Getting your CAD design for sheet metal fabrication right before you send it saves time, reduces costs, and avoids costly rework. Here is what you need to know before placing your order.
Sending a drawing to a fabricator feels straightforward. You finish the design, export a file, and send it over. But if your CAD design for sheet metal fabrication is not set up correctly, you will likely get questions back before the job even starts, or worse, parts that do not fit or function as intended.
Getting your design right at the drawing stage is one of the most effective ways to keep your project on time and on budget. This guide covers the key things to check before you hit send.
Why CAD Design for Sheet Metal Is Different from Solid Part Design
Sheet metal behaves differently from a solid machined part. It bends, stretches, and springs back slightly after forming. A design that works perfectly as a solid model may not translate directly into a manufacturable sheet metal part.
When you design for sheet metal fabrication specifically, you are designing with the manufacturing process in mind. That means thinking about bend radii, material thickness, tolerances, and how the flat pattern will be cut before the part is formed.
If your CAD software has a dedicated sheet metal environment, use it. Tools like SolidWorks Sheet Metal, Fusion 360’s sheet metal workspace, and similar modules flatten your model automatically and flag issues like impossible bends before you export. That saves your fabricator a significant amount of interpretation work, and it saves you from unexpected surprises when the parts arrive.
Choose the Right File Format
What Most Fabricators Actually Need
The file format you send matters. Different formats carry different levels of information, and not all of them are suitable for every stage of the process.
For laser cutting, most fabricators work from DXF files. A DXF is a flat 2D representation of your part’s cut profile. It should be the unfolded flat pattern, not the folded 3D model. Check that your DXF is clean, with no duplicate lines, open contours, or stray geometry. Laser cutting software reads DXF files directly, so any errors in the geometry will either cause the job to fail or require manual correction at the fabricator’s end.
For CNC machining or complex assemblies, a STEP file is the preferred format. STEP carries full 3D geometry and is compatible with virtually all CAD and CAM software. If your sheet metal project involves machined components alongside fabricated parts, supply a STEP file for the machined elements alongside the DXF for the sheet metal profiles.
DWG files are also widely accepted, particularly for 2D drawing packages with dimensions and tolerances annotated. A fully dimensioned DWG or PDF drawing that accompanies your DXF gives the fabricator a complete picture of what you need.
Always Include a Dimensioned Drawing
A DXF alone is not always enough. Include a PDF or DWG drawing with key dimensions annotated, material specification, thickness, and any surface finish requirements. This acts as a cross-check and removes ambiguity if there is any question about the geometry.
Set Your Bend Radii Correctly
Bend radius is one of the most common sources of problems in CAD design for sheet metal fabrication. Every material and thickness combination has a minimum bend radius. Go below that minimum, and the material will crack or deform during pressing.
As a general rule, the inside bend radius should be at least equal to the material thickness. For mild steel at 2mm, aim for a 2mm minimum inside radius. For harder materials or thicker gauges, the minimum increases.
Check with your fabricator what tooling they have available. Press brake tooling comes in standard sizes, and if your design calls for a radius that does not match available tooling, the fabricator will either need to source specialist tooling or the part will be made to the nearest available radius. Either outcome can cause fit issues downstream.
Specifying a standard radius from the start avoids this entirely.
Add Adequate Bend Relief
Where a bend runs close to a cutout, slot, or edge, you need bend relief cuts. Without them, the material tears or distorts during forming, leaving a part that looks and functions poorly.
Bend relief cuts are small notches added at each end of a bend line where it meets another feature. They should be at least as wide as the material thickness and at least as deep as the bend radius. Most sheet metal CAD environments add these automatically, but it is worth checking the flat pattern manually to confirm they are present.
Check Your Hole and Cutout Sizes
Small holes and cutouts close to bends are a common problem in sheet metal CAD design. If a hole is too close to a bend line, the bend will distort the hole shape. The general guidance is to keep holes at least 1.5 times the material thickness away from any bend line, and ideally further.
Very small holes are also worth reviewing. Laser cutting can achieve fine detail, but holes smaller than the material thickness can be difficult to cut cleanly and may burn out during the process. If your design has holes smaller than 1mm in 1mm material, discuss this with your fabricator before finalising the drawing.
Specify Material and Thickness Clearly
It sounds obvious, but material specification is frequently missing or vague on drawings sent to fabricators. Your CAD design for sheet metal fabrication should clearly state the material type, grade, and thickness on the drawing itself, not just in an email or a note.
For mild steel, specify the grade if it matters to your application. For stainless steel, state whether you need 304 or 316. For aluminium, specify the alloy. If you need a specific surface finish such as powder coating, hot-dip galvanising, or anodising, note this on the drawing alongside any colour or coating thickness requirements.
Getting this information into the drawing pack means it is captured formally and cannot be lost in an email thread.
Apply Realistic Tolerances
Tolerances tell your fabricator how precise each dimension needs to be. Tighter tolerances cost more time and money to achieve, so it is worth applying them only where they genuinely matter.
For laser cut sheet metal, a positional tolerance of ±0.1mm is achievable and standard. For press brake bending, angular tolerance is typically ±0.5°. Overall assembly tolerances on welded sheet metal work are wider, typically ±0.5mm to ±2mm depending on complexity.
If your drawing carries tight tolerances on every dimension uniformly, a fabricator will either price the job as high-precision throughout or come back with questions. Neither outcome is ideal. Apply tight tolerances only to features where accuracy is critical, and use general tolerances elsewhere.
Getting It Right Before You Send
A well-prepared CAD design for sheet metal fabrication saves everyone time. It reduces back-and-forth, speeds up quoting, and means your parts come back right first time.
At Ashland Engineering in Milton Keynes, the team reviews every drawing before work starts. If there are issues with your design, they will flag them clearly before production begins rather than after. They accept STEP, DXF, DWG, and PDF formats, and they work with customers across Buckinghamshire, Northamptonshire, Bedfordshire, and the wider UK on everything from single prototypes to batch production runs.
If you are not sure whether your drawing is ready, get in touch before you finalise it. Early design input from a fabricator costs nothing and can save a significant amount of time.
Contact the team at sales@ashlandengineering.co.uk or call 01908 382 599.
