A hobbyist assessed CNC lead screw accuracy by building a setup using digital calipers interfaced with a Raspberry Pi. These calipers transmit data via a 76 kbps synchronous serial protocol, requiring precise timing. Python proved inefficient, so the code was rewritten in C for better performance.
The calipers output two 24-bit values with a resolution of 0.00124 mm—eight times finer than their displayed 0.01 mm resolution. One value provides absolute positioning within a 5 mm range for long-term tracking.
Voltage level shifting was a challenge, as the calipers' 1.5V logic was below the Pi’s 1.8V threshold. A resistor-based solution adjusted signal levels. Electrical noise from servos caused instability, which was mitigated using grounding, capacitors, and debounce logic. Thousands of samples were analyzed, revealing quantization effects, but long-term averaging achieved micron-level precision.
Comparisons with a linear sensor confirmed 0.01 mm accuracy. Caliper data rates varied from 3 to 10 updates per second.
This experiment showcased a cost-effective CNC calibration method, addressing both hardware and software challenges to achieve high precision.
