Hole spacing and edge distance affect whether a punching operation distorts nearby features or pulls the sheet. A useful starting point is to relate each distance to the stock thickness, but the resulting ratios are manufacturer recommendations rather than universal design rules. This table keeps general feature-spacing guidance separate from punch-to-thickness ratios, which vary with both material and tooling. It also records a small set of corner-rounding tool constraints from the manufacturer’s guidance.

Punched Hole Edge Distance and Corner Radius

Read spacing as a ratio to thickness

Mate recommends at least two material thicknesses between holes and at least two thicknesses between a hole and the sheet edge. Its same guide gives three thicknesses between a formed feature and the edge, and six thicknesses between formed features. If a sheet is 2 mm thick, those recommendations translate to 4 mm, 4 mm, 6 mm, and 12 mm respectively. The example is simple multiplication; it does not add a safety allowance or replace a part-specific distortion analysis.

Small punches need material and tooling context

The punch diameter to material-thickness ratio changes with material. For non-guided tooling, Mate lists 0.75 for aluminum, 1.0 for mild steel, and 2.0 for stainless steel. For its fully guided tooling, the corresponding listed ratios are 0.5, 0.75, and 1.0. A lower ratio permits a smaller punch relative to the sheet, but it depends on the tool system and manufacturer recommendation. Do not transfer the fully guided values to a conventional holder, a different punch style, or a machine with different support.

Corner radii are tool-dependent

Corner rounding is not determined by sheet thickness alone. Mate describes four-way and nine-way corner-rounding tools, and says adequate performance requires at least a quarter-circle, or 90 degrees, of arc for each radius. It also specifies at least 4.7 mm of nose width between deep radii or radius groups for adequate tool strength. These are tooling constraints, not a general minimum part-corner radius. The available radius range depends on the selected tool; obtain the current tool drawing before using a radius in a part design.

Leave room for clearance and process variation

The ratios in the table do not include all design factors. Punch and die clearance, sheet strength, grain direction, burr direction, punch sharpness, part restraint, press tonnage, and the shape’s perimeter can change the result. Closely spaced holes may distort one another even when each hole is individually punchable. The design should also allow for downstream bending, forming, coating, and assembly. If a feature is near a bend or a formed wall, check the full sequence rather than treating its flat-pattern position as the final geometry.

Use the recommendation as a starting check

Before release, identify the exact material grade and thickness, punch outline, tooling guidance, die clearance, press model, and expected production condition. A test coupon can reveal distortion or burr problems before a large run, but it does not replace checking press capacity or maintaining the tool. If the required edge distance is smaller than the listed guidance, ask the tooling supplier to review the operation and approve a supported method instead of reducing the ratio without validation.

Where several features are close together, measure the clear ligament between edges as well as center-to-center spacing. The manufacturer’s wording distinguishes hole spacing from hole-to-edge distance; keep those definitions consistent when converting a drawing. Do not compare a center distance directly to an edge ligament. A CAD check should show the actual dimensions and a shop note should identify any supplier-specific departure from the recommendation.

References

• Mate: Holes, spacing and punch-to-material ratios
• Mate: Corner rounding

These figures are manufacturer guidance for punching and corner-rounding operations, not certified design minima. Confirm the part, press, material, tooling, and required edge quality with the responsible tooling supplier.