A bushing is the cheapest part in most rotating assemblies and the one most likely to end a machine’s service life. Get the clearance wrong by 0.02 mm and it seizes; pick the wrong material and it wears through in a season. Custom metal bushings let you match bore, wall, material, and lubrication to the actual load and speed instead of forcing a catalogue part to fit. This guide covers the types, materials, tolerances, and manufacturing routes buyers need to specify correctly.
What a Bushing Has to Do
A plain bushing carries radial load while allowing a shaft to rotate or slide, with no rolling elements. It absorbs misalignment, damps vibration, and is designed to wear in preference to the shaft and housing it protects. That last point is the key design intent: the bushing is a sacrificial component, and replacing it should be far cheaper than replacing what it protects.
Flanged bushings add a thrust face for axial load. Split bushings allow field installation without disassembling a shaft. Sleeve bushings are the plain cylindrical baseline. Thrust washers handle pure axial load. Choosing the wrong style is a common and expensive error, because a sleeve bushing carrying axial load will simply chew its own end face.
Material Selection Drives Everything
Bronze alloys are the workhorse. SAE 660 leaded tin bronze handles high load at moderate speed, while aluminium bronze takes heavy shock loading. Both machine well and are forgiving of marginal lubrication. Steel bushings, usually case-hardened, take the highest loads but demand reliable lubrication. Stainless bushings serve corrosive and food-contact environments. Cast iron works where cost matters and speeds are low.
Sintered bronze deserves separate mention. Produced by powder metallurgy and then oil-impregnated, it holds around 20 percent lubricant by volume within its pore structure and releases it as the shaft warms. This makes it genuinely maintenance-free for light and medium duty. Our sintered bushings and self-lubricating bearings lines cover this family, and the sintered bushings guide explains the porosity and oil-retention trade-offs in detail.
Machined vs. Sintered vs. Rolled
Machining from bar or tube is the right route for low to medium volumes, oversized dimensions, or any bushing needing tight tolerance and custom features such as grooves, ports, or non-standard flanges. It carries no tooling cost and turns around quickly. We machine these on CNC turning centres with live tooling so grooves and cross-holes are cut in the same setup as the bore.
Sintering via compacting and sintering becomes cheaper above roughly 10,000 pieces and delivers the self-lubricating porosity machining cannot. Rolled bimetal bushings, formed from strip with a bronze or polymer lining on a steel back, dominate ultra-high-volume automotive applications. The break-even between routes depends on volume, wall thickness, and whether oil impregnation is needed. Our self-lubricating bearings article compares service life across these constructions.
Bore Tolerance and Running Clearance
This is where most bushing failures originate. Running clearance is typically 0.001 to 0.002 times shaft diameter for hydrodynamic operation, so a 50 mm shaft wants roughly 0.05 to 0.10 mm of diametral clearance. Too tight and thermal growth seizes the joint; too loose and the shaft hammers, generating noise and accelerating wear.
Remember that press-fitting a bushing closes its bore. A 0.05 mm interference fit into a housing will shrink the bore by a similar amount, so bushings are commonly machined undersize and finish-honed or reamed after installation. Where the bore must be right before assembly, the interference must be calculated into the pre-fit dimension. Our honing services page covers achieving final bore geometry after press-fit, and the GD&T guide explains how to express cylindricity and concentricity so a supplier quotes what you actually need.
Surface Finish and Lubrication Features
Bore finish targets Ra 0.4 to 0.8 micrometres for most plain bearing service. Smoother is not automatically better, since a slightly textured surface retains lubricant film. Outside diameters that press into housings are typically ground by centerless grinding to hold the interference fit consistently across a production lot.
Lubrication features are worth designing in. Axial or helical grooves distribute oil along the bore; a central annular groove fed by a grease port keeps a heavily loaded bushing supplied; and blind-end designs retain grease in vertical applications. Where operation is genuinely dry, sintered or PTFE-lined constructions are the answer rather than adding grooves to a solid bronze bush.
How to Specify Custom Bushings
Send the shaft diameter and its tolerance, housing bore diameter and tolerance, bushing length, radial and axial load, rotational speed, operating temperature, lubrication regime, and environment. From that we can recommend material, wall thickness, clearance, and manufacturing route, and tell you whether a sintered part will outperform a machined one at your volume. Our centerless grinding page covers the OD tolerances we hold on press-fit diameters.
Frequently Asked Questions
How much running clearance does a bushing need?
Around 0.001 to 0.002 times shaft diameter for hydrodynamic operation, adjusted for temperature and load.
Does press-fitting change the bore size?
Yes. Interference closes the bore by roughly the interference amount, so plan to hone or ream after installation.
When should I choose sintered bronze over machined?
Above roughly 10,000 pieces, or whenever oil-impregnated self-lubrication is needed for maintenance-free service.
What bore finish should I specify?
Ra 0.4 to 0.8 micrometres suits most plain bearing service and retains a lubricating film.
Can you make split or flanged bushings?
Yes, including flanged, split, grooved, and custom-port designs.
Which material handles shock loading best?
Aluminium bronze, followed by case-hardened steel where lubrication is reliable.
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