New EiH/lne for Riding. 47 



of tlie pitch of the sci-eAv. This last adjustiaeiit is ett'ecteJ by means 

 ■of two micrometer screws (15) seen in Ph\te VIII. Any elevation 

 of the bar due to a reversed action of the screw and ratchet is obvi- 

 ated by a weight serving as a counterpoise and an upper guide bar 

 ^16). The nut has a clear run of nearly 7 inches upon the screw; 

 thia range of motion therefore represents the ruling capacity of 

 the engine. 



The thrust block (17) witli its sapphire bearing face and several 

 adjustments (7 and 7a), are important parts of the machine, which 

 call for great precision in setting, wliich will be the subject of 

 special mention latei-. The position of the thrust block is almost 

 exactly central upon the bed of the machine. Hence, it is favour- 

 ably situated with respect to any expansion of the bed due to 

 temperature changes. The effect upon the ruling of such changes 

 appears to be very slight, as seems to be proved by careful inspection 

 of a 40 hours' ruling, during the progress of which temperature 

 fluctuations amounting to 3°C. were recorded, but appeared to have 

 produced no discoverable change in the regularity of the ruling. 



The travelling carriage, Avhich supports the plates while they are 

 being ruled, is advanced by a central axial pull, directly in line 

 with the screw axis, through the agency of tlie two rods already 

 described, which serve to connect up the ruling carriage with the 

 nut. The advantage of having screw, nut and ruling table joined 

 together in a direct axial line is obvious, and, so fai- as I am aware, 

 is an arrangement which has not hitherto been adopted in existing 

 ruling engines. 



The ruling table itself is simj^le, being merely a Sijuare plate of 

 steel fitted with a detacliable, circtilar graduated revolving super- 

 table for supporting any rulings, or plates for such, requiring 

 angular adjustment. The lower j^late, serving as the base, is 6 

 inches square and | in. tliick. It slides, by means of semi-circular 

 ■grooved supports, attached to its under stirface, along two heavy 

 circular rods of steel very accurately ground and polished, and 

 resting in special supports screwed to the bed. The chief function 

 of these two rods is to act as guides or Avays for maintaining the 

 exact alignment of the ruling carriage with the screw. Most of the 

 weight of the ruling plate, and also of any load it may carry, is 

 borne by a separate under carriage rolling with a minimum of 

 friction directly upon the upper surface of the beil. 



The frame and supports of the carriage are seen in outline on the 

 plan as 27, 28 and 29. The under frame (27 and 28) supporting 



