A hole close to a sheet-metal bend can stretch or become oval when the flange is formed. That can affect fasteners and assembly. The required hole-to-bend distance is not one universal number: it depends on the material, thickness, bend radius, tooling, hole size and how the distance is measured.
Measure the same two points
Before comparing a drawing with any rule, identify whether its dimension runs from the nearest edge of the hole or the hole center, and whether the bend reference is the bend centerline, the inside radius or the tangent where the flat area begins. A center-to-center figure cannot be used as an edge-to-tangent clearance without accounting for the hole radius and bend geometry. Mark both points on the flat pattern and on the formed-part drawing.
Why a single formula is only a starting point
Design guides often use thickness plus inside radius to estimate a starting clearance. One published rule of thumb is an edge-to-bend-tangent distance of about 2t + R, where t is sheet thickness and R is the inside bend radius. It is not a universal guarantee. Requirements vary between materials, thickness bands, bend tools and whether the feature is a plain hole or a hardware installation hole. For example, Protolabs' sheet-metal DFM guide uses different feature-distance recommendations for different material and thickness ranges. The manufacturer should check the actual part before tooling or a production run.
What happens when the hole enters the bend zone
The material near the bend stretches and compresses as it is formed. If a cutout is too close, its edge can move unevenly, causing ovality or a shift in the hole position. This is especially important when a screw, insert or mating component needs a controlled fit. A visually acceptable hole can still miss the position tolerance on a formed part, so the drawing should state which dimension is critical and how it will be inspected.
Options when the hole cannot move
- Move the feature: increase the distance from the bend zone while preserving the assembly function.
- Change the bend or flange: review the inside radius, flange length or bend location together with the available tooling.
- Add a relief or slot: in some designs a cut feature can isolate deformation; its shape must be reviewed for strength and assembly.
- Make the hole after bending: a secondary operation may protect position or roundness, but it adds handling and cost. Quote it as a separate process step.
Hardware holes need an additional check. The minimum edge distance for an insert or fastener and its installation access may be more restrictive than the plain hole-deformation rule. SendCutSend's hardware-distance explanation illustrates why the center of a hardware hole and the bend reference must be defined before comparing dimensions.
What to send for a sheet-metal DFM review
Provide the flat pattern and formed 3D model, material grade and thickness, inside bend radius, bend direction, hole diameter, any hardware specification and the critical position tolerance. State whether the hole can be modified or made after forming. Our sheet-metal fabrication team can review that specific geometry and agree on a feasible process and inspection plan. The sheet-metal tolerance guide helps separate general dimensions from the features that need explicit drawing limits.
