# 🛠 Calibration & Tolerance Testing  
*PVC Friction-Fit Dial-In System*

This folder contains OpenSCAD scripts and calibration STLs used to fine-tune the press-fit connection between the modular PVC frame and 3D-printed hubs.

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## 🎯 The Challenge

PVC pipe OD varies by brand + batch.  
3D printers introduce tolerance changes due to:
- Shrinkage
- Flow variance
- Layer squish
- Heat expansion

To achieve the ideal **“firm twist, no hammer”** fit, we use **Ring Tests** to identify the correct clearance offset.

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## 📋 Test Parameters

| Setting | Value |
|--------|-------|
| Material | PLA+ (re-test per brand change) |
| Printer | Elegoo Centauri Carbon (CoreXY) |
| Wall Thickness | 3.0 mm |
| Test Height | 10 mm |
| Inner Surface | Chamfered 3 mm |

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## 🔍 Notch System — Physical Versioning

Each ring includes notches on the outer wall that define its offset.

| Notches | 1″ Offset | ½″ Offset | Fit Description |
|:------:|:---------:|:---------:|----------------|
| 1 | +0.05 mm | +0.10 mm | Extreme press-fit (heat needed) |
| 2 | +0.10 mm | +0.15 mm | Structural tight fit |
| 3 | +0.15 mm | +0.20 mm | **Current Standard — Recommended** |
| 4 | +0.20 mm | +0.25 mm | Smooth sliding fit |
| 5 | +0.25 mm | +0.30 mm | Loose / removable |
| 6 | +0.30 mm | +0.35 mm | Oversized — needs shim |

> Current Winner (as of R1): **Notch 3** on **Charlotte Pipe** + **PLA+**

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## 🚀 How to Run a New Calibration

Run this when:
- New filament
- New PVC supplier
- Temperature change in workspace

**Process**
1. Open `tolerance_test_array.scad`
2. Select correct pipe size block (1″ or ½″)
3. Render + export STL
4. Print @ 0.20 mm layer height (no supports)
5. Test each ring using **the actual pipe**
6. Update `fit_offset` in hub OpenSCAD files

➡ Files to update:
- `hub_H1.scad`
- `hub_H2.scad`
- `hub_H3.scad`

Record results in **CHANGELOG.md**

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## ⚠️ Flow Rate First

Before testing tolerances:
- Calibrate **extrusion multiplier**
- Ensure **bed leveling** is perfect
- Dry filament if needed

Bad flow = bad sockets.

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## 🌡️ Environmental + Speed Troubleshooting

| Issue | Symptom | Root Cause | Quick Fix |
|------|---------|------------|-----------|
| Thermal Expansion | Morning fit ≠ afternoon fit | Workspace heat | Test at real use temp |
| Wall Bulge | Lumpy inner walls | Overspeed / PA not tuned | Reduce **inner wall speed** |
| Elephant’s Foot | Jams only at bottom | First layer squish | Chamfer + reduce initial expansion |
| Moisture | Rough interior / blobs | Wet filament | Dry filament fully |

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## 🛠 Quick Field Repairs

| Symptom | Fast Fix |
|--------|----------|
| Slightly too tight | Sand pipe end w/ 80-grit |
| Slightly loose | 1 wrap electrical tape |
| Won’t start at all | Scrape blobs inside socket |
| Pops out | Warm PVC and flare slightly |

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## 📌 Calibration Status Log

| Round | Offset | Filament | Printer Profile | Environment | Notes |
|------|--------|----------|----------------|-------------|------|
| R1 | +0.15 mm (Notch 3) | PLA+ | 0.4mm / 0.20mm | 22°C Indoor | Current baseline |

> Update each time PVC or filament changes.

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## Folder Structure
## 📌 Calibration Status Log

| Round | Offset | Filament | Printer Profile | Environment | Notes |
|------|--------|----------|----------------|-------------|------|
| R1 | +0.15 mm (Notch 3) | PLA+ | 0.4mm / 0.20mm | 22°C Indoor | Current baseline |

> Update each time PVC or filament changes.

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## Folder Structure

/calibration
├── tolerance_test_array.scad
├── ring_notch_tests/
│ ├── 1in_ring_test_x6.stl
│ └── 1-2in_ring_test_x6.stl
├── results/
│ ├── R1_report.md
│ └── images/
└── README.md (this file)

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## Best Practices Summary

- Tune flow **before** tolerances  
- Use real pipe sections for testing  
- Store PVC indoors for consistent sizing  
- Validate at expected booth temperature

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If this README is updated, **increment version** in CHANGELOG.

Version 1.0 — Initial Documentation

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