Fillets & Chamfers

A fillet rounds an edge with a circular arc. A chamfer bevels it with a flat. Both are edge-refinement operations: pick the edges, pick the size, get a new shape. brepjs ships them as fallible operations because they are — fillets fail more often than booleans, and the failure modes are surprising.

The basic shape

import { box, edgeFinder, fillet, chamfer, unwrap } from 'brepjs/quick';

const b = box(30, 20, 10);
const verticals = edgeFinder().inDirection('Z').findAll(b);

const filleted = unwrap(fillet(b, verticals, 2));
const beveled = unwrap(chamfer(b, verticals, 1));

console.log('Filleted vertical edges with 2 mm radius');
void beveled;

fillet(shape, edges, radius) and chamfer(shape, edges, distance). Both return Result<Shape3D, BrepError>.

Selecting edges

You almost never want to fillet every edge. Use a finder to pick the ones you mean:

import { box, edgeFinder, fillet, unwrap } from 'brepjs/quick';

const b = box(30, 20, 10);

// All vertical edges
const verticals = edgeFinder().inDirection('Z').findAll(b);

// All edges of a specific length
const longEdges = edgeFinder().withLength({ min: 25 }).findAll(b);

// Specific curve type
const arcEdges = edgeFinder().ofCurveType('CIRCLE').findAll(b);

// Combine filters
const verticalsLongerThan10 = edgeFinder().inDirection('Z').withLength({ min: 10 }).findAll(b);

const filleted = unwrap(fillet(b, verticals, 2));
console.log('Filleted', verticals.length, 'edges');
console.log({
  longEdges: longEdges.length,
  arcEdges: arcEdges.length,
  verticalsLongerThan10: verticalsLongerThan10.length,
});

edgeFinder() filters chain — see Finders & Queries for the full vocabulary.

With the fluent wrapper

The wrapper accepts a finder callback inline:

import { shape, box } from 'brepjs/quick';

const filleted = shape(box(30, 20, 10))
  .fillet((e) => e.inDirection('Z'), 2)
  .chamfer((e) => e.inDirection('X'), 0.5).val;
void filleted;

The callback receives an EdgeFinder you chain filters on. The wrapper internally calls findAll and passes the result to the kernel.

Fillet all edges

When you really do want every edge filleted (a soft-blob aesthetic):

import { shape, box } from 'brepjs/quick';

const blob = shape(box(20, 20, 20)).fillet(2).val;
console.log('All edges filleted');

shape(s).fillet(radius) (no finder) applies to every edge. The functional equivalent: fillet(s, edgeFinder().findAll(s), radius).

Variable-radius fillets

When you want different radii on different edges:

import { box, edgeFinder, fillet, unwrap } from 'brepjs/quick';

let b: import('brepjs').Shape3D = box(30, 20, 10);
const verticals = edgeFinder().inDirection('Z').findAll(b);
const horizontals = edgeFinder().inDirection('X').findAll(b);

b = unwrap(fillet(b, verticals, 3));
// Re-find on the new shape — old handles refer to the old shape.
const newHorizontals = edgeFinder().inDirection('X').findAll(b);
b = unwrap(fillet(b, newHorizontals, 1));

console.log('Verticals at r=3, horizontals at r=1');

Edge handles are bound to the shape they were found on. Filleting consumes the input shape and returns a new one — old handles no longer apply. Always re-find after each operation.

Failure modes

FILLET_TOO_LARGE

The radius is bigger than the geometry around the edge can support. A box 10mm thick cannot have a 6mm fillet on its corner — the fillet would leave no flat region. The kernel detects this:

import { box, edgeFinder, fillet, isOk } from 'brepjs/quick';

const thin = box(10, 10, 1); // 1mm thick
const result = fillet(thin, edgeFinder().findAll(thin), 0.6); // ~larger than safe
if (!isOk(result) && result.error.code === 'FILLET_TOO_LARGE') {
  console.warn(result.error.suggestion);
}

Fix: smaller radius, or fewer edges.

FILLET_INVALID_EDGE

The selected edge has a curvature or geometry the fillet algorithm can't handle. Common with imported geometry — sharp creases, non-tangent meeting edges, edges shorter than the fillet radius.

Workarounds:

• Heal the input first (autoHeal)
• Skip that edge (refine the finder)
• Use chamfer instead — it has fewer requirements

FILLET_AMBIGUOUS_PROPAGATION

When you fillet an edge that meets multiple other edges at a vertex, the fillet has to decide whether to propagate to those edges. Sometimes the answer is ambiguous and OpenCascade refuses. Workaround: select all the edges that should propagate explicitly, in the same fillet() call.

Order matters

Two ways to fillet several groups of edges, only one works reliably:

// WRONG — fillet operations interact in unobvious ways
import { box, edgeFinder, fillet, unwrap } from 'brepjs/quick';
let b: import('brepjs').Shape3D = box(20, 20, 20);
b = unwrap(fillet(b, edgeFinder().inDirection('Z').findAll(b), 3));
// The edges in 'X' have moved/transformed — re-find:
b = unwrap(fillet(b, edgeFinder().inDirection('X').findAll(b), 3));
console.log('Filleted in two passes');

The two-pass version works only because we re-find edges after the first pass. The simpler approach: fillet all the edges you want at once, with the same radius:

import { box, edgeFinder, fillet, unwrap } from 'brepjs/quick';

const b = box(20, 20, 20);
const allTargetEdges = [
  ...edgeFinder().inDirection('Z').findAll(b),
  ...edgeFinder().inDirection('X').findAll(b),
];
const filleted = unwrap(fillet(b, allTargetEdges, 3));
console.log('One-pass fillet');

For different radii, two passes are unavoidable — just re-find edges after each.

Tip: chamfer is more forgiving

Chamfer fails less often than fillet. When fillet fails on imported geometry, try chamfer with the same distance — it bevels rather than blends and tolerates more curvature variation.

import { box, edgeFinder, fillet, chamfer, isOk, unwrap } from 'brepjs/quick';

const part = box(20, 20, 20);
const edges = edgeFinder().inDirection('Z').findAll(part);

const filleted = fillet(part, edges, 1.5);
const refined = isOk(filleted) ? filleted.value : unwrap(chamfer(part, edges, 1.5)); // fallback
console.log('Refined edges (fillet-or-chamfer)');
void refined;

A fillet ?? chamfer fallback can hide some classes of import-related failures without sacrificing visual quality.

Common recipes

Soften every external corner

import { shape, box, cylinder } from 'brepjs/quick';

const drilled = shape(box(40, 30, 15))
  .cut(cylinder(5, 20, { at: [20, 15, -3] }))
  .fillet(1.5).val;
void drilled;

A small uniform fillet (1–2 mm on a 30 mm part) reads as "manufactured to spec" without becoming the dominant visual feature.

Round only the rim of a bowl

import { shape, sketchCircle, edgeFinder } from 'brepjs/quick';

const bowl = sketchCircle(30).extrude(40);
const rounded = shape(bowl)
  .shell((f) => f.inDirection('Z'), 2) // hollow it
  .fillet((e) => e.inDirection('Z').withLength({ max: 200 }), 2).val;
void rounded;

Find the top circular edge with a length filter; fillet only that.

Add manufacturing draft

chamfer with very small distances simulates the slight bevel that injection-moulded parts get to release from the mould:

import { shape, box } from 'brepjs/quick';

const part = shape(box(30, 20, 10)).chamfer((e) => e.inDirection('Z'), 0.3).val;
void part;

Next steps

• Finders & Queries — selecting the exact edges you want
• Healing & Sewing — when fillets fail on imports
• Boolean Operations — the operation that creates the edges fillets refine