Planar

A planar mate keeps two faces in contact and lets the second part move freely across the first: slide in X, slide in Y, spin about Z. It is the joint of a block on a table, a tile on a floor, a workpiece on a machine bed.

Free motion	slide in X and Y, rotation about Z

In the viewport

1. Click Planar on the assembly toolbar and pick the two face connectors — the surface first, then the part that rests on it.
2. The part drops onto the surface. Drag it around: it stays flat.
3. Offset takes a Z value only, to hold the part a fixed distance above the face. Flip turns the part over.
4. Click Apply.

The code behind it

clamp.part.js

clamp.part.js

import { part, sketch, line, extrude, chamfer, color, select, connector } from 'fluidcad/core';
import { face } from 'fluidcad/filters';
import { coincident, distance, fix, horizontal, vertical } from 'fluidcad/constraints';

// A 30 × 30 × 15 mm clamp block with a chamfered top — the part that slides
// around on the base plate in the planar example.
export const clamp = part('Clamp block', () => {
    sketch('xy', () => {
        const b = line([-15, -15], [15, -15]);
        const r = line([15, -15], [15, 15]);
        const t = line([15, 15], [-15, 15]);
        const l = line([-15, 15], [-15, -15]);
        coincident(b.end(), r.start());
        coincident(r.end(), t.start());
        coincident(t.end(), l.start());
        coincident(l.end(), b.start());
        horizontal(b);
        horizontal(t);
        vertical(r);
        vertical(l);
        fix(b.start(), [-15, -15]);
        distance(b.start(), b.end(), 30);
        distance(r.start(), r.end(), 30);
    });
    const body = extrude(15);
    chamfer(2, body.endEdges());
    color('seagreen');
    connector('bottom', select(face().planar().onPlane('xy', 0)));
});

work-table.assembly.js

import { assembly, insert, mate } from 'fluidcad/core';
import { plate } from './asm-plate.part.js';
import { clamp } from './asm-clamp.part.js';

export const workTable = assembly('work-table', () => {
    const table = insert(plate).grounded();
    const block = insert(clamp).translate(-15, 8, 40).rotate('z', 20);

    // Planar keeps the two faces in contact and leaves three degrees of
    // freedom: slide in X, slide in Y, spin about Z. The block keeps the
    // position and spin its insert pose gave it; drag it in the viewport
    // and it stays flat on the plate.
    mate('planar', table.connectors.top, block.connectors.bottom);
});

Options

mate('planar', table.connectors.top, block.connectors.bottom)
    .offset(0, 0, 1)      // hover 1 above the face (Z only)
    .flip()

The in-plane X and Y are the mate's free directions, so .offset() refuses to pin them; where the block starts on the plate is the instance's own .translate(), and dragging it writes that back. .rotate() sets the rest spin; .limits() is not available.

Contact, not fastening

A planar mate does not hold the part down — the solver keeps the faces coplanar, and the part slides where you drag it. To fix a part on a surface, use fastened; to let it slide in one direction only, a slider.