Contributions from Drivers and Mechanics.
Page 18
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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 vehic.es 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 made immediately after publication. Address your letters to The Editor, Tins COMMERCIAL •MoroR, 7-15, Rosebery Avenue, London, E.C.
When You've Left Your Jack Behind.",
[894] " R.S.C." (Leeds) writes :—" I have frequently found it a difficult and unpleasant job to put on a Stepney wheel without the aid of a jack. Many drivers do not carry a jack, and they may find it useful to know of a method which I have used now for some while for putting on the spare wheel. I had a piece of wood cut 20 in. long and 6 in. wide by al in. deep. Nearly half the length of this piece of wood was tapered towards the one end. A little stop piece was next fitted to the other end, as shown in the sketch [We have had this re-drawn.--ED.]. Now, if this wedge piece be placed under the deflated tire, it will be found quite easy to push or to drive the car on to it : the stop will prevent the wheel from going too far. This little contrivance will take up very little room in the boot of a car, and it will be found to be a most-useful substitute for a. jack."
The Care of Twist Drills.
The sender of the following communication has been awarded the 10s. prize this week.
[895] " 11.M." (Darlaston) writes :—" It may be useful to include a few notes on the grinding of twist drills for the benefit of your readers. I am of opinion that few operations of workshop or garage tools are more-frequently disappointing or more-generally ineffective than the grinding or sharpening of twist drills. The principal points that should be observed when twist drills have to be done up are as follow. The cutting edges must have a proper and a uniform angle with the longitudinal axis of the drill. The cutting edges must also be of exactly equal length, and the lips of the drills must be well and sufficiently backed off. It is, of course, realized by the writer that many shops are not properly equipped with the i means to keep twist drills effectively n order. Nevertheless, there are ways and means whereby this can be carried out, even if the proper plant be not available. If the clearance of a drill be insufficient or imperfect, it will not cut, and when force is applied to it, it will resist the power of the machine of which it is for the time being a component part-, and it is likely that it will become crushed or will split. It is as well to start a drill by hand after it. has been freshly ground. The character of the chips of metal should be carefully observed, and this indication of the nature of the cutting edge should be examined.
"Drills when they are made properly have their cutting edges straight when ground to a proper angle, i
which s about 59 degrees. Grinding to a less angle than this leaves the lip hooked, and is likely to produce a crooked and irregular hole. The grinding lines which are marked on most makes of drill are placed slightly above the centre as a rule, to allow for the proper angle of point, which is a most important factor. An effective method of determining the clearance is to set the point of the drill on a plain surface, holding a scale next to it as shown in the drawing herewith. By revolving the drill, its clearance can be detected, as well as the height of its cutting lips, which should be equal. This is also a way of testing that the cutting edges are of exactly-equal length. "In order to strengthen a drill, the centre is made thicker towards the shank. As the drill is shortened through use, the centre shows thicker and will work hard in drilling. To overcome this, the centre should be thinned, care being taken to remove an equal amount of metal on each side and to keep the points central."