#Sheet metal

<sheetMetal> builds a folded sheet-metal part and its flat pattern. You draw the base outline once and hang flanges off its edges, nesting them as deep as you like. Bends are exact cylindrical sections. The flat pattern unfolds each bend by its bend allowance and comes out as drawings ready for a laser and a press brake.

<part name="bracket" material="steel">
  <sheetMetal name="bracket" thickness={2} bendRadius={2} kFactor={0.44}>
    <flange>
      <rect w={60} h={40} />                          {/* the base outline (holes allowed) */}
      <circle d={5.5} />
      <edgeFlange edge="+y" length={50}>              {/* folds up 90° from the +y edge */}
        <circle d={5.5} x={30} y={30} />              {/* holes in the flange's own coordinates */}
        <edgeFlange edge="end" length={8} direction="down" />   {/* a return lip on its far edge */}
      </edgeFlange>
    </flange>
  </sheetMetal>
</part>

tscad build bracket.tsx -o bracket.step -o bracket.dxf    # folded part + flat pattern

#Elements

Edges.

• On the base: "+x" | "-x" | "+y" | "-y", the straight outline edge whose outward normal points that way (right, left, back/top and front/bottom are aliases). If several edges point that way, the outermost is used.
• On the base, edge="front" can also name a line of a constraint sketch outline by its id, and a number picks an outline segment by index.
• On an edge flange: "end" (the far edge, over the edge's own span even when corners extend the flange), "left", "right".
• On a profiled flange: outline segments by index, or constraint-sketch line ids.

Folding. The bend starts at the edge: the parent keeps its full outline, and the flange comes after the bend, so dimensions are "bend outside". The inner radius R faces the direction of the fold. Adjacent flanges (a tray's four walls) leave open corners by default (see Corners). inset / insetEnd shorten a flange along its edge. In that case rectangular bend reliefs (reliefWidth, default the thickness, depth R + T) are cut into the parent at the bend's ends; reliefs={false} turns them off.

#Corners

Where two edge flanges hang from edges meeting at a square, convex corner of their parent (a tray's walls), corner on either decides how they meet:

cornerGap defaults to min(0.2, T / 4). Both flanges must be 90°, fold the same way, have the same radius and not be profiled. Otherwise the corner stays open, with a warning if a corner was asked for.

cornerRelief cuts a relief where the two bends meet:

• "rect": a square of side cornerReliefSize (default R + T) cut into the parent at the corner.
• "round": a disc of that radius cut into the parent at the corner.
• "tear": nothing cut. With "rect" and "round", both bends stop cornerReliefSize short of the corner. The flanges themselves keep their full length.

#Profiled flanges

With profile, an edge flange's 2D children are its outline: a tapered tab, a trapezoid, a flange with a notch, plus holes inside it. They are drawn in the flange's coordinates, and the outline must stand on the bend line: a straight edge along y = 0 from x = 0 to the flange's width, with nothing below it. length is optional (the outline's height).

<edgeFlange edge="end" direction="down" inset={10} profile>
  <polygon points={[[0, 0], [90, 0], [78, 12], [12, 12]]} />
  <circle d={4} x={45} y={6} />
</edgeFlange>

#The flat pattern

Every bend is unfolded into a strip of width BA = θ·(R + K·T), its bend allowance. The flat pattern is the union of every flange's outline (holes and reliefs cut) and the bend strips, in the base's coordinates. It comes out in CompileResult.drawings:

tscad build -o part.dxf (or .svg) writes them on those layers:

• DXF: bend lines as LINE (or an open POLYLINE with entities: "polyline"), notes as TEXT centred beside the line (° as %%d).
• SVG: bend lines as a <path> without Z, notes as <text>.

Checks (tests/sheet.test.tsx):

• flat length a + BA + b for an L bracket;
• a U channel;
• a four-wall tray's cross-shaped flat;
• insets with reliefs, holes and a hem;
• a jog's offset;
• edges named by sketch line ids;
• closed (mitred), overlapped and relieved tray corners;
• a profiled tab;
• the DXF's layers, open bend entities and TEXT notes, in both entity styles;
• folded volume = flat panels × T + Σ θ·w·T·(R + T/2) (Pappus), and = flat area × T when K = 0.5.

#Examples

• examples/sheet-l-bracket.tsx: slotted base, a hole row up the flange, a return lip.
• examples/sheet-chassis.tsx: an electronics tray with vents, standoff holes, four walls with closed corners (or overlap / open, a parameter) and round corner reliefs, a connector cut-out, and tapered mounting tabs (profiled, inset with reliefs) folded out along the side walls.

#Limits

• A profiled flange's bend is as wide as its edge minus insets. Its outline stands on that whole width.
• Edges must be straight segments of the outline.
• Corners close only between two 90° edge flanges on a square convex corner. A closed corner's mitre is exact in the folded model. The flat pattern cuts square at the mitre's inside, so the corner gets welded or ground after folding.