Why Don’t My Parts Fit? How Environment Factors Affect Machine Performance

CMS North America’s Quality Assurance and Calibration expert, Marty Sutten, offers his insights into how environmental factors can affect machine calibrations in this month’s news topic …


With design engineers demanding tighter and tighter tolerances, machine tool builders claiming near perfect accuracy and metrology companies swearing their measurements are definitive, why do my parts not fit? The most likely answer to this is environmental conditions.

High Technology Dual Concurrent Laser Calibration being carried out by means of a special fixture mounted to the left in conjunction with the main head to the right. Such a method obtains both sets of point measurement data at the same time. There are two red lines in the picture to show where the laser units are located and to where they are pointing during this procedure. 

We all know that materials change with a change in temperature; it’s known as the Coefficient of Thermal Expansion, or CTE. For example, steel changes at a generally agreed rate of 7.3ppm/degree F, Aluminum at 12.3 ppm/degree F, Invar at 0.8ppm/degree F, and carbon fiber at a highly debated 2ppm/Degree F. In the steel cutting world this generally works quite well, as the material the machine is made from is the same as the material being cut, but in our world this is not so. I think you know where we are going from here.

This article’s intent is to explore the effects of material movement and how they alter the machine, the work piece and the metrology of producing accurate parts.

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