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).
Letter to Leyland Motors offering advice on machining a difficult material, including speeds, feeds and tooling.
| Identifier | ExFiles\Box 140\3\ scan0102 | |
| Date | 5th January 1937 | |
| Rm{William Robotham - Chief Engineer}/Gry{Shadwell Grylls}/7/R.{Sir Henry Royce} 5th January, 1937. V.W. Pilkington, Esq., Leyland Motors Limited, Leyland, Lancs: Dear Mr. Pilkington, Thank you for your letter of the 29th December. We ourselves have encountered similar difficulties with this material, and even after considerable experience still find it impossible to approach cutting times on ordinary stock. Annealing from 900°C does help a little, but it is still necessary to keep down to the very slowest cutting speeds and feeds in order to avoid work-hardening the tooled surface. A cutting speed of 10 to 15 ft/min. with a feed of .004 to .008 seems to give the best results, but even so it is absolutely essential to keep cutting tools dead sharp. Edgar Allen's Stag Major is the best tool steel we know, but it is understood that Strong's "Unbeatable" can also be recommended in this connection. There are two ways of cutting threads which are fairly satisfactory. One is to screw mill to within about .003 of finished size and then finish off with a three point chaser, and the other to machine throughout in the lathe using a single point tool. The latter method is preferred but the cutting speed must be kept down to about 2 ft/min. We hope this information is of use to you. Yours sincerely, | ||