Counterbore Bridging

An Autodesk Fusion add-in that makes counterbores printable without support on FDM 3D printers.

中文文档

When a counterbore faces the print bed, the ring around the hole has nothing to print on. The usual fix is "sacrificial bridging": a few layer-high cuts above the counterbore floor, so that each layer can bridge from wall to wall. The first cut is a strip as wide as the hole, the next one turns by 90° (or by 60° for a hex hole), and the last one ends on the hole outline. The slicer then prints straight bridges instead of drooping loops.

This add-in creates those cuts as a single Counterbore Bridge feature in the timeline. You can edit it like any other feature, and it follows changes to the model.

Features

• Works with any hole shape: round, hex, square, slots, or several holes in one counterbore.
• Picks the number of cuts from the hole: one per straight-edge direction (a hex hole gets 3, a square or slot 2, a round hole 2). You can also set the number yourself.
• Cuts follow the hole's edges, or a reference edge, sketch line or axis that you pick, plus an optional angle.
• Works on bodies in components and nested components, in any orientation.
• Layer height and angle are model parameters, so you can link them to your own user parameters (e.g. layer_height).
• Double-click the feature in the timeline to change any setting, including the selected counterbores.
• English, German, Simplified and Traditional Chinese, following Fusion's language setting.

Installation

1. Download this repository (green Code button → Download ZIP) and unpack it, or clone it.
2. Put the folder into Fusion's add-in folder and make sure it is named exactly CounterboreBridging (a ZIP download unpacks as CounterboreBridging-main, rename it):
   • Windows: %appdata%\Autodesk\Autodesk Fusion 360\API\AddIns
   • macOS: ~/Library/Application Support/Autodesk/Autodesk Fusion 360/API/AddIns
3. Restart Fusion. The add-in starts automatically; if not, start it under Utilities → Add-Ins → Scripts and Add-Ins.

Usage

1. In the Design workspace, open Solid → Modify → Counterbore Bridge. To pin it to the toolbar, use the ⋮ next to the menu entry.
2. Select one or more counterbore floors: the flat face with the hole in it.
3. Optionally adjust:
   • Reference: a straight edge, sketch line or construction axis for the first bridges. Without one, the bridges follow the hole's own edges.
   • Angle: rotates the bridges away from the reference. Without a reference it only affects round holes and manual layer counts; otherwise it is greyed out.
   • Layer height: your slicer's layer height (default 0.2 mm). Accepts expressions and user parameters.
   • Layers from hole shape: on by default. Turn it off to set the number of layers yourself.
4. Click OK. Each selected body gets one Counterbore Bridge in the timeline.

To change it later, double-click the feature in the timeline, or edit its parameters in Modify → Change Parameters.

Notes and limitations

• The feature uses Fusion's Custom Feature API, which Autodesk still marks as a preview. It has been reliable in testing, but a future Fusion update could change its behaviour.
• The counterbore walls should be perpendicular to the floor.
• If the add-in is not loaded, Fusion keeps the existing geometry but cannot recompute the feature, and shows a warning on it.
• If a counterbore changes too much upstream (for example, it is moved to another place), the feature can no longer find it and turns red. Double-click it and select the floor again.

Development

• commands/counterboreBridge/geometry.py builds the cut as a single body from boolean operations; feature.py wraps it in the custom feature; entry.py has the create and edit commands; strings.py the translations.
• dev/fusion_tests.py is a regression test that runs inside Fusion. It builds test parts in a new, unsaved document (including rotated parts, components and every hole shape), creates and edits bridges, and checks the results. Run it inside Fusion with app and adsk in scope (for example from the Text Commands window in Python mode); failures end up in result["failures"].
• dev/reload.py reloads the add-in in a running Fusion. Note that the timeline icon only changes after a Fusion restart.
• dev/make_icons.py renders the icons (pure Python, no dependencies).

Credits

Thanks to Rarder44 for support for non-circular counterbores, kap1bala for the Chinese translation, BenRoe for the macOS instructions, and luxflow for tracking down the component bug.