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🛠 Calibration & Tolerance Testing
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This subfolder contains the utility scripts and STL files used to calibrate the friction-fit tolerances between the 3D-printed connectors and the PVC piping.
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# 🛠 Calibration & Tolerance Testing
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*PVC Friction-Fit Dial-In System*
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The Challenge
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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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PVC pipe outer diameters (OD) vary slightly by manufacturer, and 3D printers experience material shrinkage. To achieve a "hammer-tap" friction fit without using glue, we use Ring Tests to find the perfect offset.
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---
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📋 Test Parameters
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## 🎯 The Challenge
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Material: [Your Filament, e.g., PLA+]
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PVC pipe OD varies by brand + batch.
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3D printers introduce tolerance changes due to:
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- Shrinkage
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- Flow variance
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- Layer squish
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- Heat expansion
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Printer: Elegoo Centauri Carbon (CoreXY)
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To achieve the ideal **“firm twist, no hammer”** fit, we use **Ring Tests** to identify the correct clearance offset.
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Wall Thickness: 3.0mm
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---
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Test Height: 10mm
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## 📋 Test Parameters
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🔍 Understanding the Notch System
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| Setting | Value |
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|--------|-------|
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| Material | PLA+ (re-test per brand change) |
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| Printer | Elegoo Centauri Carbon (CoreXY) |
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| Wall Thickness | 3.0 mm |
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| Test Height | 10 mm |
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| Inner Surface | Chamfered 3 mm |
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To avoid confusion after removing parts from the build plate, each ring is physically marked with "Notches" on the outer wall.
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---
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Notches 1" Offset (mm) 1/2" Offset (mm) Fit Description
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1 +0.05 +0.10 Extreme Press-fit (Heat may be required)
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2 +0.10 +0.15 Tight Structural Fit
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3 +0.15 +0.20 Current Project Standard (Winner)
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4 +0.20 +0.25 Standard Sliding Fit
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5 +0.25 +0.30 Loose / Removable Fit
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6 +0.30 +0.35 Oversized / Needs Shim
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🚀 How to Run a New Calibration
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## 🔍 Notch System — Physical Versioning
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If you switch filament brands or buy PVC from a different hardware store:
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Each ring includes notches on the outer wall that define its offset.
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Open tolerance_test_array.scad.
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| Notches | 1″ Offset | ½″ Offset | Fit Description |
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|:------:|:---------:|:---------:|----------------|
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| 1 | +0.05 mm | +0.10 mm | Extreme press-fit (heat needed) |
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| 2 | +0.10 mm | +0.15 mm | Structural tight fit |
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| 3 | +0.15 mm | +0.20 mm | **Current Standard — Recommended** |
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| 4 | +0.20 mm | +0.25 mm | Smooth sliding fit |
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| 5 | +0.25 mm | +0.30 mm | Loose / removable |
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| 6 | +0.30 mm | +0.35 mm | Oversized — needs shim |
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Render and export the STL for your specific pipe size (1" or 1/2").
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> Current Winner (as of R1): **Notch 3** on **Charlotte Pipe** + **PLA+**
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Print with 0.2mm layer height and no supports.
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---
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Test each ring on a scrap piece of the actual pipe you intend to use.
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## 🚀 How to Run a New Calibration
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Update the off or off12 variables in the main hub.scad files with the new winning value.
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Run this when:
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- New filament
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- New PVC supplier
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- Temperature change in workspace
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⚠️ Maintenance Note
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**Process**
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1. Open `tolerance_test_array.scad`
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2. Select correct pipe size block (1″ or ½″)
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3. Render + export STL
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4. Print @ 0.20 mm layer height (no supports)
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5. Test each ring using **the actual pipe**
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6. Update `fit_offset` in hub OpenSCAD files
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Because the Centauri Carbon is a high-speed machine, ensure your Flow Rate is calibrated before running these tests. If the flow rate is too high, it will "over-stuff" the walls and make the holes smaller than the CAD intends.
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➡ Files to update:
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- `hub_H1.scad`
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- `hub_H2.scad`
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- `hub_H3.scad`
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🌡️ Troubleshooting & Environmental Factors
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Record results in **CHANGELOG.md**
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3D prints and PVC pipes are both susceptible to thermal expansion and moisture. If your "Winner" (Notch 3) suddenly feels off, check the following:
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---
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1. Thermal Expansion (The Garage Factor)
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## ⚠️ Flow Rate First
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The Issue: PVC and PLA/PETG expand when hot. A fit that is perfect in a cool morning might become "seized" in a hot afternoon garage.
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Before testing tolerances:
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- Calibrate **extrusion multiplier**
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- Ensure **bed leveling** is perfect
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- Dry filament if needed
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The Fix: If the booth is for outdoor or garage use, calibrate your rings at the average temperature of the workspace. If the fit is too tight to disassemble, use a hair dryer or heat gun (on low) to slightly soften the plastic.
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Bad flow = bad sockets.
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2. Wall Bulge (Speed & Acceleration)
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---
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The Issue: On high-speed printers like the Centauri Carbon, the printer may "overshoot" corners or circles if the Jerk or Pressure Advance settings aren't dialed in. This causes the inner walls of the socket to bulge inward.
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## 🌡️ Environmental + Speed Troubleshooting
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The Fix: If the ring feels "lumpy" inside rather than smooth, reduce your Inner Wall Speed by 25% and re-test.
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| Issue | Symptom | Root Cause | Quick Fix |
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|------|---------|------------|-----------|
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| Thermal Expansion | Morning fit ≠ afternoon fit | Workspace heat | Test at real use temp |
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| Wall Bulge | Lumpy inner walls | Overspeed / PA not tuned | Reduce **inner wall speed** |
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| Elephant’s Foot | Jams only at bottom | First layer squish | Chamfer + reduce initial expansion |
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| Moisture | Rough interior / blobs | Wet filament | Dry filament fully |
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3. Elephant's Foot (First Layer Squish)
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---
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The Issue: If the pipe fits into the top of the hub but gets stuck at the very bottom, you have "Elephant's Foot." The first layer is squished too hard against the bed, narrowing the opening.
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## 🛠 Quick Field Repairs
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The Fix: Use a deburring tool or a hobby knife to chamfer the inside bottom edge of the print. In the slicer, you can also adjust "Initial Layer Horizontal Expansion" to a negative value (e.g., -0.1mm).
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| Symptom | Fast Fix |
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|--------|----------|
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| Slightly too tight | Sand pipe end w/ 80-grit |
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| Slightly loose | 1 wrap electrical tape |
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| Won’t start at all | Scrape blobs inside socket |
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| Pops out | Warm PVC and flare slightly |
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4. Moisture Absorption (Filament Swelling)
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---
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The Issue: Wet filament (especially PETG or cheap PLA) bubbles and creates a rougher surface texture. This increased friction makes a +0.15mm offset feel like a +0.05mm offset.
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## 📌 Calibration Status Log
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The Fix: Dry your filament. If the surface of your ring test looks "fuzzy" or has tiny zits, your tolerances will never be consistent.
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| Round | Offset | Filament | Printer Profile | Environment | Notes |
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|------|--------|----------|----------------|-------------|------|
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| R1 | +0.15 mm (Notch 3) | PLA+ | 0.4mm / 0.20mm | 22°C Indoor | Current baseline |
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Quick Reference: "The Field Repair"
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> Update each time PVC or filament changes.
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Symptom Quick Fix
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Slightly too tight Sand the tip of the PVC pipe with 80-grit sandpaper.
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Slightly too loose Add one wrap of electrical tape around the end of the PVC pipe.
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Pipe won't go in at all Check for "zits" inside the print; scrape with a flathead screwdriver.
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---
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## Folder Structure
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## 📌 Calibration Status Log
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| Round | Offset | Filament | Printer Profile | Environment | Notes |
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|------|--------|----------|----------------|-------------|------|
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| R1 | +0.15 mm (Notch 3) | PLA+ | 0.4mm / 0.20mm | 22°C Indoor | Current baseline |
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> Update each time PVC or filament changes.
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---
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## Folder Structure
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/calibration
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├── tolerance_test_array.scad
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├── ring_notch_tests/
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│ ├── 1in_ring_test_x6.stl
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│ └── 1-2in_ring_test_x6.stl
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├── results/
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│ ├── R1_report.md
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│ └── images/
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└── README.md (this file)
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---
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## Best Practices Summary
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- Tune flow **before** tolerances
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- Use real pipe sections for testing
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- Store PVC indoors for consistent sizing
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- Validate at expected booth temperature
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---
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If this README is updated, **increment version** in CHANGELOG.
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Version 1.0 — Initial Documentation
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---
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