PVC-Paintbooth/calibration/readme.md

🛠 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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