Contributions from Drivers and Mechanics.
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TEN SHILLINGS WEEKLY for the Best Communication Received, and One Penny a Line of ten words for any thing else published.
Drivers of commercial-motor vehictes 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. Workshop 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 not disqualify for a prize. When writing use one side of the paper only and mention your employer's name as a guarantee of bona fides. Neither your own nor your employer's name will be disclosed. Payment will be mute immediately after publication. Address your letters to The Editor, THE COMMERCIAL MOTOR, 7-15, kosebery Avenue, London, E.C.
An Ingenious Tail-light Alarm.
The sender of the following communication has been awarded the 10s. prize this week.
[762] " CT." (Fulham) writes :—" I beg to submit the following contribution in the hope that it may prove suitable for insertion in the D. and M.' columns of the CAA.' The enclosed sketch (We have had this redrawn. —En.] illustrates a simple device for fixing inside the tail lamp of a motor vehicle, its purpose being to ring an electric bell, whenever the light goes out through any cause. It will be noticed that the device is very simple in construction. Practically any driver will be able to make and fix one for himself. The first thing required is a short piece of water-gauge glass of the usual kind_ Its length will, of course, depend upon the type of lamp used, but in my case the glass tube was about 2i in. long. The lamp is an ordinary cart lamp, a type which is usually very strong and cheap; they are preferable to the moreexpensive class of motor lamp. When the glass tube has been cut to the required length, two hard wooden plugs are made, one for each end, • and they should be shaped after the manner shown in the sketch ; those portions which are let into the ends of the tube should be a good fit. A small piston with rod attached is next required to work inside the glass tube. The piston head is preferably made of aluminium. A piece of a in. brass wire is screwed through the piston to act as piston rod ; this rod should be quite straight. The wooden plug, fitted to the top end of the tube, must have a hole through the centre. This is best done by burning it with a piece of red-hot wire, of the same diameter as that of the piston rod. The rod must be a slack fit in this hole, as there must be no possibility of air being trapped between the top of piston and the plug. A thin brass washer is next secured upon the top of this plug by two very-small screws or pins. The hole through this washer must be larger in diameter than the piston rod and fixed so that it is impossible for the rod to touch the washer. A second brass washer which may be of smaller diameter is soldered to a in. nut, this nut and washer occupying a place upon the screwed end of the piston rod outside the glass tube. It will be seen that a small brass screw passes right through the bottom plug. It is important that this screw shall be long enough for the point to pass well through the plug. The method of use is as follows : when all has been prepared, the bottom plug is put into its position, care being taken first of all to smear, with white lead, all round that part of the plug which fits in the tube. When, this. has been done, the brass screw must be put into position.and the tube then filled to a depth of about 4, in, with mercury. The piston is then put in the tube and care is taken that it works easily within the tube. The top wooden plug is next fitted in the same manner as the bottom one.. The brass washer previously mentioned is now fixed in position on the top of this plug and the nut with the washer attached should be placed upon the end of the piston rod. Its proper position must be found by trial, as so much depends upon other factors such as the type of lamp used, its ventilation, the distance of the tube from the burner, the weight and friction of the piston, etc., etc. As a guide as to what to expect from a lamp like that shown in the sketch, I have found that the maximum temperature of the mercury rises to about 130 Fahr., an.d the expansion of the mercury under the conditions shown in the sketch is about in., assuming 65 degrees Fakir. as a basis when the lamp is out.
" It will be seen that there is plenty of latitude in which to work. When it has been decided at what temperature the bell shall ring, say about 90 degrees Fehr., the lamp is heated up to that temperature. The nut with the washer attached is then screwed down on the piston rod, until the two washers make good contact one with the other. Any material rise in the temperature will then expand the mercury, raising the piston and breaking the circuit, for it is assumed that the wires to the bell have been connected properly, one round the neck of the brass screw in the bottom plug, the other soldered to the brass washer which is fixed upon the top plug.
"As I employed the above device on a steamer, I had to use a dry ::attery, with, of course, a switch and bell fixed in the driver's cah. No doubt if it were used upon a petrol vehicle, the wires could be coupled to the ignition system
instead of to a special battery. The neat device is secured to the lamp by small clips not shown. It will be seen that the electric current passes through the brass screw, the point of which is always in contact with the mercury, and flows through the mercury up the brass rod into the nut and washer. When the two washers are in contact the circuit is complete."
Gland-Packing Procedure.
[7(i3] " W.S." (Hull) writes.—" From time to time, T have seen references in your columns to methods of packing glands. Some writers seem to think that this is a thread-bare subject, but I still think there is a good deal to say upon it. Glands which are constantly blowing are the cause of a lot of waste, especially on small and quickrunning engines like those on steam wagons. 'T.D.' (Canning Town) [Letter No. 741, 21st July.—ED.] seems to think that the trouble is not so much due to the packing • as to the man. I don't agree with him that this is generally the ease. Care must be taken to see that the packing is the right size and not too large. Glands should never be packed too full. After the first day's running, I always make a practice of putting in a liner. I also always take care not to let the slide-blocks get bad, as if they do, they cause a lot of trouble with the glands. The glands give much less trouble on vertical engines than they do on horizontals. "A few words with regard to leaky tubes. I had a few spare tubes which I had cut up into lengths of about 1i in. After I expand the ordinary tubes, I insert these short ends, which I in turn expand when any leaking takes place. This is much better than having to referrule."