Rhino has no sheet metal tools of its own. UnrollSrf flattens developable surfaces, but it measures along the surface
you give it. It knows nothing about thickness, bend radius or K-factor, so the flat pattern comes out the wrong size as
soon as the material has real thickness.
SheepMetal adds the missing part as a Grasshopper plugin: it reads a part as sheet metal, unrolls it with bend compensation, and gives you the bend data and nesting the shop needs.
What a sheet metal workflow needs#
| Step | What it means | SheepMetal |
|---|---|---|
| Recognize the part | Know which faces are flanges, bends, hems and holes | Creation components turn geometry into a Sheet |
| Reliefs and seams | Cut slots where bends end and open closed corners so the part folds | Edge Relief Options, Corner Relief Options |
| Flat pattern | Unroll along the neutral axis, not the outside face | Unroller with a K-factor or bend table |
| Bend data | Angle, direction and position of every bend for the press brake | Bend Info, Sheet Info |
| Nesting | Pack the flat parts onto stock sheets | Nest Parts, Sheet Stock |
Pick a modelling route#
Use the route that matches the geometry you already have.
| You have | Use |
|---|---|
| A closed solid with thickness, e.g. a STEP | Manifold To Sheet (MTS) |
| Thin surfaces with sharp edges | Non-Manifold To Sheet (NMTS) |
| One straight fold profile (bracket, channel) | Polyline To Sheet (PTS) |
The surface route is the most flexible: you model without thickness, and each sharp edge becomes a bend. Step-by-step versions of all three are in Common Workflows.
From model to flat pattern#
- Turn the geometry into a Sheet with one of the components above. Set Thickness and Bend Radius.
- Check it with Display Sheet (DS). Flanges, bends and hems are colored, so a missed bend shows at a glance.
- Wire the Sheet into the Unroller (U). The Unrolled output is the flat pattern; Bend Axes are the fold lines.
- Set Orient to Bend Axes so identical parts always come out the same way round.
Getting the flat size right#
When metal bends, the outside stretches and the inside compresses. The flat length is measured along the layer that keeps its length, the neutral axis. Where that layer sits is the K-factor: 0 is the inside face, 0.5 the middle. Most metals fall between 0.3 and 0.5.
The Unroller's Compensation Strategy input sets how each bend is sized:
- A single K-factor: a number from 0 to 1. Empty uses 0.45.
- K-Factor Table (By Angle) (KFT): a K-factor per bend angle, for when tight and shallow bends behave differently.
- K-Factor Table (By Angle + Direction) (DSKF): also split by fold direction.
- Bend Correction Table (BCT): your press brake's measured correction per thickness, radius and angle.
Bend data for the press brake#
Wire the Unroller's Unroll Result into Bend Info (UBI). It lists angle, fold direction (up or down), bend allowance, radius and a label for every bend, with a centre point you can use to place the label in Rhino.
Unroll Mapper (UMap) moves 3D points and curves onto the flat, for marking lines or drill points. Reroll goes the other way: it maps curves drawn on the flat back onto the 3D part.
Nesting and cutting#
Once the parts are flat, Nest Parts packs them onto your stock sheets by their true outlines and reports the yield. See Nesting Sheet Metal Parts in Grasshopper.
Limits#
- Rolled and cylindrical parts are not supported.
- Non-Manifold To Sheet and Polyline To Sheet use one bend radius for all bends of a part. Hems get their own.
- Check every flat pattern before you cut. Troubleshooting covers the common failures.