Inside bend radius in sheet metal fabrication: what is the rule?

At least 1× the material thickness for mild steel, stainless and 5052. Use a larger radius, or switch to 5052, for 6061-T6. Tighter bends crack the outside of the bend, especially in hard tempers.

Flange length in sheet metal fabrication: what is the rule?

At least about 4× the material thickness. The die needs enough material to hold the flange; shorter flanges distort or need special tooling.

Hole to bend in sheet metal fabrication: what is the rule?

Keep the edge of a hole at least 2.5× thickness plus the bend radius from the bend line. Holes closer to the bend stretch into ovals.

Hole to edge in sheet metal fabrication: what is the rule?

At least 2× the material thickness. Less material at the edge tears or bulges.

Hole to hole in sheet metal fabrication: what is the rule?

At least 2× the material thickness between holes. Thin webs between holes distort when cut or formed.

Sheet metal fabrication: design rules

Flat parts cut by laser, waterjet or punch and bent on a press brake.

Typical tolerance

Typical: cut features ±0.1–0.25 mm, bent dimensions ±0.25–0.5 mm, bend angle ±1°.

Files to send

STEP of the finished shape (the shop derives the flat pattern) or DXF of the flat pattern.

Common materials

Mild steel, stainless steel, 5052 aluminium (bends well). 6061-T6 aluminium cracks on tight bends.

The rules, with reasons

Inside bend radius. At least 1× the material thickness for mild steel, stainless and 5052. Use a larger radius, or switch to 5052, for 6061-T6. Why: Tighter bends crack the outside of the bend, especially in hard tempers.
Flange length. At least about 4× the material thickness. Why: The die needs enough material to hold the flange; shorter flanges distort or need special tooling.
Hole to bend. Keep the edge of a hole at least 2.5× thickness plus the bend radius from the bend line. Why: Holes closer to the bend stretch into ovals.
Hole to edge. At least 2× the material thickness. Why: Less material at the edge tears or bulges.
Hole to hole. At least 2× the material thickness between holes. Why: Thin webs between holes distort when cut or formed.
Minimum hole size. Hole diameter at least equal to the material thickness. Why: Smaller holes need slower or special processes and cost more.
Bend relief. Add relief cuts at least as wide as the thickness where a bend ends next to flat material. Why: Without relief the material tears at the corner.

Before you ask for a quote

Material, grade and temper
Thickness
Quantity
Finish (powder coat, anodize, plating)
STEP or DXF file
Any tight tolerances marked on a drawing

Common mistakes

Holes too close to bends
6061-T6 with tight bends
Sending a flat DXF without bend lines and directions
Ignoring the finish thickness on tight-fit parts

Agents and scripts can check a design automatically with the check_design MCP tool or POST /api/design-rules. How to connect.

Request a quote Find manufacturers

Typical rules of thumb, not a guarantee. The manufacturer's own design guidelines override them: ask for them and check your design against both before ordering.