Chamfer two edges of a part

Level: intermediate · Workspace: local CAD Editor #/model · Unit: millimetres · Output: part

Chamfering removes material along a chosen edge to form a bevel. In this exercise, the Two chamfers on a part preset uses two serial operations: the second bevel is applied to the accepted result of the first. It is not a general fillet tool or arbitrary multi-edge chamfering workflow.

This is a source-backed description of an experimental local UI. The exact native volumes below come from the previously executed provider fixture. New browser/GPU interaction, pixels, downloaded files and screenshots are UNRUN for this documentation change.

1. Load the model

In a prepared Node 22+ repository workspace with dependencies already installed:

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

Open http://127.0.0.1:52010/#/model (or Vite's actual port plus #/model).

1. Under Model a part, wait for Accepted model.
2. Expand Modeling examples, open Choose an example, and select Two chamfers on a part.
3. If you already have an accepted part, save anything important and check Replace accepted model and discard its history and pending dimensions.
4. Click Load example, wait for Accepted model, and choose the named part under Visible output body.

Simply choosing another option in the example list does not alter the accepted model. Loading an example replaces the previous accepted example and its undo history only after explicit acknowledgment.

2. Understand the two setbacks and edge location

The starting block is 32 × 24 × 8 mm, with an exact initial native volume of 6144 mm³. Its sketch lies in XY and extrusion goes along +Z.

Numeric driver in Named dimensions	Initial value	What it controls
frontDistance · front bevel distance	1 mm	Equal physical setback along both planes next to the first front/top edge
backDistance · back bevel distance	2 mm	Second bevel setback on the first chamfer's result
backY · edge-selection Y coordinate	24 mm	Y coordinate identifying the second top edge; not another bevel width

The first edge is the unique X-parallel edge at Y=0, Z=max in the original block. The second selector is resolved against the first chamfered body, at the authored backY and Z=max. Equal setback is the offset on each incident face, not the diagonal width of the resulting bevel. A selector that does not uniquely identify a supported edge refuses rather than picking the nearest visual edge.

3. Edit and compare qualified results

1. Keep frontDistance=1, backDistance=2, backY=24 and inspect the named part.
2. Change backDistance from 2 to 3. The status Dimension changes pending means the edit is still draft text. Select Apply dimensions, then wait for Accepted model.
3. Use Undo to restore the prior accepted bevel and Redo to reapply the second distance. With pending text, choose Apply dimensions or Discard draft before history changes.
4. As another separate accepted edit, change frontDistance from 1 to 2 while backDistance stays 3.

Expected qualified native values from the accepted provider campaign—not new measurements from the preview:

Accepted state	After first chamfer	Final part volume
Front 1, back 2	6128 mm³	6064 mm³
Front 1, back 3	6128 mm³	5984 mm³
Front 2, back 3	6080 mm³	5936 mm³

The original blank remains 6144 mm³ in these measured cases. The lower final volume after a greater setback represents more removed material, but a visible bevel is still derived display geometry, not a universal native guarantee for arbitrary values.

4. See what a refused edit means

Only the previously accepted original part can serve as the safe reference when an invalid candidate is rejected. From a state with frontDistance=1, the provider verifies these different refusal causes:

• backY=0 attempts to select the first front/top edge that the first chamfer has already removed. It refuses with CadModelError SELECTION (operation chamfer), rather than retargeting a nearby edge.
• backY=1 selects a resulting bevel/top edge with non-cardinal adjacent support; this refuses with NATIVE / METRIC for chamfer.
• backDistance=0 violates the positive-distance requirement and refuses with PARAMETER / chamfer.

The editor must leave the accepted shape, history and authored file state unchanged when a candidate fails. Read the actual diagnostic before correcting or selecting Discard draft. Do not silently clamp, approximate or manufacture a new topology ID.

5. Save the editable model

Open Save or open a model and choose Download model to start saving part.cad.json. Verify that the browser actually wrote the file; a Download click alone is not proof of persistence.

To reopen, choose Choose model file. This only stages the UTF-8 text in Saved model data. Review it, check Replace accepted model and discard its history and pending dimensions, then click Open saved model. A successful Open rebuilds the authored sketch, extrusion, two chamfers and three named drivers; it does not restore an old screenshot or camera.

The file staging reader rejects malformed UTF-8, empty content and files larger than 262,144 bytes. A valid text decode is not proof of valid native geometry; explicit Open may refuse, preserving the previous accepted model. After reopening, re-edit backDistance to demonstrate the saved intent remains parametric.

Qualification and limits

This lesson proves a bounded serial pair of cardinal-edge chamfers on one directly extruded rectangle. The second selector and parent belong to the first result, not the original block. It does not support a third chamfer, sibling chamfer branches, arbitrary curved edges, generic fillets, unrestricted topology naming, or combinations with unverified other feature families.

The advanced two-chamfer source and native evidence has a real public typed example and immutable provider receipts. Controller tests reuse genuine baseline data through mocked Worker paths; their display of changed values cannot be upgraded to newly measured native tessellations or browser/device success.

Still UNRUN for this lesson: real React/Chromium workflow, GPU pixels, physical Download → file picker → Open, and screenshot provenance. Use the CAD browser evidence protocol before reporting these as complete.

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