support-fins/plugins/cura

Support Fins — UltiMaker Cura plugin

Extensions › Support Fins › Add Support Fins puts printfins.com breakaway fins under the selected part's overhangs: upside-down-T walls, one-layer tines where they meet the part, and a bed pad. They appear as a Support Fins object on the plate, attached to the part, before you slice.

The geometry is the website's engine itself (web/*.js, unmodified, bundled through plugins/shared/ as the Orca plugin and the Fusion add-in do it), run in an embedded V8 (mini-racer) that ships inside the plugin. Cura gets the fins the site would give the same part in the same pose, and a fix on the site reaches Cura at the next build.

Status: 0.1, experimental. Tested in Cura 5.13 on an Apple-silicon Mac.

Install

Download the package for your computer from the plugins-latest release:

Computer	File
Mac with Apple silicon (M1 and later)	SupportFins-mac-arm64.curapackage
Mac with Intel	SupportFins-mac-x64.curapackage
Windows (also Windows on ARM, which runs Cura as x64)	SupportFins-windows-x64.curapackage
Linux x86-64	SupportFins-linux-x64.curapackage
Linux ARM64 (untested: UltiMaker ships no ARM Linux Cura)	SupportFins-linux-arm64.curapackage

Drag it onto Cura's window and restart Cura when it says so. Each package carries the embedded JavaScript engine (V8) for one platform, 15–22 MB; installed on the wrong computer the plugin says which one to download instead.

If you linked a development build into Cura's plugins folder (below), delete that link first: Cura's installer can't replace a link, and keeps loading the linked build.

From source:

python3 plugins/cura/build.py             # -> plugins/cura/build/SupportFins/  (this machine; needs esbuild via npx, and pip)
python3 plugins/cura/build.py --package   # + build/SupportFins-<platform>.curapackage
python3 plugins/cura/build.py --all       # a package for every platform (CI does this)

Or link the built folder into Cura's plugins folder (Help › Show Configuration Folder, then plugins/) and restart Cura. On macOS:

ln -s "$PWD/plugins/cura/build/SupportFins" ~/Library/Application\ Support/cura/5.13/plugins/SupportFins

Use

1. Pose the part the way it will print (rotate it in Cura). The fins are fitted to that pose, the same as the website fits them to the rotation you choose there.
2. Extensions › Support Fins › Add Support Fins (the selected parts, or every part on the plate when nothing is selected). Computing fins… shows for a second or three (the engine runs in the background), then the result: walls and tines placed, plus any overhang too shallow for a fin this way up and any piece of the part that starts in mid-air. Those aren't hidden: tilt the part and run it again.
3. Turn Cura's own supports off for the part, and slice.

• The fins move with the part. Rotate or scale the part and a Fins are out of date message offers Update (it doesn't re-run by itself: that takes a second or three).
• Ctrl+Z takes the fins off again. Remove Support Fins removes them from the selected parts, or from every part when nothing is selected.
• Several parts (selected, or the whole plate): each gets its own fins. Groups: ungroup first.
• Layer height comes from the active profile, so the tines land on real layers.

Settings: Extensions › Support Fins › Support Fins Settings… The website's settings (overhang angle, tines and grip, support gap, bed pad, sway braces, cutouts, coverage), with its defaults and tooltips; Add Support Fins stays one click and uses what you saved. The dialog is built from the shared plugins/shared/engine/options.json, so a new setting on the site shows up here at the next build. Printing PETG? Set Support gap to 0.3: it fuses to supports harder than PLA.

Tines touch the part rather than bite into it. Cura's Remove Mesh Intersection (a global setting, on by default) trims the overlap between the part and the fins object, so each tine ends at the part's outer wall. That's deliberate: the tines snap off clean.

Developing

python3 plugins/cura/build.py && python3 -m pytest -q plugins/cura/tests/

The tests cover the frame mapping (Cura is Y-up, the engine Z-up), the part → engine → fins round trip, and the settings layer (SupportFins/settings.py: saved values, the dialog's rows, stale fins), without Cura. For the Cura side (menu, background job, scene, undo), drop a dev_autorun.json next to the built plugin and open a model:

echo '{"rotate_x": 35, "slice": true}' > plugins/cura/build/SupportFins/dev_autorun.json
open -a "UltiMaker Cura" web/dev-models/lbracket.stl

The plugin then tilts the part, adds fins, re-runs, undoes, removes, undoes and slices, logging each step to dev_log.jsonl and saving the G-code to dev_plate0.gcode (both next to the plugin). Add "settings": {...} (saved before the first run), "dialog": true (opens the settings dialog, logs what it shows and saves a screenshot to dev_dialog.png) and "stale": true (rotates the part afterwards and presses Update). Delete the JSON to go back to normal.