Thermal Deformation.
Compensating for cast iron expansion over a 24-hour manufacturing shift.
Structural Growth
See our Thermal Expansion Calculator for raw metrics. A CNC machine frame is largely composed of Meehanite cast iron. As the ambient shop temperature rises from morning to afternoon, or as the spindle generates heat running at 15,000 RPM, the entire frame grows.
The Ballscrew Problem
The most acute thermal issue occurs in the ballscrews. As the axis moves rapidly back and forth, the friction of the ballnut generates heat, causing the ballscrew to expand linearly. If the machine relies solely on motor encoders for positioning, a 0.002" growth in the ballscrew means the machine will cut 0.002" out of tolerance, despite the controller believing it is perfectly in position.
Solutions include:
- Hollow Ballscrews: Chilled coolant is pumped through the center of the ballscrew to maintain a strict internal temperature.
- Linear Glass Scales: Direct absolute measurement of the axis carriage, entirely ignoring the physical state of the ballscrew.