An adjustable step bearing supports axial load at the lower end of a vertical shaft and provides a way to set the supporting surface’s height. The illustrated version uses a direct screw beneath a wear pad. Turn the screw in the animation to explore the ideal relationship between threads per inch, rotation and shaft-height change.
Adjustable Step Bearing Interactive Calculator
Vary screw TPI and rotation to see how far the wear pad and vertical shaft are raised or lowered.
Equation Used
The screw lead is the axial movement from one full turn. For a single-start screw, lead equals 1/TPI inches per turn, so ideal height change equals turns/TPI. TPI means threads per inch; pitch is the axial distance between adjacent threads.
- Single-start adjustment screw.
- No backlash, thread wear, or elastic compression included.
- Positive turns represent raising the wear pad.
How the adjustable support works
The shaft end bears against a supporting pad, which transfers axial load through the adjuster and housing to the machine structure. In the direct-screw version shown, rotating the adjuster moves the pad vertically. The shaft follows the pad while it remains seated against it.
A step bearing’s load depends on the whole shaft arrangement. It may carry shaft weight and process or gear thrust, but another bearing can share or oppose axial loads. Raising the step can also affect gear position, clearances and other supports.
Principal parts
- Wear pad or thrust surface: supports the rotating shaft end.
- Adjustment screw and mating thread: change the support height.
- Locking provision: retains the specified setting.
- Housing and mounting: carry the load to the structure.
- Lubrication arrangement: serves the particular bearing material and contact design.
The bronze pad, housing proportions and running clearances in the animation are illustrative. The motion shows an adjustment from zero to the selected value and back; it is not a loaded adjustment procedure or a wear simulation.
Setting the height of a vertical shaft
Adjustable lower supports are useful where a vertical shaft’s axial position must be set during assembly or maintenance. Historical mill mechanisms are one example of the principle.
Vertical mixers, pumps and turbines use many different radial and thrust-bearing arrangements. A lower guide bearing does not necessarily carry axial load, and a particular modern machine should not be assumed to use this screw-and-pad construction.
The required height, end clearance and alignment belong to the complete machine design. Adjustment cannot substitute for inspecting a worn or damaged bearing.
Screw lead and height change
For a single-start screw with thread count T in threads per inch, lead = 1/T inches per turn. With N turns, ideal height change is Δh = N/T inches. Multiply by 1,000 for thousandths of an inch, or by 25.4 for millimeters.
Positive turns represent raising the pad in this tool; negative turns represent lowering it. Actual clockwise or counterclockwise operation depends on the screw’s handedness and the arrangement. A multiple-start screw has lead equal to pitch times its number of starts and is outside this single-start conversion.
The three Height Change cards express the same displacement in different units. They do not represent three separate movements or three bearing clearances.
The calculation excludes backlash, elastic compression, wear, thread friction and load capacity. It does not determine whether the screw can be turned under load or whether the shaft remains seated during lowering.
A separate mean-contact-pressure estimate would use load divided by actual contact area. That average alone cannot establish an adequate lubricant film, temperature, wear rate or permissible bearing duty; contact geometry, speed, lubricant and heat removal also matter.
Worked example: a quarter turn
Select 5 TPI and 0.25 turn. The lead is 1/5 = 0.200 in per turn. The ideal height change is 0.25/5 = 0.050 in, which is 50 thousandths of an inch or 1.27 mm.
For the same quarter turn at 10 TPI, the displacement halves to 0.025 in, 25 thousandths or 0.635 mm. With 5 TPI and −0.25 turn, the displayed change is −0.050 in or −1.27 mm.
These values demonstrate thread geometry. They do not specify how much a machine’s bearing should be adjusted, a permissible wear amount or a screw’s lifting capacity.
Comparing axial-support arrangements
| Arrangement | Distinguishing feature | Design considerations |
|---|---|---|
| Screw-adjusted plain step | Provides a mechanical means to set the supporting pad’s position. | Contact design, lubrication, screw load path and locking. |
| Fixed plain thrust support | Locates its thrust surface through the assembly rather than this adjuster. | Position-setting method, replacement access and contact conditions. |
| Rolling-element thrust bearing | Transfers axial load through rolling elements and raceways. | Rated loads, speed, mounting, alignment and lubrication. |
| Fluid-film thrust bearing | Uses a designed lubricant film to carry thrust in operation. | Film-forming geometry, oil supply, temperature and operating conditions. |
Each category includes many designs. No universal speed cutoff, pressure window or service interval follows from the name. Adjustability and the type of bearing contact are separate design choices.
Step-bearing questions
No. It converts single-start screw rotation into ideal axial displacement. Bearing and screw loads, stresses and lubrication are not calculated.
They show one displacement in inches, thousandths of an inch and millimeters. One inch equals 1,000 thousandths and 25.4 millimeters.
No. Delivery to the contact, lubricant properties, temperature, geometry and operating conditions also matter. Use the specified lubricant and inspection procedure for the actual equipment.
No. Load, contact dimensions, alignment, lubrication, operating environment and thermal conditions are also needed. This page does not establish a universal plain-bearing speed limit.
No. Adjustment travel, thread engagement, condition and machine clearances impose limits. Follow the specified inspection and replacement criteria instead of using extra adjustment to conceal damage.
Only if the equipment explicitly provides for that operation under its prescribed procedure. The animation does not demonstrate an approved maintenance method.
No single lubrication method applies to every material and construction. Use the specified oil, grease, water or dry-running arrangement for the actual bearing; do not substitute based on this schematic.
References and further reading
Thomson Precision Screw Assemblies distinguishes screw pitch and lead. Kingsbury thrust-bearing designs provides examples of engineered fluid-film supports, a different contact design from the simple illustrated wear pad.
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