Parametric Pipe & Duct Adapter (Round ↔ Rectangle, Offset-Capable)

This is a fully parametric duct reducer/expander for dust collection and ventilation projects such as window ducts. It generates a hollow adapter with a straight insert on each end and a smooth transition in between.

The key feature is that each end can be round or rectangular, and rectangular ends can be shifted in X/Y to line up with off-center ports (super handy for shrouds, tool ports, and awkward clearances).

Features

• Round or rectangle on either end
• Rectangle width/height + X/Y offset (move the rectangle to one side to match your port)
• Adjustable wall thickness
• Adjustable insert lengths on both ends
• Smooth transition section (length adjustable)
• Optional lead-in chamfer for easier sliding fit (round ends only)
• Optional retention stop rings (round ends only)
• Optional transition ribs for strength (round→round only)
• Optional bolt flanges with bolt circle + hole count (round ends only)
• Debug cutaway mode to check wall thickness and fit before printing

How to use

1. Open the model
   • Click ‘Customise’ above to use MakerWorld’s Parametric Model Maker, or
   • Download the .scad file and open it in OpenSCAD
2. Start with a preset (optional)
   • Choose a preset for common round hose sizes, or
   • Leave it on Custom and enter your own dimensions
3. Choose the shape for each end
   • Set Blue_End_Shape and Green_End_Shape to:
     • Round for circular ducts, or
     • Rectangle for rectangular ports
4. If you choose a rectangle
   • Set the rectangle width and height for that end
   • Use the X and Y offset settings to slide the rectangle sideways until it lines up with your port
5. Generate your model
   • Render the model (F6 in OpenSCAD, or Generate in MakerWorld)
   • Export the STL and print

Printing tips

• Print with the long axis vertical if you want the cleanest circular/rect profile, or horizontal if you want fewer supports (depends on your transition length and printer).
• For dust collection parts, 0.2–0.28mm layer height and 3–5 perimeters usually gives a strong, airtight part.
• If you need a tighter/looser fit on round ends, tweak:
  • Blue_End_Fit_Adjustment / Green_End_Fit_Adjustment
• For strength, increase Wall_Thickness and/or enable transition ribs (round→round).

Compatibility notes

• Lead-in chamfers, retention stops, ribs, and flanges are designed for round ends.
• If an end is set to Rectangle, those round-only features for that end are automatically ignored.

License / remix

Remixes welcome — if you improve rectangle-specific features (like rectangular flanges or rectangular retention lips), please share it back!