Why Does a Sheet Metal Vendor Sometimes Reject a DXF That Opens Fine in the Customer's Own CAD Software?

Because "opens fine" and "cuts fine" are different bars. Your CAD package is forgiving about geometry that a laser's nesting software is not. It'll silently close small gaps, ignore duplicate lines, and render a spline as a smooth curve without caring that the underlying file has none of that cleaned up. The software driving the laser head reads the file literally.

What actually trips the import

File looks fine. Cuts wrong. That gap between looking closed and being closed is where most rejections live.

The most common failure is an open contour. A profile that looks closed on screen but has a sliver of a gap between two endpoints, often a few thousandths wide, left over from a trim operation or an export tolerance mismatch. Your CAD viewer snaps the display together so you never see it. The CAM software sees two open endpoints and either refuses the part or tries to guess a closure, which is worse than refusing.

Duplicate or overlapping lines are the second most common issue. If a feature got drawn twice on different layers, or a fillet command left the original corner geometry underneath the new arc, the file has two cut paths stacked on each other. The laser can double-cut the same edge. That chews the kerf wider than spec and can snap small features clean off.

Third is units and scale. A DXF has no inherent unit. It's just numbers, and the header flag that's supposed to declare millimeters versus inches gets dropped or mismatched by some exporters. A part modeled at 25 mm that exports with an inch flag either shows up as a part the size of a stamp or a part the size of a dinner table, and some software clamps or rejects rather than cutting something absurd.

Splines are the other recurring one. Fillet or chamfer in 3D CAD and flatten to a DXF, and some exporters write the result as a spline rather than resolving it into arcs and lines. Splines are a sequence of control points approximating a curve, not an actual arc. A laser path generator built around arc and line primitives either chokes on it or approximates it with short straight segments that show up as facets on the cut edge instead of a smooth radius.

What to check before sending the file

Check it before you send it, not after it bounces.

Open the DXF in a 2D viewer, not just your 3D CAD's native format, and zoom in hard on every corner where two entities meet. A closed profile should show one continuous outline with no double lines. If your CAD software has an "explode" or "flatten to curves" step before DXF export, run it. That's usually what converts splines into clean arc segments.

Export at a reasonable precision, not maximum decimal places. Over-precise coordinates sometimes introduce rounding artifacts that create the exact microscopic gaps described above. Confirm the unit flag matches what you actually modeled in. If you're not sure, state the part's largest dimension in the email with the file so a reviewer can sanity-check scale on sight.

What we accept

DigiForge's sheet metal line takes STEP, STP, and DXF. A STEP file carries the solid model and its own bend data, which sidesteps most of the flat-pattern export problems above. If your part is already modeled in 3D with bends, sending STEP instead of a flattened DXF removes a whole category of failure. DXF still has its place for flat parts with no forming, but check the file the way described above before it goes out the door.