Hole-to-edge distance for sheet metal: the rule by process

Hole-to-edge distance is set by the process that makes the hole, not by the sheet. The same Ø10 hole needs two different distances depending on how it is made. Punched in 3 mm CRCA, its centre should sit at least 9.5 mm from the edge, because the material outside the hole has to survive the punch's radial load. Laser cut in the same sheet, 6.0 mm is enough, because nothing pushes the sheet and the only question is whether a 1 mm ligament survives handling, deburring and service.

That gap is why a single note on the drawing — "minimum 1.5t from edge" — is either over-conservative for a laser part or dangerously vague for a punched and tapped one. The rule is not a property of sheet metal. It is a property of the process that makes the hole and the load the hole has to carry.

This is written for the design engineer placing holes and for the buyer reading a supplier's DFM comments. It gives the number for punching, laser cutting and bolted joints, works through the arithmetic, and sets out the drawing callout that keeps the three apart. The design and CAD hub holds the rest of the rules.

Hole-to-edge distance by process: the short answer

Hole-to-edge distance is the material between the hole wall and the nearest edge of the part. The multiplier is applied to material thickness for forming processes and to hole diameter for structural joints, and mixing the two is where most of the errors come from.

• Punching and blanking: 1.5t from the hole edge minimum, 2t preferred. At 2t in 3 mm sheet that is a 6 mm ligament.
• Laser cutting, unloaded hole: 1.0 mm of ligament is the practical floor, roughly 0.33t at 3 mm.
• Laser cutting, structural hole: 0.5t to 1.0t, because the ligament has to carry load rather than just survive.
• Bolted connection: 2d from the hole centre, which is 20 mm for a Ø10 hole regardless of whether the sheet is 2 mm or 6 mm.
• Tapped hole or insert: 1.5d from the centre plus the insert's outside diameter, because the insert needs a wall around it.

The two families are not interchangeable. On a 3 mm part with a Ø10 hole, the punched rule puts the centre 9.5 mm from the edge and the bolted rule puts it 20 mm out — the structural rule is more than twice as far, and it is the one that governs if the hole carries a load.

Why punching needs more edge than laser cutting

A punch does not only cut. As the tool enters, it compresses the sheet around the cutting edge and pushes material outward. The die ring supports the sheet on the far side of the cut, but the material between the hole and the part edge sits outside that support, so it deflects down into the die relief and the hole takes on a bell-mouth.

The force is easy to estimate. Punch force is F = π × d × t × τ, with shear strength τ about 0.7 of ultimate tensile strength. For a Ø10 hole in 3 mm CRCA at 340 MPa UTS: π × 10 × 3 × 238 = 22.4 kN, or about 2.3 tonne-force on one hole. A 1.5t ligament at that thickness is 4.5 mm wide and 3 mm thick, 13.5 mm² of material, and it is unsupported on one side. It survives, but it deflects enough to roll the edge and pull the hole oval.

At 2t the same ligament is 6 mm wide and the deflection drops sharply, which is why 2t is the number to use on a visible or functional edge and 1.5t is the number to accept on a non-critical one. Below 1.5t the failure stops being cosmetic: the edge yields, the hole distorts, and on a progressive die the strip carrier can pull.

The laser removes the force and keeps the heat

A fibre laser cuts with no contact force, so the punch mechanism disappears. What remains is thermal. On 3 mm mild steel the heat-affected zone is roughly 0.1–0.3 mm per side of the kerf, so two cuts 1 mm apart leave a ligament that is partly heat-affected from both sides. That is the 1.0 mm practical floor: below it the ligament is mostly HAZ, it warps, and it has little fatigue life.

The cut quality on the ligament itself is classified under ISO 9013, which covers the geometrical specification and quality tolerances of thermal cuts. A narrow ligament can be cut to a normal quality class and still be a poor feature, because the standard describes the cut surface, not the mechanical integrity of a 0.4 mm strip beside it.

Hole-to-edge distance values for a 3 mm bracket

The table applies the rules to a 3 mm CRCA bracket with a Ø10 hole. Values are edge-to-hole-wall unless the row says centre. The Ganesh column records the process that sets the limit.

The two rows that catch people are the stainless row and the hem row. Austenitic stainless work-hardens at the cut edge, so a hole punched at 1.5t in 304 has a cold-worked ring and a notch-sensitive ligament; 2.5t is not conservatism, it is the same margin the material had before the punch touched it. A hem rolls the edge back on itself, and the rolled material needs clearance beyond the hole wall, so the edge distance is measured from the outside of the hem, not the original blank edge.

The fastener rule is not the forming rule

A bolted hole fails by shear-out along two planes running from the hole to the edge. The area resisting that is 2 × e × t, where e is the distance from the hole centre to the edge and t is the thickness. With a shear strength of 0.6 × 340 = 204 MPa in 3 mm CRCA, a hole at 2d (e = 20 mm) resists 2 × 20 × 3 × 204 = 24.5 kN. At 1.5d (e = 15 mm) it resists 18.4 kN, a 25% loss for 5 mm of material.

That is why the structural rule is expressed in diameters rather than thicknesses. Doubling the sheet thickness doubles the shear-out area, but the bolt diameter does not change, so the safe edge distance stays where it was. A 6 mm bracket and a 2 mm bracket with the same M10 bolt need the same 20 mm from the centre.

For a bearing-critical joint, the edge distance and the bearing capacity have to be checked together, and the thinner the sheet the more the bearing governs. Where the joint is a locating hole rather than a loaded one, 1.5d is adequate, because there is no sustained load to tear the ligament.

Where the edge is the datum

A hole 1 mm from the edge makes the edge itself a functional surface, and that changes the inspection plan. A CMM stylus cannot touch a 1 mm ligament without deflecting it, and a calliper reads the burr rather than the wall. On a laser part, the practical answer is to measure the hole with a pin gauge and the edge with a profile projector or an optical comparator, and to accept that the measurement uncertainty is a larger fraction of the tolerance than it would be elsewhere on the part.

Coating adds a second problem. Powder needs line of sight and a grounded surface, and a narrow ligament between a hole and the edge is exactly where the Faraday effect leaves a thin coat. The edge also takes the powder on two faces, so the film builds on the corner and thins in the gap. If the ligament is under 1t and the part is outdoor-rated, expect a coating defect there before you expect a structural one. The powder coating on laser-cut edges article covers what the cut edge does to adhesion.

What to put on the drawing

• The edge distance rule, stated as a note with the multiplier and the datum it applies to.
• Which holes are structural, so the 2d rule attaches to the right ones rather than to all of them.
• The hole size and tolerance, because the multiplier for a bolted joint is in diameters.
• The deburring or finishing route, where a narrow ligament depends on it.
• The default tolerance standard for position, usually ISO 2768-1 where nothing is called out.
• A separate callout for holes near bends, referring to the bend rule rather than the edge rule.
• Any hole that is a datum feature, marked, because its edge distance then has an inspection consequence.

ISO 2768-1 covers general tolerances for linear and angular dimensions where the drawing gives no individual tolerance, and hole position is usually one of them. It does not cover edge distance, which is a design rule rather than a tolerance, so the note has to be written.

What Ganesh actually runs

Ganesh pierces on mechanical presses from 20 T to 300 T with 250 T punching capacity, and the punch and die clearance is set per material and thickness in the in-house tool room. Laser work runs on a 12 kW fibre laser with a 40 ft × 16 ft bed, supported by 6 kW and 3 kW machines, in CRCA, mild steel, stainless, aluminium, brass and copper, up to 20 mm on the laser and 30–40 mm on the iron worker for plate.

The cutting process is chosen per part rather than per shop. A hole pattern that needs 1.5t of ligament and a tolerance of ±0.1 mm goes to the press; a one-off bracket with a hole 2 mm from the edge goes to the laser, because the laser can hold the geometry with a 1 mm ligament that the punch cannot. Typical sheet metal tolerance is ±0.5 mm, tighter on critical features by agreement, and PPAP and first article inspection are available across five units in Mumbai (Vasai) and Nagpur under ISO 9001:2015 and ISO 14001:2015.

Forming and welding follow the same logic. The 200 T, 5-axis brake with the 4,450 mm bed forms to 10 mm, and three CLOOS robotic MIG cells plus more than 30 manual stations handle the assemblies. A hole near a weld gets checked against the weld's heat input as well as the edge rule, because the ligament is the thinnest section in the heat-affected zone.

When the rule does not apply

An unloaded hole in a non-structural panel — a cable pass, a vent, a label relief — can sit closer to the edge than 1.5t if it is laser cut and the edge is not a mating face. The rule exists to protect the edge and the hole, and if neither is functional the constraint is only handling.

The rule also stops applying when the hole is not a hole. A notch open to the edge has no ligament on one side, so the edge distance question becomes a corner relief question, which is a different geometry with a different answer. And a hole that is later cut through by a trim or a bend is not a hole at all in the finished part; dimension it from the feature that survives.

Send the drawing with the hole schedule and the load path marked, or request a quotation with the material, thickness and finishing route. The review will tell you which holes need the forming rule, which need the fastener rule, and which are close enough to the edge to need a process change rather than a tolerance. The minimum hole size article covers the other half of the same problem, and the laser-cut holes and slots guide covers what the beam can do at the small end.