Most cost overruns in sheet metal do not come from the shop. They come from the design office. Here are the 7 mistakes that show up most often.
1. A bend radius that is too tight
Wanting a sharp bend, almost without radius, is tempting on the drawing. In reality, an inside radius too small relative to thickness cracks the material on the outside of the bend. The basic rule: the inside radius should be at least equal to the sheet thickness, more for hard materials like stainless or 6000-series aluminum.
2. A hole too close to an edge or a bend
A hole placed too close to an edge distorts during cutting or bending. Too close to a bend, it deforms into an oval during bending. The rule: keep a distance of at least 2 times the thickness between a hole edge and a sheet edge or a bend line.
An ovalized hole after bending means a scrapped part. And the defect comes from the drawing, not the shop.
3. Tolerances too tight "just to be safe"
Putting ±0.05 mm everywhere "to be safe" is the most expensive mistake. Every tight tolerance forces an inspection, sometimes a rework, and drives the price up. Bent sheet metal is not precision machining: a general ISO 2768-mK tolerance is enough in the vast majority of cases. Reserve tight tolerances for dimensions that truly need them.
4. Forgetting the flat pattern
A bent part does not have the same flat length as its folded length, because of the neutral axis. Designing while reasoning only on finished dimensions, without accounting for the flat pattern and K-factor, leads to wrong parts. Flat pattern calculation must be part of the design.
5. Multiplying needless bends
Each bend adds handling time, an accumulating tolerance, and a risk of tool collision. A part with 9 bends, 3 of which could be removed by smarter design, costs far more than necessary. Always look to reduce the number of bends.
6. Bends too close to each other
Two bends too close together leave no room for the press brake apron. The result: the shop cannot make the part as drawn, or must use special tooling. The minimum distance between two bends depends on thickness and tooling — when in doubt, leave margin.
7. Ignoring grain direction
On brushed stainless and aluminum, grain direction is visible and the rolling direction affects bending. A bend made parallel to the rolling direction cracks more easily. Designing without specifying grain direction leaves an uncontrolled quality risk.
Design for manufacturing
All these mistakes share one thing: they are invisible on the drawing but costly on the shop floor. This is what we call DFM — Design For Manufacturing, design thought for production.
DRAWLESS applies these rules automatically. When you describe a part, the geometry engine respects minimum radii, hole safety distances and bending constraints. The generated file is manufacturable from the start — you no longer send drawings that come back from the shop with corrections.