Factors affecting the coaxiality of Coordinate Measuring Machines (CMMs) essentially boil down to: inaccurate axint, unstable workpieces, machine inaccuracy, unstable environment, and improper methods. I have compiled this into the most practical, ready-to-use version for the shop floor, without unnecessary erbosity.
I. Machine Inherent Accuracy (Root Cause)
Geometric Accuracy
Perpendicularity, straightness, pitch, and yaw of the three axes
Indexing error of ry table/turntable (extremely influential when present)
Probe System
Bent, curved, or deformed stylus extensions
Poor repeatability of the probe, inaccurate caliboose suction cups or adapters
Motion and Transmission
Wear of guides, variation in air-bearing clearance
Vibration of lead screws, belts, or motors
II. Workpece and Fixturing (Most Common on the Shop Floor)
Workpiece Positioning
Uneven datum surfaces, burrs, or dirt
Inconsistent height of shims, uneven force dibution
Workpiece Deformation
Sagging of thin-walled parts or long shafts due to self-weight
Release of internal stresses, thermal deformation
Clamping Forceed too tight → deformation
Clamped too loose → micro-movement during measurement
III. Environment (Coaxiality is a form and position tolerance, extremely sensitive)
Temperature
Local differences (sunlight, fans, body heat)
Temperature inconsistency between workpiece and machine
Temperature gradients causing micro-deformation of columns and tables
Vibration
Floor vibraarby machine tools, personnel movement
Inadequate vibration isolation → drifting axis fitting
Cleanliness
Dust, chips, oil → distorted measurement points
IV. Measurement Method and ms (Determines Success or Failure)
Point Sampling Strategy
Too few cross-sections → inaccurate fitting
Points sampled too close together, uneven distribution
Measuring only one end, full length
Datum Establishment
Incorrect selection of datum
Datum cylinder too short or imprecise
Fitting Algorithm
Mixed use of Least Squares, Maximum Inscribed, and imum Circumscribed
Inconsistent software settings causing result fluctuations
V. Influence of Granite Table/Bed (The Part You Care About Most)
Table Flatness
Directly affects tkpiece datum surface; if the datum is skewed, coaxiality will be off.
Base Stability
Granite has low thermal expansion, but uneven support, loose leveling feet, orfluctuations can cause overall machine geometry drift.
تخميد الاهتزازات
Granite has good damping properties; however, poor vibration isolation or a poor foundation can still ruin coaxiality m
