How to 3D Print a Letter Stencil That Actually Works

A 3D printed stencil is one of the most useful things you can make with a printer. House numbers on the bins, a name on a crate, lettering on a wall, a logo on a T-shirt. It costs a few grams of filament and replaces a cutting mat, a scalpel and an afternoon.

It also fails in very predictable ways. Here's what goes wrong and how to avoid it.

Problem one: the islands fall out

Write the word BOARD in a normal font and cut it out of a sheet. The centres of the B, O, A, R and D are not attached to anything. They fall out, and your stencil paints solid blobs.

Every letter or digit with an enclosed counter has this problem: A, B, D, O, P, Q, R, a, b, d, e, g, o, p, q, and the digits 0, 4, 6, 8 and 9.

There are two fixes, and you usually want both:

• Use a stencil font. These are designed with small gaps, called bridges, that keep the counters attached. Black Ops One, Saira Stencil One, Allerta Stencil and Stardos Stencil are good examples.
• Check for loose pieces anyway. Even stencil fonts occasionally leave an island in an unusual character. The stencil maker on text3dmaker detects any loose piece and adds a bridge automatically, vertical or horizontal, and highlights bridges thinner than 0.8 mm so you can make them stronger.

Problem two: wrong thickness

Thickness is a trade-off between flexibility and durability.

The default in the generator is 0.8 mm because most people paint on something that isn't perfectly flat. At that thickness a stencil in PETG bends around a wheelie bin without cracking. PLA works for flat use but snaps when you bend it repeatedly.

Bridges matter more at low thickness. At 0.8 mm, a bridge of 0.8 mm width is a fragile thread. Aim for at least 1.2 mm bridge width if the stencil will be reused.

Problem three: paint bleeds under the edges

This is the one that makes stencilled lettering look amateur. The stencil is fine; the technique isn't.

• Hold it flat. Masking tape on all four sides, or a light coat of repositionable spray adhesive on the back. A stencil that lifts by half a millimetre lets paint wick underneath.
• Leave a generous margin. The frame around the letters is what stops overspray. For spray paint, give it at least 15–20 mm on each side.
• Spray light, from further away. Two thin coats from 25–30 cm beat one heavy coat from 10 cm every time. Heavy paint runs under the edge.
• Dab, don't brush. With a brush or sponge, press straight down with very little paint. A brush stroke drags paint under the edge.
• Lift straight up while the paint is still slightly wet, then clean the stencil before the next use.

Size and layout

Your printer's bed limits how wide a single stencil can be. The generator spreads long text over several lines automatically to keep it within a maximum width (200 mm by default), or you can set the number of lines yourself. For anything bigger, split the word into several stencils and line them up with tape.

For house numbers and bin labels, letter heights between 60 and 120 mm read well from the street. A full alphabet or 0–9 set is one button away, for when you want a reusable kit rather than a single word.

Not printing it? Export the SVG

The same design also downloads as an SVG in millimetres, ready for a vinyl cutter, a Cricut-style plotter or a laser cutter. Cut it from vinyl and you get a single-use stencil with perfect edges for glass, cars or painted walls.

Quick reference

• Stencil font, plus a check for loose pieces
• 0.8 mm for curved surfaces, 1.2 mm for flat ones
• Bridges at least 1.2 mm wide for a reusable stencil
• Tape or spray adhesive, wide frame, thin coats, dab don't brush

If you want ready-made ideas, there's a page of number stencils for bins, kerbs and mailboxes, and a letter stencil maker guide with examples.