66 ' H. J. Gra>/.s<ni : 



was obtained. The two screws rested upon supports slifj^litly in- 

 clined to each other, hence they couhl be revolved, reversed, inter- 

 locked, or interchanged without disturbing their adjustment m 

 relation to the travelling microscope. This compai-atively simple 

 and easily constructed bit of apparatus proved quite satisfactory 

 for examining the condition of the two screws, not only during 

 the preliminary grinding stage, but up to tlie final mounting of one 

 of them in the completed engine, it Avas only superseded, after a 

 number of gratings had been ruled, l)y a more rigorous method of 

 testing described on a later page. 



(iv.). — GrindiiKj irith fine abrasives and semi-automatic control. 

 — A thorough examination of the two screws under tlie microscope, 

 with the aid of the apparatus above described, tended to show that 

 it was not desiralile to continue grinding without appliances which 

 would permit of a more precise control of the operations involved. 

 Hence the following method for attaining varial)le speed control, free- 

 dom from stress, other than that due to a uniform tortional resistance, 

 and the maintenance of a more uniform temperature, was adopted. 

 An attempt to eliminate temperature changes resulting from fric- 

 tion by means of a stream of running water or oil, surrounding nut 

 and screw, proved unsatisfactory and was abandoned at an early 

 stage in favour of a reduction of srpeed and pressure. An inspec- 

 tion of Fig. 2, Plate XL, will make clear the following brief 

 description of the appartus used. Fig. 2 is a photograph of the 

 complete mechanism used at this stage, and in all subsequent grind- 

 ing operations. It comprised a strong wooden platform or plank 

 securely bracketed to the wall of the workshop in a position con- 

 veniently near the overhead driving gear of the lathe which fur- 

 nished the operating power. A strong flanged accurately bored 

 metal socket about Gin. long was screwed to the upper surface of the 

 platform. Through this a mandril passed, carrying on its upper 

 end interchangeable driving wheels, and on its opposite end l^elow 

 the platform a small chuck fitted with universal movement. This 

 chuck supports a steel rod about 15 in. long, to the lower end of 

 which the screw is attached, the latter being thus provided with a 

 free conical pendular motion of about 20° amplitude; two jockey 

 pulleys for transposing the vertical travel of the driving band, and 

 a reversing lever (not shown) complete the driving mechanism. In 

 Fig. 2, PI. XI. the screw and nut are seen in position, exactly as in 

 the operation of grinding. The details of the nut include its two 

 surrounding rings and clamping screws, previously described; also 



