Calculating Worm Gear Strength With ANSI
Based on the fixed-end beam calculation. Includes the majority of effects.
Dynamic Load
F d = F t2 K v
where:
| | F t2 | Poisson's ratio (material value) |
| | 
| circumferential force factor |
| | v 2 | gear circumferential speed [ft/min] |
Allowable Bending Force
F s = S n b 2 p y ≥ F d
where:
| | S n | limiting bending strength (material value) |
| | b 2 | gear width |
| | p | gear pitch |
| | y | form factor (Lewis factor) |
Allowable Contact Force
F w = d 2 b 2 K w ≥ F d
where:
| | K w | limiting contact strength (material value) |
| | b 2 | gear width |
| | d 2 | gear pitch diameter |
Increase of Temperature Check
Q max ≥ P z
where:
| | P z = P (1 - η + 0.3) | lost power |
| | Q max = C A (t max - t 0 ) / 33000 | heat conducted away in oil |
| | t max - t 0 = 120° F | allowable temperature drop |
| | A | gearbox surface, which conducts away the heat, A ≈ 0.3 a 1.7 for well ribbed gearbox |
| | C | transfer of heat factor, C ≈ 0.0356 n 1 + 20 for the gearbox with fan and bottom worm |
