This 6-page document discusses geometrical metrology parameters for bearing seats on shafts and in housings. It defines cylindricity, perpendicularity, and runout, explaining their importance in ensuring proper alignment and reducing premature failure of bearings and other rotating components. Cylindricity refers to how much a surface may deviate from a perfect cylinder. Perpendicularity ensures bearing surfaces are square to the shaft centerline. Runout measures deviation from true rotation and can cause misalignment if too high. The document emphasizes that following specified tolerances for these parameters is crucial for reliability.

1. April 1, 2016
Geometrical Metrology: Bearing seats
on shaft and in housings
Name: Marwan Shehata Mohamed Zeitoun
Sec: 7, No: 159

2. PAGE 1

3. PAGE 2

4. PAGE 3
Cylindricity
The cylindricity parameter refers to two, or more roundness planes used to produce a cylinder
where the radial differences are at a minimum, in short, cylindricity shows how much a cylindrical
surface of a part may deviate from a perfect cylinder
For example, a component may have the correct nominal size - diameter - but its form could be
incorrect, and therefore its function will be impaired. Classic cases of this problem are
encountered in automotive fuel injection systems, where the mating cylindrical components of
valve pumps and injectors must not allow a bypass of fuel under high pressure when not required,
namely during either deceleration or braking. These fuel injector systems are subject to ever-
increasing and stringent tolerances as greater fuel economy becomes the norm.
For the shaft and housing, the cylindricity is used to limit ‘out of roundness’, ‘taper’ and to ensure
straightness of a shaft and housing bores. If a shaft has too much cylindrical error, it could cause bearing failure. It can also
protect against any large pits or bumps.
The accuracy of cylindrical bearing seats on shafts and in housing bores of seats for thrust bearing washers and of the
support surfaces (abutments for bearings provided by shaft and housing shoulders etc.) should correspond to the accuracy
of the bearings used. This should be followed when machining the seats and abutments.
Cylindricity tolerance on the bore housing(left) and the bearing seat on the shaft(right)

5. PAGE 4
Perpendicularity
Inaccuracy in the squareness of the shaft shoulder may cause misalignment of the
bearing inner and outer rings which may reduce the bearing fatigue life by adding
an edge load in addition to the normal load. Cage fracture and seizure sometimes
occur for this same reason.
The shoulders of the shaft or housing in contact with the face of a bearing must be
perpendicular to the shaft center line.
After final assembly the axial play of the rotor should be measured with the help of a
dial gauge and. The rotor must also rotate easily and noiselessly. The
perpendicularity of the bearing relative the shaft is also important to ensure
reliability.
Perpendicularity tolerance on the shaft and the housing relative to the centerline

6. PAGE 5
Runout
A round body can be said to be running true on its axis when a dial indicator with its feeler placed against the surface of the
round body does not show any variation in reading. Run-out is caused when there is some deviation in the trajectories of
points on a section of the surface is relation to the axis of rotation (errors of position) and the movement of the axis of
rotation if bearing surfaces or bores are not exactly circular (errors of bearings). In other words, run-out is the resultant of
the radial throw of the axis, of the out of roundness of the component, and of the errors of bearings.
Total runout concerns the runout of a complete surface. For measurement purposes, the checking indicator must traverse
the full length or extent of the surface while the part is revolved about its datum axis. Measurements are made over the
whole surface without resetting the indicator. Total runout is the difference between the lowest indicator reading in any
position and the highest reading in that or in any other position.
Preloading is used to reduce the run out of the rotational axis.
LATERAL RUNOUT
Also called axial runout, it is the amount of sideways
motion or wobble in a wheel or tire as it rotates. It is
usually measured by holding a dial indicator against
the face of the rim or tire sidewall. A wheel with too
much lateral runout will wobble back and forth as it
rotates creating a shimmy that feels like dynamic
imbalance problem. It is the measurable irregularity
or wobble parallel to the axis of rotation.
RADIAL RUNOUT
Radial run-out is caused by the tool or component being rotated off centre, i.e. the
tool or component axis does not correspond with the main axis. Radial run-out will
measure the same all along the main axis.
Radial run-out is the result of a rotating component running off center, such as a
ball bearing with an offset center. This means that the rotating tool or shaft,
instead of being centrally aligned, will rotate about a secondary axis. A rotating
shaft may be less tolerant of radial run-out since the center of gravity is displaced
by the amount of run-out.
If runout is large, misalignment of shaft-to-shaft couplings or fixtures may occur. Misalignment, in turn, may subject the
couplings, shafts, and bearings to excessive loads and premature wear

7. PAGE 6
Radial runout on the bearing seats and the housing bore
References
1- Lectures notes
2- Metrology for Engineers - C. R. Shotbolt - 5th Edition
3- The drawing is taken from SKF General Catalogue P.196