Specifying electroplating on precision parts isn’t just about corrosion resistance — it’s about understanding dimensional impact. With 15+ years finishing parts for aerospace and medical sectors, small plating decisions can dramatically affect tolerances.
Most electroplating adds 0.0002″ to 0.002″ thickness depending on the finish type and part geometry. This buildup affects press fits, threaded connections, and mating surfaces. Critical dimensions need tolerance adjustments or selective masking to maintain fit and function.
Find out which plating types add thickness, how to protect key features, and when selective plating works best—plus real CNC tolerance data.
Table of Contents
Is electroplating cheaper than anodizing?
Yes, electroplating costs 30-50% less than anodizing for steel parts, but the savings depend on part complexity and volume. Zinc plating typically costs pennies per pound for simple steel parts, while Type II anodizing runs $2-4 per small aluminum part.
Real Cost Comparison (100 steel brackets, 3″x2″):
- CNC machining + zinc plating: ~$200-300 total
- Same parts in aluminum + anodizing: ~$400-600 total
- Setup cost difference: Plating $50-75, anodizing $75-125
From our machining experience, the cost advantage shrinks with part complexity. Simple barrel-plated hardware costs pennies per pound, but rack-plated complex geometries can cost $0.25-1.00 per piece. Steel parts with deep pockets or blind holes need rack plating instead of cheaper barrel processing, which eliminates much of the cost advantage.
Hidden machining costs affect the comparison. Electroplating adds 0.0005″-0.002″ thickness, so we machine critical dimensions undersize to compensate. This adds 15-20% to machining time for parts with tight tolerances. Anodizing’s thinner 0.0002″-0.0008″ coating requires less machining adjustment, keeping production time lower.
Cost advantage disappears when:
- Parts require selective masking (adds $0.50-2.00 per part)
- Tight tolerances need post-plate machining
- Complex geometries force rack plating over barrel processing
- Volume exceeds 1000+ pieces (economies of scale favor anodizing)
Design Takeaway: Electroplating saves 30-50% on simple steel parts under 500 pieces. Choose anodizing when tight tolerances or complex masking eliminate the cost advantage, or when aluminum is required for weight/conductivity.
What materials work with electroplating?
Steel, brass, and copper electroplate directly without pre-treatment, while aluminum requires zincate conversion that dissolves the oxide layer and deposits zinc for plating adhesion. Aluminum cannot be electroplated directly because exposure to air causes an insulating aluminum oxide skin, requiring zincate treatment to replace it with zinc that accepts subsequent plating.
Direct Electroplating Materials:
- Steel (1018, 1045, 4140): Best compatibility, standard cleaning only
- Stainless Steel (304, 316): Good with acid activation step
- Brass/Copper: Excellent conductivity, no pre-treatment needed
- Cast Iron: Direct plating after degreasing and light etching
Aluminum requires special pre-treatment: The zincate process uses caustic soda and zinc oxide solutions that chemically dissolve aluminum oxide and deposit zinc immersion coating. Double zincating is essential for fine-grained deposits on some aluminum types – the first zincate is stripped with nitric acid, then re-zincated.
Critical machining considerations: Threaded features work well on steel – we typically machine Class 2A threads that maintain fit after standard zinc plating thickness. For aluminum, surface preparation includes thorough degreasing and sometimes bead blasting to remove heavy oxides before zincate treatment. Blind holes deeper than 3:1 aspect ratio plate unevenly regardless of substrate material.
Heat treatment sequence matters: Steel parts heat treat first, machine second, then plate to preserve material properties. Aluminum requires T6 heat treatment before any zincate processing to avoid compromising the conversion layer.
Design Takeaway: Specify steel substrates when electroplating offers the best functional combination. Choose aluminum only when weight reduction justifies the complex zincate pre-treatment requirements.
What's the most economical plating for low volumes?
Zinc plating costs 50-70% less than nickel or chrome for volumes under 500 pieces, with barrel processing offering the lowest cost at pennies per pound for simple parts. Barrel plating costs pennies per pound for small durable parts like stampings and fasteners, while rack plating requires labor to attach each part individually, making it more expensive.
Processing Method Cost Impact:
- Barrel plating: $0.10-0.50 per small part (simple shapes only)
- Rack plating: $0.50-2.00 per part (complex geometries, delicate parts)
- Setup minimums: $50-125 regardless of plating type
Barrel plating requires smaller equipment investment and is less labor-intensive than rack plating, resulting in lower process costs. Rack plating is more labor-intensive because each part must be attached to a rack using hooks or compression contacts.
Part geometry determines processing method: Barrel plating works for small, durable parts such as stampings and fasteners that can withstand tumbling action. Rack plating is preferred for delicate parts that might not withstand cascading motion, and for large or complex components.
Material cost comparison by plating type:
- Zinc: Most economical due to material abundance
- Nickel: 2-3x zinc cost, better corrosion resistance
- Chrome: 3-4x zinc cost, primarily for appearance/hardness
Volume break points for cost optimization: Simple parts under 200 pieces favor barrel zinc plating. Labor costs are an important part of plating costs, with rack plating being more labor-intensive than barrel plating . Above 500 pieces, economies of scale start favoring other finishes with better performance characteristics.
Design Takeaway: Choose zinc barrel plating for small, simple steel parts under 200 pieces where moderate corrosion protection meets requirements. Complex geometries requiring rack setup eliminate zinc’s primary cost advantage.
How thick does electroplating get?
Most electroplating adds 0.0002″-0.002″ (5-50 µm) thickness, with zinc at 0.0005″-0.001″, nickel at 0.0003″-0.0015″, and chrome up to 0.002″ for decorative finishes. Electroplating layers range from a few micrometers to several tens of micrometers, with thickness variations occurring from point to point on parts due to geometry.
Standard Thickness by Plating Type:
- Zinc: 0.0005″-0.001″ (12-25 µm) typical for corrosion protection
- Nickel: 0.0003″-0.0015″ (8-38 µm) for wear resistance
- Chrome decorative: 0.00005″-0.0005″ (1-12 µm) over nickel base
- Chrome hard: Up to 0.002″ (50 µm) for wear applications
Can I specify thinner plating to save cost? Yes, but with performance trade-offs. Plating thickness specifications include average, range, minimum, or maximum requirements, with average providing a target within ±75 µin window. Zinc can run as thin as 0.0002″ for indoor applications, reducing material cost 30-40% versus standard 0.0005″ thickness.
How do I specify thickness on drawings? Areas requiring minimum plating thickness should be labeled on part drawings or noted on sample pieces, as significant surfaces are normally visible and subject to wear. Specify dimensional requirements as “before plating” and design necessary fit based on plating thickness range.
Thickness verification methods: Thickness can be measured at plater’s discretion unless measuring locations are indicated on prints, with considerable point-to-point variation depending on part geometry. Use magnetic thickness meters for ferrous substrates or X-ray fluorescence for precise measurement.
Design Takeaway: Specify thickness requirements and measuring locations on drawings. Use minimum functional thickness to control cost, but ensure adequate performance for your application environment.
Will plating affect my tight tolerances?
Yes, electroplating adds 0.0002″-0.002″ thickness that requires machining compensation of 0.0008″-0.0015″ undersize on critical dimensions to maintain fit after coating. Surface coating processes can compromise tolerance, requiring margin allowances in press fits, and plating affects machining tolerance significantly.
Should I machine before or after plating? Always machine critical dimensions before plating. Specify dimensional requirements as “before plating” and design necessary fit based on plating thickness range rather than requiring manufacturing to compensate afterward. Post-plate machining removes the protective coating and defeats the purpose.
Tolerance compensation by feature:
- Press fits: Machine shafts 0.0008″-0.0015″ undersize for standard zinc plating
- Threaded holes: Machine to Class 3A to achieve Class 2A after plating
- Bearing bores: Add 0.001″ to diameter, then machine to size after plating if critical
- Mating surfaces: Allow 0.001″-0.002″ for buildup variation across complex geometry
Can I plate assembled parts? Generally no for tight-tolerance assemblies. Plating and finishes involve adding material to part surfaces and can significantly affect machining tolerance. Press-fit assemblies may seize during plating due to thickness buildup in the interface.
What if parts don’t fit after plating? Prevention is better than cure. Common issues include: threads too tight (drill/tap larger initially), press fits too loose (machine tighter initially), or features out of tolerance (specify critical dimensions clearly). Hard chromium-plated areas on precision parts are often ground to final tolerance after plating when dimensional accuracy is critical.
How tight can I specify tolerances and still plate? Standard CNC tolerances of ±0.005″ work well with electroplating. Tighter tolerances like ±0.002″ require careful pre-plating compensation and may need post-plate operations.
Design Takeaway: Machine all critical dimensions 0.0008″-0.0015″ undersize before plating. Specify “dimensions before plating” on drawings. For precision assemblies requiring ±0.002″ or tighter, consider electroless nickel for uniform thickness or plan post-plate machining operations.
Can I get different colors with electroplating?
Yes, electroplating offers various colors through different metals and post-treatments, with zinc providing silver, yellow, black, or olive finishes, nickel giving silver-white appearance, and chrome offering bright silver reflective surfaces. Zinc plating colors are achieved through passivation treatments after plating, with clear/blue for natural metallic look, yellow/gold for iridescent hue, and black for darker aesthetic.
Color choice significantly impacts performance and cost. Yellow chromate provides better corrosion resistance (72-96+ hours salt spray) than clear passivation (24-72 hours). Chrome provides the best appearance retention and doesn’t change color over time, maintaining reflectivity better than silver or nickel. Black zinc typically fades to gray within 6-12 months outdoors.
Standard electroplating colors don’t match RAL or Pantone standards – zinc yellow appears more golden than paint equivalents. For precise color matching, plan on plating plus painting rather than relying on plating color alone. Colored options add 15-25% to basic plating costs due to additional processing steps.
Drawing specification requires exact passivation callouts (e.g., “Fe/Zn8/CM3” for black trivalent chromate) and environmental requirements like RoHS compliance.
Design Takeaway: Choose colors based on environment first, aesthetics second. Chrome offers best appearance durability but costs 3-4x more than zinc options.
Can plating handle complex geometries?
Electroplating struggles with complex geometries due to current density variations, with sharp edges receiving 2-3x more buildup than recessed areas, and blind holes deeper than 1:1 aspect ratio getting poor coverage or no plating. Current density increases at sharp edges leading to excessive coating buildup, while recessed areas experience the “edge effect” causing uneven thickness distribution.
Sharp edges must be rounded to about 10% of material thickness or less than 0.005″ radius to reduce current concentration. Add weep holes near bottom of blind holes deeper than the diameter to improve solution exchange and plating coverage. Parts must be plated before final assembly when possible – assembled units often fail due to poor solution circulation.
Design limits for reliable electroplating: maximum hole depths of 3x diameter, internal corner radii no smaller than 0.005″, and avoid nested geometries that trap air. Electroplating will not plate all the way into holes less than 0.5″ deep and 0.100″ diameter wide. Beyond these limits, consider electroless plating or alternative coatings.
Design Takeaway: Round all edges to 0.005″ minimum radius, add weep holes to blind features, and plan plating before assembly. For parts exceeding these geometry limits, choose alternative coatings or redesign with more generous features.
How do I specify selective plating?
Selective plating requires masking specific areas and adds $0.50-2.00 per part in labor and materials, but reduces overall costs by limiting expensive metals to functional areas only. Masking prevents plating on designated areas using plugs, tapes, or liquid maskants, with costs varying by tolerance requirements and application complexity.
Selective plating reduces material consumption by plating only required areas, cutting expensive metal costs and waste disposal expenses significantly. Break-even typically occurs with gold/silver plating on 50+ pieces or when preventing plating buildup on critical tolerance features.
Precision capabilities: liquid maskants achieve ±0.002″ boundaries on flat surfaces, but expect ±0.005″ as realistic for most applications. Tolerances of selective plating application dictate mask type and method – custom fixtures may be needed for tight tolerance critical applications. Complex masking adds $200-500 setup cost but enables precise feature control.
Mask failures during plating create expensive rework or scrap. Drawing specification must clearly define plated versus unplated areas, boundary tolerances, and include notes like “Plate contact areas only per attached detail drawing.”
Design Takeaway: Use selective plating for expensive metals or critical tolerance features. Plan for ±0.005″ boundary precision, include proper drawing callouts, and consider setup costs versus material savings for production volumes over 100 pieces.
Conclusion
Electroplating thickness affects tolerances and requires careful design planning, but proper material selection, geometry optimization, and process sequencing ensure successful results. From steel compatibility to selective masking, each decision impacts both performance and cost. Contact us to explore manufacturing solutions tailored to your electroplated component requirements.
Frequently Asked Questions
Aluminum requires expensive zincate pre-treatment that adds complexity and cost. For most applications, anodizing aluminum proves more practical and cost-effective than electroplating. Choose steel substrates when electroplating offers the best functional and economic combination.
Selective plating justifies its $0.50-2.00 per part cost when using expensive metals like gold or silver, or when preventing buildup on critical tolerance features. Break-even typically occurs above 50-100 pieces for precious metals. Include clear drawing callouts defining plated versus unplated areas.
Chrome provides the best color retention outdoors, maintaining its bright silver appearance for years. Zinc colors like black typically fade to gray within 6-12 months in outdoor environments. Yellow chromate offers better durability than clear but still degrades over time compared to chrome.
Round all edges to 0.005″ minimum radius and add weep holes to blind features deeper than 1x diameter. Parts exceeding 3x depth-to-diameter ratios or having sharp internal corners under 0.002″ radius should use alternative coatings like anodizing or remain uncoated.
Yes, zinc plating adds 0.0005″-0.001″ thickness that can shift press fits from interference to clearance. Machine shafts 0.0008″-0.0015″ undersize to compensate. Threaded holes may require machining to Class 3A to achieve Class 2A fit after plating. Always machine critical dimensions before plating.
For most CNC machined parts, ±0.005″ works well with standard electroplating processes. Tighter tolerances like ±0.002″ require careful pre-plating compensation and may need post-plate operations, significantly increasing costs. We recommend tolerancing only critical features tightly and keeping others at standard levels.
