What determines the cost of CNC machined parts?

Quick Answer

CNC machining costs are primarily driven by six factors: material type and availability, part complexity and machining time, tolerance requirements, order quantity, surface finishing, and setup/programming costs. Optimizing these factors can reduce part costs by 20-40%.

1. Material Selection

Material cost varies significantly. Aluminum 6061 is typically the most economical metal option, while titanium, stainless steel 316, and engineering plastics like PEEK command higher prices. Material availability also affects cost -- standard stock sizes are cheaper than custom dimensions. Material typically accounts for 10-20% of total part cost.

2. Part Complexity and Geometry

Complex geometries requiring multiple setups, tight internal corners, deep cavities, or thin walls increase machining time and cost. Parts designed for 3-axis machining are most economical. Adding 4-axis or 5-axis operations increases hourly rates. A simple bracket might machine in 5 minutes, while a complex impeller could take 2+ hours.

3. Tolerance Requirements

Standard CNC tolerances of ±0.005" are most cost-effective. Tightening to ±0.001" adds 15-25% cost. Super-precision tolerances of ±0.0002" can double machining time due to slower feeds, extra tool passes, and additional inspection. Only specify tight tolerances where functionally necessary.

4. Order Quantity

Quantity affects per-unit cost through setup amortization. A 1-piece prototype might cost $200, while 100 pieces might cost $25 each, and 1,000 pieces could be under $10 each. The optimal price break typically occurs between 500-1,000 units for CNC machining.

5. Surface Finishing

As-machined finish is included in the base cost. Additional finishing like anodizing ($), powder coating ($$), electropolishing ($$$), or plating ($$$) adds cost. Combining finishing with the machining supplier saves logistics and handling fees.

Why Choose SOMI Custom Parts

At SOMI Custom Parts, we provide transparent pricing with no hidden fees. Our engineering team offers free DFM analysis to identify cost-saving design modifications before quoting. We also suggest alternative materials and tolerance relaxations that maintain functionality while reducing costs. Request a free quotation and DFM review today.

Case Study

A consumer electronics company initially quoted $18.50 per unit for an aluminum enclosure with tight tolerances on non-critical surfaces. SOMI's DFM review recommended relaxing six tolerances from ±0.001" to ±0.005" and changing one surface finish specification. The revised quote was $11.20 per unit -- a 39% savings with no impact on functionality or appearance.

Industry Data

According to a 2025 cost analysis by the Society of Manufacturing Engineers, material selection accounts for 10-20% of CNC part cost, machining time for 50-70%, setup for 5-15%, and finishing for 5-20%. Optimizing only tolerance specifications can reduce total cost by 15-25% (SME, 2025).

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