A tool for designing forges and crucible furnaces. Pick a mode, choose a geometry, set dimensions, stack materials inside-to-outside, and see the resulting heat field and three quality ratings.
Modes
- Forge
- Horizontal heating chamber for blacksmithing. Bar stock goes in, gets heated red-hot, comes out for hammering. Heat is lost through walls and openings.
- Furnace
- Vertical crucible furnace. Closed chamber with lid and floor. Metal is melted in a graphite crucible inside.
- Combo
- Vertical chamber with a side slot. Lid on plus crucible inside → use as furnace; tuck bar stock through the side slot → use as forge.
Geometry
- Cylindrical
- Circular cross-section. The view shows top-down — looking down the chamber axis. Wall layers appear as concentric rings.
- Rectangular
- Box cross-section. The view shows the side cutaway with chamber, walls, lid, and floor.
Ratings
- Efficiency (0–100)
- How well the insulation holds heat in. Lower heat loss through the cold face → higher score. A typical hobby forge scores around 70 (B); a heavily insulated design with IR coating can reach 95 (A).
- Max Temperature (0–100, plus the safe service temp)
- The highest chamber temperature your stack can sustain without any layer exceeding its rated maximum. The score reflects margin above your target. The limiting layer is surfaced in the rating panel.
- Longevity (0–100)
- How long the design will last. Penalizes friable wool exposed to flux/slag, hot steel shells, and brittle hot-face materials in furnace mode. Forge mode is gentler on materials than furnace because there's no molten metal eating the lining.
What changes between modes
| Forge | Furnace | Combo |
|---|
| Default target temp | 1230 °C | 1100 °C | 1200 °C |
| Floor stack modeled | — | ✓ | ✓ |
| Side opening | — | — | ✓ |
| Crucible silhouette drawn | — | ✓ | ✓ |
| Flux penalty on materials | — | ✓ | ✓ |
Concrete example: A K-26 firebrick hot face scores 22 (out of 30) for hot-face durability in forge mode but only 6 in furnace mode. Bare ceramic wool scores 6 in forge but 0 in furnace (flux shreds it). Switch the same wall stack from forge to furnace and the Longevity grade will drop — the model is telling you that materials which work for heating bar stock won't last melting bronze.
Layer stack
Layers are listed inside-to-outside. The first layer touches the chamber gas at the rated service temperature; the last touches ambient air via natural convection + radiation. Drag layers (or use ↑/↓) to reorder; click the material name to swap; type to change the thickness.
- Hot face — dense refractory or castable. Takes heat directly and resists flux if it's a furnace.
- Insulation — ceramic wool or insulating firebrick. Keeps heat in.
- Shell — usually mild steel or stainless. Structural support, holds the wool in place.
Not modeled
The physics covers steady-state heat conduction through the wall stack with realistic convection + radiation boundaries, but a few things are deliberately out of scope:
- Burner output and combustion — you specify the chamber temperature directly
- Warm-up time — steady-state only, assumes the design has reached temperature
- Forced convection from a burner jet inside the chamber
- True 3D effects — handled via axisymmetric + 2D cartesian approximations
- Bill-of-materials / cost estimation
Real-world heat loss in operation will be ~20–40% higher than predicted because of openings, exhaust, and burner inefficiency.
Keyboard shortcuts
- 1 / 2 / 3 — switch mode
- G — toggle geometry
- U — toggle units (in/°F vs mm/°C)
- ⌘Z / Ctrl Z — undo
- ⌘⇧Z / Ctrl ⇧ Z — redo