A bushing pressed to the wrong interference, or a rolling bearing mounted with the wrong fit, can lose running clearance before the machine turns over. Both met catalog spec on the shelf; service life comes from the fits you put on the drawing and how you inspect the installed assembly. A bushing called out as a generic “bearing” and routed through black-box quoting is exactly where that intent gets lost.
For production hardware, the useful question is what the interface has to do under its real load, speed, and motion, what dimensions establish good operating conditions, and how the finished assembly gets inspected. They bring subtle influences with make-or-break performance effects.For the part you are signing off on, the useful question is what the interface has to do under real load, speed, and motion, what dimensions you put on the drawing, and how the finished assembly gets inspected. A bushing called out as a generic ‘bearing’ and routed through black-box quoting is exactly where that intent gets lost.
Plain (Sliding) Bearings – sliding contact between surfaces:
- Bushing (sleeve bearing): Cylindrical sleeve; radial loads; many materials (bronze, polymer, composite); common in pivoting and oscillating joints.
- Journal bearing: Radial loads; hydrodynamic lubrication; engine and high-speed use.
- Thrust washer: Axial (thrust) loads; flat washer design; low profile; bronze, polymer, or composite.
- Combined thrust washer/journal: Radial and axial loads; integrated design; compact envelope.
Rolling-Element Bearings – rolling contact (balls or rollers):
- Ball bearing: Ball rolling elements; radial and/or axial loads; low friction; high-speed capable.
- Roller bearing (cylindrical): Parallel rollers; high radial loads; rigid design; common in industrial applications.
- Tapered roller bearing: Tapered rollers; radial and axial loads; handles combined loads; common in automotive and heavy equipment.
- Needle roller bearing: Long, thin rollers; high load capacity in small envelope; minimal radial space; common in compact designs.
- Ceramic ball bearing: Ceramic (Si₃N₄) balls; near-zero friction; high-speed capable; corrosion resistant; used in demanding environments.
- Air bearing (foil or porous): Pressurized air film; no physical contact; low friction; ultra-high speed; used in precision and clean environments.
- Magnetic bearing (active or passive): Magnetic levitation; no physical contact; very high speed; precision control; used in specialized high-performance applications.
Note: The differences between bushings and journal bearings are ill-defined, journal bearings are commonly split shells used on an engine crankshaft to illustrate the difference.
Bushing vs bearing defined
A bearing supports relative motion between components. Rolling-element bearing and plain bearing families operate in very different ways, to deliver similar outcomes.
Ball and roller bearings carry load through rolling elements running between races. A plain bearing carries load across a sliding surface.
A bushing is a type of plain bearing, commonly a low friction, wear tolerant cylindrical sleeve installed between a shaft and housing. The terms sleeve bearing, journal bearing and bushing overlap in engineering usage, although journal bearing describes larger, hydrodynamic bearing systems that would not normally be called bushings.
This distinction matters on your drawing and your purchase order. Calling a part simply a ‘bearing’ does not establish design intent, and it is the kind of gap a silent supplier on a production run will quietly fill with whatever is cheapest.
The physics that drives the choice
Rolling contact can produce substantially lower friction than sliding contact. Under suitable operating conditions, rolling-element bearing friction can be one or two orders of magnitude below that of a lubricated bronze plain bearing.
That comparison does not provide a universal friction guide. A porous, sintered bronze bushing operating with an impregnated oil film is quite different from a solid bush running poorly lubricated at startup. Shaft finish and temperature can differentiate results further.
The bearing has to be evaluated under its intended operating condition.
Pressure-velocity, or PV, is one of the useful design quantities for a plain bearing:
PV = P × V
For a projected-area calculation on a radial bushing:
P = F / (L × d)
where:
F = radial load
L = bearing length
d = shaft diameter
Surface velocity for continuous shaft rotation can be expressed as:
V = (π × d × N) / 60
where:
d = shaft diameter in meters
N = rotational speed in revolutions per minute (rpm)
Suppose a 20 mm shaft rotates at 600 rpm. Its surface velocity is approximately:
V = (π × 0.020 × 600) / 60
V = 0.628 m/s
If the 20 mm-long bushing carries a radial load of 2 kN, projected pressure is:
P = 2000 / (0.020 × 0.020)
P = 5,000,000 Pa
P = 5 MPa
Therefore:
PV = 5 × 0.628
PV ≈ 3.14 MPa·m/s
That value can be compared with the allowable PV for the selected bearing material under the specified lubrication, temperature and duty cycle.
There is no useful universal PV limit for “bronze bushings” or “polymer bearings.” The permitted value belongs to the actual material system and real-world operating condition. A supplier datasheet that specifies PV under continuous rotation at room temperature cannot be transferred unchanged to a hot, intermittently lubricated application.
Lubrication regime
The Stribeck curve describes the change in friction as a sliding bearing moves through boundary, mixed and hydrodynamic lubrication.
At low speed or during startup, the surfaces can be separated only partially by lubricant. Asperity, metal-on-metal contact carries part of the load. As speed and film formation increase, a mixed regime develops. A sufficiently developed hydrodynamic film separates the surfaces and carries the load through fluid pressure alone.
Many journal-bearing failures begin when that film is inadequate and the shaft contacts the bearing surface. Local heating and material transfer can progress into wiping.
A plain bearing designed around hydrodynamic operation still has to survive startup and shutdown, when the full fluid film has not yet developed.
Load, speed, motion and environment
The motion profile often narrows the right approach, before detailed bearing calculations begin.
Rolling bearings are well established for continuous rotary motion, where low friction and controlled radial or axial location are important. Their standardized geometry also makes life calculations and replacement straightforward when the loading is adequately defined.
A bushing can fit into much less radial space. It also tolerates some conditions that are awkward for rolling contacts, particularly slow oscillation and shock loading, as force is distributed across a broad projected area, rather than a localized angular contact.
Misalignment requires considerable care. Some plain bearing constructions tolerate edge loading poorly. Certain rolling bearings are specifically designed to accommodate angular misalignment. The actual bearing geometry matters more than the family name.
Contamination changes the failure mechanisms. Abrasive particles entering a rolling bearing damage highly loaded raceway contacts. A plain bearing may embed some small debris, as it may be intrinsically soft material. This hard contamination will score the shaft and accelerate wear.
Oscillating motion deserves separate treatment
A joint moving repeatedly through a small angular displacement may never circulate lubricant, or allow hydrodynamic behavior to develop, irrespective of bearing type.
Small oscillations or vibration can repeatedly load the same raceway regions. Lubricant is displaced from those contacts but not recirculated and wear debris can form characteristic surface damage. This is termed false brinelling.
It should not be confused with true brinelling, where static overload plastically indents the raceway to reflect the profile of the rolling elements, resulting in cogging and fractures.
A pivoting linkage is a common case where a bushing deserves early consideration. The shaft slides across the bearing surface as the joint moves, and a suitable plain-bearing material can be selected specifically for oscillatory service.
The amplitude, frequency and load still have to fall within the chosen material’s operating limits. “Oscillating” alone is not enough to drive the selection of the component.
How to specify a bushing on the drawing
Your catalog number defines the bushing you buy. Your drawing has to define the bearing you install.
The housing bore you specify controls retention and affects the finished bushing bore. The shaft you specify sets running clearance and is the surface the bushing runs on.
Housing fit and installed bore
ISO 286 provides a system of limits and fits for mating cylindrical features. H7 is a common starting point for a press-fit housing bore, but takes the final tolerance and interference from the bushing manufacturer’s installation requirements.
Pay particular attention to installation conditions with thin-wall bushings.
Engineers Edge notes that, in general, the bore diameter changes by 70–100% of the interference, and that the change can’t be predicted precisely. The housing material distorts too, so measure the installed bore on a test sample.
A bushing that gauges correctly on your bench can come out undersized after a heavy press fit.
Where the final bore is critical, inspect it in the installed condition. If you use solid bronze, you can order it with machining allowance and ream it after pressing.
If you use wrapped thin-wall bushings, use them as fitted, following the manufacturer’s installed-bore method. ISO 3547-1:2018 covers their dimensions.
Running clearance
The operating clearance between the installed bushing bore and the shaft defines aspects of the bearing pair behavior.
If you tolerate the bore and shaft independently, the clearance range can be much wider than you expect. Calculate both extremes before you release the fit.
For a 20 mm nominal shaft:
Minimum diametral clearance = minimum bore − maximum shaft
Maximum diametral clearance = maximum bore − minimum shaft
Temperature can alter that range. An aluminum housing responds more to temperature change than a steel shaft or bronze sleeve does. If your equipment sees a wide operating-temperature range, check the fit at the temperature extremes as well as at room temperature.
Shaft finish and hardness
The shaft is a working bearing surface.
Its roughness affects lubricant-film formation and wear. A rough shaft can abrade a softer bushing, while an extremely smooth surface is not automatically optimum for every lubricated material system.
Take your shaft finish and hardness requirements from the bushing supplier’s data, and apply them to the actual running diameter. As a reference point, igus guidance gives around 60+ HRC and a finish under 4 rms for ball bearings, and says bronze needs a shaft harder than the bushing.
Some polymer and composite bushings run successfully against relatively soft counterfaces. Bronze applications generally benefit from a shaft harder than the bearing material. Rolling-bearing raceways operate at much greater hardness, with bearing steels commonly around 60 HRC for both running surfaces.
Copy a rolling-bearing hardness callout onto a bronze-bushing shaft only when you have a design reason.
Bushing materials
C93200 bronze, commonly associated with SAE 660, remains a familiar material for machined bushings. Its composition includes C93200 bronze, commonly associated with SAE 660, remains a familiar material for machined bushings. Wieland Concast gives its composition as 81–85% copper, 6.30–7.50% tin, 6–8% lead, and 2–4% zinc. Concast and Bunting both list its typical hardness as 65 BHN (500 kg load).
It requires lubrication, if durability is an issue.
Sintered bronze bearings use a porous structure that can retain lubricating oil. ASTM B438 covers sintered bronze, oil-impregnated sleeve, flange, thrust and spherical bearings within its scope. Material designation and oil impregnation need to follow the actual purchased specification.
Composite wrapped bushings use another construction. Products such as DU-type bearings combine a steel backing, porous bronze layer and PTFE-based sliding surface. Some grades can operate without external lubrication, particularly for low-stress rotation. For sliding or sliding/rotating applications, a lubricant is beneficial.
These constructions cannot be treated as interchangeable simply because their nominal dimensions match. Housing installation requirements, allowable PV and shaft recommendations differ.
Rolling-bearing materials and specification
SAE 52100 Chromium bearing steel is widely used for rolling-bearing races and balls. It provides the hardness and fatigue properties required at concentrated rolling contacts.
440C stainless steel is used where greater corrosion resistance is required and can be hardened to roughly 58 to 60 HRC.
Hybrid bearings may use silicon-nitride rolling elements with steel races. Lower rolling-element mass and other contact characteristics make them useful in some high-speed applications.
For a standard rolling bearing, the drawing will often identify an established bearing designation, rather than reproduce the raceway geometry.
ISO 492 specifies dimensional and geometrical tolerances for radial rolling bearings. ANSI/ABMA Standard 20 provides tolerance classes used for radial bearings in inch practice. ISO 281 addresses rating life.
Bearing life is a sizing calculation
The basic rating-life relationship is:
L10 = (C / P)^p
where:
C = basic dynamic load rating
P = equivalent dynamic bearing load
p = 3 for ball bearings
p = 10/3 for roller bearings
L10 is the basic rating life associated with 90% reliability under the assumptions of the calculation.
Speed converts the rating life from millions of revolutions into operating hours:
L10h = (10^6 / (60 × N)) × (C / P)^p
where:
L10h = basic rating life in operating hours
N = rotational speed in revolutions per minute (rpm)
The calculation is useful for selecting a bearing size. It does not, by itself, account for every service condition that can affect bearing life. Lubrication and contamination can overwhelm the calculated result, even where the nominal dynamic load calculation looks comfortable.
How to specify a rolling bearing installation
The bearing designation defines the bearing. The surrounding materials and machined features determine how it operates in the assembly.
A shaft seat needs the specified hardness, diameter tolerance, and appropriate surface condition. The housing bore has its own fit. Which ring requires interference depends on the direction of load relative to the ring and the application.
Too little retention can allow a ring to creep on its seat. Excessive interference expands or contracts the race and can reduce internal clearance.
That effect becomes important on precision or high-speed assemblies. A bearing purchased with the correct internal clearance can end up with insufficient operating clearance after installation, if fit and temperature were not integrated into the selection.
Shoulders and fillets also need enough geometric clearance to seat the bearing ring against its locating face. A shaft fillet larger than the bearing’s permitted corner clearance can prevent full seating, while the axial dimensions still appear correct.
Verification and acceptance
For a bushing assembly, your acceptance has to cover the installed condition. Incoming inspection of the loose bushing tells you little about how it will run.
Measure the housing bore before installation. After pressing, gauge the installed bushing bore where the fit is critical. If you specify reaming after installation, accept the bore only after reaming.
Inspect the shaft running diameter separately for size and surface texture. If your counterface requirement includes hardness, put it in the inspection plan.
Check that the material cert matches the material you called out. A certificate stating only “bronze” gives little assurance that you received the C93200 you specified.
Rolling-bearing inspection takes a different route because standard bearings are normally purchased as finished, precision components. For standard rolling bearings, your incoming controls can rely on the bearing designation and manufacturer traceability. The machined shaft and housing seats stay on your part-specific inspection list.
Either way, state the acceptance condition on your assembly drawing. If you measure a press-fit bushing only before installation, the dimension that pressing changes goes unchecked.
Failure modes
Plain-bearing wear and wiping
Wear concentrated on one side of a bushing can indicate load distribution or alignment problems. A polished or smeared surface accompanied by local heating points toward loss of the intended lubricant.
Wiping occurs when the lubricating film fails and direct surface contact generates enough heat and shear to transfer or smear bearing material.
The shaft often preserves useful evidence. Scoring can reveal hard contamination passing through the interface. A rough or damaged counterface may continue wearing replacement bushings until the shaft condition is corrected.
Rolling-bearing spalling
Spalling is associated with rolling-contact fatigue. Cracks develop beneath or near the loaded raceway surface and eventually release jagged material fragments.
Load history and bearing life matter to the investigation. SKF attributes about 36% of premature bearing failures to lubrication and 14% to contamination. Together, by our count, that is roughly half, so evaluate both before you blame the fatigue calculation.
Hard particles can create local raceway damage that later develops into a fatigue origin.
True and false brinelling
True brinelling is permanent indentation caused by excessive static or impact load. The rolling elements plastically deform the raceway.
False brinelling can develop under small-amplitude oscillation or vibration. Its damage pattern can resemble indentations at rolling-element spacing, but the mechanism is wear at repeatedly loaded contacts.
Transport vibration can produce false brinelling in equipment that is not operating at all. Oscillating joints can create the same contact condition during normal service.
Production controls around the bearing interface
Your first article should capture the dimensions that set the installed bearing condition, along with the purchased component designation.
For a pressed bushing, that may include the housing bore and installed ID together with the shaft diameter. Surface roughness or hardness can appear as separate characteristics where the drawing controls them.
AS9102 provides the FAI framework for aerospace production. PPAP can carry the corresponding characteristics into automotive and other programs that use production-part approval.
Material certificates and certificates of conformance (C of C) remain tied to their respective lots. For machined bushings, heat or material-lot traceability may be required by the program. Purchased rolling bearings may instead rely on manufacturer and batch identification.
A process change can alter the bearing condition, without altering the nominal CAD model. Revising a bushing bore spec from finish boring to reaming changes the produced surface. Changing the press operation or housing material can alter the installed ID.
Revision and process control need to encompass those characteristics, when they form part of the approved production route.
Approving a supplier for bearing and bushing hardware
Start with the finished interface shown on the drawing.
For a pressed bushing, review how the supplier establishes the installed bore. If the final size is achieved by reaming after assembly, inspect a typical representative production record from that operation, and the gauge used for acceptance.
The housing demands equal attention. Bore size and form affect the interference around the circumference, particularly in a thin housing that can distort during pressing.
For machined bronze bushings, confirm the actual alloy and inspect the material certification used on comparable work. The shop should also be able to show how it protects the finished bearing surface from burrs and embedded machining debris before assembly.
Where the supplier installs purchased rolling bearings, inspect the shaft and housing controls around the bearing. Bearing traceability does not compensate for an incorrect seat fit.
Production documentation should connect the released drawing revision to the inspected hardware and the material or purchased-component records required by the program.
For Jiga, the supplier-of-record role covers that manufactured interface. Housing fits, shaft features and any post-installation machining remain part of the production definition delivered with the assembly.
Frequently Asked Questions
What is the difference between a bushing and a bearing?
A bushing is one type of bearing. “Bearing” covers anything that supports relative motion; it splits into plain (sliding) bearings and rolling-element (ball or roller) bearings. A bushing is a plain bearing: a sliding sleeve between shaft and housing. So the useful comparison is plain bearing vs rolling bearing.
When should I use a bushing instead of a bearing?
Reach for a bushing when motion is slow, oscillating, or intermittent, when space is tight, when the joint sees shock or contamination, and when you want a simpler, lower-cost part that tolerates marginal lubrication. Rolling bearings win when you need low friction at continuous speed.
Can a bushing handle higher loads than a ball bearing?
Often yes, for static and shock loads, because a bushing spreads load across a large sliding area instead of concentrating it at rolling-element contact points. The limit is PV (pressure times velocity), not load alone, so qualify it by material, speed, and lubrication.
Which is better for oscillating or low-speed motion, a bushing or a rolling bearing?
A bushing. Rolling bearings in small-angle oscillation without full rotation are prone to false brinelling, where the elements wear flats into the races because lubricant never redistributes. A plain bushing has no rolling elements to brinell, so it is the right call for pivots and linkages.
How do I specify a bushing fit and shaft finish on a drawing?
Call out a hole-basis housing fit (commonly H7 under ISO 286) and the press-fit interference, then state the running clearance in the installed condition. Engineers Edge notes that, in general, the bore diameter changes by 70–100% of the interference, and that the change can’t be predicted precisely. Where solid bronze is supplied with machining allowance, ream it after pressing. Wrapped bushes are used as fitted, per the manufacturer’s installed-bore method; ISO 3547-1:2018 covers their dimensions. Take shaft finish and hardness from the bushing supplier’s data; igus guidance says bronze needs a shaft harder than the bushing.
