Why is Cylindricity used?
A shaft can have round sections but still taper or bow enough to compromise bearing or seal contact.
FORM CONTROL / GD&T SYMBOL GUIDE
CYLINDRICITY
Cylindricity controls the entire form of a cylindrical surface at once. It combines circularity at every section with axial straightness and taper or barrel variation; the whole surface fits between two coaxial cylinders.
INTERACTIVE APPLICATION
Cylindricity drawing and interpretation
WITH CYLINDRICITY
Two journals, two requirements
- The 0.05 frame applies to the smaller cylindrical surface.
- The 0.08 frame applies to the larger cylindrical surface.
Drawing callout
- Each leader reaches its controlled cylindrical surface.
- Neither frame contains a datum or MMC/LMC modifier.
INTERPRETATION
Two coaxial-cylinder zones
- The small and large journals are evaluated separately at 0.05 and 0.08.
- Each value is the radial separation of its two coaxial cylinders.
Full-surface control
- The complete cylindrical surface must remain inside its zone along the specified length.
- Round sections alone cannot demonstrate cylindricity.
Where is Cylindricity used?
Bearing journals, hydraulic spools, precision bores and sealing cylinders.
How is Cylindricity used?
Attach a cylindricity feature control frame directly to each cylindrical surface. In this stepped-shaft example, 0.05 and 0.08 apply independently to the smaller and larger journals.
Each leader identifies one complete cylindrical surface; the value gives its coaxial-cylinder zone width.
How it is used
The feature control frame has the cylindricity symbol and value only. Attach its leader to the cylindrical surface being controlled; no datum reference or material condition modifier is used.
How to read the annotation
Read the symbol, then the tolerance value in the drawing units. For the 0.05 callout, the full small journal fits between coaxial cylinders separated radially by 0.05; the large journal has its own 0.08 zone.
Commonly defined variable values
The controlling value is a tolerance-zone width, not a universal process grade. For this cylindricity 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 |
|---|---|---|---|
| Bearing journal | 0.01–0.04 mm | Ø40 × 100 mm shaft | Coordinate with bearing fit. |
| Hydraulic spool | 0.005–0.02 mm | Ø20 × 50 mm spool | Confirm thermal and surface-finish needs. |
| General machined bore | 0.03–0.10 mm | Ø60 × 150 mm bore | Sample the full depth. |
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 cylindricity measured in real life?
Inspect without inventing a datum. Measure the indicated feature and compare it with the requirement shown on the drawing.
- Cylindricity instrument: Scan many axial sections with a precision spindle; evaluate the complete point set together.
- CMM: Sample around the circumference at multiple lengths and fit the specified coaxial-cylinder zone.
- Shop-floor indicators: Use for screening taper or variation, but a few indicator tracks do not prove full-surface cylindricity.
ASME Y14.5-2018 (R2024)
ASME Y14.5 uses a datum-free two-coaxial-cylinder zone for the full surface. The tolerance value is a radial separation, not a diametral zone.
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
The INTERFAIC interactive GD&T course is coming soon.