Once upon a time, manufacturing involved physical drafting, the crafting of molds, and the acceptance of a lot of inaccuracy and imperfection. That started to change in 1959 with the introduction of the coordinate measuring machine (CMM), an invention created by the United Kingdom Company Ferranti that made its appearance at Paris’ International Machine Tool exhibition. Even back then, the CMM measured three-dimensional objects with great precision, and today it allows manufacturers to create customized parts with relative ease.
In this buying guide for coordinate measuring machines, we will discuss popular types of CMMs, what you should look for when purchasing a CMM, and various applications for these devices.
Popular Types of Coordinate Measuring Machines
Before we discuss buying a coordinate measuring machine or the various popular types of CMM, let’s describe the devices in greater detail.
The best starting place for understanding what a coordinate measuring machine is to comprehend how and what they measure. While CMMs can evaluate any number of different objects, these machines always function in the same fundamental way: They plot various points along X,Y, and Z axes that represent three-dimensional space. CMMs use a device known as a probe to gather this information, but the method by which a probe can take measurements varies and may include the following:
- Mechanical sensors
- Light sensors
- Laser sensors
- Optical sensors
A collection of data points is known as a point cloud. An operator may manually gather these points, or a computer may automatically generate them. The data is then used either in the manufacturing process or as part of quality assurance efforts.
While there are many different types of CMM and many different parts that can go into a system, they are typically comprised of three different components: the probe, the type data-collection device (i.e., the specific computer system), and the machinery that facilitates measuring in three-dimensional space. This final component is how CMMs are usually classified. Because most CMMs rest above a flat, table-like surface, this machinery is described by how the movement method employed relates to the scanning surface.
In the following subsections, we will discuss the four main types of CMM.
Bridge Style
This most common type of CMM features a U-shaped, bridge-like structure that rests over the machine’s table. The probe dangles from a telescoping arm that controls the Z axis by moving closer to or farther away from the table. The arm can maneuver along the Y axis by shifting parallel to the main beam of the bridge. These operations are mostly universal to bridge-style CMMs. However, the method of measuring the X axis can differ.
Bridge-style CMMs fall into two additional categories denoted by how they operate around the X plane. Fixed-table bridge CMMs move horizontally by shifting the bridge itself via motors connected to its supporting legs. Moving-table CMMs feature an immobile bridge and a mobile table.
There are several reasons why bridge-style CMMs are so common. First, they’re relatively simple in construction, which means that they cost less to purchase and to maintain. Second, they have a reputation for lasting an extremely long time. Third, they are generally far more accurate than other sorts of CMMs. However, they do face some drawbacks. Particularly large or weighty objects may not easily fit on the machine, and placing them may lead to impacts that can cause calibration issues or damage.
Cantilever
Cantilever CMMs look similar to bridge-style CMMs, differing primarily in the fact that they have only one supporting “leg” holding up the beam that houses the probe. Their relatively open construction facilitates the easy loading and unloading of scannable items, and cantilever CMMs are often employed in automated facilities. That unique design, though, requires a rigid beam positioned at a right angle to the one supporting leg, an accommodation that limits cantilever CMM applications.
One of the cons of a cantilever CMM is that the rigidity of the beam restricts the size of the mappable item. This means that cantilever devices are usually only employed to measure tinier items. Add with the ease of access, you can understand why these sorts of CMMs appear in automated manufacturing contexts.
Gantry
At first blush, gantry-type CMMs sound similar to bridge CMMs, featuring a probe suspended by a U-shaped structure — or rather U-shaped structures. Whereas a bridge CMM features a single U-shaped support system that bridges the width of the machine’s table, a gantry CMM places a pair of bridge-like supports at the sides of the table and connects them via a beam that holds the probe.
Due to their greater structural support, gantry CMMs excel at accommodating projects that require a greater scale. Indeed, they often require custom designs and the pouring of their own foundations. But while this makes them ideal for large projects, it also means they’re expensive to install, operate, and service.
Horizontal Arm
Though horizontal-arm CMMs bear some superficial resemblance to cantilever devices, they excel at different functions. Horizontal-arm CMMs feature a single post rather than a large supporting wall, and they come in two basic configurations, namely a plate-mounted CMM with a top- or side-mounted probe and a rail-mounted pair of arms that can operate independently.
Horizontal-arm CMMs function exceedingly well in situations that require lots of space to move items into and out of the machine. But they’re far less accurate than the other types of CMM available.
Bridge Style vs Cantilever vs Gantry vs Horizontal Arm
We’ve alluded to some of the advantages, disadvantages, and specific use cases for the four main types of coordinate measuring machines. It’s worth remembering that when you’re looking at a CMM machine for sale, fully conceptualizing the purpose for which you need the device is every bit as important as the CMM machine price.
- If your application involves automation and relatively small samples, then you should consider a cantilever CMM. Due to their open designs and the unyielding dimensions of the beam, they work well with fast loading and items of more modest dimensions.
- Consider turning to a horizontal-arm CMM if your scanning process requires more flexibility in loading and unloading. Their lack of accuracy is compensated for by their single- or dual-arm configurations, making them appropriate for many different kinds of projects.
- Gantry CMMs are the opposite of flexible. Requiring their own foundation and supportive infrastructure, they’re designed to not move. However, their inflexibility allows them to function on a greater scale than any other CMM. For the manufacturing of massive items, a gantry CMM will likely be your best bet.
- Finally, bridge-style CMMs combine accuracy, affordability, and longevity into a single package, making them a highly attractive option for the vast majority of projects. Still, bridge CMMs cannot typically accommodate excessively heavy or large items, which risk damaging the machine.
What to look for when buying a Coordinate Measuring Machine
Cost and CMM type are only a few of the considerations that you must keep in mind when looking at a new or used CMM machine for sale. Other factors include:
- Physical dimensions and your operating space
- Measurement requirements
- Characteristics of different materials to measure
- Physical size of different materials to measure
- Operating environment considerations (e.g., contaminants, risk of physical impacts)
- Machine performance
- Programming, training, and maintenance expenses
- Calibration and part reliability requirements
Applications for Coordinate Measuring Machine
If you’ve been wondering what a coordinate measuring machine is used for, then understand that CMMs find numerous applications throughout many different technical and manufacturing fields. While the following subsections are far from exhaustive, they offer examples of common use cases for the four main types of CMM.
Applications of Bridge-Type CMMs
This most popular type of CMM finds incredibly wide use due to its accuracy and durability. Some of these uses include the following:
- Manufacturing of machined and pressed parts
- Creation of plastic moldings
- Casting and forgings
- Touch trigger and non-contact inspection
- Rapid prototyping
- Scanning, digitizing and reverse engineering
Applications of Gantry CMMs
Size and scale are the defining characteristics of gantry-type CMM applications. Primarily used in industrial contexts, these CMMs take up large amounts of space and can deal without outsized tasks, including the following:
- Household appliances and white goods inspection
- Die and Mold Applications
- Flush and Gap Inspection
- Assembly Plant Setup
- Large volume part inspection
- Telescope optics
- Aircraft Component Inspection
- Manufacturing of very large parts
Applications of Horizontal-Arm CMMs
When an organization needs scanning flexibility, horizontal-arm CMMs often come into play. They’re often substituted if the items involved don’t require excessive clearance, but still need more flexibility than a bridge CMM, such as in these applications:
- Automotive panel and body inspection
- Aerospace component production
- Inspection of bigger components such as mold tools, castings, housing, etc.
- Defense-related manufacturing
- Integrated in-line inspection
- Appliance assembly
- Railway installation and repair
- Digitizing, scanning, and reverse engineering
Accessories for Coordinate Measuring Machine
When purchasing a CMM, understand that you will find many different types of accessories in addition to spare parts. These are primarily designed to accommodate the needs of different use cases, offering additional functionality, screening, or protection. Some include:
- Air bearings
- Add-on workstations
- Manual controls
- Portable / cloud-based controls
- Multi-sensor probes
- Non-contact probes
- Probe extension bars
- Probe change racks
- Rotary scanning tables
- Dust-proof enclosures
Finding Coordinate Measuring Machines on Surplus Record
At Surplus Record, we understand that the process of searching for coordinate measuring machines can be daunting. However, if you use the information in this buying guide and thoroughly search the listings here on Surplus Record, you’re almost certain to find the ideal CMM for your particular application.
Once you’ve determined what kind of CMM you need, it’s easy to search the inventory listed on Surplus Record. You can use the search bar anywhere on our website and type in “Coordinate Measuring Machine.”
Top manufacturers of CMMs include Brown & Sharpe, Mitutoyo, Zeiss, Keyence, and Wenzel.
We also work with a variety of dealers who specialize in coordinate measuring machines. You can also find dealers in your area or by name who specialize in CMMs.
