Inspecting with CMMs 220

This class compares the advantages and common uses of various CMM components and software applications.


Class Name:
Inspecting with CMMs 220
This class compares the advantages and common uses of various CMM components and software applications.
Number of Lessons:
Additional Language:
Related 2.0 Class:
Inspecting with CMMs 361

Class Outline

  • Objectives
  • Coordinate Measuring Machines
  • Types of CMMs
  • Environmental Factors
  • Bearings
  • Cartesian Coordinates
  • Polar Coordinates
  • Manual Controls
  • Direct Computer Controls
  • Scales and Encoders
  • Single-Point Contact Probes
  • Continuous Analog Scanning
  • Non-Contact Probes
  • CMM Software
  • CMM Programming
  • CMM Applications
  • Summary


  • Describe factors that affect CMM selection for a given operation.
  • Match different types of coordinate measuring machines with appropriate operations.
  • Describe how coordinate measuring machines prevent or compensate for environmental influences.
  • Compare the characteristics of air bearings and mechanical bearings.
  • Identify a working plane.
  • Identify the axes in the polar coordinate system.
  • Compare the characteristics of manual and joystick controls.
  • Describe the operation of a direct computer control.
  • Describe the interaction of the scale with the encoder.
  • Compare the characteristics of hard probes and touch-trigger probes.
  • Describe continuous analog scanning.
  • Describe the operation of a laser probe.
  • Describe the operation of a video probe.
  • Identify types of software used on a coordinate measuring machine.
  • Describe different methods for programming a coordinate measuring machine.
  • Describe ways to incorporate CMMs into production processes.

Job Roles


  • MSSC Quality Practices and Measurement


Vocabulary Term Definition
air bearing A device that, through the release of compressed air, lifts one part slightly off another so that the parts may glide past each other.
axis member The moving part of a CMM that corresponds with an imaginary line formed by the Cartesian coordinate system.
bearing A friction-reducing device that allows one moving part to glide past another moving part.
bridge-type CMM A type of CMM with two vertical supports and a horizontal beam holding the probe. The bridge-type CMM is the most common type.
calibration The comparison of a device with unknown accuracy to a device with a known, accurate standard to eliminate any variation in the device being checked.
cantilever CMM A type of CMM with a single, moveable vertical support with a suspended horizontal arm that holds the probe. Cantilever CMMs provide easy access to the staging table.
Cartesian coordinate system The system that describes the location of an object by numerically expressing its distance from a fixed position along three imaginary linear axes.
CNC machine A machine controlled by a computer that runs special programs driven by numerical data. CNC machines are very rigid and are capable of fast cutting speeds.
computer-aided design A method of designing two- and three-dimensional objects using computers and software.
continuous analog scanning A method of gathering coordinates that requires that the stylus stay in constant contact with the part's surface.
coordinate measuring machine A sophisticated measuring instrument with a flat, polished table and a suspended probe that measures parts in three-dimensional space.
direct computer control Completely hands-free machine operation that is directed by a software program.
encoder An opto-electronic device that detects the incremental lines on a scale to determine positioning. An encoder is also known as a reader head.
feature recognition Software that, when given a small amount of data like a set of coordinates, can recognize the part in question.
footprint The amount of physical floor space that a machine takes up in the shop.
gantry-type CMM A type of CMM similar to the bridge type but much larger. Gantry CMMs can measure parts the size of a car.
guide way The stationary part of a CMM that corresponds with an imaginary line formed by an axis in the Cartesian coordinate system.
hard probe A solid contact probe consisting of a precision ball or tapered shape that is mounted to a shaft. Operators use hard probes to manually inspect the surface of a part.
joystick control A vertical handle or lever that allows remote, but hands-on, operation of a machine.
laser probe A measuring device that projects a narrow beam of light onto the part’s surface. A lens on the probe then reads the beam's position.
linear axes Imaginary perpendicular lines that serve as reference points in the coordinate system.
macro A single computer command that executes a series of commands or actions.
manual control A control that requires complete hands-on operation.
mechanical bearing A small, highly polished, metal ball that allows objects resting on it to flow smoothly and freely. Mechanical bearings are usually used in multiples.
micron A measurement equal to one twenty-fifth of a thousandth of an inch (0.00004 inch).
non-contact probe A type of probe that consists of a laser or scanning system that does not contact the part surface. Non-contact probes are used to inspect small, flexible parts.
non-prismatic Surfaces or objects that generally do not have angles. Non-prismatic surfaces include a sphere or the contour body of an automobile.
operating system The software on a computer that allows files to be created and organized, manages the interaction of different programs, holds data in memory, and performs other functions.
opto-electronic device A mechanism that uses light to generate an electronic signal or that interprets light as an electronic signal.
origin The fixed, central point in a coordinate system. The origin has a numerical value of zero.
part program A string of software commands that tells a coordinate measuring machine how to inspect a part.
pixel A small dot that, when alongside other dots, forms a cohesive image like a television picture.
planar condition Geometric space that is two-dimensional or flat, such as a disk.
plane An imaginary surface that is perfectly flat or level.
polar coordinate system The system used to measure circular-planar or spherical objects from a common point of origin. The R-axis indicates the distance from the origin and the Θ-axis indicates the angle from the positive X-axis.
portable CMM A type of CMM consisting of a moveable arm with multiple joints that holds a probe. Portable CMMs can be taken to the part for inspection.
probe A device attached to the Z-axis ram that gathers measurement data from the workpiece.
radial Projecting from a common origin or center point, as in the spokes of a wheel.
reader head A common name for an encoder.
resolution The smallest change in a measured value that the instrument can detect.
reverse engineering A type of design in which a finished piece is examined to determine how it was made. The data collected allows the original to be reproduced.
sample A representative part from a larger group.
scale A series of fine lines that is located along the axis member of a CMM. When read by an encoder, the scale tells the CMM the axis coordinates.
servomotor A small motor that can move machine components in very small, precise increments.
software The programs and instructions that control the computer hardware functions and operations.
spherical condition Geometric space that is three-dimensional or round, such as a ball.
stitch-scanning A measurement method in which a series of individual points on a part are touched and their positions recorded. The CMM then estimates the surface location between these points.
stylus A spherical portion of the probe that is mounted on the shaft and makes contact with the part. The stylus is usually a synthetic ruby.
tolerance An unwanted but acceptable deviation from a given dimension. Tolerances indicate the allowable difference between a physical feature and its intended design.
touch-trigger probe A type of contact probe that detects a feature on a part and generates an electronic signal to record its dimension. Touch-trigger probes are the most accurate and commonly used probes on the CMM.
video probe A measuring device that takes a digital image of the part. The image is then broken up into tiny dots, which are measured and counted by the software.
working plane A combination of two axes of the Cartesian coordinate system that together form a two-dimensional area.