STLBenchFree online STL to DXF converter
STL to DXF — a contour you can actually cut
Drop a model, choose where to slice it, and download a DXF with closed contours and its holes marked. Most converters take the other route and write every triangle out as a 3DFACE: a valid file, thousands of unconnected faces, and nothing a cutter can follow. Slicing gives the shape you would cut a plate to, in millimetres, with circles kept as circles. Nothing is uploaded.
- 100% free
- No signup
- Closed contours
- Holes stay holes
- Nothing uploaded
Drag a file anywhere on this page to open it. F fits the view, W switches shading, G the grid, R spins it.
How to convert STL to DXF
Three steps. The second is a decision about the part, not a setting to leave alone.
Drop the .stl
Any mesh this site reads works — OBJ, PLY, 3MF, GLB. Look at it first: which way it is oriented decides what a cut through it will look like, and rotating the part is easier than guessing.
Choose where to cut
Pick the axis and the height. A section halfway up a bracket gives its outline with the bores in it; a section near the base gives the footprint you would actually cut a plate to. The result appears as contours, with a count of how many closed.
Download the DXF
R12 ASCII with closed polylines, in millimetres, holes marked as holes. That is a file a laser, router or waterjet will nest and cut without anyone opening CAD to fix it first.
Technical specifications
| Reads | .stl, .obj, .ply, .3mf, .glb, .gltf, .fbx, .step |
|---|---|
| Writes | .dxf — R12 ASCII, closed polylines, millimetres |
| Operation | Planar section at an axis and height you choose |
| Holes | Marked by nesting depth, not by contour direction |
| Circles | Contours that fit a circle are written as CIRCLE entities |
| Not produced | Projected views, hidden lines, dimensions |
| Open paths | Counted on screen rather than silently dropped |
| File size | No fixed limit — past 100 MB you are told what it will cost this tab, then it opens |
Frequently asked questions
Why not just export the triangles as a DXF?
Because that is what everyone else does and the result cannot be cut. DXF has a 3DFACE entity, so a converter can dump every triangle of the mesh into one and produce a technically valid file — thousands of unconnected three-sided faces with no outline, no closed path and no notion of inside. Open it in cutting software and it either refuses the file or tries to cut every triangle edge. What a cutter needs is a contour: one closed loop per boundary. Getting there means slicing the model, not transliterating it.
So this is a section, not a projection?
A section, and the distinction is worth being clear about. A projection is what you see looking at the part — the silhouette, including features behind other features. A section is what you would see if you sawed through it at a given height: the material the saw passes through. For fabrication a section is almost always the useful one, because it is the shape of the plate you would cut. A true projected drawing with hidden lines is a drafting operation, and this is not that.
Are the holes kept?
Yes, and marked as holes rather than left as more outlines. Each contour is tested for containment, and a contour inside an odd number of others is inner material — the closed flag and the nesting both come out right, which is what cutting software reads to decide where to start the cut. A file that gets this wrong produces a plate with its holes filled in, discovered after the sheet is scrap.
The cut came out fragmented. Why?
Usually because the mesh is not watertight where you cut it. Slicing walks the triangles, collects the segments crossing the plane and chains them into loops; if the mesh has holes or duplicated faces at that height, the chain breaks and you get open paths instead of a contour. The panel counts open versus closed, so it shows rather than hides. Moving the cut a fraction often steps past a bad patch. A vertex sitting exactly on the plane used to cause this too — that case is handled here rather than left to floating point.
What about curves — do circles stay circles?
Where a loop turns out to lie on a circle, it goes into the file as a CIRCLE entity rather than as its segments — a cutter following a polygon chatters at every vertex and leaves the facets on the edge. But the tessellation is the ceiling: a bore that was exported as twelve segments is a twelve-sided polygon in the file, and fitting recovers the circle it came from. Everything else is a polyline at the resolution of the mesh you gave it — the DXF cannot be smoother than its source.
Is my model uploaded?
No. Reading the mesh, slicing it, chaining the contours and writing the DXF all happen in this tab.
Two files called DXF, only one of them cuttable
Search for this conversion and most of what you find writes triangles. The DXF format has an entity called 3DFACE, a mesh is a list of three-sided faces, and the mapping is obvious enough that it takes an afternoon to implement. The output opens in AutoCAD, so it looks like a success. Send it to a laser and the software either rejects it or offers to cut sixty thousand tiny triangle edges, because there is no closed path anywhere in the file and nothing that says which side is material.
The conversion people actually want is a dimension lower. A cutter works from a flat outline: one closed loop for the perimeter, one for each hole, and enough information to tell them apart. Producing that from a mesh means intersecting it with a plane — collecting every triangle edge that crosses, chaining the segments end to end into loops, and then working out which loops sit inside which. Only then is there something a machine can follow.
Two details decide whether it is reliable. The first is what happens when a vertex lies exactly on the cutting plane, which is common because parts are modelled on round numbers and people cut at round heights; treated naively the segments fail to meet and the contour shatters into fragments. Counting an exact hit as just above the plane fixes it, consistently, everywhere. The second is nesting: a hole is decided by how many contours enclose it, never by which direction the loop runs, because directions coming out of a mesh are not something you can trust.
If what you have is already flat, going the other way is on DXF to STL, which extrudes a drawing to a thickness you type. And if the model is a machined part rather than a print, STL to STEP rebuilds its surfaces instead of flattening it.
Where the conversion happens
Every number on this page is worked out by JavaScript running in the tab you are reading it in. The model you open is read straight off your own disk — it is never uploaded, logged or kept, which is also why these tools carry on working after you disconnect from the network.
One point particular to slicing: it is real computation over every triangle in the model, which is the excuse most converters use for wanting the file on their server. It happens in the tab here instead, and the visible consequence is that dragging the cut height redraws the contours immediately rather than after a round trip.