Tolleranze di Lavorazione CNC —
Norme, Accoppiamenti e Tolleranze Geometriche
Una guida pratica alle tolleranze, finiture superficiali e GD&T per pezzi lavorati CNC. Comprendere queste norme aiuta a progettare pezzi fabbricabili, misurabili ed economicamente efficienti.
Capire le Tolleranze di Lavorazione CNC
Una tolleranza è il range ammissibile di variazione dimensionale per una caratteristica prodotta. If a shaft is designed at 25.000 mm with a tolerance of ±0.01 mm, any shaft measuring between 24.990 mm and 25.010 mm is acceptable. Tolerances exist because perfect accuracy is physically impossible — and unnecessary: most parts function perfectly within a defined range.
Tighter tolerances cost more — not because precision is inherently expensive, but because it requires slower feed rates, additional finishing passes, higher-grade tooling, and more time on CMM inspection. A ±0.005 mm hole might require a finish boring operation and 100% CMM inspection where a ±0.05 mm hole is inspected by sampling. Specify only what function demands.
The table below covers Ginwate's standard, tight and precision tolerance capabilities across our main processes. Where no tolerance is called out on a drawing, we default to ISO 2768-m (medium) for linear dimensions and ISO 2768-K for geometric tolerances.
Capacità di Tolleranza per Caratteristica
Intervalli di tolleranza standard, stretta e di precisione per tutti i principali tipi di caratteristiche. Values for aluminum unless otherwise noted.
| Feature | Standard | Tight | Precision |
|---|---|---|---|
| General Linear Dimensions | ±0.1 mm | ±0.01 mm | ±0.005 mm |
| Hole Diameter (milled) | ±0.05 mm | ±0.01 mm | ±0.005 mm |
| Shaft / Pin Diameter (turned) | ±0.05 mm | ±0.005 mm | ±0.003 mm |
| Bore Diameter (turned) | ±0.05 mm | ±0.005 mm | ±0.003 mm |
| Swiss CNC Diameter | ±0.01 mm | ±0.005 mm | ±0.003 mm |
| 5-Axis Compound Features | ±0.02 mm | ±0.005 mm | ±0.001 mm |
| Flatness | 0.1 mm / 100mm | 0.02 mm / 100mm | 0.005 mm / 100mm |
| Parallelism | 0.1 mm | 0.02 mm | 0.005 mm |
| Perpendicularity | 0.1 mm | 0.02 mm | 0.01 mm |
| Concentricity / Runout | 0.05 mm TIR | 0.01 mm TIR | 0.005 mm TIR |
| True Position (milled hole) | ±0.1 mm dia. | ±0.02 mm dia. | ±0.01 mm dia. |
| Thread Pitch Diameter | 6H / 6g class | 5H / 5g class | 4H / 4g class |
| Surface Finish Ra | 1.6–3.2 μm | 0.8 μm | 0.4 μm |
| Surface Finish Rz | 12.5 μm | 6.3 μm | 1.6 μm |
| Angular Tolerance | ±0.5° | ±0.1° | ±0.05° |
Precision tolerances require DFM review, additional inspection and may increase lead time. Availability depends on material, part geometry and feature size. Contact us to confirm.
Gradi di Tolleranza ISO
ISO 2768 definisce le tolleranze generali per le dimensioni lineari. Gradi di precisione superiori costano di più e aumentano i tempi di consegna.
Finitura Superficiale (Valori Ra)
Ra (rugosità media) è la specifica di finitura più comune. Le nostre macchine raggiungono Ra 0,4 μm standard e Ra 0,2 μm con rettifica fine.
Tolleranze Geometriche (GD&T)
GD&T fornisce un linguaggio per comunicare l'intenzione progettuale oltre le semplici dimensioni lineari.
Referenced to a machined datum face. Use 5-axis for compound angle perpendicularity.
Requires precision datum registration. Achievable on grinding to 0.002 mm.
Affected by fixturing spring and material stress relief. Grinding recommended for tight flatness.
Measured in CMM. Achievable through cylindrical grinding after turning.
Combined roundness + straightness. Grinding post-turning for <0.005 mm.
Use coordinate boring or jig boring for ≤0.02 mm. 5-axis reduces repositioning error.
Measured during turning or on CMM. Grinding after turning for <0.005 mm TIR.
Full surface runout. Requires accurate live-centre between-centres turning.
5-axis machining and tilted-head boring for tight angular features.
Complex surface profiles verified on CMM. 5-axis recommended for bilateral tolerance.
All GD&T measurements performed on Zeiss CMM with Calypso measurement software. First-article inspection reports available with FAIR documentation.
Tolleranze Raggiungibili per Materiale
Material properties — thermal expansion, machinability, and springback — affect achievable tolerances. Here are the tightest tolerances we routinely hold for each material.
| Material | Tightest Achievable | Notes |
|---|---|---|
| Aluminum (6061, 7075) | ±0.003 mm | Best machinability. Standard tight tolerances routinely achieved. |
| Brass (C360) | ±0.003 mm | Free-machining. Excellent dimensional stability. |
| Stainless Steel 303 | ±0.005 mm | Good machinability vs other SS grades. Work-hardening limited. |
| Stainless Steel 316L | ±0.005 mm | Work-hardens. Requires sharp tools and controlled feeds. |
| Titanium Ti-6Al-4V | ±0.005 mm | Low thermal conductivity increases tool wear. Achievable with correct tooling. |
| 4140 Alloy Steel | ±0.005 mm | Heat treat distortion possible — machine after final heat treatment where possible. |
| PEEK | ±0.01 mm | Plastic creep under clamping load. Requires careful fixturing strategy. |
| Delrin (POM) | ±0.01 mm | Absorbs moisture — allow for environmental dimensional change in tight-fit applications. |
Consigli di Progettazione per le Tolleranze
Applicare questi principi riduce i costi e i tempi garantendo che i pezzi soddisfino i requisiti funzionali.
- Apply tolerances only where functionally required — tighter-than-necessary tolerances increase cost significantly (±0.01 mm may cost 2–5× more than ±0.1 mm for the same feature).
- Use GD&T rather than coordinate tolerances for mating features — true position controls location far better than bilateral +/- dimensions on X and Y separately.
- Provide a datum hierarchy on your 2D drawing — without clear datums, our engineers cannot guarantee that measured dimensions will match design intent.
- Specify surface finish only on functional surfaces — 'all surfaces Ra 0.8' adds unnecessary cost and lead time. Leave non-functional faces as machined.
- Design features to be accessible from one setup direction where possible — repositioning introduces additional error. 5-axis helps when this is unavoidable.
- Consider material spring-back for thin-walled parts — aluminum walls <2 mm and titanium walls <1.5 mm can deflect during cutting, effectively moving the surface from its nominal position.
- Thread callouts must specify form, class and depth — 'M8 thread' alone is ambiguous. Use 'M8×1.25 – 6H × 20mm deep' to be complete.
- For press or interference fits, specify the fit class (H7/p6, H7/n6) and let us calculate the actual dimension limits — ISO 286 fit notation is unambiguous and internationally understood.
Revisione DFM Gratuita
Carica il tuo disegno con la richiesta di preventivo. I nostri ingegneri esaminano ogni file per conflitti di tolleranza e problemi di progettazione — gratuitamente, prima dell'inizio della produzione.
Carica File per la RevisioneReport di Ispezione Disponibili
- First Article Inspection Report (FAIR)
- CMM Dimensional Report (Zeiss)
- Surface Roughness Certificate (Ra/Rz)
- Material Test Report (MTR / Mill Cert)
- PPAP Level 1–3 Documentation
- AS9102 First Article Inspection
Servizi Correlati
Fresatura CNC
Tolleranze e capacità di fresatura 3, 4 e 5 assi.
Tornitura CNC
Specifiche di tolleranza tornitura e Swiss e limiti di diametro.
Lavorazione 5 assi
Tolleranze più strette su geometria composta in un solo staffaggio.
Tutte le Capacità
EDM, rettifica, ispezione CMM e panoramica completa del parco macchine.
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