1 74 On cutting Screws by Means of 



the nearer arm of the rest G, and the tool held on the 

 further one, F, then a left-handed screw will be cut of a 

 thread the distance between the turns of which will vary- 

 according to the distance of the point at which the tool is 

 held between the centre and extreme end ; for, as the 

 lathe turns to us, the arms receive a forward motion, except 

 the further arm, F, of the rest, which receives a backward 

 motion ; but when the lathe turns from us, then the further 

 arm receives a forward motion ; and as the tool meets the 

 wood, so it cuts a left-handed screw. It may be apprehended 

 that a piece of wood so far removed from the collar, K, 

 might spring in its motion ; but this may be obviated by 

 not making use of the traversing chuck, B, till the screw is 

 to be turned ; for, as the cutting of it is light work, there 

 will be little resistance, and of course but little spring ; or 

 the traversing screw, B, may be turned on the manderil A. 

 Another disadvantage would seem to arise from the impos- 

 sibility of cutting screws when the poppet head is made use 

 of, to prevent the springing of a long piece of wood. But 

 this may be obviated by lengthening the intermediate arm, 

 E, to the part where we intend cutting the screw, and thus 

 we have the same screw as that of the traversing one : if a 

 finer or coarser screw should be required, then, by having 

 an arm of the rest to slide in and out, and the intermediate 

 arm to be connected to the centre of the rest, we have just 

 the same power of turning screws as in the former case. 

 A socket, S, is represented, the lower part of which slides 

 on the rest, and may be fastened firm to it by a screw : the 

 upper part, that turns on a pivot, admits the intermediate 

 arm to slide through it, which arm is held stationary in it 

 by a screw. Should the difficulty that might arise from 

 turning screws with a plain lathe be obviated by this me- 

 thod, I shall feel a double gratification in the reflection that 

 that time which was spent in amusement has tended to tfre 

 advantage of others. 



To Mr. Tilloch*. 



Dublin, April 27, 1804. 

 SIR, James-street, 43. 



T perfectly agree with you, that was the rest to make a 

 right angle with the piece of wood on which the screw was 



f In answer to a letter stating the objection mentioned in the begin- 

 ning of the present letter, which we have published, as tending to explain 

 more fully Mr. klealy's invention.— j-Edjt. 



to 



