Roller Bearings
Part of Gear Making
How roller bearings work, when to use them over plain bearings, and how to improvise or fabricate them in a post-industrial workshop.
Why This Matters
Roller bearings — which include both ball bearings and cylindrical/tapered roller bearings — replaced plain bearings in most machinery during the 20th century for good reasons: they work well without continuous oil supply, they tolerate shock loads, they start spinning easily from rest, and they maintain their performance over a wide speed range. Any machinery you salvage from the pre-collapse world will be full of roller bearings, and keeping these machines running requires understanding how to inspect, repack, and if necessary improvise replacements.
More importantly, the strategic question for a rebuilding civilization is: when do you use precious salvaged roller bearings versus making plain bearings yourself? Roller bearings should be reserved for high-speed, high-precision applications (electric motor shafts, lathe spindles, generators) where their advantages matter most. For slow-moving, heavily loaded machinery (millstones, pump cranks, waterwheel shafts), well-made plain bearings are preferable because they can be fabricated locally.
Understanding roller bearings also means you can recover functional bearings from scrap machinery, clean and repack them, and extend their service life by years. In a world without bearing supply chains, this skill is genuinely valuable.
How Roller Bearings Work
All roller bearings share the same principle: rolling elements (balls, cylinders, cones, or needles) separate the rotating inner race from the stationary outer race, converting sliding friction into rolling friction. Rolling friction is roughly 10-50 times lower than sliding friction for equivalent loads, which is why roller bearings run cooler and require less lubrication.
Ball bearings use spherical balls that contact both races at a single point. This gives low friction but limits load capacity — the tiny contact area means high stress. Ball bearings are best for high-speed, moderate-load applications: electric motors, spindles, fans.
Cylindrical roller bearings use cylinders that contact the races along a line rather than a point. Higher load capacity than balls, but less tolerance for misalignment. Good for heavy radial loads at moderate speeds.
Tapered roller bearings have conical rollers that can handle both radial and axial (thrust) loads simultaneously. Used in wheel hubs, gearbox shafts — anywhere the shaft is pushed sideways while also being pushed endwise.
Needle bearings are very thin, long cylinders. They fit in extremely tight spaces and handle high radial loads, but require good surface finish on the shaft itself which acts as the inner race.
Inspecting and Recovering Salvaged Bearings
The bearing salvage process:
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Disassembly: Press bearings off shafts with a bearing puller or a tube of matching diameter pressed against the inner race only. Never strike the outer race to remove a bearing from a shaft — you’ll brinell (dent) the race.
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Cleaning: Soak in solvent (kerosene, diesel, or denatured alcohol) for 30 minutes. Agitate by hand. Air dry. Use a stiff brush on the outer surfaces; avoid lint-producing rags inside.
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Inspection: Rotate slowly by hand. Feel for:
- Roughness or grinding — damaged rolling elements or pitted race surface
- Catching or clicking — cracked race, damaged cage, embedded debris
- Excessive looseness — worn races (too much play allows oscillation damage)
- Rust pitting — severe surface damage that causes fatigue failure quickly
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Decision: A smooth-spinning, non-pitted bearing can be repacked and reused. Any roughness means progressive failure; relegate rough bearings to non-critical low-speed applications.
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Repacking with grease: Fill about 30-50% of the internal space with grease. Over-packing causes churning heat. Use lithium-based grease where available; tallow works in emergencies for low-speed applications but has poor high-temperature performance. Replace seals or shields if damaged.
Improvised Roller Bearings
Making precision ball bearings from scratch without hardened steel and grinding equipment is not practical. However, several improvised approaches work for lower-speed applications:
Caged roller bearing from drill rod: Drill rod (precision ground steel rod available from metalworking suppliers) can be cut into cylindrical rollers. Grind the ends flat. Fabricate inner and outer races from turned steel. The key challenge is hardening the races — without hard races, rollers brinell them quickly. Case harden by packing in charcoal and heating to bright red, then quench in oil.
Bronze cage plain bearing (hybrid): A thick bronze bushing bored to running clearance, with shallow pockets machined around the bore, each holding a small cylinder of hardened steel. The cylinders roll rather than slide. This is effectively a needle bearing and works well for moderate speeds.
Thrust washer bearings: For axial loads only, a stack of hardened steel washers with bronze washers interleaved, all running in a grease-packed housing. Simple to make, adequate for pump thrust loads, mill shaft axial loads.
Captured ball thrust bearing: Drill matching hemispherical pockets in two steel washers (using a ball-end mill or careful filing), press-fit hardened steel balls salvaged from ball mills, lock screws, or bearing suppliers. Clamp together. Works for crane hooks, steering pivots, low-speed thrust loads.
Lubrication and Failure Prevention
Most roller bearing failures result from lubrication problems, not mechanical overload.
Grease packing is standard for sealed or shielded bearings. The grease should be replaced whenever the machine is disassembled, or annually for continuous-service machines. When repacking, wipe out all old grease before adding new — mixing incompatible greases can cause them to separate into a liquid oil and solid soap, destroying lubrication.
Oil bath lubrication suits large, open bearings: the bearing runs partially submerged in an oil reservoir. Change oil annually or when it becomes dark and gritty.
Contamination prevention: A bearing destroyed by dirt or water far outlasts one destroyed by overload. Seals and shields must be intact. In dusty environments, felt labyrinths packed with grease around the housing prevent particle ingress.
Temperature monitoring: A bearing running too hot (above 70°C / 160°F) is failing. Causes: overlubrication (grease churning), underlubrication, misalignment, overload, contamination. Act before failure, not after.
The key principle for bearing stewardship in a resource-constrained environment: use plain bearings wherever possible, reserve roller bearings for applications where their specific advantages matter, inspect everything regularly, and repair proactively rather than waiting for catastrophic failure.