aopab/jscad-codegen

Generate, validate, and render JSCAD v2 CAD scripts from natural language prompts

1.64x

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Geometry Positioning — Common Mistakes and Fixes

Name: aopab/jscad-codegen
Rating: 94.6 (1 reviews)
Author: aopab

The Problem: Inline Position Math

When building multi-part models (boxes, enclosures, assemblies), computing positions inline inside translate() or center: causes parts to protrude, misalign, or float in space. The math is opaque and hard to verify.

Symptom: Ribs/walls/shelves sticking out of the box. Parts not flush.

Root cause: Different parts using different position formulas that don't share a common reference frame.

The Fix: Declare Coordinates Once

Step 1 — Declare all dimensions as constants

const wall = 3;
const hddW = 101.6;
const hddH = 26.1;
const hddD = 146;
const gap = 2;
const cols = 4;
const rows = 2;

Step 2 — Derive inner and outer dimensions

const innerW = cols * hddW + (cols - 1) * gap;
const innerH = rows * hddH + (rows - 1) * gap;
const innerD = hddD;

const outerW = innerW + 2 * wall;
const outerH = innerH + 2 * wall;
const outerD = innerD + wall;   // back wall only — front open

Step 3 — Derive named center coordinates

In JSCAD, all primitives are centered at origin by default. center: sets where the center of the primitive lands in world space.

// Y: front (open) = -outerD/2, back (wall outer face) = +outerD/2
// Inner depth spans: Y = -outerD/2  to  Y = outerD/2 - wall
// Center of inner depth:
const innerYCenter = -outerD / 2 + innerD / 2;   // = -wall/2

// Z: bottom plate top face = +wall/2, top plate bottom face = wall + innerH
// Center of inner height:
const innerZCenter = wall / 2 + innerH / 2;

Step 4 — Use named centers everywhere

// ✅ All parts share the same reference — easy to verify alignment
const bottom = cuboid({ size: [outerW, outerD, wall],
  center: [0, innerYCenter, 0] });

const top = cuboid({ size: [outerW, outerD, wall],
  center: [0, innerYCenter, wall + innerH] });

const leftWall = cuboid({ size: [wall, outerD, outerH],
  center: [-(innerW/2 + wall/2), innerYCenter, innerZCenter] });

const rib = cuboid({ size: [gap, innerD, outerH],
  center: [ribX, innerYCenter, innerZCenter] });   // same innerYCenter!

const shelf = cuboid({ size: [innerW, innerD, gap],
  center: [0, innerYCenter, wall + hddH + gap/2] });

Checklist Before Writing Any Part

All dimensions declared as named constants
innerYCenter, innerZCenter (and innerXCenter if needed) computed once
Every center: uses only those named constants — no inline arithmetic
Back wall, ribs, and shelf all use the same innerYCenter
Cutter shapes for boolean subtract are larger than the wall they cut (add +2 to the cutting dimension to avoid co-planar faces)

Quick Reference: Center Formula

For a box with walls only on some sides:

Open front (no front wall):
  outerD = innerD + wall          (back wall only)
  innerYCenter = -wall / 2        (shifts all inner parts toward open front)

Walls on both sides:
  outerD = innerD + 2 * wall
  innerYCenter = 0                (centered, no shift needed)

Z (bottom and top walls):
  innerZCenter = wall / 2 + innerH / 2
  bottom plate center Z = 0
  top plate center Z    = wall + innerH