Carve a channel through a model

Run a tapering, curving tube through any shape and subtract it — dice towers, lamp cords, marble runs.

A channel is a hole that bends. Anything that has to get from one part of a model to another — a die tumbling down a tower, a lamp cord leaving a shade, a marble, a length of wire — needs one, and it is the same move every time: build the empty space as a solid, then subtract it.

The sweep IS the hole. That is the mental flip worth making early. You are modelling the space you want to be empty, so draw the cross-section at the size the passage should be, not the size of the wall around it. Until you subtract it, it is an ordinary solid you can move, rotate, and re-edit like any other.

Taper is what makes a chute work. Each path point carries a size multiplier — ×1 is the cross-section as you drew it, ×3 is three times as wide — and the size blends smoothly between points. A dice tower wants a wide mouth necking down to a narrow exit, which is three points and two numbers. It is a multiplier rather than a millimetre diameter because your cross-section can be any shape at all, and a square duct has no "diameter"; the read-out beside each field does the arithmetic so you can still work in millimetres.

Smooth rounds the corners off, so place points where you want the run to HEAD. It curves each corner by as much as the neighbouring legs allow, which means the run passes close by an intermediate point rather than exactly through it — the two ends stay exactly where you put them, which is what matters for breaking the surface. Want the channel to hug a particular spot? Put points either side of it rather than on it.

If the tube disappears, the panel says why, and it is telling you something true: a run that bends tighter than it is wide would have to pass through itself, so it refuses rather than exporting a broken solid. Move the points further apart, soften the bend, or make the cross-section narrower at that point.

Break the surface at both ends. A channel that stops flush with the outside leaves a skin over the opening. Push the first and last points a little way outside the model — the extra length is subtracted into thin air and costs nothing.

Last, check what is left. A channel through the middle of a part can leave walls thinner than your printer can lay down, and the print check is what catches that before the print does.

1. Add a Sweep — it carries a cross-section along a path, which is the tube you are about to cut away.
2. Click Edit cross-section and draw the hole's shape: a circle for a cord, a square for a duct. Keep it one simple closed outline.
3. Click Draw path and click along the route, viewed from the side — or type each point's X, Y and Z into the Properties panel.
4. Tick Smooth path so the run curves instead of turning square corners.
5. Set the × under each point to taper the run — wide at the mouth, narrow at the exit. The millimetre width beside each field is what it works out to.
6. Move the sweep so it passes through your model and breaks the surface at both ends.
7. Select the model first, then the sweep, and Subtract — the tube becomes the channel and the model keeps everything else. Order matters: subtract keeps the FIRST body. If the model disappears and you are left holding the tube, press Flip order in the Properties panel.
8. Run the print check to confirm the walls left around the channel are thick enough, then export.