A curved step bearing supports the bottom of a vertical shaft on a curved seat. This section shows the shaft, supporting step, surrounding oil reservoir and fixed housing. The calculator idealizes the loaded region as a spherical cap and compares axial load with its projected area.
Curved Step Bearing Interactive Calculator
Compare axial load with the projected area of an idealized spherical contact cap. See the vertical shaft, curved step and oil reservoir. Fixed 6 and 10 MPa comparisons are not bearing ratings.
Equation Used
- Axisymmetric spherical-cap geometry.
- Specified projected loaded region is used as entered.
- Axial load without an applied moment.
- No inferred material limits or film thickness.
Spherical-cap idealization. No material, lubrication, elastic-contact, allowable-load or wear-life model.
A rotating shaft on a fixed curved support
Hiscox figure 1276 identifies a curved step bearing with an oil reservoir. The section view shows the curved step and surrounding reservoir. A moving highlight indicates shaft rotation; the housing and reservoir remain fixed.
For the spherical-cap calculation, R is the curvature radius and θ is the cap half-angle measured from the vertical centerline. The drawing is auto-scaled, so its millimetre dimension labels establish the physical size. Rotation rate, oil level and the visible interface thickness are illustrative.
Compare nominal load and geometry
Use the load, curvature radius and cap angle to explore how the nominal projected-area pressure changes. This can support an initial geometry comparison, but it cannot establish a suitable bearing material, oil or operating speed.
A larger projected radius reduces W/A at the same axial load. A real loaded contact may occupy less than the entered idealized cap, and the pressure may vary across it.
Projected area is not curved surface area
The projected contact radius is a=R sin θ. Its circular projected area is A=πa²=πR²sin²θ. With load W in N and area in mm², p=W/A is in MPa.
The spherical surface area would instead be 2πR²(1−cos θ). The calculator uses the projected area because the specified load is axial. For an ideal uniform normal pressure over the spherical cap, integrating its axial component also gives W=pπR²sin²θ. Nonuniform pressure and elastic contact are not solved.
The third result is simply 6A/1000 kN. The fourth is 100p/10 percent. The 6 and 10 MPa values are comparison pressures, not allowable load or wear limits.
Example projected-area calculation
At R=100 mm and θ=20°, projected radius is about 34.20 mm and projected area is about 3675 mm². An axial load of 18,000 N gives approximately 4.898 MPa. The 6 MPa comparison corresponds to about 22.05 kN, and p/10 MPa is about 48.98 percent.
Doubling load doubles nominal pressure. Doubling curvature radius at the same cap angle multiplies projected area by four and reduces nominal pressure to one quarter.
What is needed beyond this model
This tool does not calculate a hydrodynamic film, frictional heat, material strength, wear, alignment capacity or life. It cannot classify a design as acceptable simply because its nominal pressure falls below either displayed reference.
Surface conformity, clearances, shaft guidance and lubrication conditions influence a real bearing. The idealized cap and the fixed numerical pressure comparisons must not be treated as measured contact or manufacturer ratings.
Curved-step questions
Is the area the curved contact surface?
No. It is the circular area projected perpendicular to the axial load.
Is 6 MPa the bearing’s rated capacity?
No. The third result is a numerical comparison at a fixed pressure.
Does the animation show shaft misalignment?
No. The shaft remains vertical and rotates; alignment limits are not supplied.
Why does changing load not deform the drawing?
Elastic properties are absent. Load changes nominal pressure, not prescribed geometry.
Side-load review for actuator-driven Curved Step Bearing Mechanism
For actuator installations involving curved step bearing mechanism, deflection and side load deserve a separate check. A bracket that looks strong at rest can twist under dynamic load and put bending into the actuator shaft.
When comparing a cylinder to an electric actuator, convert the discussion into stroke, force, speed, duty cycle, and installed length. Matching one specification is not enough.
Where the surrounding member deflects, the actuator can see a different load path than the drawing suggests. That is why bracket stiffness and real installed alignment belong in the actuator selection review.
- Keep side load out of the actuator rod by guiding the moving member separately.
- Verify pin diameter, clevis width, bracket stiffness, and alignment under load.
- Check that deflection will not change the actuator load path during operation.
For FIRGELLI actuator projects, compare product families through the FIRGELLI actuator families and use the linear actuator replacement finder when replacing an actuator from another manufacturer. The selection should stay tied to real stroke, force, and mounting dimensions.
Reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, printed page 315, figure 1276, for the curved step and oil-reservoir construction. The calculator compares axial load with the projected area of an idealized spherical cap.
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