The Xometry app works best with JavaScript enabled!
Xometry Logo
CapabilitiesIndustriesResourcesSuppliesBecome a SupplierFind Suppliers
Sign In
Cookie Policy
Xometry stores cookies on your computer to provide more personalized services to you, both on this website and through other media. By using this website, you consent to the cookies we use and our Privacy Policy.
BlogSupplier Shop Tips
CMM inspection and measurement of part QA

How to Select the Best CMM for Your Machine Shop

The accuracy and repeatability of your measurements are as important to your product output as the quality of your actual manufacturing tools.

Team Xometry - Xometry Contributor
By Team Xometry
 4 min read
SIMILAR STORIES
5 Steps to Create and Maintain a Facebook Presence For Your Machine Shop
September 17, 2020
 4 min read
Video: How Will It Grow? Part 2
September 18, 2020
 3 min read
Video: How Will It Grow?
September 17, 2020
 3 min read

Modern manufacturing operations increasingly depend on the performance of Coordinate Measuring Machines (CMM’s). The accuracy and repeatability of your measurements are as important to your product output as the quality of your actual manufacturing tools. There are several criteria to consider when selecting a CMM for your shop to ensure accurate and repeatable measurements:

Measuring Range

A CMM’s measuring range is primarily determined by the physical size of the largest part to be measured. However, the configuration of the part and the inspection routine may require the use of measuring probe extensions or holding fixtures. This may significantly increase the minimum measuring range. As a guideline, the CMM’s X, Y, and Z measuring ranges should be twice the length, width, and height of the largest part to be measured.

Accuracy

Environmental conditions like temperature, floor vibrations, and contaminants (dust, dirt, oil, etc.) can affect a CMM’s measuring accuracy. CMM manufacturers usually specify ideal atmospheric conditions and deviating from these may affect the CMM’s accuracy. To compensate for this, we recommend applying an acceptable ratio of maximum permissible error to tolerance, which represents the maximum error a CMM can have on a measurement compared with the tolerance of the measurement being taken. Ratios typically range from 1:3 to 1:20, with 1:5 and 1:10 being the most common. To maintain a 1:5 ratio the maximum permissible error of the CMM must be 1/5th of a dimension’s tolerance.

Types of CMM

A CMM’s probe arm orientation determines its type. There are five types of CMM:

Bridge

This is the most popular type of CMM. The probe arm is vertical and suspended on a horizontal beam supported by two vertical posts forming a bridge-like structure over the part to be measured.

Cantilever

The probe arm is mounted vertically on a horizontal cantilever which is itself mounted to a rigid structure. The probe arm moves vertically while the cantilever cannot move vertically. Machine rigidity limits the size of the cantilever, so they are primarily used to measure small parts.

Gantry

Gantry CMM’s are similar in construction to bridge-type machines, but are much larger and used to measure very large parts. Vertical support columns of gantry CMM’s are floor-mounted and require substantial foundations specified by the manufacturer to ensure rigidity and accuracy.

Horizontal-Arm

A horizontal-arm CMM looks similar to a cantilever CMM, but with its motions inverted. The probe arm moves horizontally while the entire cantilever moves vertically. Horizontal-arm CMMs are used to measure very large parts such as vehicle bodies.

Articulated-Arm

The articulated-arm CMM has an articulated multi-axis arm that allows the measuring probe to be positioned in many different directions. The articulated-arm CMM is very popular for portable measuring machines.

Types of Probes

The type of probe fitted to a CMM will have as big an effect on the quality of measurement as any other criteria we have discussed so far. Probes are divided into two main categories:

Contact Probes

Contact probes are contained in a probe housing. They consist of a stylus that is attached to a bearing plate which is then connected to a pressure sensor. Contact probes physically touch the part when taking a measurement. These probes can be further classified into two subtypes:

  1. Touch trigger probe - intermittently touches a part to measure individual points.
  2. Analog scanning probe - dragged across a part to measure contoured surfaces.

Non-Contact Probes

Non-contact probes are used where it is not possible for the measuring probe to physically touch parts, such as for very small parts or deformable parts. There are two types of non-contact probe:

  1. Laser probe - uses a laser to triangulate coordinates.
  2. Vision probe - uses a high-definition camera to generate many measurement points for comparison against an electronic model.
Team Xometry - Xometry Contributor
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.

Quick Links

  • Contact Us

  • Help Center

  • Our Story

  • Xometry Go Green

  • Careers

  • Legal

  • Press

  • Refer a Colleague

Locations

  • 7529 Standish Place

    Suite 200

    Derwood, MD 20855

  • 7940 Cessna Avenue
    Gaithersburg, MD 20879
    240-252-1138


  • 7315 Wisconsin Ave
    Suite 300 East
    Bethesda, MD 20814


  • 446 East High Street
    Lexington, KY 40507


  • 11777 San Vicente Blvd
    Suite 747
    Los Angeles, CA 90049


  • 117 Wright Industrial Cove
    Jackson, TN 38301


  • Ada-Lovelace-Str. 9
    85521 Ottobrunn, Germany
    +49 32 22 109 8186
    www.xometry.eu

Xometry Go Green Initiative
2.0M+
LBS OF C02 OFFSET

Xometry
© 2021 Xometry, All Rights Reserved