sheet metal design rules
Sheet Metal Design Rules
Sheet metal is a folded product, not a carved one. The flat pattern is what gets cut, and every bend moves material, stretches the outside face and pulls the inside in. The design rules that matter are the ones that keep the flat pattern predictable — because a part that cannot be unfolded correctly cannot be made at any price.
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- Min bend radius
- 1× thickness (soft) to 2× (hard)
- Hole to bend
- ≥ 2.5× thickness + radius
- Bend tolerance
- ±0.2 mm typical per bend
- Sheet thickness
- 0.5–6 mm in our range
Sheet metal design is the discipline of designing the flat pattern without drawing it. Every rule below exists because the material moves during forming, and the flat pattern has to predict how much.
Specifications
| Thickness range | 0.5–6 mm (laser), thicker by waterjet |
|---|---|
| Min bend radius | 1 × t mild steel · 1.5–2 × t stainless |
| Hole to bend | ≥ 2.5 × t + inside radius |
| Bend tolerance | ±0.2 mm per bend typical |
| Laser cut tolerance | ±0.1 mm on profile |
| MOQ | From 50 pieces |
Frequently asked questions
What is the minimum bend radius for sheet metal?
About one times the material thickness for mild steel and aluminium, and 1.5–2 times for stainless steel and hard aluminium grades. Below that the outside of the bend cracks.
How far should a hole be from a bend?
At least 2.5 times the thickness plus the inside bend radius, measured from the bend line to the hole edge. Closer than that, the hole distorts as the material flows during forming.
What is K-factor in sheet metal?
The position of the neutral axis in a bend, as a fraction of the thickness. It is what converts a 3D part into a flat pattern, and it typically falls between 0.33 and 0.45 for cold-rolled steel.
Should I supply the flat pattern with my drawing?
No. Give the finished dimensions and let the shop apply its own K-factor. A flat pattern generated for one tool set is usually wrong for another.
Why does my part crack at the corner where two bends meet?
Because the material has no room to flow. A corner relief notch — a small cutout where the bends intersect — removes the stress concentration and stops the tear.
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