# Walls and holes

Minimum wall thickness by wall type, and the limits for holes, slots, edge distance and drain holes.

**Use this when:** you set wall thickness, hollow a model, or add holes and slots.

**Don't use this for:** warping of large flat panels. Read Strength and warping.

## Walls

Wall rules keep walls from failing in printing, washing and handling. They do not prevent warping or breakage under load, which depend on the whole shape.

| Wall | Minimum | Preferred | Rule |
| --- | --- | --- | --- |
| Supported (braced by nearby geometry) | 0.8 mm | 1.2 mm | `WAL-01` |
| Unsupported (free-standing) | 1 mm | 1.5 mm | `WAL-02` |
| Structural (carries load or forms a closed sleeve) | 1.5 mm | 2 mm | `WAL-03` |
| Hollow shell (needs drain holes) | 1.2 mm | 2 mm | `WAL-04` |
| Fragile decorative detail | 0.6 mm | 1 mm | `WAL-05` |

| Rule | Name | Limit (mm, per side for gaps) |
| --- | --- | --- |
| `WAL-01` | Supported wall | Wall braced by adjacent geometry. min: 0.8; preferred: 1.2. Bands: AUTO_PASS ≥1.2; REVIEW 0.8–<1.2; ROUTE <0.8. |
| `WAL-02` | Unsupported wall | Free-standing wall. min: 1; preferred: 1.5. |
| `WAL-03` | Structural wall | Wall carrying load or forming a closed sleeve. min: 1.5; preferred: 2. |
| `WAL-04` | Hollow shell | Shell of a hollowed object; requires drain holes (HOL-06). min: 1.2; preferred: 2. |
| `WAL-05` | Fragile decorative detail | Non-load decorative fins and frills. min: 0.6; preferred: 1. |
| `WAL-06` | Thickness transitions | Adjacent thickness ratio above 3:1 is REVIEW (differential shrinkage, warping, sink). |
| `WAL-07` | Thin perimeter tips | Thin flared rims, points and tips at the outer extremes are damaged by supports, handling and warping. Tip thickness ≥1.5 mm MATTE / ≥2.0 mm GLOSSY, with a rounded end (r ≥0.5 mm). MATTE: 1.5; GLOSSY: 2; CLEAR: 2. |

## Holes and slots

![Diagram: a hollow part in cross-section with one drain hole at the bottom left and one at the top right.](/docs/diagrams/drain-holes.svg)

*A hollow part needs at least two drain holes of 3.5–4.0 mm at opposite ends of the cavity (`HOL-06`), and a shell of at least 1.2 mm (`WAL-04`).*

A hole that prints is not necessarily accurate. Orientation, depth, curing and finishing change its final size. Holes that need precision are drilled or reamed after printing (`HOL-04`).

| Rule | Name | Limit (mm, per side for gaps) |
| --- | --- | --- |
| `HOL-01` | Minimum printable hole | Holes below 0.8 mm are ROUTE. min: 0.8. |
| `HOL-02` | Functional hole | Holes ≥1.0 mm AUTO_PASS; 0.8–<1.0 REVIEW. min: 1. Bands: AUTO_PASS ≥1.0; REVIEW 0.8–<1.0; ROUTE <0.8. |
| `HOL-03` | Open slot or gap | Minimum 0.5 mm in MATTE; GLOSSY/CLEAR use the GLOSSY static clearance (0.8 mm). MATTE: 0.5; GLOSSY: 0.8; CLEAR: 0.8. |
| `HOL-04` | Precision hole | Holes needing better than standard tolerance are post-drilled or reamed, or ROUTE. |
| `HOL-05` | Deep narrow hole | Depth/diameter above 5:1 is REVIEW (hard to wash and cure, tends to close up). |
| `HOL-06` | Drain holes | Hollow parts need at least two drain holes of 3.5–4.0 mm, placed at opposite extremes of the cavity. diameter: 3.5–4.0; count: ≥2. |
| `HOL-07` | Edge distance and bridges | Material between a hole or slot and the nearest outer edge must be ≥ max(2.0 mm, 1.5 × wall); CLEAR ≥ max(2.5 mm, 1.5 × wall). Thinner bridges are REVIEW down to 1.2 mm and ROUTE below. MATTE/GLOSSY: max(2.0, 1.5·t); CLEAR: max(2.5, 1.5·t). Bands: AUTO_PASS ≥ required; REVIEW 1.2 – < required; ROUTE <1.2. |

## Use instead

- **Wrong move:** hollowing a model without drain holes. **Why:** uncured resin stays trapped inside. **Right move:** add at least two drain holes of 3.5–4.0 mm at opposite ends of the cavity (`HOL-06`). The print panel's drain hole tool places 5 mm holes and asks for at least one per hollow pocket. That alone does not meet `HOL-06`: add a second hole at the opposite end of each cavity.
- **Wrong move:** a slot close to the outer edge. **Why:** the thin bridge cracks. **Right move:** keep at least max(2.0, 1.5·t) mm of material to the edge, max(2.5, 1.5·t) on clear (`HOL-07`).

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Last checked: 2026-11-09. Womp version: Womp web app, November 2026.