In case you have no prior knowledge about coordinate measuring machines, or CMMs in short, then this informative article is for you. If you’re a fabricator yourself, you probably know that it’s essential that the measurements of the physical dimensions and geometric characteristics of the final manufactured object match the ones of the 3D model. Because even a slight deviation can jeopardize the entire manufacturing process and set you back to square one. Enter coordinate measuring machines.
In today’s market, there are four primary types of coordinate measuring machines: the bridge, gantry, cantilever, and horizontal arm CMMs. The one you will select for your measuring project should be determined by what you wish to use it for. All CMM machines have three orthogonal axes (X, Y, and Z) that operate in a 3D coordinate system and relay calculated data to check the accuracy of the part or component being measured.
Suppose you’re on the brink of selecting the proper CMM machine for your job. In that case, this article will look at the four main types of coordinate measuring machines and their best-known applications so that you can make an informed decision and pick the kind of machine that will suit your project and needs.
A standard 3D bridge coordinate measuring machine permits probe movement along all three axes, which are orthogonal to each other in a 3D cartesian coordinate system where each axis sensor monitors the probe’s position with micrometre precision. In the bridge CMM, the contact point of the position sensors permits the measuring of the component’s surface and is repeated to generate a “point cloud” which identifies the surface areas of interest.
The bridge measuring machines are known as the workhorses of coordinate measuring machines and come in a reasonably basic structure that’s relatively easy to build. As with any other piece of machinery, the bridge CMM comes with a long list of pros and cons in its functions. For instance, it can be quite challenging to access the part which needs to be measured because of the machine’s upright holding for the X-axis beam. In addition, heavier elements and components that need to be reckoned with this machine may require a crane or a lift truck to place them on the CMM, which can lead to the device getting knocked.
On the other hand, for measuring machined parts with higher tolerances, there’s no better measuring device for accuracy than the bridge coordinate measuring machine.
The gantry coordinate measuring machine is pretty similar in structure to bridge CMMs, but is usually much, much larger. The gantry CMM has the bridge raised on pillars, increasing the overall measuring volume compared to the bridge CMM. Most gantry coordinate measuring machines have a substantial foundation and are commonly mounted directly to the facility’s floor.
The measuring range of each gantry machine can vary from 1x2x1m XYZ to 5x12x5 XYZ, and it’s possible to have even more extensive, custom-made machine units built. Speaking of the pros and cons of this machine, with the gantry CMM, it’s far safer to load heavy parts as they can be loaded directly on the facility’s floor. Also, it’s easy to insert surface plates for smaller measuring components, which makes the measurement operations less time-consuming for the operator.
On the other hand, the cost of building its foundation is significantly higher than for other CMMs, this type of machine is not portable, and it can take up a lot of space. Therefore, the gantry CMMs are mainly used in the aerospace industry, where the measuring component’s size is enormous.
The cantilever CMMs are commonly used to measure smaller parts or components precisely. Compared with the bridge CMM, cantilever CMMs permit access to the user on three different sides. However, cantilevers also only allow for probe movement on X and Y, creating certain limitations on the size of the X beam.
Lastly, the horizontal arm CMMs were first manufactured in Germany and were initially used as scribing tools. The early models were fully manual and much harder to operate with when compared to today’s horizontal arm CMMs. In addition, this measuring machine is different from the previous three types because it has two axes mounted on a saddle that moves up and down the horizontal axis.
Gantry and bridge CMMs have fantastic accuracy but are semi-flexible. Horizontal arm CMMs deliver the least accuracy but have the most considerable flexibility of all measuring machines. Nevertheless, whichever you choose, the level of accuracy on all types of CMMs is still far higher than it would be without one, making your production runs way more cost-effective.
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