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).
Continuation of a report on a visit to National Broach Co. concerning gear manufacturing processes.
| Identifier | ExFiles\Box 174\2\ img066 | |
| Date | 27th March 1937 guessed | |
| -2- Visit to National Broach Co. - Cont'd.{John DeLooze - Company Secretary} (2) The reason tooth shaving is beneficial lies in the chip formation. With a shaping or hobbing process the chip is of considerable size and generally discoloured (very light cuts merely burnish) involving tooth pressure of around 1,000 lbs, resulting inevitably in distorted involute form and general errors. With a shaving process the chip is very fine and entirely free from temper discolouration, tooth pressures are low and tooth deformation does not occur (see photo 3) intrinsically, therefore a more accurate gear is obtained (see chip samples). The recommended procedure is to hob as quickly as possible, to rough shave, using a coarse shaving gear taking two cuts (.004 off the diameter each time) at 100/hr. floor to floor, and then to finish shave also with two cuts (taking .002 off the diameter). This gives an accurate gear more quickly than by a slower hobbing process. The shaver will correct helix angles - I saw a gear of .004 lead error on 6" corrected in 36 secs. to less than .0005, also it will correct pitch errors and tooth from errors. I saw similar improvements - see graph taken while I watched. Note that it has been found that for a carburised gear the soft tooth form should be about .003 to .004 above the true involute near the tip (for method of obtaining this see on); for gears to be cyanided it should be low near the tip. After hardening the gear should be very lightly hot lapped for cases where the distortion is slight and irregular. Where the distortion is greater it is recommended that a rough gear grind be made to bring the gear within .001 and then following by a quick lap on a machine similar to a shaving machine. The point to bear in mind with regard to lapping is that the gear tends to have the average tooth form of the last 100 gears lapped. National Broach recommend soft laps. | ||