EQS Equally spaced
Equally spaced · Anotaciones de plano · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “8× ⌀6.6 EQS on ⌀120 bolt circle” states a equally spaced requirement.
What controls
Note stating that the features of a pattern, circular or linear, are distributed at exactly equal intervals, so each individual spacing does not have to be dimensioned. The spacing declared this way is exact theoretical geometry: it carries no tolerance of its own, and the permissible variation is set by the feature control frame that governs the pattern. Put another way, equal spacing defines where the features should be, and the feature control frame says how far they may deviate.
How to verify
CMM measurement of the complete pattern with a single alignment to the datum reference frame, evaluating each feature against its true position. On the shop floor, a pin-type functional gauge is the quick way to check the whole pattern at once. Measuring the distance between adjacent features with calipers is not equivalent: errors from one feature to the next can cancel out and hide an accumulated deviation from the theoretical geometry.
Common mistakes when interpreting it
- Assuming equal spacing carries its own tolerance: it is theoretical geometry, and the tolerance comes from the feature control frame.
- Checking the pattern by measuring distances between adjacent features, which masks the accumulated error.
- Programming the pattern with rounded angles on patterns with many features.
How to get it in the workshop / if it comes out of tolerance
It is common on flange bolt circles and on linear hole patterns. When programming, calculate the positions from the exact pitch rather than rounded values: on a pattern with many features, rounding the angle accumulates error until the last holes fall out of tolerance. Also check the starting point of the pattern, because the angular position of the first feature is usually defined by a separate dimension.
Error that grows along the pattern: it almost always comes from calculating positions with rounded values or from accumulating incremental moves instead of working in absolute coordinates. All features shifted as a group: it is the origin or the starting orientation, not the spacing. And if the pattern fails as a whole but every hole checks out relative to its neighbor, you are measuring the wrong thing.
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