How to prepare a DXF or SVG for CNC routing
Most CNC quotes don't stall on price. They stall on questions. What units is this in? Which lines are cut through and which are pockets? Why does this outline have a gap? Is the text still a font? Every question is a day lost, and every fix the maker makes is design time on your bill. Sort these out before you post and you'll get bids faster and lower.
Formats, best first
- DXF. The default for 2D CNC work. Every CAM program reads it (VCarve, Aspire, Fusion, Carbide Create, SheetCAM for plasma), and every CAD and vector program can export it.
- SVG. Common from Inkscape, Illustrator and online design tools. Fine for most router work, but check the scale (below).
- AI, EPS or vector PDF. Usually accepted. Convert text to outlines and remove clipping masks first.
- STEP or STL. Only for 3D carving (relief signs, contoured parts). Say so in the brief.
- PNG or JPG. Not a cut file. A maker can trace it, but tracing a logo cleanly takes time and they'll charge for it. Send a raster only as a reference, or if you're happy to pay for drawing.
Draw at 1:1 and state the units
SVG has no fixed physical unit, so a part drawn at 12 in can open at a different size in another program depending on the export settings. DXF stores numbers without always saying whether they're inches or millimeters.
Draw at full size. Put the units in the file name and the brief. shelf-bracket_in.dxf. Then add one dimensioned reference rectangle on its own layer, labeled, so the maker can check the import at a glance.
Closed paths, no duplicates
Every shape that's cut out must be a closed path. A tiny gap at a corner means CAM can't tell inside from outside, so it can't offset the toolpath for the bit. In Inkscape, use Path → Combine and check node joins; in Illustrator, Object → Path → Join; in CAD, run the open-contour check.
Duplicate lines are the second big problem. Two paths stacked on top of each other look like one, but CAM sees two shapes and may cut twice or refuse to make a pocket. Copy-paste, autotrace and exports from 3D software all produce them.
Convert text to outlines (Object to Path, Create Outlines). If the maker doesn't have your font, the machine substitutes another one.
Design for a round bit
This is the one that catches people coming from laser cutting. A router bit is round, so it cannot cut a sharp inside corner. Every inside corner gets a radius equal to the bit's radius: about 1/8 in for a common 1/4 in bit.
That matters for anything that fits together:
- Slots and tabs. A square tab won't seat fully in a slot with rounded corners. Add dog-bone or T-bone relief cuts at inside corners so the tab sits flush. Most CAM programs can add them automatically; say if you want the maker to.
- Small details. A gap narrower than the bit can't be cut at all. If your design has 1/8 in gaps, it needs a 1/8 in bit or smaller, which cuts more slowly.
- Outside corners are sharp with no extra work.
If you're unsure, write "please add dog-bones to inside corners that need to fit" in the brief.
Say what's cut, pocketed and carved
A laser cuts or engraves. A router does more: it can cut through, cut a pocket to a set depth, carve a V-groove, or carve a 3D surface. The maker needs to know which is which, and how deep.
- Put cut-through profiles on one layer.
- Put pockets on another, with the depth in the layer name:
pocket_0.25in. - Put V-carve artwork on its own layer.
- Mark anything that's a reference only.
If your program doesn't do layers, use colors and explain them in the brief.
For V-carved lettering, the stroke width of your font sets how deep the V-bit goes. Bold letters on thin plywood can cut deeper than you'd expect. The V-carve depth calculator shows the depth for a given line width and bit angle, so you can pick a font weight before you finish the design.
Material thickness is a guess until it's measured
Sheet goods are rarely their nominal thickness. A sheet sold as 3/4 in plywood may measure a little under, and Baltic birch is metric (18 mm). If parts slot together, draw slots at the thickness you think the material is, and ask the maker to measure the actual sheet and adjust. Better: write "slots must fit the sheet you cut from" in the brief.
Tabs and hold-down
Parts cut free on the last pass can shift, chip or get thrown by the bit. Makers leave small tabs to hold them in the sheet and then cut and sand them off. You don't need to draw tabs; the maker adds them in CAM. If tab marks matter on a visible edge, say which edges are visible.
A checklist to paste into your post
- File: DXF or SVG at 1:1, units stated, plus a reference rectangle.
- Closed paths, no duplicates, text converted to outlines.
- Layers or colors for cut-through, pockets (with depths) and V-carve.
- Material and thickness, and whether you're supplying it.
- Which parts must fit, and whether dog-bones are OK.
- Largest finished size, so the maker can check their bed.
- Visible faces and edges, so tabs and clamps go elsewhere.
- Quantity, finish, deadline, ZIP code or "local pickup."
No file? Post anyway
Plenty of jobs start as a sketch on paper. Dimension it clearly, photograph it straight on, and say you need drawing as part of the job. Makers who offer design will quote it as a separate line.
When the file is ready, post the job once and let makers bid. Posting is free, there's no buyer fee, and your payment is held until the parts arrive and you confirm delivery.