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).
Formula sheet for setting a hob pressure angle checking fixture, with examples for straight and spiral gash hobs.
| Identifier | ExFiles\Box 136\5\ scan0347 | |
| Date | 15th January 1940 guessed | |
| HOB PRESSURE ANGLE CHECKING FIXTURE #T-464 PAGE 2 FORMULA FOR SETTING FIXTURE FOR EXTREMELY ACCURATE CHECKING A CORRECTION FOR THE THREAD ANGLE OF THE HOB SHOULD BE MADE, AS IN THE FOLLOWING FORMULAS, USING THE AXIAL P.A. Φn=NORMAL P.A. Φa=AXIAL P.A. 12=CONSTANT F=Nº OF FLUTES v=HELIX ANG. D=PITCH DIA. .5=DIA. OF PINS K=CAM STR. GASH HOB Tan Φa = (Tan Φn) / (Cos v) β = Φa / 2 SETTING = Sin β x 12 + .5 EXAMPLE: Φn = 16.5° v = 1°55' Tan Φa = .296214 / .999441 = .296380 Φa = 16°30'32" β = (16°30'32") / 2 = 8°15'16" SETTING = .143569 x 12 + .5 = 2.2228 SPIRAL GASH HOB FOR R.H. THD. TOP COMING USE Φa₁ FOR R.SIDE + Φa₂ FOR L.SIDE. FOR L.H. THD. TOP COMING USE Φa₂ FOR R.SIDE + Φa₁ FOR L.SIDE. Cot Φa₁ = (Cos v / Tan Φn) - (Tan v x F x K / π x D) Cot Φa₂ = (Cos v / Tan Φn) + (Tan v / π) SETTING R.{Sir Henry Royce} OR L. SIDE = [Sin( (Φa₁ or Φa₂) / 2 )] x 12 + .5 EXAMPLE: Φn=16.5°, v=3°16', F=14, D=2.9216, K=.150, R.H. TOP COMING Cot Φa₁ = .998375 / .296214 - (.057076 x 14 x .150) / (3.141593 x 2.9216) Cot Φa₂ = .998375 / .296214 + (.057076 x 14 x .150) / (3.141593 x 2.9216) Cot Φa₁ = 3.357393 ; Φa₁ = 16°35'10" Cot Φa₂ = 3.383510 ; Φa₂ = 16°27'54" SETT. R.S. = [Sin( (16°35'10") / 2 )] x 12 + .5 SETT. L.S. = [Sin( (16°27'54") / 2 )] x 12 + .5 SETT. R.S. = .144236 x 12 + .5 = 2.2308 SETT. L.S. = .143190 x 12 + .5 = 2.2183 FORMULA SHEET 2 CHART #2 FIG. 13 [Diagram Text] MICHIGAN TOOL CO. DETROIT A B C D E FIG. 15 | ||