Preparing SVG for 3D Extrusion: Fixes

Rule #1: Close Your Paths

For an object to be 3D printed, it must be "watertight". In 2D terms, this means every shape must be a closed loop.

If you drew a line but didn't connect the end back to the start, Vextrude doesn't know what is "inside" and what is "outside", so it cannot extrude it.

Beware of Self-Intersections

This is the most common error. If a path crosses over itself (like a figure-8 loop drawn as a single line), it creates mathematical ambiguity.

Strokes vs. Fills

3D engines extrude Fills (the color inside the shape), not Strokes (the outline).

If you have a logo that is made of thick lines, you must convert those strokes to paths (Object > Path > Outline Stroke) before uploading. Otherwise, the 3D converter will ignore them.

Why Your Holes Disappear

You extrude a letter "O" and get a solid blob. The counter — the hole in the middle — is gone. Nothing is wrong with your path; the file is telling the renderer to fill it.

An SVG shape with an inner boundary is a compound path: one path element containing two subpaths. Which parts count as "inside" is decided by the fill-rule attribute, and it has two possible values that disagree with each other.

Under evenodd, a point is inside when a ray drawn from it crosses the outline an odd number of times. The centre of an "O" crosses twice, so it is outside, so it becomes a hole. Under nonzero — the SVG default — direction matters: the renderer adds 1 for each clockwise crossing and subtracts 1 for each counter-clockwise one, and fills anything that does not total zero. If both subpaths of your "O" were drawn in the same direction, they sum to 2, the centre fills, and the hole vanishes.

This is also why two separate shapes stacked on top of each other rarely behave the way you expect. If they are separate paths, the extruder builds two overlapping solids with internal walls buried inside the mesh. Union them first.

An SVG Has No Real-World Size

This surprises people the first time they print. An SVG describes coordinates in a viewBox, and those numbers are unitless. A file marked width="100mm" and a file marked width="100px" can contain byte-identical geometry.

So when a converter turns your vector into a mesh, it has to pick a mapping from SVG units to millimetres. If your badge comes out 4 mm across or 900 mm across, the geometry is fine — the scale assumption differed from yours.

The reliable habit is to stop trusting the file and set the size explicitly after conversion, then check one known dimension. If a keyring is meant to be 40 mm wide, measure the width in your slicer before you print. It costs ten seconds and saves a spool.

It matters more than it sounds for small features. A 0.3 mm gap between two letters is below the width of a standard 0.4 mm nozzle, so the slicer will simply not print it, and the letters fuse. Scale first, then judge whether the detail survives.

Live Text Is Not Geometry

A <text> element in an SVG is not a shape. It is a string plus a font reference, and it renders correctly on your machine only because that font is installed. Any tool that extrudes outlines has nothing to work with.

Convert text to outlines before exporting: Type > Create Outlines in Illustrator (Shift+Ctrl+O), or Path > Object to Path in Inkscape (Shift+Ctrl+C). Do it on a duplicate layer — once outlined, the text is no longer editable as text.

If you specifically want editable 3D lettering rather than a one-off conversion, a dedicated text tool is the better route, because it keeps the typeface live and lets you change the wording without going back to your vector editor.

What Gets Silently Dropped

Extrusion cares about filled outlines. Several things that look essential on screen contribute no geometry at all, and they tend to disappear without an error message:

• Gradients and filters. A drop shadow or blur is a raster effect. There is no 3D equivalent of a soft edge, so it is discarded.
• Clipping paths and masks. The visible result on screen is the intersection of two shapes, but the underlying path is still the full uncropped one. You will get the whole shape, not the cropped version. Apply the clip destructively first — Object > Clipping Mask > Release, then use Pathfinder to actually cut the shape.
• Embedded raster images. A PNG inside an SVG is still a PNG. It has no outline to extrude. Trace it to vector first.
• Zero-width strokes and hairlines. A line with no fill and no measurable width encloses no area.

A quick way to see what an extruder will see: in your editor, turn off every fill. Whatever disappears is what you will lose.

Node Count Decides Your File Size

Every anchor point on your outline becomes vertices in the mesh, multiplied by the extrusion — front face, back face, and a wall between them. A path with 8,000 nodes does not produce a slightly larger STL than one with 300; it produces a dramatically larger one, and it will make the preview stutter.

Auto-traced artwork is the usual culprit. Tracing a photo or a scanned logo often leaves thousands of nodes describing what is visually a smooth curve. Run a simplify pass — Object > Path > Simplify in Illustrator, Path > Simplify (Ctrl+L) in Inkscape — and watch the outline while you do it. You can usually remove most nodes before the silhouette visibly changes.

The same applies to circles. A true circle described with four Bézier arcs stays smooth at any scale. The same circle traced as 400 straight segments is heavier and, at large print sizes, visibly faceted.

A Two-Minute Pre-Flight Check

Before converting anything, run through this. It catches nearly every failure described above:

1. Text converted to outlines.
2. Strokes expanded to filled paths.
3. Overlapping shapes unioned into one.
4. Holes still visible with fills on — if not, check the fill rule.
5. Clipping masks applied destructively.
6. Node count simplified on any traced artwork.
7. No embedded raster images.
8. Everything you want extruded has a fill, not just a stroke.

If a conversion still fails after all eight, the fastest diagnostic is to delete half the shapes and try again. Whichever half breaks it contains the problem path, and you can bisect from there in a couple of rounds.