Update October challenge: Change to 25mm x 50mm cylinder in vase mode

- Replace pre-supplied model with standard cylinder specification
- Update to vase mode printing (~6g filament vs 250g limit)
- Add vase mode specific tips and requirements
- Update timeline to reflect model spec release date

challenges.md

@@ -19,7 +19,8 @@ Experience the clarity of 3D Fuel's "Clearly Natural" filament in this transpare
   - PCTG (Polyethylene Terephthalate Glycol)
   - PLA (Polylactic Acid)
 - **Maximum Filament Usage**: 250g per entry
-- **Model**: Pre-supplied design (will be distributed to participants)
+- **Model Specification**: Cylinder - 25mm diameter × 50mm height
+- **Print Mode**: Vase mode (approximately 6 grams of filament)
 
 #### Competition Categories
 
@@ -36,7 +37,9 @@ Experience the clarity of 3D Fuel's "Clearly Natural" filament in this transpare
 
 #### Submission Requirements
 
-- **Weight Verification**: Final print must be weighed to confirm 250g filament limit
+- **Model Compliance**: Cylinder must measure 25mm diameter × 50mm height
+- **Vase Mode**: Must be printed in vase mode (single perimeter wall)
+- **Weight Verification**: Should use approximately 6 grams of filament
 - **Documentation**: Include photos showing transparency (with light sources)
 - **Settings Documentation**: Share printer settings used (layer height, temperature, speed, etc.)
 - **Process Notes**: Brief description of techniques used to achieve clarity
@@ -67,15 +70,16 @@ Experience the clarity of 3D Fuel's "Clearly Natural" filament in this transpare
 ### 📅 Timeline
 
 - **Challenge Announcement**: October 1, 2025
-- **Model Distribution**: October 3, 2025
+- **Model Specification Released**: October 13, 2025
 - **Submission Deadline**: October 28, 2025
 - **Judging Period**: October 29-30, 2025
 - **Winner Announcement**: October 31, 2025
 
 ### 💡 Tips for Success
 
-- Experiment with layer heights (smaller often helps with clarity)
-- Consider post-processing techniques (vapor smoothing, sanding)
-- Optimize print orientation for minimal support material
-- Temperature tuning can significantly impact clarity
-- Consider printing speed adjustments for better layer bonding
+- **Vase Mode Settings**: Ensure single perimeter, no infill, no top layers
+- **Layer Height**: Experiment with smaller layer heights (0.1-0.2mm) for better clarity
+- **Print Speed**: Slower speeds in vase mode often improve surface quality
+- **Temperature Tuning**: Optimal temperature is critical for transparency
+- **Cooling**: Proper part cooling helps maintain wall quality in vase mode
+- **Post-Processing**: Light sanding or vapor smoothing can enhance clarity