Text for 3D printing

Solid letters, or hollow ones

STL carries no paint, so the fill and outline switches are read as “what geometry to extrude”. Fill alone gives the letterform as a solid block — badges, signs, keycaps. Outline alone extrudes just a band of the stroke width around its edge, giving hollow letters with a wall of a known thickness: useful for inlays, light boxes and anything you plan to pour resin into. Both together give the solid plus its surrounding band.

Size, depth and what the slicer assumes

Font size is the letter height in geometry units, and STL has no unit header — slicers read the raw numbers as millimetres. So the unit selector scales the solid rather than declaring anything, and the default keeps one geometry unit equal to one millimetre.

• At the millimetre default, a font size of 100 prints letters 100 mm tall; switch the unit to work in centimetres or inches instead.
• Extrusion depth is yours to set, in the same unit. Left alone it is a fifth of the text height, which reads well for standing letters.
• Set the depth here rather than stretching the Z axis in the slicer — extruding keeps the letter faces flat and the walls exactly vertical.
• Raise the curve accuracy for large prints: curves are flattened to segments before triangulation, and a polygonal “O” starts to show at 200 mm.

One part, or one part per letter

Letters that do not touch are separate solids in the same file, and a slicer will treat them as separate objects on the plate. If the word has to come off as a single part, use a script face whose letters overlap or close the letter spacing until they do, and turn weld contours on so those overlaps are unioned instead of left as walls inside the model. Within a single glyph the contours are always unioned regardless of that setting, so a stem crossing a bowl never leaves an internal seam.

Thin strokes and the nozzle

A hairline serif or a light weight can end up narrower than one extrusion width, and the slicer will thin it out or drop it altogether. Two ways round that: dial the weight up — variable-font axes are exposed, so you can add weight without changing typeface — or switch to outline mode, where the band is exactly the stroke width you asked for, which makes it easy to land on a multiple of your nozzle diameter.

Or emboss it onto a model instead

When the text belongs on something you have already modelled, export the outline rather than the solid and extrude it in your CAD tool. DXF declares its unit in the file header, so the sketch arrives at the intended size in Fusion 360, FreeCAD or Onshape; SVG is the import Tinkercad and Blender prefer. Either way the letters come in as closed contours — counters included — ready to be raised as a boss or cut in as a pocket.

Questions

Will the STL slice without repairs?

It should. The caps are built from the same boundary edges the vertical walls are stitched along, so the solid closes with no unmatched edges — Cura, PrusaSlicer, Bambu Studio, Orca and Simplify3D all take it as-is. The file is ASCII STL, which is larger on disk but reads everywhere.

Why did my print come out the wrong size?

Almost always a unit assumption, because STL cannot declare one: the slicer reads the numbers as millimetres. Check that the unit selected here is the one you meant, and remember that font size is a letter height in geometry units, not points.

Is there a base plate under the letters?

No — the letters are the model. Their bottom faces sit at z = 0, so they land flat on the plate. If you want a backing plate, add one in your slicer or CAD, or overlap the letters so they print as one connected piece.

Can I print text curved around a surface?

Not from here: the geometry is planar and extruded straight along one axis. Export DXF or SVG instead and project the imported sketch onto the surface in your CAD tool, which is where a wrap belongs anyway.