From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Analysis of forces in a worm and nut mechanism, specifically the 'joggling' condition.
| Identifier | ExFiles\Box 67\4\ scan0329 | |
| Date | 13th July 1927 guessed | |
| contd :- -3- Case 11. Nut is now driving worm i.e. condition is that known as 'joggling'. Forces in vertical plane : Fn = P cos θ + μP sin θ Fw = P sin θ - μP cos θ [Diagram of forces on a nut on an inclined worm] Labels on diagram: P, Fn, μP, NUT, WORM, Fw, (Direction of motion of worm (plane)) Fw / Fn = (sin θ - μ cos θ) / (cos θ + μ sin θ) = (sin θ cos γ - sin γ cos θ) / (cos θ cos γ + sin γ sin θ) = sin (θ - γ) / cos (θ - γ) = tan (θ - γ) now η = (2 πγ Fw) / Fn = Fw / (Fn tan θ) = tan (θ - γ) / tan θ With const. γ, η increases with θ, hence, with given lead of worm, advantage of SMALL pitch diameter. for parking In experiments carried out with .940 worm (θ = 12° 5'), and load of 3250 lbs. (1) Force at 20" radius to raise = 38 lbs. (2) Force to resist drop same radius = 11 lbs. (1) Corresponds to 'parking'; in this case, T = Fw γ = Fn γ tan (θ + γ) ∴ tan (θ + γ) = (38 X 20) / (.7 X 3250) = 760 / 2275 = .334. (.7 = γ = Pitch radius) contd :- | ||