A collar bearing carries axial thrust through shoulders on a rotating shaft bearing against stationary thrust surfaces. A footstep supports the shaft end. The arrangement illustrated here follows a historical vertical-shaft collar-and-step bearing, generalized to the selected number of loaded annular faces.
Collar Bearing and Step Interactive Calculator
Split an entered axial thrust between equally loaded collar faces and an assumed footstep share. The diagram shows the selected number of collars, a fixed keyed bronze sleeve and the rotating shaft. Force units are US short ton-force; 1 short tonf = 2,000 lbf.
Equation Used
- Downward axial load; no radial load calculation.
- Selected footstep share is imposed rather than solved.
- All remaining collar faces carry equal thrust.
- No contact pressure, lubrication, temperature or capacity prediction.
Generalized axial section after Hiscox figure 1282: rotating collars, split stationary bronze sleeve with an anti-rotation key, and a footstep. Each annular face appears twice in section but is counted once. US short ton-force is explicit. Lubrication film thickness and deflection are not resolved.
Rotating collars and a stationary sleeve
Hiscox figure 1282 shows a collar bearing and step for a vertical shaft. Its description identifies a split bronze thrust sleeve and a key to prevent that sleeve from rotating. The animation distinguishes the rotating steel parts from the fixed bronze sleeve and footstep.
The lower face of each collar transfers the entered downward thrust to a matching stationary ledge. Each annular face appears as a left and right portion in the axial section; those two visible portions are one face, not two separate collars.
The separate end view shows shaft rotation. The shaft remains at a fixed axial position in the section. Oil-film thickness, wear and elastic deformation are not drawn or calculated.
A historical thrust-bearing arrangement
Collar and footstep bearings illustrate how a vertical shaft can transfer axial load into a supporting housing. This page is an idealized load-sharing study, not a specification for a restored mill or a modern bearing.
Multiple collars do not automatically divide load equally. Michell Bearings’ historical account describes the adjustment needed to achieve even loading in multi-collar thrust blocks. This calculator assumes equal sharing between the loaded collar faces; it does not solve their actual distribution from stiffness and clearances.
Axial force balance
Let total downward thrust be W, the number of loaded annular faces be n and the selected footstep share be s percent. The footstep force is W × s/100. The remaining combined collar force is W × (1 − s/100).
Assuming equal sharing, each face carries W × (1 − s/100)/n. Summing all n face forces and the footstep force returns W. The percentage per face is 100 × face force/W.
All force entries and outputs use US short ton-force, with 1 short tonf equal to 2,000 lbf. No mass-to-force conversion is implied. Contact pressure would also require the loaded area; friction power would require speed, radius and a suitable lubrication/friction model.
Worked axial-load split
With 20 short tonf total thrust, two loaded faces and 0% footstep share, the collars carry 20 short tonf combined, or 10 short tonf each. The footstep contribution is zero in this assumed split.
Changing the footstep share to 25% gives 5 short tonf at the step and 15 short tonf across the collars. Each of the two collar faces then carries 7.5 short tonf. The balance is 7.5 + 7.5 + 5 = 20 short tonf.
What this calculation cannot determine
Increasing the face count divides the assumed collar load among more faces. It does not itself establish lower operating temperature, equal actual loading or a safe bearing rating. Clearances and relative stiffness can make real loading uneven.
The step-share slider describes a chosen load case. It does not calculate the load split from shaft deflection or adjustment. Geometry, material, lubrication, speed and thermal information are needed for bearing design beyond this equilibrium calculation.
Collar-and-step bearing questions
Are collar faces radial or axial load surfaces?
The faces modeled here carry axial thrust. Radial guidance may also exist in the assembly, but radial loads are not part of this calculation.
Why does one collar show two contact strips?
A section through an annular surface cuts it on both sides of the shaft. Those strips belong to one annular face.
Does adding collars guarantee equal load sharing?
No. Equal sharing is an explicit simplifying assumption. Real clearances, stiffness, wear and adjustment affect the distribution.
Why is the bronze sleeve fixed?
Hiscox specifies a key to prevent the split thrust sleeve from rotating. The shaft and its collars rotate against the stationary bearing surfaces.
Can this tool rate bearing capacity?
No. It accounts for an assumed axial-force split. It does not calculate pressure, lubrication film, temperature or allowable load.
References
- Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, printed page 316, figure 1282: collar bearing and step, split bronze sleeve and anti-rotation key.
- Simmons and Henderson, Naval Thrust Bearings, manufacturer technical history explaining the adjustment and load-sharing difficulties of multi-collar thrust blocks.
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