Tài nguyên/Machining Documentation

CNC Machining Documentation

Comprehensive reference for CNC machining tolerances, surface finishes, material machinability, thread standards, and design guidelines — everything you need to design parts for precision machining.

1. General Tolerances — ISO 2768

ISO 2768 is the international standard for general tolerances on linear and angular dimensions. Use these tables as a quick reference for your designs.

Kích Thước Tuyến Tính (ISO 2768-1)

Kích Thước Danh Nghĩa (mm)	Tinh (f) +/-	Trung Bình (m) +/-	Thô (c) +/-
0.5 – 3	0.05 mm	0.1 mm	0.2 mm
3 – 6	0.05 mm	0.1 mm	0.3 mm
6 – 30	0.1 mm	0.2 mm	0.5 mm
30 – 120	0.15 mm	0.3 mm	0.8 mm
120 – 400	0.2 mm	0.5 mm	1.2 mm
400 – 1000	0.3 mm	0.8 mm	2.0 mm

Độ Phẳng & Độ Vuông Góc (ISO 2768-2)

Chiều Dài Danh Nghĩa (mm)	H (Tinh)	K (Trung Bình)	L (Thô)
≤ 10	0.02 mm	0.05 mm	0.1 mm
10 – 30	0.05 mm	0.1 mm	0.2 mm
30 – 100	0.1 mm	0.2 mm	0.4 mm
100 – 300	0.2 mm	0.4 mm	0.8 mm
300 – 1000	0.3 mm	0.6 mm	1.2 mm

2. Surface Roughness Standards

Surface roughness (Ra) is measured in micrometers (µm). The achievable finish depends on the material, tooling, and machining parameters.

3.2

Ra 3.2 μm

Rough Machining

Non-critical surfaces, clearance faces, weld prep

1.6

Ra 1.6 μm

Standard Machining

General-purpose parts, moderate load surfaces

0.8

Ra 0.8 μm

Fine Machining

Bearing seats, sealing surfaces, fits & clearances

0.4

Ra 0.4 μm

Precision Finish

Sliding surfaces, hydraulic components, cosmetic faces

0.2

Ra 0.2 μm

Ultra-Precision

Optical surfaces, high-pressure seals, precision bearings

0.05

Ra 0.05 μm

Mirror Finish

Decorative, optical reflectors, medical implants

3. Material Machinability Reference

Machinability ratings help predict how easily a material can be cut. Ratings are relative to steel 1212 (100%).

Vật Liệu	Đánh Giá	Độ Khó	Ghi Chú
Brass C360	100%	Easiest	Benchmark material - highest speed, best finish
Aluminum 6061-T6	90%	Easy	Excellent chip formation, use polished flutes
Aluminum 7075-T6	70%	Easy	Slightly abrasive, carbide tooling recommended
Aluminum 5052	60%	Moderate	Gummy - use sharp tools, increased clearance
Carbon Steel 1018	55%	Moderate	BUE risk at low speeds, coolant required
Stainless Steel 303	50%	Moderate	Free-machining grade - sulfur improves chip break
Alloy Steel 4140	35%	Hard	Pre-hardened to 28-32 HRC, reduce speed 50% vs 1018
Stainless Steel 304	25%	Difficult	Work-hardens - rigid setup, constant feed essential
Stainless Steel 316	22%	Difficult	Similar to 304, use flood coolant, avoid dwell
Titanium Grade 5	18%	Very Difficult	Low thermal conductivity - slow speed, high feed, sharp carbide
Magnesium AZ91D	95%	Easy	Excellent machinability - fire safety precautions required
Copper C110	20%	Difficult	Extremely gummy - sharp HSS, high rake angle

4. Thread Standards & Tapped Hole Design

Standard thread specifications and design guidelines for CNC-machined tapped holes. Thread milling is recommended over tapping for tight-tolerance applications.

Metric Coarse (M)

Phạm vi: M2 - M48

Bước: 0.4 - 5.0 mm

General fastening, ISO standard

Metric Fine (MF)

Phạm vi: M8x1 - M48x3

Bước: 1.0 - 3.0 mm

Precision adjustment, thin-wall applications

UNC (Unified Coarse)

Phạm vi: #0 - 2"

Bước: 80 - 4.5 TPI

General fastening, ANSI standard

UNF (Unified Fine)

Phạm vi: #0 - 1-1/2"

Bước: 80 - 12 TPI

High-strength, vibration-resistant joints

NPT (Pipe Thread)

Phạm vi: 1/8" - 2"

Bước: Tapered 1:16

Fluid fittings, pneumatic connections

Thread Milling

Phạm vi: Any form

Bước: Any pitch

Best for hard materials, large diameters, blind holes

Hướng Dẫn Độ Sâu Ren

Độ sâu ren không được vượt quá 3× đường kính danh nghĩa đối với lỗ mù. Đối với lỗ thông, đảm bảo ít nhất 1,5× đường kính ăn khớp ren hoàn toàn. Phay ren được ưu tiên hơn taro đối với các chi tiết giá trị cao — một mũi taro gãy có thể làm hỏng toàn bộ chi tiết.

5. Design for CNC Machining — Quick Reference

Minimum Wall Thickness

0.5 mm for metals (aluminum). Increase to 0.8 mm for plastics. Walls thinner than 0.5 mm risk vibration and deflection.

Internal Corner Radii

Minimum R = tool radius (typically 0.5-3 mm). Sharp internal corners are impossible - always add a radius matching standard end mill sizes.

Cavity Depth

Max depth <= 4x tool diameter for standard end mills. Deeper cavities require extended-reach tooling and reduced feed rates.

Hole Diameter

Standard drill sizes recommended. Avoid non-standard diameters where possible. Minimum hole size: 0.5 mm for metals.

Undercuts

Standard undercuts require T-slot or dovetail cutters. Width limited to tool diameter. Design reliefs where possible.

Text & Engraving

Minimum text height: 1.5 mm for legible engraving. Use stick fonts (single-line). Avoid serif fonts at small sizes.

Thin Floor Sections

Minimum 0.5 mm floor thickness in metals. Thinner sections risk warping from machining stress or clamping force.

Setups & Orientations

Design parts to minimize setups. Each additional setup adds cost and datum error. Plan locating features.

6. Achievable Tolerances by Feature Type

Đặc Tính	Tiêu Chuẩn	Chính Xác	Ghi Chú
Linear dimension	+/-0.1 mm	+/-0.005 mm	ISO 2768-f standard; precision with measurement
Hole diameter	+/-0.05 mm	+/-0.005 mm	Reamed or bored holes achieve tighter tolerances
Hole position	+/-0.1 mm	+/-0.02 mm	Depends on machine - 5-axis is most accurate
Flatness	0.05 mm	0.01 mm	Per 100 mm; larger surfaces need face milling
Perpendicularity	0.05 mm	0.01 mm	Single-setup machining preferred
Concentricity	0.05 mm	0.01 mm	Single-setup boring achieves best results
Surface finish	Ra 0.8 um	Ra 0.2 um	Post-process: polishing, lapping, superfinishing
Angular tolerance	+/-0.5 deg	+/-0.05 deg	5-axis direct; 3-axis requires sine fixturing
Thread fit class	6H / 2B	4H / 3B	Thread milling for precision classes