When I design a sheet metal part with holes near a bend, I start by checking two details: the distance from the hole to the bend line and the size of the bend relief. A practical starting point is to keep the nearest edge of the hole at least 2 times the material thickness from the theoretical bend line, then verify the result against the material, inside radius, tooling, and forming method. For example, a 2 mm thick sheet may require approximately 4 mm or more of hole-to-bend clearance, but the final value should be confirmed through the supplier’s bending process.
Bend relief is the slot, notch, or extended cut placed at the end of a bend to prevent tearing, distortion, and uncontrolled material deformation. Correct hole clearance protects the hole shape and position, while correct bend relief controls how the bend terminates at an edge or corner. In this guide, I explain the design logic, common dimensions, material considerations, inspection points, and how a CNC forming and bending supplier such as Jinhui can support production-ready designs.
This guide is intended for mechanical engineers, product designers, purchasing teams, and buyers sourcing custom sheet metal components. It is especially useful when a part includes mounting holes, slots, fastener openings, flanges, or folded corners close to a bend. I also recommend it for teams moving a prototype into repeat production, because a design that bends successfully once may still create variation when material batches, tooling, or production volumes change.
Hole clearance is the distance between a hole edge and the bend line, bend tangent, or finished bend region. The correct reference depends on the drawing standard and supplier’s process, so I avoid treating “distance from the center of the hole” as the only design rule. A hole positioned too close to a bend can elongate, ovalize, shift, or become partially pulled into the bend radius.
The risk increases when the hole is large, the material is hard, the bend radius is tight, or the part uses a thick sheet. A hole may also be affected by springback and local stretching even when there is no visible crack. For this reason, I specify the datum and measurement method clearly on the drawing, preferably using the bend tangent or a controlled feature established by the manufacturing process.
Bend relief is a deliberate opening that allows the material to deform without producing an unwanted tear at the end of a bend. It is commonly used where two flanges meet, where a bend terminates near an outside edge, or where several bends intersect. Without sufficient relief, the material may buckle, split, leave a sharp uncontrolled corner, or create interference during assembly.
Typical relief forms include rectangular slots, obround slots, and tear-shaped or semicircular openings. A basic starting point is to make the relief depth at least equal to the bend length through the affected area, with a width that is commonly related to material thickness. These are starting guidelines rather than guaranteed production values, because the required geometry depends on the material, bend radius, tooling, and tolerance scheme.
A hole near a bend can change shape because the surrounding material experiences tension and compression during forming. This can affect screws, rivets, bushings, pins, and alignment features. If the hole is used for a precision locating function, I recommend increasing the clearance, using a post-bending machining operation, or discussing an alternate forming sequence with the supplier.
When a bend ends without adequate relief, stress can concentrate at the corner. The result may be a crack, a visible notch, or a flange that is not flat. This is more significant for materials with limited ductility, protective coatings, grain-direction sensitivity, or a small inside bend radius.
Clearance and relief details influence setup time, inspection requirements, and the number of secondary operations. A design that allows a standard press brake tool and a predictable bend sequence is generally easier to quote and manufacture than one requiring special tooling or manual correction. At Jinhui, I review these factors as part of a manufacturability discussion rather than evaluating the hole or relief as an isolated feature.
I use the following framework as an initial design screen, not as a substitute for a production trial or supplier review:
For example, if T equals 1.5 mm, a 2T starting rule gives 3 mm from the selected bend reference to the nearest hole edge. If the hole controls the position of a dowel or bearing component, I would not release that value without confirming the bend radius, tolerance, and inspection method.
The relief should extend far enough to separate the bend zone from the adjacent edge or intersecting flange. If the relief is too shallow, the material can still tear beyond the slot. In many designs, I begin with a relief depth related to the full bend region and then confirm it against the selected inside radius and forming direction.
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A narrow relief can concentrate stress at its end, while an unnecessarily wide relief can weaken the flange or expose an unwanted opening. A preliminary width of about 1 to 2 times the sheet thickness is often considered during early design, but the final width should be adjusted for the material and tooling. For a 3 mm sheet, this starting range would be approximately 3 to 6 mm.
Rounded relief ends can reduce sharp stress concentration compared with an abrupt square termination, although the selected shape must remain compatible with laser cutting, punching, or other fabrication methods. If the part will be powder coated, plated, or painted, I also consider whether the relief creates a coating trap or an edge that requires deburring. Jinhui can review relief geometry together with cutting, deburring, bending, and finishing requirements.
Material selection affects both hole clearance and bend relief. Aluminum, mild steel, stainless steel, galvanized sheet, and high-strength steels can respond differently because of their ductility, work-hardening behavior, coating, grain direction, and required bend radius. I avoid applying one universal clearance table across all materials unless it has been validated for the specific process.
Thickness is another primary variable. Thin sheet may be more vulnerable to distortion around a hole, while thick or high-strength sheet may require a larger inside radius and more relief to avoid cracking. The planned process also matters: laser cutting, CNC punching, press brake bending, and secondary drilling each create different opportunities for controlling feature position and edge quality.
A drawing may state that a hole is 5 mm from a bend, but the result is unclear if the reference is not defined. The theoretical bend line, tangent line, and finished outside surface do not represent the same location. I recommend adding a clear datum or detail view when the hole is functionally important.
A hole that overlaps the bend allowance or radius area is likely to deform unless the design and process specifically account for it. Moving the hole outward, changing its shape, or adding a local relief may be more economical than repairing the feature after bending. If the hole must remain close, I ask the supplier to evaluate the tooling and forming sequence before final release.
Cut edges and relief slots can retain burrs, sharp corners, or coating-related issues if finishing is not specified. These conditions can affect assembly safety and dimensional inspection. I include requirements for edge treatment, surface finish, coating, and critical edge locations in the purchasing documentation.
When I evaluate a CNC forming and bending supplier, I look beyond the ability to bend a single sample. The supplier should be able to interpret drawings, identify feature risks, explain bend references, and communicate when a design requires a process change. I also check whether the supplier can coordinate cutting, bending, inspection, finishing, packaging, and repeat-order control.
| Evaluation point | Questions to ask |
|---|---|
| Design review | Will the supplier review hole clearance, bend relief, radius, and bend sequence before production? |
| Process capability | Can the supplier support the required material, thickness, feature size, and forming method? |
| Quality control | Are critical hole positions, flange angles, bend dimensions, and surface conditions clearly inspected? |
| Commercial support | Can the supplier explain tooling, MOQ, sample quantities, lead time, and secondary-operation costs? |
Jinhui supports custom sheet metal manufacturing projects involving CNC forming and bending, with design feedback focused on practical production requirements. I can provide a drawing, 3D model, material grade, thickness, quantity, tolerance requirements, surface finish, and application details for an initial review. When a hole is close to a bend or a relief is unusually small, this information helps the manufacturing team recommend a more reliable geometry.
For quotation and engineering review, I recommend sending the critical dimensions rather than relying only on a general tolerance note. Useful information includes the hole function, preferred bend radius, bend-angle tolerance, inspection datum, finishing requirement, and whether post-bend machining is acceptable. Jinhui can then help distinguish between a design that is suitable for direct forming and one that may benefit from a revised feature location or additional process step.
Hole clearance and bend relief are small drawing details with a direct effect on part quality, assembly fit, and production stability. As a starting point, I consider approximately 2T clearance from the appropriate bend reference and a relief width around 1 to 2T, while treating both values as material- and process-dependent guidelines. The safest final design is the one reviewed together with the actual sheet material, bend radius, tooling, tolerances, and manufacturing sequence.
If you are preparing a custom sheet metal part, the next step is to share the drawing, model, material, thickness, quantity, and critical functional requirements with Jinhui. I can help identify high-risk holes, clarify bend references, assess relief geometry, and develop a practical CNC forming and bending solution for production.
If you are looking for more details, kindly visit Sheet Metal Bending Guide: Hole Clearance and Bend Relief.