Rotating equipment & shafts
Flatness, soft foot and shaft alignment are different checks
Why a flat-looking base does not prove the machine is correctly supported.
Flatness describes surface geometry. Soft foot concerns how the machine contacts its supports. Shaft alignment concerns the relative shaft axes. These checks are related, but they answer different questions.
A small example
If two foot stations 400 mm apart differ by 0.12 mm in height, their straight-line slope is 0.12/400 = 0.0003 rad for small angles. A uniform shim change can shift the machine without removing that slope.
Start with a supported machine and valid measurements, then follow the applicable alignment method. Precision Alignment develops the geometry, stiffness and fabrication reasoning.
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