Twisted Extrudes
Use Twist to make an extrude spiral as it rises instead of going up straight. Select a region, press E, and set the Twist field in the extrude popover. The profile rotates as it climbs, so the walls come out as a smooth spiral rather than a stack of flats: a vase, a knurled grip, a duct that turns as it goes up.
What it does
The field takes degrees, up to 3600 either way, which is ten full turns positive one way and negative the other. Zero is a straight prism, and the field sits at zero until you say otherwise.
The rotation happens about the profile's own centre, not about the sketch origin. A square drawn off to one side twists where it stands. Position the profile before you set the angle. If you have used a CAD package that rotates about the sketch origin instead, expect the shape to stay exactly where you drew it here.
Draft angle has no control in this release. Draft is a taper that opens or narrows the section as it rises. The extrude popover has no field for it, so you cannot set one here. You may still see draft named on a document that came from a script.
| Range | −3600° to 3600° |
| Rotates about | The profile's own centre |
| Works with | Any end condition, and with draft |
| Silently ignored when | The region has a hole, or Stepped profile is on |
The two cases where it does nothing
Both cases are quiet, so learn to recognise them on sight.
A region with a hole comes out straight. The twisted prism is built by lofting between rotated copies of one loop, and that construction has no answer for a second loop inside the first. Rather than fail, the extrude falls back to the straight prism and drops the twist. To get a twisted part with a hole down it, twist the solid and cut the hole as its own feature afterwards.
A stepped profile wins. Turning on Stepped profile takes over the shape of the prism entirely, and the Twist field is disabled while it is on.
Why a big twist on a detailed profile can go wrong
The spiral is not a mathematical surface. It is a loft through a stack of intermediate sections, one every four degrees, between eight and 240 of them. That is enough for the shapes people twist. It stops being enough when the profile has many edges and the twist is large: once the rotation between two neighbouring sections exceeds the angular spacing of the profile's own edges, the loft can link the wrong pair and the faces cross.
Give a lot of twist a simple profile. A hexagon can take ten turns; a hundred-tooth gear cannot. If the result comes out tangled, take the turns down before you take the detail out.
See also
- Extrude and Cut: the fields a twist sits on top of
- Stepped Extrudes: the other control that takes over the prism
- Helical Sweep: when you want a spiral rather than a twist