# NIMS Core CNC Milling Skills 141

“NIMS Core CNC Milling Skills” covers the skills necessary for CNC milling-related job roles within the NIMS Level 1 Machining standard. This course introduces offsets on the CNC mill, as well as homing the machine after a full shut down.

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

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## Class Details

Class Name:
NIMS Core CNC Milling Skills 141
Difficulty:
Beginner
Number of Lessons:
12

## Class Outline

• Introduction to Offsets
• Machine Zero and Program Zero
• Homing a CNC Mill
• 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 in Action

## Objectives

• Describe offsets.
• Identify machine zero and program zero.
• Describe how to perform a homing procedure on a CNC mill.
• 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.

## Certifications

NIMS
• CNC Milling: Operations-FastTrack
• CNC Milling: Programming, Setup, and Operations-FastTrack

## 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.
CNC Computer numerical control. A sophisticated machining device that uses a computer to carry out machining operations. CNC machine tools are much more sophisticated than their manual counterparts.
computer numerical control CNC. A sophisticated machining device that uses a computer to carry out machining operations. Computer numerical control 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 mills 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.
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.
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 stores its home position even when shut down.
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.
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.
jog controls Buttons on a CNC machine control unit 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 axes movement using the jog control buttons. Some machines have a combined handle/jog mode.
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 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.
operators 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.
perpendicular An angle formed by two lines. Perpendicular lines intersect one another at a 90 &#deg; 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.
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.
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.
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.
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.
touches 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.
workpiece Any metal or other material that is being machined. Workpieces are usually held in a workholding device during 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 machining 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.