3D print a jack-o'-lantern that fits your LED tea lights

A printed jack-o'-lantern is the most satisfying Halloween print there is: switch the LED on, turn off the light, and the face appears. It is also the one that most often goes wrong, because the tea light does not fit, or the glow is a dull smudge through a wall that is too thick. Both are numbers. Here they are.

Measure the tea light first

Measure yours with a ruler or a calliper: brands differ, and a 1 mm miss is the difference between a lantern that drops over the candle and one that sits on it.

Wall thickness: the glow

Light through printed plastic depends on the wall and the colour:

• White or natural PLA, 1.2 to 2 mm walls: the whole pumpkin glows softly, the face glows bright. The best look.
• Orange PLA, 1.6 to 2 mm: a warm glow, the face stays the brightest part.
• Black or dark PLA, any wall: only the cut-outs light up. Classic and spooky.
• Over 3 mm: the body stays dark in any colour.

Ask for the wall as a number ("2 mm walls"): the AI keeps it, and you can change it later with a quick edit (1 credit).

The face: cut through, and printable

The eyes, nose and mouth are holes through the front wall. Two rules make them print cleanly:

1. Triangles point up. A triangle eye with its point at the top prints without supports; upside down, its flat top bridges.
2. Gaps of at least 2 mm between teeth, or they fuse into one blob.

Three ways to make it

By hand, free. A square lantern: start from the open box shape and type 60 x 60 x 70 mm with 1.6 mm walls: a floor and four walls, already open on one side. Tap the front wall and use Cut with the polygon to draw two triangle eyes and a jagged mouth, corner by corner, through. Add a name in raised Text on a side wall. Print it open side up, as it comes, and turn it over the tea light: the floor becomes the lid. Nothing to pay, the download included.

With the AI, a real pumpkin shape. Round, ribbed, with a stem: describe it with the tea light's numbers (the first prompt below). The AI writes it as a parametric model, so the size, the ribs and the wall stay numbers you change in the viewer.

Remix one you downloaded. Found a pumpkin on Printables whose opening is 2 mm too small? Upload the STL and ask for the opening: "make the opening at the bottom 39 mm across". How to change a downloaded STL.

Print settings

• No supports for a pumpkin open at the bottom: the dome closes in gently. If the AI's dome is too flat, ask for "a dome no flatter than 45 degrees".
• 0.2 mm layers, 2 or 3 walls, 15 % infill. The infill hardly matters on a shell.
• Vase mode works for a plain round lantern without a face, then cut the face with a hobby knife. With a face, print it normally.

What it costs

Shaping a part by hand (a hole, a cut, an added shape, text, rounded corners, a shell, every size typed in millimetres) is free, and so is downloading what you shaped. With the AI, a new part or a design change spends 3 credits, a small change 2 credits and a quick edit (a changed size or number) 1 credit; downloads are included in every plan, 4 credits without one. A new free account also gets its first AI part free (not offered in every country): some accounts get the credits right away, others confirm with a card first (a free trial, nothing charged that day); downloading the part spends 4 credits without a plan, like any AI work (every plan includes downloads).

The Halloween code: SPOOKY40

40% off your first month of any plan with the code SPOOKY40, until 2 November (first subscription). It applies itself at checkout when you came through one of these Halloween pages, and you can type it on the payment page too. Start with Maker: 50 credits a month for $7.99, cancel anytime. The hand tools, and the download of what you shape with them, are free without it. Every Halloween part and its prompt on one page: Halloween 3D prints.