Drop-Slot Spherical Bearing Sizer
v1.0 · English Units · IN718 / ToughMet TX02 AT110
1. Reference Diagram Drop-slot spherical bearing reference diagram showing OD, ID, sw, rf, Db, Dr, B, W, hs dimensions
Left: front view showing OD, ID, slot width sw, and fillet rf. Right: section view showing housing width W, slot depth hs, ball diameter Db, race sphere diameter Dr, and inner width B.
2. Bearing Geometry
AS81935 size preset
Housing ODin
Housing width, Win
Ball diameter, Dbin
Race sphere dia., Drin
Bore diameter, IDin
Ball inner width, Bin
Slot width, swin
Slot depth, hsin
Fillet radius, rfin
Contact angle, αdeg
3. Fit Tolerances (symmetric ±)
Ball Db tolerance, ±in
Race Dr tolerance, ±in
fit range loading...
4. Applied Loads
Radial load, Frlbf
Axial load, Falbf
FoS yield−
FoS ultimate−
FoS galling−
5. Materials
Housing material
Ball material
Friction coeff., μ (DFL assumed — Dicronite)−
loading...
6. Thermal Conditions
Assembly temp, T0°F
Low op temp, Tlow°F
High op temp, Thigh°F
ΔT loading...
7. Margin Summary
Computing margins...
Margin of Safety MS = (Allowable / Applied) − 1. MS > 0 = passing, MS < 0 = failing. Only failing checks are listed above; see §8 Results for all margins.
Note: peak stress at the slot fillet is not computed — FEA is required to validate the local stress concentration before final release.
8. Results
Calculating...
9. Calculation Sheet

Notes and Assumptions

  1. Equivalent load: Peq = Fr when Fa/Fr ≤ e = tanα; otherwise Peq = X·Fr + Y·Fa with X = 0.6, Y = 1/tanα. Computed live in §7.1 based on contact angle and load ratio.
  2. Projected bearing stress: σb = Peq/(d·B), compared to ball compressive yield (ToughMet is anti-galling; conservative allowable is Syc/FoS).
  3. Hertzian contact stress between ball (Rb) and race (Rr), sphere-in-socket (concave), with effective radius R* = Rb·Rr/(Rr−Rb). E* uses both material moduli and Poisson ratios.
  4. Galling allowable uses tested-couple data when available (e.g., IN718 + ToughMet AT110 = 105 ksi), divided by FoSgall. For untested (Custom) material pairs, the conservative fallback min(Sy,housing, Syc,ball)/FoSgall is used.
  5. Thermal fit check: Δdiametral = D·(αh−αb)·ΔT, added to nominal fit. Negative values = loss of clearance / induced interference; positive = growing gap.
  6. Thermal interference adds to mechanical net-section stress: at the worst-case fit (tight + high temp, or interference at low temp depending on CTE mismatch), induced hoop pressure is computed via Lamé thick-wall formula and added to the net section result for the total housing margin.
  7. Loader slot geometry per NHBB convention: two slots machined 180° apart into one axial face of the race, extending from the face down to the spherical ID. Slots do NOT cut through the housing OD.
  8. Load direction Fr should be oriented 90° to the slot axis to avoid loading into the slot cutouts.
  9. Axial face stress uses annular race face minus two slot footprints (2× ws × (D−d)/2). Net section uses 2×t×Weff with Weff = W − hs at the slot section.
  10. FEA validation required: the closed-form net section calc reports the average tensile stress across the slot ligaments. The actual peak stress at the slot fillet (where any failure would initiate) is higher due to local stress concentration that depends on rf, sw, and the surrounding 3D geometry. No reliable closed-form Kt exists for this configuration — use FEA to confirm the peak stress is below the material yield/ultimate allowables before releasing a design.
  11. Dissimilar material galvanic risk (Cu alloy vs. Ni alloy) is not flagged here; consider coating or isolation in corrosive service.
Ready Drop-Slot Spherical Bearing Sizer v1.0