly.
MCU Machine control unit. A small, powerful computer that controls and operates a CNC machine. MCUs can be used to store offsets.
mills A milling machine, either manual or CNC. Mills allow for the precise, rapid creation of complex parts.
offsets A numerical value stored in the CNC controls that repositions machine components. Offsets are used to adjust for variations in tool geometry, part size, and other factors.
operator A person who is trained to operate a CNC mill. An operator has numerous responsibilities, including ensuring the proper running and maintenance of the mill.
origin The central point in a coordinate system. The origin is used to calculate any other points in the coordinate system.
part program A series of alphanumerical instructions used by a CNC machine to perform a sequence of operations necessary to machine a specific workpiece. Part programs typically include offsets.
part programmers The person responsible for the creation of a part program. The part programmer translates the workpiece design into program instructions for the CNC machine.
perpendicular An angle formed by two lines. Perpendicular lines intersect one another at a 90° angle.
pockets An interior recess that is cut into the surface of a workpiece. Pocket dimensions are affected by the dimensions of the cutting tool.
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 measurement of the distance between the outer edge of a cutting tool and its center. Tool radius is used to calculate CRC.
referencing Locating a tool, workpiece, or machine component in a known position. Referencing improves the accuracy of a cutting operation.
semi-automatic tool compensation A CNC machine setting that automatically records tool length offsets. Semi-automatic tool compensation involves touching off a tool and pressing the offset button on the MCU.
slots A narrow channel cut into the surface of a workpiece. Slot dimensions are affected by the dimensions of the cutting tool.
spindle A rotating component of a CNC mill, aligned along the Z axis. On a CNC mill, the spindle holds the cutting tool.
surface finish The degree of smoothness of the surface of a manufactured part. Surface finish is the result of the surface roughness, waviness, and flaws remaining on the part.
taper A conical section of the toolholder that allows the tool to be held in the machine spindle. The toolholder is used to determine the gage line for calculating tool length offset.
tool length offsets An offset that accounts for variations in tool length along the Z axis. Tool length offsets must be calculated for each tool.
toolchanger A device on a CNC mill that arranges multiple cutting tools in order and then positions these cutting tools for replacement. The toolchanger allows the CNC mill to change tools much more rapidly than could be done by hand.
toolholder A mechanism used to rigidly hold a cutting tool in place during machining. Multiple toolholders are held in the toolchanger.
toolpath The path the tool takes to complete a part. The toolpath is defined by the part program.
touching off Determining the exact location of a tool tip by touching it against an object with a known measurement. Touching off is an integral step in setting an offset.
vertical mill A mill in which the spindle is oriented vertically. On a vertical mill, the Z axis describes up-and-down movement, the X axis describes left-to-right movement, and the Y axis describes towards-and-away movement.
wear offsets An offset designed to account for changing tool dimensions caused by wear. Wear offsets account for part deflection, tool wear, and other factors.
workpiece Any metal or other material that is being machined. Workpieces are usually held in a workholding device while milling.
workshift offsets An offset that adjusts the location of every tool loaded in a machine by changing the position of the spindle. Workshift offsets may also be called fixture offsets.
worktable The component of a maching center that supports the workpiece and any workholding devices during machining. The worktable is often used as a base from which to calculate tool length offsets.
X axis On a vertical mill, the linear axis describing the horizontal left and right motion of the cutting tool or worktable. On a horizontal mill, the X axis describes movement towards or away from the operator.
Y axis On a vertical mill, the linear axis that describes horizontal tool motion toward and away from the operator. On a horizontal mill, the Y axis describes vertical movement.
Z axis On a vertical mill, the linear axis that describes vertical tool motion toward and away from the workpiece. On a horizontal mill, the Z axis describes horizontal left-to-right movement.