SignShell

Hollow 3D-printable sign letters for Autodesk Fusion: a shell and a snap-fit lid for every letter, with mounting slots, material/cost/time estimates and export in print orientation.

Getting started

Open or create a Design with design history turned on. The design type must be Assembly or Hybrid: every letter becomes its own component, which Part designs do not allow.
In the Solid tab, open Create → Create Letters, type your text and choose a font. The letters are previewed as solid blocks while the dialog is open.
Before printing a whole sign, make a Fit test piece once for your printer and filament.
Click OK. Every letter is hollowed and gets its lid; this takes about a minute for 20 letters.
Open Utilities → Add-Ins → Report & Export to see material, cost and print time, and to write the print files.

Create Letters

All lengths use the document units. Each letter is made of two parts: the shell (face and side walls, open at the back) and the lid that closes the back. Repeated characters share one component, so the geometry of each character is built only once.

Option	Meaning
Text	The sign text. Spaces keep their width but create no part.
Font	Installed fonts. If the font lacks a character of your text, the dialog names it and OK stays disabled.
Letter height	Real height of a capital letter (measured on H), whatever the font.
Depth	Total thickness of the letter (shell).
Wall thickness	Face and side walls, and the lid plate.
Nozzle	Optional. Rounds the wall to a whole number of extrusion lines (at least two), e.g. 1.5 → 1.6 mm (4 walls × 0.4 mm).
Front edge / Edge size	None, Chamfer or Fillet on the edge of the letter face only.
Lid type	Inset: the lid sits inside the back opening, flush with the back, invisible from the side. Cap: the lid covers the whole back including the wall edge; the letter is one wall thicker (shown in Wall info).
Lid clearance	Gap between lid and shell. 0.2 mm suits most FDM printers.
Snap depth	How far the snap bumps of the lid reach behind the ledge of the shell. Larger holds tighter. 0 turns the snap fit off.
Mounting slots	Adds screw slots to the lids (see Mounting).
Letter spacing (%)	Extra space between characters, in percent of the letter height.
Wall info	The wall actually used, and the total thickness for a cap lid.
Preview	Shows solid letters while the dialog is open. Turn it off for very long texts.
Fit test piece	Makes a short letter I with the current wall, clearance, lid and snap settings instead of the text.

How the lid holds

Inside the shell, along the wall, runs a ledge. An inset lid rests on it, so it cannot be pushed in too far. The ledge slopes back to the wall at 45° on the side facing the letter face, so the shell prints face down without supports. Small snap bumps on the rib of the lid click past the edge of the ledge and rest on that slope. No glue is needed.

Messages after creating a sign

Message	What to do
Created solid	The strokes are too thin to hollow with this wall. Use a bolder font, a larger letter height or a thinner wall. Small separate parts (a dot, a small caron) always stay solid.
Too narrow for the snap fit	That part has no ledge or bumps; glue its lid.
No mounting slot	Mount or glue that part differently, e.g. with double-sided tape.
Front edge reduced	A fallback hollowing method was needed; the edge was made smaller so the wall stays intact.

Fit test

Printers and filaments differ. Before a large sign, tick Fit test piece, click OK, export it with Report & Export and print both files (a few grams of filament).

The lid should go in with a firm push and click. Too loose: raise Snap depth by 0.1 mm. Too hard or cracking: lower it by 0.1 mm.
The lid does not enter at all: raise Lid clearance by 0.1 mm.

Mounting

Screw the lids to the wall, then click each letter onto its lid. The screw heads end up hidden inside the letter. Each lid gets up to two vertical slots with a reinforced boss under the screw head; the slots allow ±3 mm of adjustment up and down before tightening.

Slots are made for 4 mm screws (for example 4 × 30 mm with 6 mm wall plugs) and pan heads up to 8 mm. Where those do not fit, 3 mm screws with heads up to 6 mm are used.
Mark the slot centres on the wall through the lid, drill, then fix the lid with the screw in the middle of the slot so you can still adjust both ways.

Report & Export

Works on signs made with Create Letters. Choose the sign, the material and the price per kilogram, the file format (STL or 3MF) and an output folder. The table shows, per character, the quantity and the approximate mass, cost and print time of one piece, plus the total for the sign.

Estimates assume 100 % infill (the walls are thin), a 0.4 mm nozzle, 0.2 mm layers, an effective flow of 12 mm³/s and 3 minutes extra per printed part. They are approximate.
Materials: PLA, PETG, ASA and ABS with typical densities and prices; the price can be overwritten.
For each character two files are written, named after the character and how many are needed, e.g. O_x4_shell.stl and O_x4_lid.stl. Characters that are not allowed in file names are spelled out (S-caron, dot). A report.csv with the table and the assumptions is written next to them.
Files are written only into the folder you choose. Your design is not modified.

Printing

The files are already in print orientation: shells lie face down, lids lie flat side down. Do not rotate them.
No supports are needed. Disable automatic supports in your slicer.
Because the walls are thin, the infill setting hardly matters; two or more perimeters are recommended.

Troubleshooting

Problem	Solution
"Fusion cannot use the font"	A few installed fonts cannot be used for sketch text in Fusion. Choose another font.
OK is disabled	The message under the options says why (empty text, missing characters, wall thicker than half the depth, invalid value).
Report & Export finds no sign	Only signs created with this version of SignShell are recognised. Create the sign again.
Creating takes long	Thin or decorative fonts at large sizes need slower fallback methods; a minute or two is normal for those.

SignShell 1.0.0 · SenseOfLayers · Windows · Support: info@senseoflayers.com