Draw the centerline of a run and CADdillo renders it as double-line ductwork at its true plan width, turns every corner into a radiused elbow, and tapers between sizes when you ask it to. Free, in a browser tab, exporting DXF that opens in AutoCAD.
Nothing to install. 2D plan drafting — not 3D, not BIM.
The centerline is the entity and the walls are generated from it. That is what lets you stretch a trunk line across a corridor and get a wider drawing rather than a broken one.
The DUCT command (alias DU) behaves like a polyline. Click a start point and keep clicking; the two wall lines follow at the plan width you selected. Type a length mid-drag to fix a run exactly, in feet and inches if that is how you think.
Turns generate as radiused elbows on the standard convention: a throat radius of half the duct width, which puts the centerline radius at one width and the heel at one and a half. Real arcs, three snap points per bend, and no mitred corner to clean up by hand.
Select a run and pick a different width from the properties panel — walls and elbows regenerate. Where a trunk steps down to a branch, TRANSITION draws the taper between the two sizes. Export DXF when you are done.
Duct and pipe share one generator here — they differ only in their size table and their bend radius. Which means the duct side gets the same treatment: real widths, real arcs, joints that behave.
6, 8, 10, 12, 14, 16, 18, 20, 24, 30 and 36 inches, or the metric preferred series from 150 to 900 mm. The metric list is the real series, not the imperial one converted into awkward numbers.
Throat radius at half the width puts the centerline at one width and the heel at one and a half — the radiused elbow a mechanical plan is expected to show, generated from the corner you drew.
Two same-size runs meeting end to end lose their end caps and the walls flow through, so a branch reads as continuous duct. Move one away and the caps come back — nothing to remember to clean up.
A trunk stepping down to a branch is the TRANSITION command: from size, to size, taper drawn. It couples to the runs on both ends like any other piece.
The limits are on the page on purpose. Better here than halfway through a coordination sheet.
Yes. CADdillo's editor is free at app.caddillo.com and includes the DUCT command. It runs in a browser tab with nothing to install and no CAD licence, and it draws real double-line ductwork rather than single lines you have to thicken yourself.
Yes. You pick a plan width and the walls are drawn at that width from a standard table — 6 to 36 inches imperial, 150 to 900 mm metric — with a custom width allowed for anything the table does not cover. A rectangular duct shows its width in plan and carries its height in the tag text, which is how a plan drawing is conventionally read.
Automatically, and to the standard radiused convention: the throat radius is half the duct width, so the centerline radius equals one width and the heel radius is one and a half. Each bend is real arc geometry with three snap points, so a dimension or an adjoining run attaches to the bend itself.
Yes — that is the TRANSITION command (alias TRA or REDUCER). It asks for the size you are coming from and the size you are going to, then draws the concentric taper between them. You can also just change a run's width in the properties panel if the whole run should be a different size.
Yes. DXF export writes the drawn double-line geometry together with the centerline and the size data, so an AutoCAD, BricsCAD, LibreCAD or DraftSight user sees the complete layout. Open the same DXF back in CADdillo and the runs come back as live runs you can restretch and resize.
