the Common Vice and Vice-Chuck. • 281 



cation of the nut alike for all distances to which the cheeks may 

 be opened, the screw must be bent, or some other contrivance 

 must be had. 



When the screw is bent, the separation between the threads 

 on the convex side is greater than that on the concave side of 

 the screw, — so that no nut can passably revolve upon such a 

 screw, and apply properly to the threads at the same time. 

 The line of the strain is the straight line which joins the two 

 ends of the bent screw, and thus there is a tendency to straighten 

 the screw or change its form. In every point of view the bent 

 screw is bad. 



In the bench-vice, again, the screw revolves in the nut. The 

 nul-box is generally long, so that the screw cannot be formed 

 in a curve ; hence, to allow for the angular motion, the nut 

 must be suffered to work loosely on one arm, while the shoulders 



There is also this further advantage, that a turn of the screw produces 

 always the same angular motion in the arms ; a circumstance which is pecu- 

 liarly recommendatory in jointed compasses and callipers. 



Considering the frequent and essential application of vices to the useful 

 arts, your Committee most earnestly recommend the form proposed by Mr 

 Wilson to the notice and adoption of the members of the Society. They beg 

 also to recommend, that a notice of this improvei^nt should have a promi* 

 nent place in the Society's Transactions, in order to its adoption in the manu- 

 factories of the South. A very slight deviation from the common forms of 

 the tables and bench-vices will, without the slightest additional cost, give 

 them prodigious advantages. 



The case where the screw is firmly fixed in one arm of the vice, is com- 

 pletely solved by Mr Wilson ; but that in which the screw is jointed on the 

 fixed arm, does not seem so satisfactorily made out. The investigation of the 

 true curve with that arrangement would be rather intricate ; and it is a ques* 

 tion if, seeing the perfect action of the fixed screw or screw-box, it be worth 

 while to joint it. 



In the case, again, of spring-callipers and compasses, a peculiar curve is 

 needed ; the form of which depends on the form and flexure of the spring. 

 The investigation of this form is beyond the power of the present methods 

 of analysis, as it necessarily requires the subsidiary investigation into the 

 form of the spring itself, an investigation which has not as yet been accom- 

 plished. Still the principle of Mr Wilson's contrivance is applicable to these 

 cases ; and the forms can be discovered with sufficient nearness for practical 

 purposes. 



Edinburgh, 2\st June 1837. 



