128 



<;I!1IT1N<; DEVICES. 



Iii the above description of testing machines, no par- 

 ticular mention has been made of the methods and appliances 

 which are used for holding or gripping the ends of tension 

 specimens. These will now be described. 



72. Gripping Devices For specimens of ductile sub- 

 stances such as wrought iron or steel or copper, whose 

 ends have not been specially prepared for the purpose, 

 hard steel wedges are employed for holding the 

 ends in the testing machine. On Fig. 55 is shown a 

 -sketch of the gripping arrangement used in the Buckton- 

 Wicksteed testing machines, for flat specimens. The grips 



FIG. 5(i. 



used on almost all other machines are similar in principle, 

 with modifications in detail. In this figure, A and B are 

 the two testing machine shackles, of which A is linked to 

 the weighing beam and B to the ram of the straining 

 cylinder. In the centre of each of these shackles is a 

 conical hole, into which fit a pair of conical seating 

 blocks D, D. These are made conical on the outside so as 

 to fit the holes in the shackle, and have tapered recesses or 

 grooves on the inside, in which rest the wedges themselves, 

 E, E. These wedges are made smooth on the back and 

 rough or serrated on the inside surface which comes against 



Iron and Steel Institute, 1888. 



