How do CMMs measure flatness: QCT’s guide to how do CMMs measure flatness: Coordinated measuring machines can be used to measure dimensional metrology, including ‘flatness’.
The flatness of the optically flat surfaces are measured by techniques using the CMM stylus. The stylus can be operated or programmed to take specific, accurate measurements along the surface of the object and compare the data automatically to produce a report on the flatness of the object.
The effects of the CMM head probe’s scanning speed as well as the width of the step increments on the flatness measurements taken are examined individually by unique measuring subroutines. The software will take care of the range or comparison and compare that against a tolerance for ‘flatness’ that will give an accurate indication about the quality and form of the surface examined.
Without getting too complicated, no surface is completely flat. For example, you might consider both a sheet of steel and a pane of glass ‘flat’. However, on closer inspection the surface of a sheet of steel features many undulations across the surface from the manufacturing process. A plank of unfinished wood will also feature many undulations across the surface, and these will be able to be felt by human hand. The CMM’s job then is to measure the undulations across these surfaces and show you, through the software program, the ranges on each item. You may then look at your data and consider the glass to be the ‘flattest’, the steel to be of ‘medium flatness’ and the wood to be the least flat item. Contact QCT today for more information.
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