Sheet metal parts are cut from flat sheet of even thickness, then bent into shape. This page explains the terms used across the SheepMetal docs.
Parts of a sheet#
SheepMetal sorts every face of a part into one of these types. Display Sheet colors them, Sheet Info counts them, and Explode Sheet splits them apart.
- Flange: a flat area of the part. Holes and cutouts sit in flanges.
- Bend: the curved strip that joins two flanges. Its surfaces are cylinders.
- Hem: an edge folded back onto itself, to stiffen it or remove a sharp edge.
- Thickness face: the narrow faces around the outline and inside holes that show the material thickness.
- Holes: an I-Hole (isolated) sits inside one flange. An NI-Hole (non-isolated) crosses a bend, so it cuts into more than one face. A C-Hole is a countersink hole, with a cone for a flat-head screw.
Sides and the root face#
- Root face: the flange the part is built from. It stays in place when the part is unrolled. Set it with the Root Face input on the creation components.
- Side 0 and Side 1: the two faces of the sheet. Side 0 is the side of the root face.
- Bend direction: a bend folds Up or Down, relative to Side 0.
- Bend angle: how far a bend folds, in degrees. A right-angle bend is 90°.
Ways to model a part#
- Manifold: a closed solid with real thickness. Use Manifold To Sheet.
- Non-manifold: thin surfaces with no thickness and sharp edges. Non-Manifold To Sheet adds the thickness and turns each sharp edge into a bend.
- Profile: a polyline cross-section pulled straight. Use Polyline To Sheet.
Reliefs and seams#
- Edge relief: a small slot cut where a bend line ends at the edge of the part, so the metal does not tear.
- Corner relief: a cut where two or more bends meet, so the bends do not collide.
- Closed corner: a corner where the faces go all the way round, like a box corner. It cannot be flattened unless it is cut open somewhere. That cut is the seam.
Unrolling#
When metal bends, the outside stretches and the inside compresses. The layer in between keeps its length: the neutral axis. The flat pattern is measured along it.
- Bend radius: the inside radius of a bend.
- K-factor: where the neutral axis sits, as a fraction of the thickness from the inside. 0 is the inside face, 0.5 the middle. Most metals fall between 0.3 and 0.5. Use the value your shop has measured.
- Bend allowance (BA): the length of the neutral axis through the bend.
BA = (π / 180) × Angle × (Radius + K × Thickness), with the angle in degrees. - Bend deduction (BD): how much shorter the flat is than the two flanges measured to where they would meet.
BD = 2 × (Radius + Thickness) × tan(Angle / 2) − BA. - Compensation strategy: how the Unroller sizes each bend. A single K-factor, a K-factor table, or a press-brake correction table.
Design tips#
- Use a bend radius of at least the material thickness.
- Keep holes away from bends, or they stretch.
- Keep the thickness even across the whole part.