CNC bending tolerances explained (and how to spec them)

Why bends vary

Every bend stretches and springs back a little. Material thickness, grade, grain direction and batch-to-batch variation in the sheet all affect the final angle and flange length. A CNC press brake controls this very consistently, but tolerances build up across several bends.

Specifying tolerances sensibly

• Dimension from the features that matter — mounting holes, mating faces — rather than chaining dimensions across every bend.
• Use the same inside bend radius throughout a part where you can; it reduces tool changes.
• Keep flanges at least four times the material thickness long so the part sits properly in the tooling.
• Keep holes clear of bend lines, or they will stretch into ovals.
• Apply tight tolerances only where they're needed. Everything else can use a general tolerance, which saves inspection time.

Our approach

We calculate flat patterns with the correct bend allowances for your material and check first-off parts against the drawing before running the batch. If a tolerance looks tighter than the design needs, we'll say so at the quoting stage.