The Red Book at a Glance: Punched Holes

Definition of Punched Holes

Identification of these punched holes can provide the basis for determining the inspection parameters. Roll-over is the natural consequence of the punching process, the mechanical properties of the material being punched, and the die application of techniques employed.

Specification and Measurement of Punched Holes

1. Dimension feature size limits only.
2. Feature size is to be measured only in the burnished land area or punch side.
3. Shape deviations within the feature size limits are permissible.

Special Purpose Holes

1. Dimension only those elements that affect part function.
2. When dimensioned:
   1. Burnished land to be specified as minimum only.
   2. Burr height to be specified as maximum only.

Recommended Minimum Ratios of Punched Hole Diameters to Stock Thickness

Limitations are established in common practice for most economical production. Recommended ratios are applicable to all common metals.

P = Punched Hole Diameter (0.062 min. dia.)

T = Stock Thickness

Spacing of Hole Edge to Part Edge and Adjacent Holes

Economical minimum spacing of punched holes to a straight edge or other hole is established. Distortion is not more than 5 percent of metal thickness.

T = Thickness

S = Space

P = Punched Diameter

L = Length

Avoid minimum values of “S” where possible.

Piercing – Adjacent to Bends

Illustration “A” indicates that the minimum inside distance required from the edge of a hole to a bend is 1-1/2 times the material thickness (T) plus the bend radius (R).

Otherwise, distortion will occur as indicated in Illustration “B” — or piercing after form must be considered.

Illustration “C” indicates a similar condition to “A”, except for openings with an edge parallel to bend. In this case the following requirements apply for economical tooling and production:

When “L” = up to 1 — 2T + R (minimum).

When “L” = 1 to 2 — 2-1/2T + R (minimum).

When “L” = 2 or more — 3T to 3-1/2T+ R (minimum).

Minimum recommended tolerances are shown below: (on multiple bends each bend is made separately).

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