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wcchun1234 edited this page May 11, 2026 · 2 revisions

Geometry Model

This page documents how CutCase thinks about box geometry.

Canonical Dimensions

CutCase uses inside dimensions internally:

  • W: inside width
  • D: inside depth
  • H: inside height
  • T: material thickness

If the user enters outside dimensions, the app converts those values to inside dimensions before panel generation.

Outside Dimensions

Open box:

outsideWidth  = W + 2T
outsideDepth  = D + 2T
outsideHeight = H + T

Closed box:

outsideWidth  = W + 2T
outsideDepth  = D + 2T
outsideHeight = H + 2T

The open box only adds bottom thickness vertically. The closed box adds bottom and top thickness.

Base Panels

Panel base sizes:

Panel Size
front W x H
back W x H
left D x H
right D x H
bottom W x D
top W x D

The top panel exists only when the box is closed.

Edge Types

CutCase uses three edge types:

  • A
  • B
  • flat

A and B are complementary finger patterns. Flat edges do not add tabs.

Open Box Edge Map

For an open box:

Panel Top Right Bottom Left
front flat B A B
back flat B A B
left flat A A A
right flat A A A
bottom B B B B

Closed Box Edge Map

For a closed box:

Panel Top Right Bottom Left
front A B A B
back A B A B
left A A A A
right A A A A
bottom B B B B
top B B B B

Finger Pattern

The finger pattern is generated from:

  • edge length
  • target finger width
  • material thickness
  • effective kerf

The segment count is adjusted:

  1. Start with floor(edgeLength / desiredFingerWidth).
  2. If the count is even, subtract one.
  3. Ensure at least one segment.
  4. Center the remaining margin.
  5. If a small end margin would be weaker than material thickness, reduce count by two when possible.

A and B Parity

Tabs appear on alternating segments:

  • A: odd segments
  • B: even segments

Using an odd segment count keeps A and B complementary along mating edges.

Kerf Model

CutCase currently applies a simple effective-kerf model to tab widths.

Effective kerf:

effectiveKerf = kerf * fitScale

Fit scales:

Fit Scale
loose 0.65
standard 1.0
tight 1.35

This is useful for fast iteration, but it is not a full polygon offset engine.

Lid Geometry

A lift-off lid adds five generated parts:

  • lid top
  • lid front lip
  • lid back lip
  • lid left lip
  • lid right lip

The lid top size:

lidWidth = W + 2T + 2 * overhang
lidDepth = D + 2T + 2 * overhang

The lip strips sit inside the box footprint and are reduced by clearance.

Divider Geometry

Divider positions are evenly distributed across the inside box span.

For N dividers:

position(i) = length * i / (N + 1)

Front-back dividers:

  • span the inside depth
  • stand vertically
  • are placed across the width

Left-right dividers:

  • span the inside width
  • stand vertically
  • are placed across the depth

Divider Interlock Slots

When enabled, crossing dividers receive half-depth slots.

Slot width:

slotWidth = materialThickness + effectiveKerf

Slot depth is approximately half the divider height.

The goal is to let divider panels slide into each other in a grid.

Panel Features

Features are normalized against the selected panel.

Each feature has:

  • stable id
  • type
  • panel name
  • local x/y position
  • shape dimensions
  • operation
  • warnings

Feature coordinates are clamped so the shape remains inside the panel bounding area.

Design Validation

Validation runs after panel layout and feature normalization. This matters because the validator uses final dimensions, clamped finger width, effective kerf, generated add-ons, and actual feature positions.

The validator returns issue objects:

{
  severity: "warning",
  code: "feature-overlap",
  message: "Cut features on front overlap or leave less than 0.15 mm between cuts.",
  panel: "front",
  featureId: "hole-a",
  relatedFeatureId: "hole-b"
}

Validation results are:

  • shown in the production summary
  • included in buildSvg() results
  • embedded in exported SVG metadata
  • covered by geometry tests

SVG Layout

Panel polygons are generated in local coordinates, then placed onto the sheet layout with a row-based layout engine.

Each laid-out panel receives:

  • translated polygon points
  • bounds
  • origin
  • label location

The same normalized panel list drives SVG export and feature hit testing.

3D Placement

Each panel receives a 3D placement basis:

  • center
  • right axis
  • up axis
  • outward axis

The Three.js preview extrudes the 2D panel polygon by material thickness and applies the placement matrix.

Current Geometry Limitations

  • no full polygon boolean engine
  • no full contour offsetting
  • no dogbone generation
  • no DXF output
  • no automatic nesting
  • no collision detection between arbitrary features and finger joints

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