CNC Machining DFM: A Practical CAM Review Checklist
CNC quotes that vary by 40% on the same drawing usually mean different assumptions about tool access, setups, and tolerances — not just hourly rates. A structured DFM/CAM review before release catches unreachable radii, unnecessary 5-axis features, and over-toleranced faces that inflate cycle time. This guide covers what to check on aluminum and steel parts for industrial and IoT products.
Why CNC DFM Differs from Sheet Metal or Molding
CNC machining removes material — every internal corner needs a tool that fits. Deep pockets, thin walls, and small radii drive tool length, chatter, and deflection. Unlike injection molding, there is no "fill" forgiveness: if a 2 mm radius is modeled but the shop uses 3 mm end mills as standard, you pay for extra setups or EDM.
Start reviews with the shop's preferred tool library: corner radii, max depth-to-diameter, and minimum wall thickness for your alloy.
Tool Access, Setups, and Feature Order
Setup count dominates cost on low-volume parts. Ask: can all critical features be reached from two orientations? Are undercuts necessary or can splits use inserts?
Deep pockets: Keep depth ≤ 4× tool diameter where possible; add floor draft or split the pocket.
Tapping and holes: Coordinate thread depth with blind-hole drill limits; avoid partial threads in thin walls.
Chamfers vs fillets: External fillets often need ball-end time; replace with chamfers on non-cosmetic edges when ID allows.
Drawings That Match Shop Reality
Over-dimensioned drawings slow programming and invite dispute. Datum on functional interfaces; ISO 2768-mK or equivalent for general machining; tighten only pin bores, gasket lands, and mating faces.
Include material, temper, and finish (anodize type/thickness) on the title block. For assemblies, document screw torque and thread-locker where relevant.
CAM Review and Quote Alignment
Before cutting steel, request a CAM sanity check or run AI DFM analysis on STEP exports. Align three quotes on the same revision with a DFM change log — quote spread should collapse when geometry is unambiguous.
Ohmframe supports CNC DFM reviews, drawing cleanup, and supplier-ready packages for industrial IoT, medical, and consumer metal parts.