Custom keychain generator — a logo in, a printable tag out

• The tag sizes itself around your artwork and then grows to make room for the ring hole — you never end up with a hole cut through the edge of the plate.
• Sensible strength out of the box: a 3 mm tag with a 1.5 mm ligament of plastic beside the 4 mm hole, and artwork standing 1.8 mm proud so it survives being rubbed against keys.
• Rounded rectangle or round tags, with the corner radius scaled to the tag so nothing prints as a sharp point.
• Artwork and tag are separate heights in one solid, so a filament change at Z 3.0 mm gives you a two-colour keychain on a single-nozzle printer.
• Watertight STL that slices without repair, plus an SVG outline of the same tag at true millimetre scale for acrylic or leather blanks.
• Private and free: the image is traced in your browser, never uploaded, and there is no account or watermark on the file.

1. Drop the artworkA high-contrast PNG or JPG works best — a black logo on white, a name typed in a bold font, a screenshot of an icon. Transparent PNGs are composited over white so only the visible shape traces.
2. Size the tagWidth sets the artwork, not the plate: 35 mm of artwork gives a tag around 38 mm across, taller again once the ring tab is added above it. Raise Base thickness if the keychain will live on a car key.
3. Print it flatDownload the STL and print it face-up on the bed with no supports. Three walls and 20% infill is plenty; PETG survives more abuse than PLA on a keyring.

Keychains fail in exactly one place: the strip of plastic between the ring hole and the edge of the tag. That strip is loaded every time the keys swing, and on a printed part it is a stack of layer seams, which is the weakest direction the part has. Three millimetres of tag with at least 1.5 mm of material beside a 4 mm hole is the point where PLA stops snapping — the preset ships that geometry. Going thinner is only safe in PETG or in a tag you print with the hole in a solid area rather than a narrow tab. Above the tag, the artwork wants 1.5 mm minimum: below that a raised letter is two or three layers and shears off. If you want a slimmer keychain, take it out of the artwork (1.5 mm) before you take it out of the tag.

Because the tag and the artwork are two flat heights in the same solid, you can colour them separately without an AMS or a second extruder. Slice the STL, find the layer where Z passes 3.0 mm — the top of the tag — and insert a colour change there (M600 on Marlin, the pause-and-swap button in PrusaSlicer, Bambu Studio or Cura). The first 3 mm print in the tag colour, everything above it in the artwork colour, and the boundary is dead flat because the artwork sits on the plate rather than being embedded in it. If your slicer shows the change one layer early, nudge it up: the seam is more forgiving above the transition than below it.

• The ring hole is a fixed 4 mm circle — big enough for a split ring or a lobster clasp, but not for a carabiner gate; enlarge it in a mesh editor if you need one.
• The tag is centred on the artwork, so wide artwork gives a wide tag; crop the image rather than expecting the plate to reflow around it.
• Only one hole is punched, at the top edge. Multi-hole tags and keyring chains are not generated.
• A traced silhouette is one flat height, so shaded or photographic artwork should be simplified to a two-tone logo before it becomes a keychain.