For DRIVERS, MECHANICS & FOREMEN.
Page 25
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TEN SHILLINGS is paid to the sender of any letter which, we publish on this page. and an EXTRA 'FIVE SHILLINGS to the solder of the one which we select as being the best each week. All notes are edited before being published. Mention your employer's name, in confidence, as evidence of-gond faith. Address, D., M. and F., "The Commercill Motor," 7-15; .Rosebery Avenue, London, E.G. 1
Lamps Alight.
On Saturday, April 3rd, light your lamps at 8.4 in i
London, 8.22 n Edinburgh, -8.14 in Newcastle, 8.19 in Liverpool, 8.12 in Birmingham, 8.14 in Bristol, and 9.0 in Dublin.
Welding a Broken Cylinder.
The sender of the following cOnimunieation has been awarded the extra payment of 5s. this week.
[-2070] " H.M." (West Bromwich) writes :β" It is most important when welding a casting which is, in any sense of the word, complicated that the whole body of the metal shall be gradually raised to a comparatively high temperature, at least to red-heat, that it should be maintained at that temperature while the welding is being carried out, and that it should be just as carefully and gradually cooled when the welding operation is completed. "Take a cylinder casting, for example. Any attempt to weld it locally without pre-heatin_g would cause unequal expansion which might easily have the effect of distorting the cylinder beyond repair. or causing other and more serious cracks.
" Ccinsider, for example, repair of the cylinder crack, as shown at B in the accompanying. sketch! [Which we have had redrawn.βEnd The casting' must, as a preliminary, he heated up to red-heat The proper way is to build a firebrick box of a convenient size to receive the casting and leave a space of 6 ins, at least between the outside of the casting and the inside of the box. 'Lay the cylinder upon charcoal within this furnace, pack the space round the casting with broken charcoal, arid light the latter. When the charcoal is properly burning, a sheet of asbestos, in which are. punched a few'. holes, should be laid on top of thefurnace and the cylinder left until it becomes dark red all over. When this stage is reached the asbestos covering may be removed and a, hole cut to allow of access to the broken cylinder, then close furnace again and allow, 'fire gradually. and slowly to die out. " When, welding such a crack as the one shown in the drawing, it is necessary to be careful that neither dirt, scale, nor melted metal beallowed to
run down inside the water jacket, as anything of the kind would have the effect of blocking up the water passages. To prevent the inside of the cylinder from becoming scaled owing to contact with thedlot gases it should be coated with oil and graphiteADefore it is put in the furnace. This coating will easily clean off when the welding is finished."
Hints on Drill Making.
[2071] " A.W." (Shrewsbury) writes-:β" The handiest of all machines to have about a garage is undoubtedly the drill. From the lordly radial clown to the humble sensitive, all are aswelcome to the man who has any odd jobs to do as to him who is regularly engaged on the more convenient and generally more congenial work of manufacturing. " It is a fact that anyaviece of metal, if properly ,shaped for the purpose, will cut another, provided that other is not harder than itself. The most ex cellent material from which to make drills is thai
obtained from old files or chisels. Mill spindles which can generally be picked up cheaply, if not, indeed, from the scrap heap, are also useful, but it must be remembered that they are only mild steel.
"All kinds of processes are used in workshops for hardening steel for drills, and hardly two men can be found who agree as to the best method. The following is a list of those which have .beers brought to my notice from time to time :β
"Boil the water which is intended for quenching before use. Put a little oil on the surface of the drill before quenching. Put salt in the water. -Use only clean, fresh, cold water. Dip the drill in the -matei point first, and gradually lower it in until it is cold. Plunge the drill straight in to the full depth, and
keep perfectly still thereafter until cold. Spray the water on the drill. And so on aci infinitum. Each instruction contradicts the last. The main procedure is : First harden the steel by heating to redness ; then re-heat and quench comparatively
sio"AwlYiter the drill is hardened it must be ground. The usual home-made drill is what is called by some the D bit. The angle between the two cutting edges should be 90,degpees, if the drill is going to be used for general purpose work. If it is to be used for cutting thin sheets the angle should be-greater than .90 degrees, but for drilling .particularly hard metal the angle may be more acute. The grinding must be done very carefully, and it is most important that the two halves are exactly alike and symmetrical about the centre line, otherwise all the work-of drilling will tend to be performed by one side only, and the drill ivy break under the unequal strain. " Holes diameter may easily be drilled in brass, using an ordinary joiner's braces-the drills for that purpose haae to be made with square shanks. In iron an.. eighth of an inch will be found the limit for comfort. Larger holes than these 'may -be made bydrilling a leading hole of small size, and following up with larger and larger drills. Other types besides those to which I have referred are 'suitable for general worisheet metal, and hard steel For surfacing round a -drilled hole, or for counter boring, a drill with cutting edges square with the centre should be used, and it must have a projecting point or nipple equal in diameter to the existing hole. Very often, for certain purposes, it ig essential that the drilled hole should have a square or flat bottom. "The drill for this must be .quite fiat at the end, and 'the two opposing cutting edges should be divided by a, slight V-shaped nick or cut."