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 clarifying the required tolerance for the gaps in annular gap Lodge plugs.
| Identifier | ExFiles\Box 79\1\ scan0086 | |
| Date | 25th January 1917 | |
| COPY. Messrs.Rolls-Royce Ltd., Wd{Mr Wood/Mr Whitehead}12/NJ23117. BH/HB.{C. E. Harcombe} Nightingale Road, Derby. 25th Jan.1917. X. 601. Re Lodge Plugs Dear Sirs, We are in receipt of your letter of the 23rd inst. and are sorry that our previous letters regarding the tolerance required for the gaps in the annular gap plugs have not made the position clear to you. To use your own phraseology, we mean that if the inside diameter of the annular ring is .030" larger than the diameter of the central electrode, the air gap on one side may be .010" and on the other side .020". We have measured up a number of the nickel stampings used for the 20/1000ths annular gap plugs and we find that the inside diameter of the annular ring is .037" larger than the diameter of the central electrode. The air gap on one side may, therefore, be .0135" and on the other side .0235" which closely approximates your requirements. We do not recommend making the gap any smaller because we already experience great difficulty in centring the centre electrode after the annular ring is in position due to the spring in the centre electrode, and the fact that it cannot be bent over far enough to give it a permanent set. There is also a danger of the central electrode warping slightly when hot with the danger of short-circuiting the gap. We trust that we have now made the position quite clear (contd.) ENCLOSURE No 182 "JUSTSO" | ||