9. These advantages are best described by comparing it with the ordinary outside framing submitted to the principal strains which it has to resist.
11. With the inside framing the centre line of the connecting rod is only 10 inches distant from the centre line of the frame, and the total distance between the bearings is 43 1/2 inches; but where the framing is outside the wheels, these dimensions are necessarily 20 inches, and 72 inches respectively; and the effects of the strain on the crank, in this case, would be, to its effect with the inside framing, as 14 is to 8.
"We have the very remarkable discovery announced, (says the Commentator,) that the nearer the points of support are to each other, the steadier the superstructure; and Messrs. Bury and Co. prefer a base of 43 1/2 inches, to one of 72 inches! The statement of the 'effects of the strain on the crank' is erroneous, as all six-wheeled engines are, I believe, provided with inside framing to resist the strain of the cylinders."
12. For this reason, when the principal frame is placed outside the wheels, it becomes necessary to have an additional inside framing, to prevent the fracture of the axle. These additional inside frames not only cause an increase of friction on the bearings of the cranked axle, but also throw a considerable strain on the boiler, which then becomes the medium of connexion between the inside and outside frames, the inside frames being fixed at one end to the bottom of the smoke-box, and at the other end to the fire-box, while the principal frame is attached, by long brackets, to the body of the boiler.
"This paragraph (12) is strictly in keeping with the whole of the circular. The framing, both outside and inside of the wheels, in the four and six wheeled engine, is attached to the smoke-box and the fire-box, and also generally to the boiler. Messrs. Bury and Co.'s framing is, in my opinion, very defective in point of durability; and as a mechanical arrangement, inferior to any thing of the kind made by those persons who ' are convinced that their plan was not perfect.'"
13. The fact, that the use of four additional inside frames occasions six bearings on the axle, (that axle being only 6 feet long,) renders the system of principal outside framings so objectionable, that that circumstance alone should suffice to cause their rejection, for it is well known to practical men, that it is impossible to key so many bearings perfectly true, and to maintain them so when the engine is working; and even if this provision were attained, the aggregate friction on the four inside, and the two outside bearings, would be much greater than when it is all thrown upon two bearings; because, in the first place, all the friction due to the weight of the boiler is borne by the two outside bearings alone, and that which results from the pressure of the steam, through the medium of the connecting rod, is thrown upon the four inside bearings; the pressure on the outside bearings is vertical, and the mean pressure on the inside bearings is nearly horizontal. So that, if, instead of acting separately, these two amounts of pressure were thrown on the same bearings, the friction would only be due to the resultant of the pressures, and would, consequently be much reduced.
This (13) is denounced as a very " uncandid paragraph, if not something worse." *' Messrs. Bury and Co. must be aware that not more than one or two frames at the most have been put into engines made within the last six years. I do not understand what can be meant by ' it is well known to practical men, that it is impossible to key so many bearings, etc.' It is not usual to key bearings. Whatever may have been intended, this paragraph is not likely to deceive any one in the smallest degree acquainted with the subject."
14. Another important feature is the strain to which locomotive engines are liable, from the pressing or striking of the flanges of the wheels against the rails, when travelling on a curve.
15. In engines with the bearings inside the wheels, the weight of the boiler has a tendency to bend the axle down in the centre, while the pressure of the flange against the rail acts upon it in a contrary direction, and thus one strain counteracts the effect of the other. If the bearing is outside the wheel, the weight of the boiler tends to bend the axle upwards, and a strain on the flange of the wheel acting in the same direction and in addition to it, when the breakage of an axle takes place, these joint actions tend to force the wheels under the engine, and there being no flange on the outside of the wheel to prevent it, the engine is thrown off the rails, which, it is evident, cannot happen with an engine having inside framing, because the weight of the bearings presses the flange of the wheel against the rail, and assists the length of the journal in keeping it from falling or being thrown off the rails.*
"The introductory part of this paragraph (15) is not disputed; but Messrs. Bury & Co., in adopting inside framing, did no more than copy Mr. Blenkinsop, Mr. Stephenson, and many others. As to the concluding part, Messrs. Bury & Co. may consult the Prussian Journals of May last" (1842) " and the evidence given at a late inquest on the London and Birmingham Railway."
16. Several instances have occurred on the London and Birmingham railway, when an axle has broken, that not only have the wheels remained on the rails, but the driver has been able to proceed with the train to the nearest station.
"This admission is more than might have been expected, seeing that Messrs. Bury and Co.'s engines are perfect."
17. The stiffness of the single inside framing is not only a remedy against the excessive wear and tear which are consequent on a less perfect union between the parts of the engine, but its simplicity allows the whole machinery to be arranged in a more compact form, and constructed with greater solidity, with this additional advantage, that the engine driver, while standing on the foot-plate, can inspect the whole of the machine, and detect any derangement requiring his attention.