DFM Guidelines for CNC Machining
Design for Manufacturability rules we use daily to reduce cycle time, avoid tooling issues, and cut costs without affecting function.
I've seen thousands of designs come through our shop. The ones that machine well have one thing in common: the designer understood what a cutting tool can and can't do. Here's what I wish every engineer knew before sending us a STEP file.
Design Parameter Reference Table
| Parameter | Good Design | Problematic | Impact | Recommendation |
|---|---|---|---|---|
| Wall Thickness | > 1mm (metal), > 1.5mm (plastic) | 0.3-0.8mm walls | Vibration, deflection, poor finish | Increase wall thickness or add ribs |
| Internal Corner Radius | > 3mm (16mm end mill) | Sharp internal corners | Requires EDM or smaller tool + slow feed | Design radius = cutter dia / 2 + 0.5mm |
| Hole Depth | < 3× diameter (standard drill) | > 10× diameter | Peck drilling, chip evacuation issues | Use gun drilling or step-drill |
| Pocket Depth | < 4× tool diameter | > 6× tool diameter | Tool deflection, poor surface, long cycle | Design shallow pockets or split into features |
| Thread Depth | 1.5-2× diameter | > 3× diameter | Tap breakage, slow threading | Use thread inserts for deep threads |
| Undercuts | None or minimal | Complex undercuts | Special tooling, 5-axis, or EDM | Design as separate part or use standard tool |
| Tolerance Density | 20% features toleranced | 80%+ features toleranced | Unnecessary inspection cost | Only tolerance critical features |
See: Tolerances Guide · Surface Finishes · GD&T Guide
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