Fuse an L-bracket in CAD Editor

Level: beginner → intermediate · Route: local #/model · Units: millimetres

This hands-on lesson builds two rectangular extrusions into a connected L-bracket with the editor's qualified union operation. Unlike a generic Boolean modeling claim, the recipe is deliberately limited to supported integer-axis box material. The goal is to edit, inspect, save and reopen real authored geometry while distinguishing authoritative native evidence from viewport triangles.

Load the existing L-bracket

In a configured workspace using Node 22+, run:

pnpm --filter @barocss/cad-editor build:library
pnpm --filter @barocss/cad-editor-app dev

Open http://127.0.0.1:52010/#/model (or your Vite port plus #/model).

1. Wait for Accepted model under Model a part.
2. Expand Modeling examples, then Choose an example.
3. Choose Fuse an L-bracket. If a model is already accepted, first save any work you need and check Replace accepted model and discard its history and pending dimensions.
4. Choose Load example. Merely choosing a preset does not replace the accepted model.

The recipe has five authored feature nodes: sketch → extrusion for base, sketch → extrusion for leg, then base.union(leg). It preserves three separately named outputs: base, leg, and the union result bracket.

Understand the dimensions

The fixed base is an XY rectangle 32 × 8 mm, extruded 8 mm in +Z. The leg is a separate rectangle running from minimum XY [legMinX, legMinY] to maximum [legMinX + legWidth, 24], extruded by legHeight.

Under Named dimensions, the leg has four numerical drivers:

Parameter	Initial value	Meaning
legMinX	−0 mm	Leg origin X
legMinY	−0 mm	Leg origin Y; moving it also changes leg length
legWidth	8 mm	Leg X width
legHeight	8 mm	Leg +Z extrusion height

The initial negative zero is an intentional part of the authored native fixture, not a required typing trick for normal use. The leg's maximum Y stays at 24 mm; moving its starting Y changes its length, not only its position.

Widen the leg and see the accepted result

1. Change legWidth from 8 to 12.
2. The status Dimension changes pending indicates draft fields; the previously accepted geometry remains unchanged.
3. Select Apply dimensions and wait for Accepted model. Use Visible output body to select bracket if another output is visible.
4. Change legMinY from 0 to 8, then Apply dimensions again to create the measured face-contact join.
5. Use Undo/Redo to review accepted changes. Choose Discard draft if you want to abandon an unaccepted value.

The following results are copied from the existing qualified native provider fixture, not a freshly executed browser, and the volumes belong to the complete bracket output:

Accepted stage	Exact restricted native volume	Generated panels
Initial L-bracket	3072 mm³	14
legWidth:12	3584 mm³	14
Then legMinY:8	3584 mm³	14

The result is a bounded single-body orthogonal-cell native union. Exact integer-cell material volume is not a volume calculated from approximate rendering pixels.

Learn why a union can refuse

Starting from the accepted face-contact state above, staging legMinX:32 produces edge-only contact and the native provider fixture refuses with operation union and cause CONTACT. Starting instead from that same accepted state, legMinX:40 leaves disconnected material, which the single-body authoring contract refuses rather than silently selecting one piece.

Do not apply these values as a new initial recipe; their known behavior is for the stated preceding accepted state. On refusal, the previous accepted bracket, saved authored text, visible output, and history remain authoritative. Correct or Discard draft. Refusal is safer than silently welding an edge, dropping a disconnected piece or pretending that all solid Booleans are admitted.

The tested recovery edits legWidth:8, legMinY:-0 return the qualified native bracket to 3072 mm³. After a fresh authored Open, changing legHeight:16 yields the measured 4608 mm³ result with 20 generated panels. These values are qualified provider evidence, not untested UI promises.

Choose outputs and save without losing geometry

Under Visible output body → Choose one output to inspect, select base, leg, or bracket. This changes only the view, not the authored union graph or saved named outputs. All three are retained and validated.

Open Save or open a model and choose Download model to initiate part.cad.json; verify that the browser actually stores it. Choose Choose model file to stage its UTF-8 source in Saved model data. Then explicitly check Replace accepted model and discard its history and pending dimensions and choose Open saved model. File staging alone cannot accept a native model.

A generic Open initially selects the last validated saved output. The canonical saved order for this recipe is base,bracket,leg, so it initially shows leg. Select bracket again before concluding the union disappeared. Re-edit legHeight or another supported field to confirm that the stored recipe remains parametric.

What this qualifies—and what it does not

• bracket belongs to the source-qualified orthogonal-cell family; the two original direct rectangular extrusion outputs belong to convex-planar.
• The baseline qualified result has three occupied cells, one body and shell, 14 generated panels, 16 global native vertices and 28 global native edges. Do not count derived mesh triangles as native B-Rep edges or assume generated union face IDs remain stable after edits.
• The current consumer rejects unsupported edge-only joins and multiple disconnected components. The existence of this exact constrained operation does not establish arbitrary curved Boolean union, tolerance healing, general CSG, topology renaming, or manufacturing certification.
• Browser clicks provide approximate derived face selection. A face hit may report contributing native operand faces but does not certify persistent topology or exact material classification.

Next, learn a composed cut: Cut a through-slot in an L-bracket uses the distinct built-in Cut a slot in a bracket preset. It preserves both the uncut union and the slotted result, instead of inventing an unrestricted Boolean tool.

The developer reference Fuse two rectangular extrusions includes the runnable TypeScript source and fixed native provider evidence.

Evidence status

Source inspected: current modeling preset, accepted numeric fixture and native report, saved output order, and staged-file UI. Not executed in this documentation change: Node source-drift script, site build, live Chromium/React interaction, GPU pixels, physical Download → Open and screenshots. These checks remain UNRUN until separately measured. A successful Markdown link check is not a substitute for a native or browser acceptance.

First part · CAD Editor overview · Native modeling reference