When procurement managers and mechanical engineers submit a Request for Quotation (RFQ) to a fabrication shop, the speed and accuracy of the quote depends entirely on the clarity of the drawing package. Estimators review dozens of RFQs daily; packages with missing specs or incompatible files are frequently pushed to the bottom of the queue.
By adopting a standardized drawing preparation protocol, you eliminate guesswork, eliminate costly rounds of back-and-forth emails, and ensure the shop quotes your exact technical intent.
1. The Ideal CAD File Package: The "Rule of Three"
For sheet metal, precision machining, and welded assemblies, the most efficient quote submissions provide three complementary file types:
- 1. 3D Solid Model (.STEP or .STP): Standard AP203 or AP214 format. The universal 3D CAD model allows CAM programmers to immediately assess part geometry, verify bend sequences, check CNC milling tool clearance, and extract accurate bounding box volumes.
- 2. 1:1 Flat Pattern DXF (.DXF): For sheet metal parts, export the flattened 2D profile at a 1:1 scale with zero title blocks, dimensions, or drawing borders. CAM software imports clean DXFs directly into laser nesting programs within seconds.
- 3. 2D PDF Drawing (.PDF): The legal master document. Contains title block specifications, GD&T tolerances, tapped hole callouts (which cannot be modeled reliably in DXFs), surface finish requirements, and critical inspection dimensions.
Ensure your DXF export contains only cut contours. Remove bend lines, tangent lines, and text notes, or place them on a separate hidden layer. If bend lines exist on the cut layer, the laser cutting machine will treat them as cutting paths, slicing your part in half!
2. The Essential Information Checklist on 2D Drawings
An estimator must never assume an unspecified property. Ensure your PDF drawing clearly communicates:
- Exact Material Grade: Never specify generic "Mild Steel" or "Stainless." State the specific alloy and temper: e.g., "Mild Steel CR4 / IS 2062 Gr B", "Stainless Steel AISI 316L", or "Aluminium 5052-H32".
- Material Thickness: Specify sheet metal thickness in millimeters (e.g., 2.0 mm, 3.0 mm) rather than historical gauge numbers, which vary widely between ferrous and non-ferrous standards.
- Tolerances (General vs Critical): State a clear general tolerance block (e.g., ISO 2768-m for general fabrication, or ±0.2 mm) and call out specific tight tolerances (e.g., bearing bore $\varnothing 35\text{ H7}$) only where functionally necessary. Over-tolerancing non-critical features multiplies quoting costs.
- Threads & Inserts: Explicitly designate thread pitches (e.g., M6x1.0, M8x1.25) and state whether threads must be masked prior to powder coating or plating.
- Surface Finish & Color: Specify the exact finish, such as "Epoxy-polyester powder coat RAL 7035 light grey, 80 µm DFT" or "Abrasive sand blast to Sa 2.5 profile".
Powder coating adds 60 µm to 100 µm per side (120 µm–200 µm on slot widths or hole diameters). Always indicate on your drawing whether critical fit dimensions apply before or after surface coating. If threads or tight dowel holes are not masked, powder buildup will require manual re-tapping on the assembly line.
3. CAD File Format Comparison for Fabrication Quoting
Review how different digital formats function during the fabrication quoting workflow:
| File Format | Primary Use Case | Advantages | Limitations |
|---|---|---|---|
| STEP (.step / .stp) | 3D CAD model interchange | Universal compatibility; full 3D solid geometry | Does not capture thread tolerances or finish callouts |
| DXF (.dxf) | 2D Flat sheet profiles | Directly imported into laser nesting CAM software | 2D only; no forming angles or thickness metadata |
| Vector PDF (.pdf) | Master manufacturing drawing | Legally binding; displays GD&T, finishes, notes | Cannot be automatically nested in laser CAM software |
| Native CAD (SLDPRT / IPT) | Proprietary CAD files | Full feature tree retained | Version mismatch issues if supplier uses different software release |
Have CAD Files Ready for Quotation?
FabXE's applications engineering team provides rapid turnaround on fabrication, CNC machining, and surface finishing quotations. Upload your STEP, DXF, and PDF drawings via our secure RFQ portal.
Frequently Asked Questions
Yes. Our custom engineering support team can reverse-engineer physical components or convert hand sketches into production-ready 3D CAD models and 2D manufacturing drawings for an engineering fee, or as part of a turnkey manufacturing order.
Always request quotes at tiered volumes (e.g., Prototype: 1–5 units, Batch: 50 units, Production: 500 units). Fabrication machine setup costs and sheet material nesting efficiencies vary significantly with volume, allowing you to identify the optimal economic batch size.