Even with modern CNC equipment, machining problems still trace back to a handful of root causes. Below are the most common issues we see, what causes them, and how to prevent them.
1. Overcutting of the workpiece
Causes:
- Tool deflection — the tool lacks sufficient strength, or is too long or too small, causing deflection
- Operator error, e.g. uneven allowance left on the part (0.5 mm left on the side of a curved surface but only 0.15 mm on the bottom)
- Improper cutting parameters
Improvements:
- Tool selection principle: use a larger, shorter tool whenever possible
- Add a corner-cleaning program and keep the allowance as even as possible — ensure the side and bottom allowances are the same
- Use the machine’s feed-rate override function and let the operator fine-tune the speed for optimal cutting performance
2. Centering and manual operation errors
Causes:
- Inaccurate manual operation by the operator
- Centering performed at inconsistent points or heights
Improvements:
- Manual operations should be repeatedly checked, and centering should be done at the same point and height
- Check whether the mold sides are perpendicular with a dial indicator; significant deviations should be discussed with the mold technician
3. CNC crashes
Causes:
- Incorrect Z-axis tool setting depth
- Incorrect centering or data entry (e.g. failure to account for tool radius when measuring from one side)
- Using the wrong tool (e.g. a D10 tool instead of D4)
- Running the wrong program (e.g. A7.NC instead of A9.NC)
- Incorrect manual control direction on the handwheel
- Wrong direction during manual rapid feed (e.g. pressing +X instead of −X)
Improvements:
- Pay attention to the tool setting depth for different reference positions (bottom, top, analyzed surface)
- Double-check tool numbers and program names before cycle start
- Verify movement direction before any manual rapid feed
The takeaway
Most CNC issues are preventable with disciplined setup: even allowances, correct tool selection, verified tool settings and checked programs. At SeaForest, our machinists follow standardized setup and in-process inspection procedures on every job — which is how we hold tolerances as tight as ±0.01 mm across production runs.
Have a part that others said couldn’t be made? Send us your drawings — our engineering team will review the geometry and recommend the right process.