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How Do I Measure The Flatness Of 6061 T651 Aluminum Plate?


When manufacturers pick out a material for their applications, it’s easy to get caught up in trying to distinguish between the many grades of aluminum available and to lose sight of some of the other important considerations that go into having a successful product run. Even after you know what grade you are going to use, you still need to determine the size, shape, and other specifications that can shape the success or failure of your project. For instance, understanding flatness and how to measure it can be vital to ensure your application is successful.

In manufacturing, flatness is defined as the deviation of an optic from a perfectly flat surface. There are a number of ways to measure flatness, but one of the most popular methods involves RMS, which stands for Root Mean Square, and is calculated as the standard deviation of the optical surface from the ideal surface.

Whenever parts need to be conjoined across a surface area, in particular in an air-tight (or liquid-tight) fashion, flatness becomes a critical quality for the finished surface. Such surfaces are usually machined or ground to achieve the required degree of flatness. When a precise level of flatness is needed, high-definition metrology is necessitated, which is the technical term for measurement. High tech machinery is used to make sure the various plates, bars, angles, and other products are exact.

When measuring flatness on your own, there are simple techniques you can use. For example, let’s say you have 6061 T651 aluminum plate that must be produced at a certain flatness tolerance. This alloy plate has a standard Aluminum Association tolerance of .1” for a thickness range from 0.25” to 0.624” and a tolerance of .075” for a thickness range of 0.625” to 8.” Taking a certified 24” straight edge with a taper gage, you must arrange the metal plate on a flat inspection surface and lay it with the concave surface facing upwards. Place your straight edge anywhere on the span so that both edges are in contact with the surface. If a .06” taper gage is unable to fit under the straight edge, then the plate is within the flatness tolerances for the Aluminum Association.

At Clinton Aluminum, we’re more than just a material supplier. Our mission is to work with our customers to make sure they have just the right material at the exact specifications required. When you have questions about flatness or anything else to do with your process, we’re here to help. Contact one of our friendly and knowledgeable representatives today.

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