Why do tight tolerances increase CNC machining costs?
Why Do Tight Tolerances Increase CNC Machining Costs?
Tight tolerances—typically defined as ±0.01 mm or finer—are essential for high-performance components but significantly impact CNC machining costs. At Neway, we apply tolerance engineering based on functional necessity, ensuring that precision is delivered only where it adds value. Here's why tight tolerances increase cost, and how buyers can optimize for performance without overspending.
Slower Machining Speeds and Multiple Passes
Achieving tight tolerances requires reducing cutting speeds and feed rates to prevent tool deflection, heat buildup, and vibration. This often doubles or triples the machining time compared to general tolerance work. In many cases, additional semi-finish and finish passes are programmed to gradually approach the final dimension.
High-Precision Tooling and Tool Wear Compensation
Parts requiring ±0.005 mm or better must be cut using calibrated tools such as diamond-coated end mills, ultra-sharp inserts, or ground finishing tools. These tools cost more and wear faster. Tool wear compensation routines and in-process measurement systems further increase cost.
Specialized Fixtures and Thermal Control
Tight tolerances on critical dimensions often require custom fixtures with precise datum control and stable clamping. Additionally, temperature variation of just 5°C can alter metal dimensions by 5–10 microns. Therefore, production environments must support CNC machining service under thermal stability conditions.
Increased Inspection and Quality Control
Dimensional verification of high-precision parts requires CMMs, laser micrometers, or optical comparators. Quality control time increases by 3–5× due to multiple inspection points, documentation, and tolerance validation per ISO 2768-fH or AS9100 standards.
More details: What is the Tightest Tolerance Neway Can Achieve
Higher Scrap Rate Risk
Minor tool wear or thermal drift can cause deviations beyond ultra-tight limits, especially in superalloy machining. Rejections or reworks increase the effective cost per part, which is built into price quotations.
Case Example: Aluminum 7075 Bracket (±0.01 mm vs ±0.05 mm)
Tolerance Level | Machining Time | QA Time | Cost Increase |
|---|---|---|---|
±0.05 mm (standard) | 25 min | 5 min | — |
±0.01 mm (tight) | 55 min | 20 min | +70–120% |
Tighter specs result in longer cycle times, more tool checks, and QA cycles.
Design Recommendation
Apply tight tolerances only to mating, sealing, or rotating features. Use looser tolerances (±0.1–0.2 mm) on non-functional surfaces. Discuss with your CNC partner to identify critical dimensions and simplify inspection.
Manufacturing Services You May Need
Neway offers comprehensive CNC machining solutions including tight-tolerance production, CMM inspection, and superalloy part machining. We serve aerospace, medical, and industrial sectors with ±0.01 mm precision and full quality traceability.
