English: Hardened 52100 Bearing Outer Ring CNC Case: Raceway Roundness and Finish Handoff
Direct answer: a hardened 52100 outer ring reaches stable raceway roundness when pre-heat-treatment stock is balanced, clamping is proven at low pressure, hard turning removes a continuous allowance, and free-state roundness is separated from chuck-state readings. Carbide prepares the annealed blank; CBN finishes the 60–62 HRC raceway. This is a hypothetical case.
The tolerance stack crosses heat treatment
The ring is Ø126 × 24 mm with an internal crowned raceway, 0.012 mm free-state roundness, 0.015 mm raceway-to-OD runout, Ra 0.2 µm and a shallow lubrication groove. Datum A is the raceway-derived axis, B one face and C the OD clocking mark. The route drawing reserves 0.35 mm diametral raceway stock and 0.20 mm per face before hardening; final stock is verified after quench, not assumed from nominal growth.
Before hardness: create uniform stock
In the annealed state, a positive coated-carbide insert faces and bores; a carbide groover forms the lubrication channel undersize. Soft jaws grip a broad OD band, and turning alternates faces to keep wall thickness balanced. The bore, OD and faces remain concentric enough that heat-treatment movement produces removable, not intermittent, stock. Parts are marked outside functional surfaces and tempered to the specified 60–62 HRC.
After hardness: clamp only what inspection can release
Post-heat-treat roundness and stock are mapped before cutting. Precision-bored six-segment jaws contact the OD over a wide band; hydraulic pressure is qualified by measuring the ring both clamped and released. A wiper CBN insert hard-turns the raceway with constant surface speed and no dwell. A generated-radius path creates crown rather than relying on a form tool that would amplify force. Two semi-finish passes remove the variable skin; the final pass takes a continuous 0.06 mm radial allowance.
Surface integrity decides whether grinding remains
White-layer risk rises with worn edges, low feed and heat. Acoustic signature, cutting force and surface trend trigger insert indexing. The lubrication groove is finished with a sharp CBN-compatible tool and its exits receive programmed edge breaks. If the specification requires residual-stress or subsurface limits beyond validated hard turning, a controlled grinding or superfinishing handoff remains; the article does not claim hard turning universally replaces grinding.
Measure in the same state the drawing defines
A roundness machine measures the released ring at three axial planes and separates harmonic lobing from simple eccentricity. A CMM relates raceway axis to B and OD; an air gauge checks diameter after thermal soak. A profilometer traverses along and across the raceway to record Ra and lay, while an approved etch or metallographic audit validates surface integrity by sampling plan. Final inspection occurs after demagnetization and cleaning.
FAQ
Can 52100 bearing raceways be hard turned instead of ground?
Sometimes, if roundness, finish and surface-integrity validation are met; demanding applications may still require grinding or superfinishing.
Why measure bearing rings after unclamping?
Thin rings can look round in the jaws and spring into lobing when released.
Which tool finishes 60–62 HRC 52100?
CBN is used for the continuous raceway finish here; carbide handles the annealed-stage roughing required by the route.
Related: free-state ring inspection and size-versus-position inspection logic.
