Most CNC problems fall into a few categories with predictable causes. Working through them systematically — changing one variable at a time — is the fastest route to a fix.
Common problems
| Problem | Likely causes | First fixes |
|---|---|---|
| Chatter / vibration | Too much stickout, bad speed, weak workholding | Shorten tool, change RPM, tighten setup |
| Poor finish | High feed, dull tool, no finish pass | Light finishing pass, sharp tool, climb mill |
| Broken tools | Overload, recutting chips, full-width cuts | Lighten cut, clear chips, trochoidal corners |
| Wrong dimensions | Tool deflection, wear offsets, thermal growth | Spring pass, update offsets, let machine warm up |
Start with rigidity (stickout, workholding) and speeds/feeds, since they cause the majority of issues. For dimensional errors, separate consistent errors (offset/tool-size problems) from varying errors (deflection, heat, or workholding movement — fix the root cause).
Frequently asked questions
What causes most CNC problems? Insufficient rigidity and wrong speeds/feeds.
How do I fix chatter? Reduce stickout, adjust spindle speed, improve workholding.
Why are my parts the wrong size? Consistent errors are usually offsets; varying errors point to deflection or movement.
Keep a simple log of what you changed and what happened — tool, stickout, speed, feed, and result. Patterns emerge fast, and next time the same symptom appears you’ll fix it in one move instead of starting the trial-and-error over again.