To make a sheet metal part easier to bend, keep holes and slots away from the bend zone and add bend relief where a bend meets an edge or cutout. As a preliminary design rule, measure hole clearance from the nearest edge of the hole to the bend tangent line, and consider a clearance of at least the inside bend radius plus twice the material thickness. For a relief, a starting point is a width at least equal to the material thickness and a length that extends beyond the bend area. These are design guidelines, not universal guarantees; material, tooling, bend geometry, and shop capability can change the result.
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At Jinhui, we use these details as part of manufacturability review for CNC forming and bending projects. Clear drawings help us assess whether features are likely to distort, crack, or interfere with forming before a quote is finalized. This guide explains how to apply the rules, where they have limits, and what information to provide when requesting a bending quote.
Hole clearance is the distance between a hole or slot and the bend zone. The bend zone is the region of material that deforms as the sheet is formed around the punch and die. If a hole sits too close, forming can pull it out of round, stretch its edge, or shift its position relative to other features.
For design checks, identify the bend tangent line—the point where the flat sheet transitions into the curved bend—and measure from that line to the nearest edge of the hole. This reference is more useful than measuring from the hole center because hole diameter affects how much material remains between the opening and the bend. On a drawing, make the measurement reference clear to avoid different interpretations during design review.
Bend relief is a notch or cutout that gives material room to deform where a bend ends at an edge or intersects another feature. Without adequate relief, the material may tear, buckle, or leave an unwanted web of material at the corner. Common shapes include rectangular, rounded, and obround reliefs; the best choice depends on the part geometry and the manufacturing process.
Relief is not a substitute for checking the complete flat pattern. Its size and position should account for the bend line, inside radius, sheet thickness, and adjacent features. The fabricator should review the relief alongside the formed part, not only as a 2D cutout.
A practical starting guideline is to keep the nearest hole edge at least the inside bend radius plus twice the sheet thickness from the bend tangent. For example, with 1.5 mm sheet and a 1.5 mm inside radius, this rule gives a preliminary clearance of 4.5 mm: 1.5 mm + (2 × 1.5 mm). This is a screening value, not a production guarantee; the actual safe distance depends on material behavior, bend method, tooling, and the hole’s size and shape.
If a hole must be closer, ask the fabricator to review the geometry rather than assuming it is unmanufacturable. Options may include moving the hole, changing its shape, adjusting the bend sequence, or adding a local feature to control deformation. A close hole may also be acceptable when its position or shape is not functionally critical, but this should be agreed before production.
As an initial layout, relief width is often set no smaller than the material thickness, while relief length extends beyond the bend tangent enough to clear the deformed area. One possible starting check is a relief length of the inside radius plus the material thickness. For a 1.5 mm sheet with a 1.5 mm inside radius, that gives a preliminary length of 3 mm and a minimum width starting point of 1.5 mm.
These dimensions should be treated as starting values for review, not mandatory specifications. A larger relief may be needed for certain materials, bend configurations, or intersecting flanges, while a design may use a different shape to meet appearance or strength requirements. Confirm whether the relief edge is exposed, requires deburring, or affects the part’s fit with adjoining components.
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This process is most useful before a design is released for production. Catching a feature conflict at the drawing stage can make it easier to compare design changes than after parts have been cut or formed. When the design cannot change, make the constraint explicit so the supplier can evaluate process options and quote assumptions.
Measuring from the hole center can make clearance appear larger than the remaining material actually is. Use the closest hole edge and the bend tangent as the reference points, and state the dimensioning method on the drawing when there is room for ambiguity. For a slot or irregular opening, check the nearest edge along the direction toward the bend.
Radius-plus-thickness guidelines are useful for early design, but they do not capture every material and process variable. Material strength and ductility, grain direction, bend radius, tooling, and forming sequence can affect the result. Avoid treating a rule of thumb as a guaranteed minimum without supplier confirmation.
A bend that runs directly into an edge or intersecting feature can concentrate strain at the termination. Review whether a relief is needed and whether its edges require finishing. If the relief is visible or close to a mating part, include its location and acceptable edge condition in the requirements.
A useful RFQ package gives the supplier enough information to assess the part without making assumptions about critical features. Include a dimensioned drawing and, when available, a 3D model and flat pattern. Specify material, thickness, finish, quantity, tolerances, bend angles, inside radii, and any restrictions on marks or exposed edges.
Call out holes near bends and identify which dimensions are functionally critical. If a feature cannot be moved, explain why and provide the acceptable tolerance or inspection requirement. This helps the supplier distinguish between a design preference and a requirement that affects fit, assembly, or product performance.
For CNC forming and bending inquiries, Jinhui can review supplied part files and drawings for hole clearance, bend relief, and related geometry considerations. We can discuss design questions such as whether a feature needs to move, whether a relief should be adjusted, and which details need clarification before quotation. Final recommendations depend on the specific part, material, and production requirements rather than on a single generic clearance rule.
To start a review, send your drawing or model with the material and thickness, target quantity, finish requirements, and critical dimensions. If you are still developing the design, identify any features that are difficult to change so the discussion can focus on practical alternatives. This gives both teams a clearer basis for evaluating manufacturability and preparing a bending quote.
Good hole clearance and bend relief reduce the risk of distorted openings, torn edges, and avoidable redesigns in sheet metal bending. Start by measuring from the nearest feature edge to the bend tangent, use radius-and-thickness relationships only as preliminary guidelines, and review relief wherever a bend terminates at another edge or cutout. Because material and tooling affect the outcome, confirm borderline geometry with the fabricator before production. Prepare a clear drawing package and contact Jinhui for a manufacturability review and bending quote.
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