You upload a drawing, set the layer to draw with a pen, and the machine carefully outlines every stroke: two lines where you wanted one, with a hollow middle. Thicker pens make it worse. Engraving does the same thing, and so does foiling, and so does scoring.
Nothing is broken. The file is doing exactly what it says.
Why does it draw two lines?
Every ordinary image tracer follows the edge of what it sees. That is the right answer for cutting, because a blade has to travel around a shape to cut it out. A pen stroke two millimetres wide is a long thin shape, so its edge is a long thin loop, and a pen asked to follow that loop goes down one side, around the end, and back up the other.
What you want is not the edge. It is the middle: one open path running down the centre of each stroke, which the tool goes over exactly once. That is a centre-line or single-line file, and it is a different thing from a normal SVG, not a setting inside one.
What is a single-line file, exactly?
Two differences from a normal cut file. The paths are open — they have a start and an end rather than closing into a loop — and they have no fill, only a stroke that exists to make them visible on screen. The machine follows the path itself, so the width of your pen or engraving tip decides how thick the mark is, not the file.
That is also why a single-line file looks wrong in a preview: a hairline skeleton rather than solid letters. It looks right when it is drawn.
How do I make one from my drawing?
Use the single-line tracer. Drop in a photo or scan of a drawing, handwriting or a signature and it finds the middle of every stroke by thinning the ink one pixel at a time from both sides until only the centre survives, then follows that centre into paths that stop where strokes end and meet where strokes cross.
A few things it does that matter in practice:
- Joins strokes through junctions, so the pen goes straight through a crossing instead of lifting. On a leafy drawing that took one test from thirty-one separate lines to sixteen.
- Trims the little side branches a wobbly line leaves behind, which would otherwise be visible as whiskers.
- Puts the lines in a sensible order, so the pen travels as little as possible between them.
- Tells you the line width at your finished size, so you can match a pen to it.
What images work, and what will not?
Drawings, handwriting, signatures, doodles and line art on a plain background work well, especially with strokes of roughly even width. Scan or photograph in flat light: a shadow across the page becomes a thicker stroke.
Filled shapes do not work, and the tool says so rather than handing you a mess. A solid circle has no centre line worth drawing — thinned, it becomes a dot — and bold lettering becomes a thin spine down the middle of each letter. For filled artwork you want the ordinary converter, which cuts the outline.
A photograph is not a drawing either. Run it through the coloring page maker first to get line art, then trace that.
What about single-line fonts?
They are real, and they are the right answer for text. A single-line or "sketch" font is drawn as strokes rather than outlines, so it draws correctly without any tracing. If you have one installed, use it. This tool is for everything a font cannot give you: your own handwriting, a child's drawing, a signature, a sketched logo.
Then what?
Download the SVG — free, no account — upload it, and set the layer's operation to Draw, Score, Foil or Engrave depending on the tool you have. In Silhouette Studio that is a sketch action; in LightBurn it is a line layer. For lasers and CNC there is a DXF export with each line as an open polyline.
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