Contributions from Drivers and Mechanics.
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Drivers of commercial-motor vehicles and tractors, and mechanics and foremen of garages or shops, are invited to send short contributions on any subject which is likely to prove of interest to our readers. Workshi,p tips and smart repairs ; long and successful runs ; interesting photographs all are suitable subjects. Send a post-card, or a letter, or a sketch to us—no matter how short, or how written, or how worded. We will "knock it into shape" and prepare sketches, where necessary, before publication. The absence of a sketch does nut disqualify for a prize. R'hen meriting use one side of the paper milt, and mention your employer's name as a guarantee of bona fides. Neither your own nor your employer's 'manic will be disclosed. Payment will be made immediately after publication. Address your letters to The Editor, TsH COM E RC IAL MOTOR, 7-15, kosebery Avenue, London, E.C.
A Novel Method of Remagnetizing Magnets.
'The sender of the following communication has been awarded the /us. prsze this .week.
[711] " G.S.C." (Slough) writes :—" I enclose you a rough diagram [We have had this redrawn.—En.] which shows a method of remagnetizing the magnets of a lowtension magneto. Most of the public-service cars with which I have to deal are fitted with low-tension ignition, and, as no doubt many of your readers are aware, the magnets of this system occasionally become weakened. The idea, which I will describe to you, occurred to me some months ago, and, since then, we have invariably treated weak magnets in this way, with entire satisfaction ; in fact, it is now our standard method. The usual pair of coils was used, and two brass bobbins were made which were a sliding fit on the legs of the magnets. Four lb. of 18 s.w.g., double, cotton-covered wire were wound on each bobbin, and the current we used was 5 snips. at 50 volts. Instead of the coils' being directly coupled to the main current, we interposed what is known as a Wenhelt electrolytic interrupter, which was put into series with the bobbins, I am not able authoritatively to explain why the inclusion of this interesting electric device should account for such an increase in the amount of magnetism which it is, in this way, possible to retain in the. magnets: I can only record the fact that sueh a result is achieved. Personally, my theory is that the high-speed interruption of the current, for which the Wenhelt device is responsible, sets up a vibration in the steel, and so, powerfully assists in the correct resetting of the molecules or particles of the metal. NIost of your readers will know that there is every reason to assume that, when a bar of steel is magnetized, the molecules or particles, of which that bar is supposed to consist,
arrange themselves with their opposite poles adjacent to each other. It is, of course, due to the breakdown of this arrangement that de-magnetization occurs. When, however, it is desired to re-magnetize, these little particles have to be assisted to re-arrange themselves in their original positions. It is quite usual, during the passing of the current round the poles in the ordinary methods of re-magnetizing, to tap the steel smartly, in order to assist this re-arrangement, The Wenhelt interrupter is really an electro-chemical make-and-break device; it interrupts the constant flow of a direct current very many times in a minute—something like 1,000 times is quite
common. I believe the theoretical explanation of this arrangement is that the passing of the current decomposes the acid in which the terminals are immersed, and so, instantaneously, the liquid medium through which the current flows is removed, again to be replaced when the bubble of gas that has been generated has passed away from the platinum point. The general arrangement of the rest of the apparatus. I think, will be quite clear from the diagram. I believe I am correct in saying that this interrupter is of the type which is used extensively in connection with X-ray apparatus, and it is in that connection that its utility has been principally realized. I can strongly recommend any of your readers who have low-tension magnetos to re-magnetize, to consider the advisability of employing one of these interrupters in the circuit.
A Word for the Police. Patching a Wheel.
[7121 " F.A.W.D." (Leeds) writes :—" 1 should like to say a word or two with regard to letter, No. 701, in your issue of the 51h inst., which was in reference to the trouble into which your correspondent got for driving by candle light. My experience with the police in Ibis district is such that I cannot but praise them. I don't think they would have stopped me under similar circumstances. I have, on many occasions, had trouble owing to the slipping of my wagon on greasy setts, and I have then taken such precautions to get along that have brought me well within the clutches of the law. There is no doubt that I might have been hauled before the beak' many times if the police had liked to have taken the necessary steps. I have frequently had trouble with the tail lamp in windy weather, and, instead of receiving a summons, a friendly constable has often lent me a hand to keep it alight. I find the greatest difficulty in keeping an ordinary lamp alight on a windy night in this district, particularly when I am running over setts, where the vibration seems to put out the very beet of lamps. Perhaps some of your correspondents can suggest what is the best form of lamp to use for conditions like these.
" I should like to tell you of the way in which the wheel of a horse-drawn lorry, which was carrying a 15-to-, casting, was admirably repaired in this district a little while hack; it might perhaps assist some of my fellow readers who are in trouble with the wheels of their
wagons or trailers. The excessive load had started ' the wheel all over, and it would have been unsafe to proceed, as the spokes were all loose and the hub was in a very groggy ' condition. The driver decided to have a number of strong ash wedges cut, and each of these, was carefully shaped so that it could be driven between a pair of spokes and, also so that it would fit tightly fietween the hob and the felloe. Suitable care was taken with the fitting, and when the wedges were all driven in, the whole wheel, of course, was of solid wooden construction. The wedges took the load off the spokes, and, at the same time, kept them in position. They were all nailed up together to prevent any creeping, and were quite satisfactory for the rest of this journey. It would, of course, be unsafe to rely on anything of this sort for a wheel which had to act as a driver, but it saved excessive delay and made a very-good temporary job in this instance," The Fitter's Screwdriver.
[713] " S.C." (Glasgow) writes: " Several of your contributors have spoken, in the Drivers' and Mechanics" columns of your journal, of the spoiling of screwed, parts when they are being worked upon in a vice. Now those same contributors must know that fitters and mechanics often make a mess of the heads of bolts and screws, when tightening them up on a job. It is of tightening up small slot-headed screws, with a screwdriver, that I would speak. Certainly nine fitters out of ten, when screwing up button-headed or cheeseheaded brass screws, make a real mess of the affair. The ordinary screwdriver used by the fitter is, as a rule, at fault; it is generally made out of an old file—round, seilare or flat, whichever is first at hand. Usually it is too hard or too soft at one end, the temper either nut having been brought down far enough or having been brought dawn too far. The fitter requires a greater pull on his screws than does his colleague the carpenter. lie has to resort to various devices for obtaining this result, such as by applying the jaws of a small spanner to the flat sides of the screwdriver shank, and so getting a much-greater leverage. The litter follows fashion and does not make. a screwdriver to suit his special job. fie generally copies the tool used by his wood-working mate. The carpenter wants a driver which will enter almost any size of slot, and another point is that, as a rule, he doesn't need to employ so much pressure to withdraw or drive a woodserew, as does the fitter whose screws are, more often than not, fixed very tightly, and perhaps routed, " The screwdriver is a tool which is so much used by fitters and mechanics on jobbing, and which, as a rule, gives so much trouble when so used, that the simple form of this tool which I have long used with satisfaction should have some interest for those that follow the D. and M.'
columns. The sketch I send needs little explanation.
[This has been redrawn. En.] It will be seen that the flats of the screwdriver, near the working end, taper slightly towards the handle.. This provision ensures a good grip on the sides oh the slot in the screw, so that the end does not mount the head and tear it up. The fitter's screwdriver is usually ground taper towards the end and is, as a rule, worn and twisted at the corners. On the pattern which I use, a small hole, OT two small holes at right angles to each other, are drilled in the shank, the temper having been lowered for the purpose of drilling. These hetes allow a small tommy-bar to be used in order to obtain a greater leverage. The end of the screwdriver, it may he added, need not be weakened by reason of this special shape. It should be just narrow enough to enter the slot in the screw, and the metal just above the point may be wider than that at, the point.
" Your readers will see that this suggested form of screwdriver tends to shear the head of the screw through the slots and not to mount the head, like that of the carpenter's taper-ended tool."
How To Rivet Wheel Tread-plates.
J.A." (Manchester) writes :—'• I think you will agree with me that there is nothing more annoying, nor calculated to give steam wagons a worse name, than the clatter and noise which some of these vehicles make, when the tread-plates on the wheels get loose. Especially is this the case when the wheels are of the all-steel pattern. I know of several users in this district, who have adopted the composite or all-wood type of wheel with a continuous smooth tire, owing to the difficulty they have had in keeping the cross plates fast on any pattern of builtup all-steel wheel.
" In my opinion smooth tires are of very-little use in this district, owing to their tendency to skid on the least bit of a hill—especially when a trailer is in use—if the roads are a bit greasy, which is the rule here rather than the exception. The choice, therefore, for the present, appears to he. between cross plates, with grooves to get a grip of the road, and rubber tires, which are almost prohibitive at the present prices.
"I think a little study of the usual method of riveting on these steel plates, will make it plain that, fitted in this way, they can scarcely be expected to keep fast very long—at any rate in this district, where the work is almost all on granite setts end tram-rails—and where the hammering effect is so severe between the wheels and the roads.
"The common method of filling is to bore the plates taper right through, and then to leave the rivet heads about A in. above the tread plates, with the evident intention that the hammering effect an the read will expand each rivet in its hole and so keep it tight. I am quite certain, however, that this does not take place in practice. The effect is just the same as it would be if you took a big hammer and kept hammering at the head of the rivet, without the use of a holding-up dolly on the other side it would only loosen the rivets. Consequently, with this system, when the beads of the rivets are worn off the plates at once become loose.
" Some while ago, I suggested to our foreman that, when a plate came loose, it should be taken off and a straight hole, of larger bore than the rivet hole and big enough to take tile head, should be drilled nearly halfway through the plates to form a sort of cup for the rivet heads to fit in, 'this method was tried and it has answered very satisfactorily. The rivet should be hammered right into the straight hole, and the heads left below the level of the tread plates, which thus protect them from the jar and vibration. The holes gradually close in over the Lops of the rivets, and the sides also close in round them and tighten them up, so that, after a while, it is almost impossible for a plate to conic off_ We have had verylittle trouble since we started treating the treads in this way. And we have, without a shadow of doubt, saved ourselves a lot of time and worry.
" I may say, in conclusion, that our wheels are of the built-up steel type, and they are the original ones which were supplied with the wagon, nearly five years ago. During this time they have done about 30,000 miles, and look good enough for double that distance yet. Of course, they have had new tread plates on when required."