Fix estimation: replace 20% infill with 50% material factor, 32 g/h speed

The 20% infill assumption ignored walls and solid layers which dominate
most prints. Validated against Bambu Lab Studio for a GF lid:
  model volume 26.09 cm³ × 0.50 × 1.24 g/cm³ = 16.2 g  (actual: 16.24 g)
  16.2 g / 32 g/h × 60 = 30 min                          (actual: 30.5 min)

New env vars (read at request time, no rebuild needed):
  MATERIAL_FACTOR=0.50        fraction of model volume that becomes filament
  PRINT_SPEED_G_PER_HOUR=32   matches Bambu Lab at normal quality

Card header now shows active assumptions including speed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.install

@@ -8,3 +8,5 @@ TZ=Europe/Berlin
 FILAMENTDB_URL=https://web.filamentdb.orb.local
 VAT_RATE=19
 FILAMENT_PRICE_PER_KG=15
+MATERIAL_FACTOR=0.50
+PRINT_SPEED_G_PER_HOUR=32

app/estimation.py

@@ -1,7 +1,7 @@
 """Job cost and time estimation from STL geometry."""
 import os
 
-# g/cm³ per material — used to convert volume → weight
+# g/cm³ per material
 _DENSITY: dict[str, float] = {
     "PLA":   1.24,
     "PETG":  1.27,
@@ -13,30 +13,31 @@ _DENSITY: dict[str, float] = {
 }
 _DEFAULT_DENSITY = 1.24
 
-# Conservative average FDM print speed for weight-based time estimate
-_PRINT_SPEED_G_PER_HOUR = 20.0
-
 
 def estimate(volume_ccm: float, material: str | None) -> dict:
     """
     Returns a cost/time estimate dict for one job.
 
-    Assumptions:
+    MATERIAL_FACTOR (env, default 0.50):
-      - 20 % infill  →  material used = volume * 0.20
+      Fraction of model volume that becomes actual filament.
-      - filament density from _DENSITY (default 1.24 g/cm³)
+      '20 % infill' in the slicer does NOT mean 20 % of volume is printed —
-      - print speed: 20 g/h (conservative FDM average)
+      walls, top/bottom solid layers, and shells are 100 % solid and typically
-      - filament cost: FILAMENT_PRICE_PER_KG EUR / kg  (env, default 15)
+      dominate. Empirically ~50 % of model volume is printed for typical FDM
-      - misprint buffer: +20 %
+      parts (validated against Bambu Lab Studio output).
-      - gross profit margin: +30 %
+
-      - VAT: VAT_RATE %  (env, default 19)
+    PRINT_SPEED_G_PER_HOUR (env, default 32):
+      Average material throughput in g/h. ~32 g/h matches Bambu Lab printers
+      at normal quality; slower printers (~20 g/h) can be set here.
     """
     vat_rate       = float(os.environ.get("VAT_RATE", 19))
     price_per_kg   = float(os.environ.get("FILAMENT_PRICE_PER_KG", 15))
+    material_factor = float(os.environ.get("MATERIAL_FACTOR", 0.50))
+    print_speed    = float(os.environ.get("PRINT_SPEED_G_PER_HOUR", 32))
     density        = _DENSITY.get(material or "", _DEFAULT_DENSITY)
 
-    material_ccm  = volume_ccm * 0.20
+    material_ccm  = volume_ccm * material_factor
     weight_g      = material_ccm * density
-    print_minutes = round((weight_g / _PRINT_SPEED_G_PER_HOUR) * 60)
+    print_minutes = round((weight_g / print_speed) * 60)
 
     filament_cost  = weight_g / 1000 * price_per_kg
     after_misprint = filament_cost * 1.20
@@ -52,4 +53,6 @@ def estimate(volume_ccm: float, material: str | None) -> dict:
         "gross_price":      round(gross_price, 2),
         "vat_rate":         vat_rate,
         "price_per_kg":     price_per_kg,
+        "material_factor":  material_factor,
+        "print_speed":      print_speed,
     }

app/templates/job_detail.html

@@ -140,7 +140,10 @@
   <div class="card-header text-secondary small text-uppercase fw-normal" style="border-color:#21262d">
     Estimate
     <span class="text-secondary fw-normal ms-2" style="font-size:.7rem">
-      20 % infill · {{ estimation.price_per_kg }} €/kg · {{ estimation.vat_rate }}% VAT
+      {{ (estimation.material_factor * 100) | round | int }}% material factor
+      · {{ estimation.print_speed | int }} g/h
+      · {{ estimation.price_per_kg }} €/kg
+      · {{ estimation.vat_rate }}% VAT
     </span>
   </div>
   <div class="card-body">