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).
Modifications to the 20 HP chassis gears to increase their strength.
| Identifier | ExFiles\Box 6\4\ 04-page217 | |
| Date | 3rd May 1929 | |
| R.{Sir Henry Royce} C. H.{Arthur M. Hanbury - Head Complaints} X5310 BY/G/3.5.29. 20 HP. CHASSIS - GEARS. ------------------------- Further to my memo BY7/G.1.5.29. in looking over the gearbox pieces I noticed that the third speed gear has 14 1/2° obliquity. In the interest of strength, particularly in view of possible developments, these gears should at once be made 20°, as we shall thereby obtain an increase of strength of at least 25%. In addition you can rest assured that no gears will have any hard lines along the base of the tooth where the flank runs into the bottom of the space, the Gear Grinding Co. having as the result of pressure we brought to bear upon them introduced a truing apparatus which will ensure the curves running correctly into one another. In addition to the increase of strength by altering the obliquity, I would also propose to use a nickel steel with a minimum of 5.25 of nickel and approximately .12 of carbon. This would give us a tensile strength of 75 tons in the core, whilst it would still retain sufficient toughness to represent a thoroughly sound working gear, as the elongation would be from actual figures 18%, with a reduction of area of 60%. The izod figures would be not less than 55 ft. lbs. By our usual practice the comparable figures we should obtain are as follows :- Brinell 248/286. Ultimate Tensile 50/58 tons per sq.in. Elongation Minimum 20% Reduction in Area. 60% Izod. 60 to 80 ft. lbs. The only other proposal which would be workable would be to use the air hardening mild nickel chrome case hardening steel, which we use already for aero gears. This steel, however, is rather more difficult to grind, inasmuch as it has a tendency to develop grinding cracks, unless the grinding has been very carefully carried out. Personally I would prefer the 5% case hardening nickel with the increased nickel content. We have of course from time to time actually used casts having these characteristics for various purposes, so that it only means we select the gear steel from the higher range of our hardness list. BY.{R.W. Bailey - Chief Engineer} 137 | ||