What is a ʼSweepʼ (1 rail vs. 2 rails) in Rhino?
Short Answer
In Rhino, a sweep creates a surface by moving one or more profile curves along rail curves. The most common professional method is Sweep1 for one rail and Sweep2 for two rails, with Sweep2 used when both edges must be controlled. It can fail if rails or sections are poorly aligned.
What You Need to Know Before
Warning: Sweep failures in Rhino usually come from bad curve structure, especially mismatched profile directions, profiles not intersecting rails, or rails with kinks. A sweep may also twist unexpectedly if seam positions and curve directions are not checked before running the command.
How to Do a Sweep in Rhino
Command: Sweep1 / Sweep2
Shortcut: Sweep1 / Sweep2
Quick Steps:
- Start Sweep1 or Sweep2 from the Surface menu or type the command in the command line.
- Select the rail curve for Sweep1, or the two rail curves for Sweep2, then press Enter.
- Select the profile curves in order, then review options like MaintainHeight, ClosedSweep, or Refit cross sections, and press Enter to create the surface.
Variables & Settings
Key Setting: Refit cross sections / MaintainHeight
Expert Setting: Refit cross sections simplifies section curve data for a lighter surface, while MaintainHeight helps preserve profile shape during the sweep. In production modeling, these options directly affect surface smoothness, editability, and accuracy.
Why it Fails
Cause 1 (Geometry): Profile curves do not touch both rails in Sweep2, or do not intersect the rail correctly in Sweep1, causing failure or distorted surfaces.
Cause 2 (layers/Locks): Rails or section curves are on locked layers, hidden, or hard to select because sub-objects or overlapping curves are being picked instead.
Cause 3 (Command/Logic): The wrong sweep type is used—Sweep1 when both side boundaries must be controlled, or Sweep2 with non-matching rail structure, causing twisting or uneven results.
Quick Fix & Best Practice
- Quick Fix: Run Dir to verify curve directions, then use Rebuild or SimplifyCrv on inconsistent rails or sections before repeating Sweep1 or Sweep2.
- Manager’s Verdict: Use Sweep1 for fast, standard forms driven by one path. Use Sweep2 when edge control matters, such as product skins or trimmed side-defined shapes, but clean the input curves first.
FAQ
What is the difference between Sweep1 and Sweep2 in Rhino?
Sweep1 uses one rail; Sweep2 uses two rails to control both sides of the surface.
Why does Sweep2 twist in Rhino?
Twisting usually happens when profile directions, seams, or rail structure do not match.
Can sweep create a solid in Rhino?
Only if the sweep result is closed or later capped with commands like Cap.
.