How does different surface finishing treatments affect the total cost of custom parts?

Quick Answer

Surface finishing adds 5-50% to the base CNC machining cost. As-machined: 0% added cost. Bead blasting: 2-5%. Anodizing Type II: 5-10%. Powder coating: 8-15%. Zinc/nickel plating: 10-20%. Electropolishing: 15-30%. Hand polishing/buffing: 20-40%. Hard coat anodizing (Type III): 15-25%. Chrome plating: 25-50%. Higher quantities reduce per-unit finishing cost significantly. SOMI provides transparent cost breakdowns showing finishing costs separately.

Cost by Finishing Type

Bead blasting: $2-15 per part. Setup cost: minimal. Suitable for all quantities. Anodizing Type II: $5-30 per part, $50-200 minimum batch charge. Color adds $2-10. Quantity discount: 30-50% at 1,000+ parts. Powder coating: $8-40 per part, $100-300 minimum. Color changes add setup. Best for 100+ parts. Electropolishing: $5-50 per part. Minimum $100-200. Batch process, so cost per part decreases significantly at higher quantities.

Hidden Cost Factors

Part size: Larger parts cost more to finish due to more material, longer processing time, and larger tanks/fixtures needed. Geometry complexity: Parts with deep internal cavities, blind holes, and complex internal features may require specialized fixturing or manual touch-up. Tape/plugging: Areas that must remain uncoated (conductive surfaces, sealing surfaces) require masking -- adding $2-20 per part. Quality level: Cosmetic vs functional specifications affect cost. A Class A automotive finish costs 50-100% more than a standard industrial finish.

Cost Savings Strategies

Design parts with the finish in mind: avoid sharp corners that cause coating buildup, specify minimum shelf life if appearance is critical, and combine parts of the same finish in a single batch. Using the same supplier for both machining and finishing eliminates packaging, shipping, and handling costs between processes, typically saving 10-20% of total finishing cost.

Why Choose SOMI Custom Parts

At SOMI Custom Parts, we manage finishing in-house or through closely integrated partner facilities, eliminating the cost and risk of shipping parts between separate suppliers. Our quoting system provides detailed finishing cost breakdowns and recommends cost-saving alternatives. For example, if your design specifies electropolishing, our engineers may suggest whether bead blasting would achieve the required appearance at 50% lower cost.

Case Study

A client specified electropolishing for 500 CNC-machined 316L stainless steel parts at a quoted finishing cost of $12 each. SOMI's engineers reviewed the application and determined that passivation + bead blasting would achieve the same corrosion resistance and appearance at $4 each -- saving $4,000 on the order. The client approved the alternative, and the parts passed all functional requirements.

Industry Data

Finishing costs represent an average of 15-25% of total CNC part cost (NAMRC Machining Survey, 2025). Companies that integrate finishing with machining through a single supplier report an average 18% reduction in total part cost and 30% shorter lead times compared to using separate finishing vendors (MFG Monthly, 2025).

Related Questions

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