Metal Panel Cutting, Bending, and Shop Fabrication

Metal Panel Cutting, Bending, and Shop Fabrication

Shop fabrication is where raw flat-sheet metal becomes the trim profiles, flashings, and panels that protect a building. Before any tool touches metal, every student must complete the tool-identification and hazard checklist and confirm PPE is in place: cut-resistant gloves rated ANSI A4 or higher, safety glasses, and hearing protection are required throughout every fabrication activity. Any PPE violation requires an immediate stop, correction, and restart of that activity.

Understanding the Sheet Stock

This lab uses 24-gauge Galvalume steel—a hot-dipped aluminum-zinc alloy-coated steel. The coating resists corrosion far better than bare steel and is the industry standard for exposed metal roofing trim. "24-gauge" refers to the sheet's thickness in the U.S. standard gauge system; the higher the gauge number, the thinner the metal. 24-gauge sheet is stiff enough to hold a clean fold yet thin enough for hand tools and a portable brake to shape accurately.

Edges cut from sheet metal are razor-sharp. Even with gloves on, never drag a bare hand along a freshly cut edge. After cutting, immediately deburr or fold raw edges away from the installer's contact surface.

Cutting Tools and Their Hazards

Aviation snips come in three colors: red handles cut left curves, green handles cut right curves, and yellow handles cut straight or wide curves. Snips are best for short cuts, notches, and starting an interior cut. The waste strip curls sharply—keep it controlled and dispose of it in the scrap bin immediately.

Electric shears use two blades that shear the metal with minimal distortion. They make long, straight cuts quickly. Keep both hands behind the cutting head; never reach across the cut line while the tool is running. Unplug or release the trigger lock before changing blades or clearing jams.

Nibblers punch out a continuous narrow strip of metal chips (the "nibble"). They are excellent for curves and for cutting without distorting the panel face. Metal chips are sharp projectiles—keep bystanders clear and wear eye protection. Dispose of chips promptly.

Marking and Measuring

Accurate marking is the foundation of accurate fabrication. Use a scribe (a hardened steel point) rather than a pencil or marker on bare metal; a scribed line is precise and does not smear. Lay a steel square or straightedge along the cut line before scribing to keep the line true. Measure from the same reference edge for every dimension on a single piece to avoid stacking errors.

The Portable Brake: Making Accurate Bends

A portable sheet-metal brake clamps the sheet between an upper clamping bar and a lower bed, then a bending leaf rotates upward to form the angle. Key operating points:

1. Set the clamping depth by aligning the scribed bend line with the front edge of the upper clamping bar. Even a 1/16-inch misalignment shifts the leg length of the fold.

2. Clamp firmly before bending. A loose clamp allows the sheet to slip and ruins the angle.

3. Bend in a single smooth motion to the required angle. Stopping partway and restarting can leave a crease in the face.

4. Account for springback. Steel springs back a few degrees after the bending leaf returns. Experienced fabricators overbend slightly and test on scrap until the final angle is correct before bending the production piece.

A hem fold is a tight 180-degree fold that turns a raw edge back on itself, eliminating the sharp cut edge and adding stiffness. To make a hem: first bend the edge to about 45 degrees on the brake, then flatten the fold completely using the brake or hand seamers.

Hand Seamers

Hand seamers are flat-jaw pliers used to make small bends, close hems tightly, and adjust a fold that is slightly off angle. Place the jaw squarely on the bend line and apply even pressure. Hand seamers excel at detail work and field corrections but are too slow for long production bends.

Shop Drawing Discipline

Every fabricated piece follows a shop drawing—a dimensioned sketch showing all leg lengths, bend angles, and the finished profile. Verify each dimension with a tape measure before moving to the next operation. Check at three points along the length of any piece: at each end and at the center. Variation across the length can indicate a twisted blank or an uneven brake clamp.

Gable Rake Trim and Eave Drip Edge

Gable rake trim covers the sloped edges of a roof, protecting the sheathing edge and giving a finished appearance. It typically has two or more hem folds.

Eave drip edge runs along the low edge of the roof, directing water off the deck and into the gutter. A typical eave drip-edge profile has a flat top flange, a vertical face, and a short outward kick at the bottom. Dimensions on the shop drawing must be met within ±1/8 inch at every check point; tighter is better. Burrs on any edge that an installer's hand could contact must be removed before the piece is accepted.

Quality Check and Go/No-Go Gauges

A go/no-go gauge is a physical template cut to the exact profile of the finished piece. Slide the finished piece into the gauge: if it fits through the "go" slot and does not fit through the "no-go" slot, dimensions are within tolerance. Combined with three-point tape measurement, the gauge gives a fast, objective acceptance test.