Defining basic perforation patterns
Requirements which are not covered by or do not conform to these criteria should always be specified by submitting a drawing of the full sheet, with unperforated margins clearly marked, together with details of the required perforated pattern and its orientation relative to the sheet.
The basic perforation patterns most commonly used can be defined by determining the following criteria:
1. Hole shape – Hole size – Orientation of hole relative to edge of plate
2. Hole pattern – Distance between hole centres (pitch)
3. Orientation of pattern relative to edge of plate
4. Plain (unperforated) margins between holes and edges of sheet
Length (of sheet/plate) = will always be taken to be the longer of the two dimensions
Width or height (of sheet/plate) = the shorter of the two dimensions
Pitch = measurement from centreline of one hole to centreline of next hole
Bridge = measurement from edge of one hole to edge of adjacent hole – ie the amount of solid material between holes
Hole types are described according to shape and orientation;
R = Circular (Round)
C = Square
CD = Square, diagonals parallel to panel edges
H = Hexagonal
LR = Round ended slots (‘Obrounds’)
LC = Square ended slots
Hole sizes are specified in millimetres, width (w1) x length (w2), following the shape code for the hole.
Hole Pattern & Pitch
Following the code for hole shape and size, the pattern is specified using codes for arrangement (pattern) and spacing between hole centres (pitch)
For the T pattern (60º staggered pitch) and square U pattern (pitches equal in both directions), only the pitch p is stated.
For shapes R, C, CD, H in the U or Z arrangements, both pitch p1 & p2 are stated as p1 x p2 with the shorter pitch p1 stated first.
If relevant to the requirement, the pattern should be defined further by specifying whether the straight row of holes should run parallel to the long side or short side of the panel.
Plain Margins should be specified along long and short sides of the panel, or each panel side if the margins or sides are not symmetrical about the centre lines of the panel.
Open Areas for perforating patterns
(NB letters used in figures below do not reflect ISO7806 / BS6511 designation)