Tutorial 9: Shape Effects — Twist and Taper/Bulge

Step 1

Apply Twist

Switch to a Square cross-section so the twist is clearly visible. Add Twist from the Shape category in the effect picker.

Set the Rotation parameter to 90 degrees. The 3D preview shows the square base gradually rotating as it rises — at the top, the square is rotated 90° from the bottom.

Step 2

Adjust the rotation

Try different rotation values:
- 45° — subtle twist, the top is slightly rotated
- 180° — half turn, dramatic spiral effect
- 360° — full rotation, the top aligns with the bottom again
- 720° — two full rotations, creating a tight helical spiral

Watch the 3D preview with each value. On a square cross-section, 90° creates a visually satisfying quarter-turn where each face transitions smoothly into the next.

Step 3

Apply Taper/Bulge

Disable or remove Twist. Add Taper/Bulge from the Shape category. This effect scales the cross-section radius at different heights:

Key parameters:
- Top Scale — multiplier for the radius at the top. Values > 1 widen the top; values < 1 narrow it.
- Bottom Scale — multiplier for the radius at the bottom.
- Bulge — adds a mid-height radial expansion (positive values) or contraction (negative values).

Step 4

Create a taper

Set Bottom Scale to 1.0 and Top Scale to 0.5. The mesh narrows toward the top — a tapered shape. Now swap: Bottom Scale 0.5, Top Scale 1.0 — the mesh widens toward the top.

Step 5

Add a mid-height bulge

Set Top Scale and Bottom Scale both to 1.0 (no taper). Increase the Bulge parameter. The mesh swells outward at mid-height, creating a barrel or pot-belly shape. Negative bulge values create a concave waist.

Step 6

Verify structural behavior

Enable the inner wall in Shell settings. Add a Twist effect and set "Inner Follows Effects" to OFF. Observe:
- The inner wall still twists along with the outer wall
- Surface effects (if any) are skipped on the inner wall, but Twist always applies to both

This is because shape effects are structural — they change the overall geometry in a way that must be consistent between inner and outer walls. If only the outer wall twisted, the walls would intersect.

Step 7

Stack Twist + texture

Create a compelling combination:
1. Add Twist at 180° — the overall shape spirals
2. Add Knurling (depth 0.5 mm) below Twist — the knurling pattern is applied to the already-twisted mesh, so the diamond grid follows the twist
3. Now reverse the order: move Knurling above Twist — the knurling is applied first to the straight mesh, then the entire textured surface is twisted

Compare the two orderings. The visual difference is subtle but important for design intent.

Step 8

Create a twisted taper

Stack both shape effects:
1. Taper/Bulge — Top Scale 0.6, Bulge moderate
2. Twist — 360°

The result is a shape that simultaneously narrows and spirals — like a twisted spire or unicorn horn. The order matters:
- Taper then Twist — the taper is applied first, creating a cone, which is then twisted
- Twist then Taper — the twist is applied first, then the tapered shape is applied to the twisted mesh

Step 9

Non-linear twist with growth curve

Add a Twist effect and open its Growth Curve editor. By default, twist is linear (constant rotation rate). With the growth curve, you can create:
- Accelerating twist — curve rises slowly at the bottom, steeply at the top. The bottom barely rotates; most of the twist happens near the rim.
- S-curve twist — slow start, fast middle, slow finish. Creates a natural-looking twist with gentle transitions.
- Step twist — sharp step in the curve creates an abrupt rotation change at a specific height, like a broken twist.

Draw the curve and watch the 3D preview update.