Ntw Engine for Ruling. 69 



length had been traversed, i.e., about one-third of the nut should 

 generally remain engaged upon the screw. 



Regarding the re-distribution of the abrasive as the grinding 

 proceeded; this was usually done by using a flat camel's hair 

 lacquering brush to collect any excess oil and abrasive and transfer 

 it back to the central and upper portion of the screw, in advance 

 of the travelling nut in either direction ; whilst additional supplies 

 of oil and abrasive were carefully inserted into the slotted nut by 

 means of a piece of leather cemented to a strip of aluminium or 

 zinc. This proved both safe and satisfactory, as only the edge of 

 the leather, charged with abrasive, came into contact with the re- 

 volving threads. After about three hours of carefully controlled 

 work, it was customary to run the nut off the screw, detach it and 

 thoroughly wash out the threads with kerosene, with the aid of a stiff 

 tube brush. The screw also avouIcI be dismounted and similarly 

 treated. In this, and all other operations involving reversal or 

 detachment of the nut, attention was constantly required to avoid 

 the accidental introduction of dust, hairs, or any kind of fibrous 

 material, which might cause the nut to jamb or seize. Attention 

 Avas also directed to any temperature change by inserting a sensitive 

 thermometer into the nut whenever the latter was detached ; three 

 degrees being the limit of variation at this stage of the work. 

 After cleaning the nut and screw, it was usual to make a fresh 

 examination of the latter under the microscope; its condition, in 

 respect to the action of the abrasive upon it, being noted. At the 

 same time the diameter of the screw was measured with a micro- 

 meter ; the measurements obtained providing data for adjusting the 

 travel of the nut upon it, and to some extent, for any increase or 

 decrease in pressure; though, as a rule, the latter was more accu- 

 rately controlled, during the operation of grinding, by the sense 

 of touch. No precise record of the time taken to reduce the surface 

 of the threads to a uniformly smooth condition was made at this 

 stage, but for this particular grade of abrasive, it was not less than 

 40 hours; the work lieing distributed over a fortnight or more. 

 Inspection then showed a decided improvement in the condition and 

 appearance of the screws. The scoring due to the coarser emery 

 had practically disappeared; at the same time the form of the 

 thread had been well maintained, and the gauging was uniform 

 and good. It was therefore decided to proceed with the next finer 

 grade of abrasive, viz., .0005 inch alundum and carborundum in 

 -equal parts; the grinding operations and other procedure being 



