202 TORSION TESTING ATTACHMENTS. 



pencil is at the centre of the disc. As the 

 moves and the moment on the shaft is increased, 

 the pencil is caused to move outwards in a radial direction, 

 by means of a reducing mechanism, a distance proportional 

 to, but less than, the distance traversed by the weight it si -It'. 

 The increase of twisting moment is accompanied by a 

 torsional strain consisting of a rotation of the end of the 

 specimen attached to the worm wheel with respect to the 

 other end. The strain is recorded on the diagram by a 

 rotation of the disc through the same angle as the shaft 

 has been twisted through. This rotation is effected through 

 a train of mechanism consisting of four equal spur whrrls 

 and a small counter shaft, connecting the worm wheel and 

 the disc, it being assumed that the worm wheel rotate 

 through exactly the same angle as the end of the shaft. 

 There is an error here, but it may be considered negligible 

 for the purpose for which the autographic diagram is to be 

 used. 



This particular machine will break in torsion circular 

 steel shafts up to f in. diameter. 



For machines of this type, the specimen shafts are 

 prepared with enlarged ends, as shown on Fig. 9o. These 

 enlarged ends are provided with pairs of keyways corres- 

 ponding to the feather keys in the holders. 



FIG. 95. Wicksteed's Torsion Test Bar. 



112. Torsion Attachments to Tension Testing Machines. 



On Fig. 26 is shown a photographic view of a small tension 

 testing machine made by Messrs. Buckton, and it will be 

 seen that there is a torsion arrangement very similar 

 to one last described. The existence of this attachment 

 does not in any way interfere with the use of the machine 

 for tension purposes, but it is always there to be used 

 when required. 



Similar arrangements for torsional testing have recently 

 been attached to some of the larger machines by the same 

 makers. Among these may be mentioned the torsion attach- 

 ment applied to the 100-ton tension machine at the Brad- 

 ford Technical School. This is capable of taking specimens 

 up to 2 in. in diameter and 12 in. long on the measured 



