422 REPORT— 1869. 



On the Influence of Form considered in relation to the Strength of 

 Railway Axles and other portions of Machinery subjected to rapid 

 alternations of Strain. By F. o. Bramwell, C.E. 



[Plates III. & IV.] 



Before the days of railways, wlien uot only was there much less machinery 

 oil which to found observations, but such machinery as there was was 

 worked under far lighter strains and with far fewer alternations of those 

 strains in a given time than the machinery of the present day is subjected 

 to, the question of the influence of form was not an obtrusive one ; and, in 

 fact, so long as tlie weakest part of any piece of maclainery, such as a shaft, 

 had the sectional area due to the efficient resistance of the strains that could 

 be ascertained as coming upon it, little or no attention -^as paid to the 

 manner in which this smallest sectional area was to be associated with en- 

 largements formed for the purposes, in the case of shafts, of receiving wheels 

 or of acting as collars. 



As an instance of this, few engineers in the pre-railway days would have 

 hesitated to make a cast-iron crank-shaft for a steam-engine in the manner 

 shown in fig. 1, Plate III. They would have taken care to give the bearings 

 (or journals as they are called) A A such a diameter as was jiidged to be suffi- 

 cient, having regard to the area of the piston, the pressure, and the length 

 of stroke ; but they would have made the body part, B, of the shaft and the 

 end, C, in the eye of the crank of a much larger section than that of the 

 bearings A A, would probably have made these parts square, and would without 

 hesitation liave formed the junctions of the small parts A A mth the large 

 parts B and C abruptly with right angles, as drawn in fidl lines, and with- 

 out any attempt to ease off the change in form by a bold curve, as sho-«Ti 

 by the dotted Hues. 



The square shoulder woiild be left, in order to get a good endway bearing 

 against tlie sides of the supporting brass ; and few, if anj', engineers in those 

 days would have imagined that if the bearings A A were large enough, the 

 making the shaft at B and C of a greatly increased section, and the making the 

 junctions of these sections with the sections A by right angles, could in any 

 way be prejudicial to the strength of the bearings A A. The opinion was 

 (and, on the face of it, by no means an unreasonable opinion) that if the 

 bearings A A were strong enough, the fact of any neighbouring part being 

 stronger could not in any way detract from the value of A A. 



Occasionally, however, there were occurrences which might have aroused 

 attention, but which, it is believed, were allowed to pass by, being accepted 

 as mere workshop accidents, and not thought worthy of inquiry by the 

 skilled engineer of the time ; and still less were they treated as problems to 

 be solved by scientific men outside the profession of engineering. 



Fig. 2, Plate III., illustrates one of these occui'rences. It shows a form of 

 eccentric rod commonly then in use. In such a rod the ends A A were made 

 of long screws to carry nuts to tighten against the lugs of the eccentric 

 band, as shown dotted at B B ; these ends (A A) were forged in short lengths, 

 say, from C, and after having been turned at the parts A A and screwed, were 

 welded at C to the body of the rod. 



It was by no means a common thing, but occasionally it did happen, that, 

 in the act of making the weld at C, tlie screwed end snapped off at D close 

 to the enlarged part without any blow whatever having been struck upon 

 the end. It has been said the occurrence was not a common one; but it was 



