Definition
A coordinate measuring machine probes a part with a touch probe or an optical head and records the measured points in a coordinate system. Planes, circles and axes are derived from those points, so geometric tolerances such as position, perpendicularity and runout can be checked as well.
What it means for the calculation
Measuring on a coordinate measuring machine is a separate item with its own rate and its own queue. Writing the measuring program costs time once, the measuring itself costs time per piece, and a tight tolerance often needs more probing points and therefore a longer measuring cycle. As soon as a drawing carries geometric tolerances with datums, hand tools are usually no longer enough and the inspection room enters the lead time.
Where this comes up
Rarely named on the drawing itself. It follows from the requirements: geometric tolerances with datums, tight position tolerances and a requested inspection report all point to a measurement on a coordinate measuring machine.
Common mistakes
Folding inspection time into the milling machine rate, which leaves the inspection room invisible in the calculation. Also forgetting that a part just off the machine has to cool down before it can be measured reliably, which adds lead time without adding machine time.
Measuring on a coordinate measuring machine is a separate item with its own rate and its own queue. Writing the measuring program costs time once, the measuring itself costs time per piece, and a tight tolerance often needs more probing points and therefore a longer measuring cycle. As soon as a drawing carries geometric tolerances with datums, hand tools are usually no longer enough and the inspection room enters the lead time.
See how Blake reviews a partFrequently asked questions
Is a coordinate measuring machine needed for each tolerance?
No, many size tolerances can be checked with hand tools; geometric tolerances with datums usually do need one.
Does a coordinate measuring machine also measure surface roughness?
No, roughness is determined with a separate instrument.
Does a measuring program cost time again for each run?
Programming is a one-off per part; running it costs time per piece.