WEDDING THE WHEEL TO THE SHAFT.
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Some Useful Advice from Our Driver and Mechanic Readers.
NLY THOSE who graduated from general engineering to motorcar engineering, and whose experience of the latter dates back almost to its commencement, know of the difficulties which were at first encountered in devising efficient means of securing a wheel to its revolving shaft. The troubles which were met with appeared chiefly to be the result of the high speed and, consequently, frequent reversals of the stresses which, although already encountered in other branches of engineering, were seldom experienced to the intensity and degree which seemed unavoidable in this newer branch of the art; or, if they were there, there was always opportunity for using materials of ample dimensions. When, in addition, the connection had to be such as to allow of the wheel sliding endways upon th.e shaft, without to any extent diminishing its security against relative rotary movement of the one upon the other, the troubles were increased many many times. Even to-day, with a couple of decades of experience as a guide, difficulties with keys and keyways are far from being unknown.
One of the biggest advances in design, bearing on this subject, was the introduction of the castellated shaft, itself made practicable by the perfecting of the breaching machine. Even this, however, has its troubles, notably when worn, since it is not easy to take up wear whether it has occurred on the sides of the splines on the shaft or in the keyways in the wheel. An excellent workshop method of enlarging worn splines is conveyed in a letter from " T.M.," of Brighton. He mounts the shaft, AS shown in the accompanying sketch., in a
vice, the jaws of which are protected by copper clams. The underside of the shaft, too, is supported either by a block of hardwood, a piece of copper or bronze, or in some other method devised to support the shaft without injuring it. Three tools are necessary—an ordinary flat chisel and two creasing" tools. The latter are simply cold chisels with the edges trimmed off, one being somewhat thicker at its point than the other.
These tools are used successively, commencing with the chisel, which is followed up by the thin creaser, the thick one being used last. A line is first cut along the centre of the top surface of the spline with the chisel. It is broadened by the thin creaser, and the spline subsequently spread by hammering the thick creaser along the groove thus formed. This process is continued until the required thickness of spline is obtained. Hollow shafts should he supported .inside by means of a tightly fitting mandrel before commencing this operation, otherwise distortion is likely to occur.
The same correspondent tells us' that he has an idea for the design of a machine for file above purpose. His proper course is to get in touch with a patent agent, who will advise him as to the procedure to adopt.
" W.H.," of Glasgow, had trouble with a sprocket pinion of a well-known maker's chain-driven chassis. The keyways in both shaft and wheel were worn. Apart from this defect, howeyer, both of them were .quite sound, the teeth of the latter being as good as new. The key• way in the sprocket was widened sufficient to cut away the worn portion; that in the shaft was deepened, using a flatnosed drill and a narrow chisel for the purpose. A new key was then made, of irregular dross-section, as shown in the sketch, being wider at the top, where it fitted the sprocket, than at the base, where it bedded into the slot in the shaft. The repair proved to be quite satisfactory and did not spoil the shaft for the subsequent reception of, a new sprocket with standard key, as would have been the ease had the keyway in the shaft been widened in the same way as that in the sprocket.
" G.T.P.," of Porth, had no keys or splines to trouble about, but he got into difficulties all the same. The wheel he had to deal with was a sliding pinion of a gearbox, acquired to replace one which had been brokers. The replacement part proved to be too small in the hole, which was case-hardened and could not therefore be enlarged in the lathe. Neither a grinding machine, nor the necessary furnaces for softening and rehardening thewheel were available, even if it had been advisable so to treat a wheel the material of which was unknown. in the end this contributor managed to make the wheel fit by treating the bore with nitric acid applied with a stick.