Hole-to-edge distance affects whether a stamped hole can be produced without edge distortion, tear-out, or an unstable remaining web. It can also influence punch loading, tolerance stability, die strategy, and long-term production consistency.
For stamped parts, A ≥ 1.5t—where A is the distance from the hole edge to the nearest part edge and t is material thickness—is a practical DFM starting point. It is not an absolute stamping limit. The minimum geometry that can be manufactured and the geometry that provides a robust high-volume production window are not always the same.
How Is Hole-to-Edge Distance Measured?
Hole-to-edge distance is the shortest remaining material between the edge of a pierced hole and the nearest outside edge of the part. It is an edge-to-edge measurement, not a hole-center-to-edge dimension.
For basic stamped-part DFM:
- A = hole-to-edge distance
- B = hole-to-hole spacing
- t = material thickness
- d = hole diameter
This distinction matters because a center-to-edge dimension includes the hole radius. For punching analysis, engineers need the actual width of the remaining ligament that resists local deformation during piercing.
Minimum Hole-to-Edge Distance: How to Use the 1.5t Guideline
A general design guideline for stamped parts is:
A ≥ 1.5t
The same starting relationship applies to the solid web between adjacent holes:
B ≥ 1.5t
| Material Thickness (t) | General Starting Distance (1.5t) |
|---|---|
| 0.3 mm | 0.45 mm |
| 0.5 mm | 0.75 mm |
| 0.8 mm | 1.20 mm |
| 1.0 mm | 1.50 mm |
| 1.5 mm | 2.25 mm |
| 2.0 mm | 3.00 mm |
| 3.0 mm | 4.50 mm |
These values provide a useful first DFM check. Single-operation or progressive punching may permit smaller distances under suitable conditions, while high-strength materials, critical dimensions, or demanding production requirements may justify additional margin.
The guideline is best understood through three separate questions:
General guideline → Process feasibility → Production robustness
The first asks whether the geometry meets a common design starting point. The second asks whether an appropriate die and punching strategy can produce it. The third asks whether the process can maintain the required dimensions as material and tooling conditions vary during production.
Why Do Some DFM Guides Recommend 2t?
Manufacturing guides may specify 1t, 1.5t, or 2t because they often address different materials, processes, tooling arrangements, and acceptable risk levels. These values should not be treated as interchangeable universal standards.
A larger edge-to-hole distance leaves more material around the pierced feature and can provide additional margin for edge stability, tooling wear, and dimensional repeatability. For precision metal stamping, the engineering objective is therefore not simply to find the smallest possible distance, but to maintain enough process margin for reliable production.
Why Does a Small Hole-to-Edge Distance Cause Distortion?
During piercing, the punch loads and plastically deforms the sheet before shearing and fracture complete the hole. Material surrounding a hole located well inside the part provides relatively balanced support.
As the hole approaches a free edge, this support becomes asymmetric. The remaining ligament has less material available to constrain local deformation.
The resulting engineering chain is:
Narrow ligament → asymmetric support → localized plastic flow → edge displacement → dimensional variation
Depending on material behavior and geometry, the result may be edge bulging, distortion around the hole, or tear-out of the remaining web.
| Design Condition | Primary Manufacturing Concern |
|---|---|
| Insufficient edge distance | Edge bulging or distortion |
| Extremely narrow ligament | Tear-out |
| High-strength material | Increased punch and local material loads |
| Small hole in thick material | Punch deflection or breakage |
| Marginal geometry in long runs | Reduced dimensional consistency |
This becomes especially important when both the pierced feature and outside profile participate in assembly or positioning.
Hole Diameter, Edge Distance, and Material Strength Work Together
Hole-to-edge distance should not be evaluated independently from hole size. As hole diameter decreases relative to material thickness, the punch becomes more slender while still carrying the load required to penetrate the sheet.
For conventional unprotected punching tooling, typical minimum round-hole dimensions vary with material strength.
| Material | Typical Minimum Round Hole Diameter |
|---|---|
| Steel, Rm > 690 MPa | d ≥ 1.5t |
| Steel, 490 MPa < Rm ≤ 690 MPa | d ≥ 1.3t |
| Steel, Rm ≤ 490 MPa | d ≥ 1.0t |
| Brass / Copper | d ≥ 0.9t |
| Aluminum / Zinc | d ≥ 0.8t |
This creates four useful DFM conditions:
| Hole Size | Edge Distance | Primary Concern |
|---|---|---|
| Adequate | Adequate | Normal stamping process window |
| Too small | Adequate | Punch strength and tool life |
| Adequate | Too small | Ligament and edge deformation |
| Too small | Too small | Combined tooling and part-quality risk |
In practice, this matrix must also be read together with material strength. Identical d/t and A/t ratios can produce different punch loads and deformation behavior in aluminum, mild steel, and high-strength steel.
A design may therefore pass the 1.5t edge-distance check while still using a hole that is too small for reliable punching. Conversely, increasing hole diameter does not correct an unstable ligament when the hole remains too close to the edge.
Tool Support Can Shift the Practical Hole-Size Limit
Minimum punched-hole size is also affected by tooling support. With appropriate punch protection or guidance, smaller punches can be supported against deflection and bending more effectively than in an unprotected arrangement.
For example, referenced punching guidance gives minimum round-hole sizes as low as approximately 0.5t for high-carbon steel, 0.35t for low-carbon steel or brass, and 0.3t for aluminum or zinc when protective tooling is used. These values describe minimum hole size rather than minimum hole-to-edge distance.
The comparison reinforces an important point: geometric limits cannot be separated from tooling design. A dimension that is impractical with one punch arrangement may be feasible with another, although tooling complexity and production reliability must still be evaluated.
Hole-to-Hole Spacing Uses the Same Ligament Principle
A general starting guideline for adjacent punched holes is:
B ≥ 1.5t
Here, the critical feature is the solid ligament remaining between the two openings. If it becomes too narrow, deformation associated with one piercing operation can influence the material around the neighboring feature.
For precision parts, the concern is not limited to visible tearing. Hole position, web geometry, and part-to-part repeatability can become increasingly sensitive to punch arrangement, material variation, and station sequence.
In progressive tooling, the finished drawing also does not necessarily show how much material supported each hole at the moment it was pierced.
Hole-to-Edge and Hole-to-Bend Are Different DFM Problems
These two distances are often discussed together, but they address different failure mechanisms.
Hole-to-edge distance is primarily a piercing and ligament-stability problem. Too little material between the hole and free edge can contribute to bulging, tear-out, and dimensional variation.
Hole-to-bend distance is primarily a forming problem. Material around a bend or drawn region undergoes tension and compression, so a nearby hole can stretch, shift, or lose its original geometry.
For bent or drawn stamped parts, sufficient clearance should therefore be maintained between a hole and the adjacent forming region. Thickness- and bend-radius-based formulas used in sheet metal DFM should be treated as forming-specific guidance rather than substituted directly for the 1.5t hole-to-edge guideline.
How Hole-to-Edge Distance Affects Tolerance Stability
Minimum manufacturable geometry and robust tolerance capability are not necessarily the same.
When a feature sits close to the process limit, material-property variation, punch-to-die clearance, punch wear, and burr growth can have a greater effect on the finished relationship between the hole and outside edge.
This is especially important when a functional dimension runs from a pierced hole to a blanked outer edge. Variation from both operations contributes to the final dimensional relationship:
Pierced-hole variation + outer-profile variation → functional hole-to-edge variation
The nominal ligament may therefore satisfy the drawing while the functional relationship becomes difficult to maintain within a tight tolerance over a long production run.
Burr growth can also become more significant on narrow ligaments because there is less surrounding material and functional clearance around the feature. Tool maintenance and burr control become part of dimensional stability rather than merely cosmetic quality.
For precision components, the relevant question is not only whether the feature can be stamped, but how much process capability remains around the specified tolerance.
When Hole-to-Edge Distance Changes the Stamping Process
A small change in edge distance can alter the manufacturing strategy.
Consider the referenced example of a Q235 steel blank with a material thickness of 2 mm. Using the general guideline:
1.5 × 2 mm = 3 mm
When hole dimensions, spacing, and edge distance satisfy the applicable minimum values, the example is considered suitable for compound blanking.
If the hole-to-edge distance is reduced to 1 mm:
1 mm < 3 mm
the referenced process analysis considers compound blanking and conventional single-operation blanking unsuitable. Progressive blanking becomes the viable route for that specific example.
This should not be interpreted as a universal rule that every feature below 1.5t requires a progressive die. It demonstrates a broader manufacturing principle:
Feature geometry can change the tooling and process strategy.
Why Progressive Die Sequencing Can Change What Is Possible
Progressive die stamping introduces another variable: when the hole is pierced relative to creation of the final outside contour.
If the outside edge already exists when the hole is pierced, only the final narrow ligament supports the operation. A progressive die may allow the hole to be pierced earlier while additional strip material still surrounds the feature.
A possible sequence is:
Pierce hole → retain strip support → perform subsequent forming → trim final outside contour
The final part can therefore have a relatively small apparent hole-to-edge distance even though more material supported the hole at the piercing station.
This leads to an important engineering distinction:
Finished hole-to-edge geometry ≠ material support available at the piercing station
Whether this strategy is practical depends on strip layout, carrier strength, punch support, station sequence, downstream forming, and final tolerance requirements. It must be engineered into the progressive die rather than assumed from the finished drawing.
What to Do When a Hole Must Remain Close to the Edge
When functional requirements prevent moving a hole farther inward, DFM should focus on preserving support and avoiding unnecessary secondary operations.
Increase the Remaining Ligament
Moving the hole is normally the simplest solution. If its functional location cannot change, the surrounding edge, flange, or local geometry may sometimes be modified to increase the available web.
Reconsider the Piercing Sequence
In a progressive die, piercing the hole before final trimming may preserve additional support during the critical operation. This approach must also maintain strip and carrier stability through subsequent stations.
Use Secondary Processing When Necessary
Drilling, reaming, or CNC machining can be considered when stamping cannot reliably produce a functionally critical feature in its required location.
These operations add handling, cycle time, inspection, and cost. For high-volume OEM production, they are generally most appropriate when the functional requirement cannot be resolved through part or die design.
Hole-to-Edge Distance in High-Volume Precision Stamping
A marginal feature may produce acceptable first-article samples while still creating an unstable long-term process. Tool wear, burr development, die clearance condition, strip behavior, and incoming material variation all become more important as production continues.
High-volume DFM should evaluate:
- Punch strength and support
- Punch-to-die clearance
- Piercing station sequence
- Strip and carrier stability
- Tool wear and burr development
- Hole position repeatability
- Edge dimensional consistency
- Inspection requirements
- Scrap risk
- Secondary processing
The functional consequence varies by application. On connector terminals, hole or slot position can influence downstream locating and automated assembly. On EMI shielding components, local edge distortion can affect fit and flatness against the enclosure.
For automotive brackets, mounting-hole position relative to the blanked profile can affect fixture and assembly alignment. On battery contacts, narrow webs around pierced locating or fastening features can influence dimensional stability during downstream assembly.
These applications illustrate why a minimum geometric rule alone is not enough. High-volume precision stamping requires a process window that remains capable as normal production variables change.
Hole-to-Edge Design Checklist for OEM Stamped Parts
| Check | Engineering Question |
|---|---|
| Edge distance | Is A ≥ 1.5t as an initial DFM check? |
| Hole spacing | Is B ≥ 1.5t? |
| Hole diameter | Is d/t suitable for the material and punching method? |
| Material | How do strength and ductility affect the controlling constraint? |
| Remaining ligament | Is enough material available to resist local deformation? |
| Forming | Is the feature near a bend or drawn wall? |
| Strip layout | How much material supports the hole at the piercing station? |
| Tooling | Is the punch adequately supported for the feature size? |
| Tolerance | Does the hole-to-edge relationship control assembly or fit? |
| Production volume | Will normal tool wear reduce process capability? |
| Secondary operations | Can additional machining be avoided? |
The goal is to distinguish a geometry that passes a basic guideline from one that can be manufactured reliably at the required tolerance and production volume.
Frequently Asked Questions
What Is the Minimum Hole-to-Edge Distance for a Stamped Part?
A general DFM starting point is A ≥ 1.5t, measured from the hole edge to the nearest outside edge. The practical requirement can change with material strength, feature geometry, tooling, tolerance, and production conditions.
Is 1.5t an Absolute Stamping Limit?
No. It is a general design guideline rather than a universal manufacturing capability limit. Some die arrangements may support smaller distances, while tight-tolerance or demanding production conditions may require additional margin.
Is Hole-to-Edge Distance Measured From the Hole Center?
No. For this DFM check, measure from the nearest edge of the hole to the nearest outside edge of the part. This measurement represents the actual remaining ligament.
How Does Material Strength Affect Hole-to-Edge Design?
Material strength affects punching load and can change which constraint controls the design. Higher-strength materials may increase demands on punch strength, while every material still requires sufficient ligament width to control local deformation.
What Is the Minimum Distance Between Two Punched Holes?
A general starting guideline is B ≥ 1.5t, measured between the nearest edges of adjacent holes. Precision features may require additional consideration of material behavior, punch arrangement, and progressive die sequence.
Does Hole-to-Edge Distance Affect Progressive Die Design?
Yes. Hole location can influence strip layout, piercing sequence, carrier strength, punch support, and the station where the final outside contour is produced. Piercing before final trimming can sometimes preserve more material around the feature during the punching operation.
Design Hole Spacing Around the Production Process
The 1.5t hole-to-edge distance guideline provides a useful starting point for stamped-part DFM, but it does not define an absolute production capability. Hole diameter, material strength, remaining ligament, punch support, tolerance requirements, and die sequence all influence the practical limit.
For custom OEM stamping projects, the more important question is whether the hole-to-edge relationship can remain stable throughout the intended production volume. A robust design connects part geometry → material behavior → piercing strategy → tolerance control → high-volume manufacturing reliability.
Designing around that complete engineering chain helps reduce tooling risk, secondary processing, dimensional variation, and avoidable production instability before the part enters mass production.
