Why is Perpendicularity used?
A tilted hole can misalign a bolt or pin even if its size and position at one face appear acceptable.
ORIENTATION CONTROL / GD&T SYMBOL GUIDE
PERPENDICULARITY
Perpendicularity controls the orientation of a plane or axis relative to one or two datums. Depending on the specified feature, the tolerance zone may be between two planes perpendicular to a datum, between two lines perpendicular to a datum, or inside a cylinder whose axis is perpendicular to a datum. The examples below distinguish a cylindrical axis zone from a two-plane surface zone.
INTERACTIVE APPLICATION
GD&T perpendicularity example: cylindrical feature axis and upright face
NO SEPARATE CONTROL
The axis and face lean away from square
- No separate 90° orientation zone is stated for either feature.
Limitations
- A tilted hole can misalign a bolt or pin even if its size and position at one face appear acceptable.
- A pin can catch and an upright mating face can leave a wedge-shaped gap.
PERPENDICULARITY CONTROL
The axis and face stay square to datum A
- The derived axis stays inside a ⌀0.08 mm cylindrical zone normal to datum A.
- The upright face stays between two planes 0.08 mm apart and normal to A.
Advantages
- The pin inserts more reliably and the face meets its mating part more evenly.
- The drawing states the intended requirement for inspection and assembly.
Where is Perpendicularity used?
Bolt holes, locating bores, upright faces, pins and bearing supports.
Steps to add perpendicularity tolerance
The axis and surface examples use different zone shapes but both are perpendicular to the lower datum face A.
The axis lies within a ⌀0.08 mm cylindrical zone perpendicular to datum A; the upright surface lies between two planes 0.08 mm apart, also perpendicular to A.
On the drawing
- Select the datum face and attach a datum feature symbol to it.
- Determine the acceptable perpendicularity tolerance for the axis or surface.
- Attach the feature control frame to the controlled feature: use ⟂ | ⌀0.08 | A for the axis's cylindrical zone, or ⟂ | 0.08 | A for the surface's two-plane zone.
Perpendicularity controls orientation at 90° to datum A, not feature size or location. The diameter prefix identifies the cylindrical axis zone; the surface zone has no diameter prefix.
Commonly defined variable values
The controlling value is a tolerance-zone width, not a universal process grade. For this perpendicularity example, the drawing states the controlled feature and applicable extent.
Scroll the table sideways to see every column.
| Application | Illustrative starting value | Example feature | Notes / caution |
|---|---|---|---|
| General mounting hole | ⌀0.05–0.15 mm | Ø12 × 50 mm bore | Check position separately. |
| Locating bore | ⌀0.02–0.08 mm | Ø20 × 40 mm bore | Include mating pin clearance. |
| Upright machined face | 0.05–0.20 mm | 100 mm face | Surface zone has no ⌀ prefix. |
These are planning examples, not universal rules or guaranteed process capabilities. Set the actual tolerance from function, size, length, process capability, inspection method and the standard specified on the drawing.
How is perpendicularity measured in real life?
Establish datum A from the lower face. Probe the controlled bore at several depths, then compare its derived axis with the zone normal to A.
- CMM: Establish datum A, sample the bore at several depths and evaluate its derived axis.
- Functional gauge: With an applicable material requirement, a datum-seated gauge can check assembly at the specified boundary.
- Surface check: For a face rather than a hole, use a square or indicator against a datum simulator and scan the face.
ASME Y14.5-2018 (R2024)
ASME Y14.5 likewise distinguishes surface and axis perpendicularity. A material modifier changes the boundary only when valid and explicitly shown.
ASME Y14.5 edition reference. Examples are learning schematics; use the complete requirements on the drawing.
LEARN BY DOING
Practise GD&T on engineering drawings
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