The Need for Low Replacement Cost.
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By an Engineer Contributor.
Some of the "One Day's Work" articles and the statements to be found amongst " What Users Tell Us " show how successful the use of commercial vehicles has proved for a wide variety of trades, and they afford convincing evidence that one by one each obstacle in the way of the adoption of motor vehicles for business purposes has been removed. We should not, however, allow these statements to lull us into the belief that there are no problems left for solution by designers and manufacturers.
The elimination, or rather the avoidance, of the physical limitations of horse transport is a very powerful factor enabling motorvans and wagons to show lower costs per mile, or per ton-mile, than any other road form of transport. The first-cost bar to the maii with small capital is one which will automatically be removed as the process of standardization progresses, and when manufacturers not only standardize individual parts, but concentrate their energies upon the production of a few models only.
Cheapest Not Always the Best.
The time for detail standardization is undoubtedly within view, but it is too much to expect it for another four or five years ; meanwhile the most-important factor which—apart from fuel considerations —dominates the use, and should dominate the selection, of motor vehicles, is that of low maintenance costs. In so far as the extent of consequential reolaxementa that, are involved by any partiesilar failure goes, this cost is within the maker's control.
Some makes may be kept in a state of mechanical efficiency at a remarkably-low rate for replacement outgo, although their initial price is by no means the lowest in the market. On the other hand, there are B24 certain makes for which their builders, in competition with other manufacturers, are prepared to quote cut-threat prices, in order to secure business, and in this way a purchaser is led to believe he is making a good bargain. This may be so in some cases, if the service he requires of the machine is one that is particularly favourable to its design and construction, but the wagon may turn out to be something in the nature of a money-eater, if the bill for repairs mounts up to a serious figure, because even the simplest repair often entails the replacement of several parts.
A Gear-wheel Example.
Take, for instance, a couple of wheels in a gearbox ; one wheel of the meshing pair may be a particularlyexpensive piece to replace, and it may have fewer teeth than the. other wheel with which it engages, and which probably is a less-expensive piece to produce. The teeth of the smaller pinion are called upon to do far more work than the larger pinion, and . the briefest consideration of such a case would convince a designer that it would be advisable to make the gears of two qualities of material, the smaller and ' more-expensive piece being made of a steel that would ensure a. longer life for the expensive piece than for the other wheel; yet one often finds that both pieces arc made from precisely the same grade of steel, and, when a renewal is necessary, it is the expensive part that has to be replaced. It, should be remembered that it is not desirable to replace one member only oi a pair, because a new wheel will not run so quietly with an old wheel as with another new wheel, but, although silence of running is certainly a desirable factor' the average user cannot afford to scrap parts which are not half worn, even if he has to sa.crifiee a little in the way of quietness. Provision of equality of wear-resisting wheels meets. this difficulty.
Again, while on the subject of gearboXes, I call to wind, some constant-mean boxes in which one half oi the engaging coupling is made as an integral portion of the gearwheel. It this coupling is of such large dimensions that the driving pressure on the .'eaces is very low, and the relative velocities of the two parts of the clutch are not so different as to cause chipping when engaging, there can be no objection to making both wheel and coupling in one piece, in fact it. would be preferable that it should be so; but, in the cases I have in mind, the engaging couplings are of very small size in proportion to the loan they have to transmit, with the result that the coupling jaws are soon so badly bruised as to constitute a source of danger, because the two halves of the coupling will not hold in mesh. When this stage is reached, it is an expensive job to renew both, coupling and gear wheel. In such cases, I eontend, the coupling should bemade an entirely-separate piece., designed to be as cheap as possible, and spigoted on to thegear wheel, or the gear wheel spigoted on to the coupling, as the case may be.
The Fitting of the Shackle Bolt.
Another case I eaff to mind concerns the replacement of spring-shackle bolts. In this particular instance, these small components are allowed to turn freely in the shackles, in the spring itself, and in the bracket which is fastened to the frame, and neither the bracket nor the spring eye is bushed. The oscillating motion on spring-shackle. bolts, a-nd the face that their lubrication is more often neglected than otherwise, cans-es more or less rapid wear, A thoughtful de-signer would make provision for preventing the shackle bolt from turning within the shackle, not by the fitting of a light stop-pin or grub screw that is totally inadequate for the purpose, but by providing a square neck or a T-head on the bolt, with a notched bess on the shaekle„ so as to prevent any possibility of the bolt's turning within the shackle. The shackle bolt then would turn within the spiing eye and the shackle bracketon the frame, both of which provide very much greater wearing sur faces than the shackles. When a shackle bolt is worn a new one can be fitted at very low cost, -whilst, if both spring eye and frame bracket he bushed, and the bushes made interchangeable, these bushes may also be replaced at low cost. In the case I have in mind, however, when a shackle bolt becomes worn badly and they do wear badly in a remarkably short space of time), a repair can only beeffected by replacing the shackle bolts with others of larger size, by the enlargement of the holes in the shackles, spring eyes and Name bracket. The result is a job which is no longer standard ; if an owner desire to retain standard parts, he must replace shackle bolts, shackles and frame bracket, and have the spring eye bushed, thus running up to a east of over a sovei eign for each spring for a repair which at most should cost five or six shillings.
Steering-gear connections of thefork type on so-me chassis are also designed, or shall I say made, with the same lack of consideration or rep.air costs, arid one often finds that the pin of such, a joint is free to turn as it pleases, both in the fork and the eye pieces. The use of snugs, set-pins, etc., is totally inadequate to prevent such pins from turning ; a.piece, registering registering in a slotted facing on the forked
piece, is probably the only effective way of preventing their turning, and, if the eyepiece be bushed, the joint can be brought into its original state by the replacement of the pin and bush only with standard parts, whereas, when the pin is left loose, both fork and eye piece have to be bored: and a new pin of larger size fitted. I would make a similar complaint with regard to torque-rod connections, small univer sal-joint pins, and the connections for brake rods. A manufacturer, by disregarding these small but important details, is enabled to cut down manufacturing costs to a certain extent, and, as a result, is able to offer his machines at lower_ prices than another manufacturer who also studies c-oat of maintenance.
Faulty Clutch Design..
The clutch anthits operating mechanism are among the least considered details in the construction of some motor vehicles. The -fact that a clutch will take up smoothly, and hold when it has taken up, appears to satisfy some designers and builders, but the user is most certainly entitled to further consideration ; for instance, it should be possible to remove the inner cons, so that it may be refaced with leather, Ferodo, etc., without necessitating the removal either of the gearbox or the whole of the operating mechanism, yet it is not every chassis that meets this condition. In the majority, it is possible to remove the clutch without dismantling the gearbox, but in some of these eases the pedal shaft and a whole host of minor connections have to be disturbed before the. cone can be removed. Then, again, with dutch connections, one -often finds that hardened-steel pins are allewed to turn in malleable-iron levei.s, phosphor-brenze bridles,. etc. With what result? The lever or the bridle wears, and the pin retains its original dimensions. Tins is not design. The pin is the cheapest part to replace, and if a bronze pin, or a soft mild-steel pia of the same dimensions, is not strong enough for the job, then thediameter of the pin should be increased—not the hardness of the material itself. We tco often find, small-diameter pins which have to sustain fairly-high pressures, and there is no valid reason why their diameters should not beincreased. .Weight considerations have to be taken into acoount most certainly, but weight considerations should not become an obsession with a designer; every part should have ample wearing surface, in proportion to the*load it,has to carry, and, in addition tothis, the designer should at no time lose sight of theaccist for replacement to the user.
The Use of Studs in Aluminium.
Before concluding, I would make a protest against the unnecessary use of studs, particularly in aluminium. A stud and nut are cheaper than a bolt and nut in a reamered hole; weadmit that the latter cannot be used in every case, but wherever possible it should be fitted in preference to, a stud. If a stud must be fitted, particularly in aluminium, it should pass right through the metal, and be riveted over on the underside, instead of being simply screwed down into a blind hole. Oil covers, gearbox covers, etc., are too frequently held in place by means of studs and nuts, and, as the-se must frequently be removed, it does not take long to work a stud looae in its boss, and strip the thread in the tapped hole ; the only remedy is to clean the hole. out and tap it for a larger-sized stud. In a few more weeks, the same thing happens again, and there comes a time when it is impossible to fit a larger stud. If it be not possible to drill right through and rivet the stud over at. the back, then the next-size-larger stud should he used, and, when the stud has been screwed into position, a small hole should be drilled right through the boss and the stud, and a hard-steel cotter driven through. could enumerate some other instances of lack of consideration for the user, which is tantamount to an equal lack of regard for his own ultimate reputation by the manufacturer, but the foregoing should be sufficient to put intending purchasers on their guard, and to help them to discriminate in making a selection of a new vehicle. I hope, too, that these remarks may have some effect upon manufacturers, and drive home to them the economic advantages attending the careful consideration of every detail from the replacement point of view, even if it necessitate charging slightly-higher prices,