How to Prepare Technical Drawings for CNC Machining RFQ to Get Accurate Quotation

1. Why Complete Drawings Matter for Your RFQ

1.1 The Core Principle

When sending an RFQ (Request for Quotation) to a CNC machining manufacturer, a complete and clear technical drawing is the most critical document.

1.2 The Cost of Incomplete Drawings

Incomplete or ambiguous drawings often lead to:

• Delayed replies
• Inaccurate pricing
• Prototype rework
• Extra production costs

1.2.1 The Goal

If you want to receive a precise quotation quickly, your technical drawings need to cover all necessary manufacturing information.

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2. Choose the Right Drawing File Format

2.1 The General Rule

CNC suppliers prefer vector engineering files rather than simple image screenshots.

2.2 Recommended Formats

2.2.1 2D Drawing

PDF is recommended for dimension checking.

2.2.2 3D Model

STEP or IGES files are the best choice.

2.2.2.1 Why STEP/IGES

These formats allow machinists to directly import the model into CAM software to calculate:

• Material consumption
• Machining time
• Tool paths

2.3 Formats to Avoid

JPG and PNG pictures alone cannot support accurate cost evaluation, which will force manufacturers to estimate roughly and cause price deviation.

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3. Mark Full Dimensions & Tolerances

3.1 Dimension Labeling

All key features must have clear dimension labels.

3.1.1 What to Mark

• Overall size
• Hole position
• Thread size
• Groove depth
• Chamfer radius

3.2 Tolerance Definition

3.2.1 Geometric Tolerances

Define geometric tolerances for precision areas, such as:

• Flatness
• Concentricity
• Perpendicularity

3.2.2 General Tolerance Standards

Specify general tolerance standards, for example ISO 2768, or custom tolerance requirements.

3.2.2.1 Cost Implication

Tighter tolerances raise machining cost.

3.2.2.2 Recommended Practice

• Only add strict tolerance marks for functional surfaces
• Keep non-critical features at standard tolerance to save budget

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4. Specify Material Information

4.1 Where to Write It

Clearly write down the material grade on your drawing or RFQ sheet.

4.2 Material Categories

4.2.1 Metals

• 6061-T6 aluminum
• 7075 aluminum
• 304 stainless steel
• C360 brass

4.2.2 Plastics

• POM
• PEEK
• PC
• Nylon and other engineering plastics

4.3 Surface Treatment

If surface treatment is required, list it together:

• Anodizing
• Powder coating
• Passivation
• Bead blasting
• Electroless nickel plating

4.3.1 Why It Matters

Different materials and finishes greatly affect machining difficulty and unit price.

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5. Note Special Requirements

5.1 Where to Add Notes

Add special notes on the drawing for any extra requirements.

5.2 Typical Special Notes

• Deburring requirement
• Sharp edge removal
• Thread specification and depth
• Inspection requirement: CMM test, first article inspection (FAI) report
• Packaging requirement for delicate precision parts
• Batch type: prototype, low volume run or mass production

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6. Common Mistakes to Avoid

6.1 List of Frequent Errors

• Missing 3D model and only providing blurry 2D screenshots
• Overlooking tolerance marks on key mating surfaces
• No material or surface finishing description
• Conflicting dimension data between 2D drawing and 3D file
• Changing drawing version without updating the revision number

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7. Final Tip: Before You Submit

7.1 Double-Check Revisions

Before submitting your RFQ, double-check drawing revisions.

7.2 The Benefits of a Well-Organized Package

A well-organized drawing package helps CNC engineers:

• Understand your part in a short time
• Shorten quotation lead time
• Reduce misunderstandings during production

7.2.1 The Takeaway

Clear drawings benefit both buyers and custom machining factories.