# Basics of the CMM 120

This class identifies the major types and components of the coordinate measuring machine and describes the coordinate system.

details Other tabs

## Class Details

Class Name:
Basics of the CMM 120
Description:
This class identifies the major types and components of the coordinate measuring machine and describes the coordinate system.
Version:
1.0
Difficulty:
Beginner
Number of Lessons:
16
Spanish, Chinese
Related 2.0 Class:
Inspecting with CMMs 361

## Class Outline

• Objectives
• What Is the CMM?
• Parts of the CMM
• Types of CMMs
• The Coordinate System
• Positive and Negative Directions
• What Is a Datum?
• Machine and Part Coordinates
• Alignment
• Measured and Constructed Features
• The Probe
• Contact Probes
• Non-Contact Probes
• CMM Software
• Summary

## Objectives

• Define the CMM.
• Identify the main components of the CMM.
• Identify the common types of CMMs.
• Describe the Cartesian coordinate system.
• Distinguish between positive and negative directions on the CMM.
• Define a datum.
• Distinguish between the machine coordinate system and the part coordinate system.
• Describe the purpose of alignment.
• Distinguish between measured and constructed features.
• Describe the probe.
• Describe how a contact probe inspects a part.
• Describe how a non-contact probe inspects a part.
• Describe the purpose of software for the CMM.
• Identify the advantages of a CMM.

## Certifications

MSSC
• MSSC Quality Practices and Measurement

## Glossary

Vocabulary Term Definition
alignment The process of relating the part coordinate system to the machine coordinate system. Alignment allows the part to be positioned anywhere on the staging table.
axes Imaginary lines perpendicular to one another that are used to define the position of objects in three-dimensional space.
bridge A horizontal beam that supports the z-axis ram and probe. The bridge provides a stable area for movement of the probe.
bridge support A vertical column that holds up the bridge. A bridge-type CMM has two bridge supports that slide back and forth on the staging table.
bridge-type CMM A type of CMM with a horizontal beam holding the probe. The bridge-type CMM is the most common type.
cantilever CMM A type of CMM with a single, moveable vertical support that suspends a 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.
constructed feature A feature on a part that is reproduced mathematically from other existing features. Constructed features are reproduced from measured features.
contact probe A type of probe that directly contacts the surface of the part it is measuring. Contact probes are the most common types of probes.
coordinate measuring machine A sophisticated measuring instrument with a flat polished table and a suspended probe that measures parts in three-dimensional space.
datum A point of reference from which measurements are taken. A datum can be a hole, line, or any three-dimensional shape.
forming A metalworking process that bends, punches, or shapes sheet metal.
gantry CMM A type of CMM similar to the bridge type but much larger. Gantry CMMs can measure parts the size of a car.
guide rail A component perpendicular to the bridge that guides the movement of the bridge supports.
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.
home position The central point in the Cartesian coordinate system that has a value of zero. Home position is also referred to as the origin.
horizontal CMM A type of CMM with a horizontal arm supporting the probe. The horizontal CMM makes it easy to load large, heavy parts.
machine coordinate system The coordinate system in which the X-, Y-, and Z-axes are mapped specifically to the components of the CMM. These axes remain the same even if the part changes.
machining The process of removing metal to form or finish a part, either with traditional methods like turning, drilling, cutting, and grinding, or with less traditional methods that use electricity or ultrasound.
measured feature A feature on a part that is measured by making contact with various points on its surface.
measuring axis Linear axis that represents the motion and position of the probe. This is also referred to as the Z-axis.
non-contact probe A type of probe that consists of a laser or scanning system that does not contact the part. Non-contact probes are used to inspect small, flexible parts.
origin The fixed, central point in the Cartesian coordinate system. The origin has a numerical value of zero.
part coordinate system The coordinate system in which the X-, Y-, and Z-axes are mapped specifically to the features of the workpiece. Each part has its own part coordinate system.
perpendicular An angle formed by two lines at a right angle. The corner of a piece of paper is formed by perpendicular lines.
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.
repeatability The ability to obtain consistent results when measuring the same part with the same measuring instrument.
ruby A gemstone mineral that is wear resistant. A ruby sphere is often used as the stylus.
software The coded instructions, formulas, and operations that structure the actions of a computer.
staging table The flat surface on which a part is measured. The staging table must be stable to ensure accurate measurements.
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.
thermal stability The ability of a material to resist changes in physical shape or size as its temperature changes.
tolerance The unwanted but acceptable deviation from a desired dimension.
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.
X-axis When facing the front of the CMM, the linear axis representing motions and positions along a line parallel to the table and to the left and right of the observer.
Y-axis When facing the front of the CMM, the linear axis representing motions and positions along a line parallel to the table and toward and away from the observer.
Z-axis When facing the front of the CMM, the linear axis representing motions and positions along a line perpendicular to the table that runs from top to bottom. The Z-axis is also referred to as the measuring axis.
Z-axis ram The device positioned on the Z-axis that holds the probe. The Z-axis ram can be raised or lowered.