Fillet

Fillet rounds edges with a given radius, replacing the sharp edge with a smooth transition between its two faces.

In the viewport

1. Click Fillet on the toolbar. A small panel opens beside the model.
2. Click the edges to round. Hold Ctrl or Shift to add edges one by one, double-click an edge to take the whole bucket it belongs to, or right-click a pick for the multi-select menu: the tangent chain the edge belongs to, edges of the same type or equal length, the producing feature's buckets (Extrude End Edges, Side Edges …) and Select other. Hovering a menu item previews what it would select.
3. Type the radius and click Apply.

1234

1. 1
   Selection

   The edges to round, numbered in pick order. The count beside the label is how many you have; the ✕ on a chip drops that pick, and clicking a picked edge again drops it too.
2. 2
   The chips

   One per edge. What gets written depends on what they add up to: a whole bucket of one feature becomes an accessor like e.endEdges(), a subset becomes e.endEdges(0, 2), and anything else becomes a select() with an edge filter.
3. 3
   Radius

   The rounding radius, as a number, an expression or a parameter name. Too large a radius for the surrounding faces makes the feature fail — the timeline row reports it.
4. 4
   Apply

   Writes the statement and adds the timeline row; Exit writes nothing.

From sharp to rounded

The same plate before and after two fillets:

Beforeextrude(30)

A 100 × 60 × 30 plate straight out of the extrude. Every edge is sharp.

Afterfillet(5, …)

Radius 5 on the four top edges and radius 3 on the four bottom ones — two fillet statements, each aimed at one bucket of the extrude.

The plate

box.part.js

import { sketch, extrude, line } from 'fluidcad/core';
import { coincident, distance, fix, horizontal, vertical } from "fluidcad/constraints";

// The plate before any rounding: every edge is sharp.
sketch("xy", () => {
    const sg1 = line([-50, -30], [50, -30]);
    const sg2 = line([50, -30], [50, 30]);
    const sg3 = line([50, 30], [-50, 30]);
    const sg4 = line([-50, 30], [-50, -30]);
    coincident(sg1.end(), sg2.start());
    coincident(sg2.end(), sg3.start());
    coincident(sg3.end(), sg4.start());
    coincident(sg4.end(), sg1.start());
    horizontal(sg1);
    vertical(sg2);
    horizontal(sg3);
    vertical(sg4);
    fix(sg1.start(), [-50, -30]);
    distance(sg1.start(), sg1.end(), 100);
    distance(sg2.start(), sg2.end(), 60);
  })

const e = extrude(30)

The complete file

import { sketch, extrude, fillet } from 'fluidcad/core';
import { line } from 'fluidcad/core';
import { coincident, distance, fix, horizontal, vertical } from "fluidcad/constraints";

sketch("xy", () => {
    // Four lines drawn at their intended positions — the coordinates are
    // guesses the constraints below turn into an exact 100 x 60 rectangle.
    const sg1 = line([-50, -30], [50, -30]);
    const sg2 = line([50, -30], [50, 30]);
    const sg3 = line([50, 30], [-50, 30]);
    const sg4 = line([-50, 30], [-50, -30]);
    // Coincident joins the corners into a closed loop
    coincident(sg1.end(), sg2.start());
    coincident(sg2.end(), sg3.start());
    coincident(sg3.end(), sg4.start());
    coincident(sg4.end(), sg1.start());
    // Horizontal / vertical square the sides up
    horizontal(sg1);
    vertical(sg2);
    horizontal(sg3);
    vertical(sg4);
    // Fix pins one corner so the profile cannot slide; the two distances
    // set the width and height. The sketch is now fully constrained.
    fix(sg1.start(), [-50, -30]);
    distance(sg1.start(), sg1.end(), 100);
    distance(sg2.start(), sg2.end(), 60);
  })

// The plate to round. `e` keeps the extrude so its edges can be named.
const e = extrude(30)
// Radius 5 on the four top edges — what the Fillet tool writes when the
// picks cover a whole bucket of the extrude.
fillet(5, e.endEdges())
// A smaller radius on the bottom edges.
fillet(3, e.startEdges())

Targeting edges in code

Pass the edges after the radius:

fillet(5, e.endEdges())        // top edges of the extrude
fillet(3, e.sideEdges())       // side edges
fillet(2, c.internalEdges())   // internal edges from a cut

Or leave them out and fillet the last select() result:

import { select } from 'fluidcad/core';
import { edge } from 'fluidcad/filters';

select(edge().verticalTo("xy"))
fillet(5)                      // fillets the selected vertical edges

See Selection and filters for the filters.

Rounding a sketch corner instead

This page is about rounding the edges of a solid. To round a corner inside a sketch — trimming two lines and inserting a tangent arc before anything is extruded — use the sketcher's own tool, described on the sketch Fillet tool page.