CAD File Prep for CNC Routing: STEP vs. DXF, and the Mistakes That Slow Your Quote Down

The fastest quotes come from the cleanest files. Our platform reads your CAD directly — no human retracing your geometry — which means the quality of what you upload determines how fast you get from file to price. This guide covers which format to send, what our importer fixes automatically, and the handful of mistakes that account for almost every stalled quote we see.

STEP vs. DXF: send STEP if you can

A .STEP (or .stp) file is a full 3D solid model. When you upload one, our system detects the stock thickness from the solid itself, recognizes pockets and dados with their actual depths, finds holes with real diameters, and extracts the outer profile — automatically. You confirm what it found and you're pricing. Nothing to tag, nothing to explain.

A .DXF is a flat 2D drawing. It's a perfectly good input — CNC routing is mostly a 2D-and-depths game — but DXF has no concept of depth. A rectangle inside your part outline could be a through-cut window, a 0.25" deep pocket, or a decorative engraving; the file simply doesn't say. So DXF uploads get an interactive tagging step where you click each profile and tell us what it is. It takes a minute or two, and our layer-naming convention can eliminate it entirely (see the layer-naming guide). But if your part started life in Fusion 360, SolidWorks, Onshape, or Rhino as a solid, export the STEP and skip the tagging.

What our importer fixes for you

Real-world files are messy, so the importer auto-cleans on upload and reports every fix: it closes small gaps between segments that should connect, joins chains of separate lines and arcs into continuous polylines, heals malformed arcs, removes duplicate overlapping entities, and splits multi-part files into individual parts. If the file needed surgery, you'll see exactly what we did in a cleanup list — no silent changes.

The mistakes that actually stall quotes

• Open outer profiles — the part boundary doesn't fully close, so there's no valid part to cut. Usually a stray gap from trimming; run your CAD's join/close command before exporting.
• Double lines — two entities stacked on the same path, common in files traced from artwork. The cleaner catches most, but heavily traced art can hide dozens.
• Wrong or ambiguous units — a 24-inch part exported as 24 mm. We flag suspicious sizes, but check your export dialog: units belong to the file, not to hope.
• Text left as live text — fonts must be converted to outlines/curves before export, or the geometry may not survive the trip.
• Interior details smaller than the tooling — features below our 0.125" minimum tool diameter can't be routed as drawn; inside corners always carry at least a 1/16" radius.
• Splines where arcs belong — some drawing programs export everything as splines, which balloons file size and slows parsing. Export as arcs and lines if your CAD offers it.
• Scale-ruining export options — 'fit to page' or plot-scaled DXF exports silently resize geometry. Always export at 1:1.

Design for the tool

A router bit is round, which has two design consequences worth internalizing. First, inside corners can never be perfectly sharp — the smallest tool leaves a 1/16" radius. If a square part must fit into a routed pocket, either radius the part's corners to match or add small 'dog-bone' reliefs at the pocket corners so the mating part seats fully. Second, slots and channels must be at least as wide as a real tool: anything narrower than 0.125" isn't routable as drawn.

Depth callouts deserve a moment of care too. In STEP files, model pockets and dados at their true depth — what's in the solid is what gets quoted and cut. A surprising number of files arrive with every pocket at a default 0.1" from a sketch-extrude habit. The feature report will show you each depth before you confirm, so errors get caught — but modeling it right the first time is faster.

The pre-upload checklist

• Exported STEP if the design exists as a solid; DXF at 1:1 scale otherwise
• Outer profile fully closed, no stray construction geometry left in the file
• Text converted to outlines
• Interior features at or above 0.125" tool width; inside-corner strategy decided
• Pocket and dado depths modeled at true depth (STEP) or known and ready to tag (DXF)
• One design per file, or distinct parts clearly separated — the importer will split them

Do those six things and your upload goes from file to confirmed feature report to live price in about the time it took to read this section. That's the whole point.