For DRIVERS MECHANICS & FOREMEN.
Page 27
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A PRIZE OF TEN SHILLINGS is awarded each week to the sender of the best letter which we publish on this page ; all others are paid for at the rate of a penny a line, with an allowance for photographs. All notes are edited before being published. Mention pour employer's name, in confidence, as evidence of good faith. Address, D., M. and P., The Commercial Motor," 7-15, Rosebery Avenue, London, E.C. 1.
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Lamps Alight.
On Saturday,. November 15th, lightyour lamps at 4.40, in London, 4.25 in Edinburgh, 4.32 in Newcastle, 4. :45 in Liverpool, 4.43 in Birmingham, 4.50 in Bristji, and 5.23 in Dublin.
Improving Bolt Design.
' The sender of the following communication has been awarded the 1O. prize this week.
[2029] "JIM." (West Bromwich) writes :—" When a bolt breaks, in tension, it usually goes through the thread, and the reason should be fairly apparent to even the tyro amongst mechanics. It is because at the bottom of the thread the section of metal available to resist the stress is least. However, in case there should be any doubt about this, a number of
experiments were carried out some years ago by eminent engineers with the -object of demonstrating this fact, which object was definitely achieved. As a matter 'of fact there are quite aomieber of bolts which are broken before they perform any useful function whatever, simply owing to carelessness in strewing up.. Every workman knows, for example, how easy it islo break bolt,itt this manner, and even the sturdy 'five-eights' may be very seriously strained, by injudicious use of the spanner. Mechanics and drivers, .-therefore, should exercise discretion when securing nuts in the process of any repairs or overhauls which they may be called Upon;to carry out. "Now I have been studying this matter a little for myself, and have formed a theory of iriy own. The usual type of bolt_ is depicted in sketch .A [We have had this re-drawn.--ED.]. Most of the thread iS supported within the nut. There is invariably a little of it inside theftiole, which the bolt fills, and I think that, -owing to 'the. reduction in diameter there, most of' the stretch which inevitably occurs when the bolt is tightened uptakes place in that short'length. Gonsequently. the elastic limit is soon reached, and the bolt. breaks. In Marine and largestationaryengine.practke: the bolt is frequently made as shown in sketch, B • for as much of, its length as is eonvenient, theioltis turned down to the;saree'diameter as the bottom of the-thread of the screw. So made, it
stretches underload throughout almost its whole length, instead of only at one oi two threads. "so. get the same effect in the smaller bolts which are commonly used in motor vehicles, I have frequently adopted the expedient which is illustrated la sketch C. I turn down the bolt, from imintediately below the head, to the beginning of the thread, to a diameter .equarko that at the bottom of. the thread. Then, to fill up the hole' which the bolt is supposed to fit, I surround it with a tube of the requisite thickness. The tube or bush must either be split, or it may be made from sheet metal."
Repairing a Ford Van Pulley.
[2030] ' E.H." (Middlesbro') writes :—" Ford spares, when readily obtainable,, are so comparatively inexpensive that in many cases it hardly pays to attempt to improvise Substitutes. The fact that the following, repair was called for twice in one day, on two different vehicles, would seem 'rather to show that it is one for which there may be frequent need, and on that account at least I hope you may think it worthy of reproduction.
"In the course of overhauling one of the firm's brim (a Ford, with Tonlode attachment), the fan pulley was found to be worn to such an extent that there were actually holes right through the rim. The standard–sPare Meet i1bh circiunstanee is a complete fan asSenibly, and as everything but the pulley rina Was in .tip-top order itseemed to be rather a waste to scrap , it. • " I proeured a piece of Sheet "brass, a full in. thiek,,ahd the same width as the pulley rim, It in., and bent it round a, mandrel the same size as the pulley. I then cut right through the worn pulley, assembled the new brass rim in place, and carefully and thoroughly soldered the lot together. Trimmed up with-a smooth file and a piece of emery cloth it made a very nice job indeed. "By a strange coincidence,' a' Ford touring car came in for attention the same day, and it was found to be suffering from the same trouble. It was repaired in the same way, and I am glad to say that both repairs have since given complete satisfaction. I enclose a sketch [whiCh we have had re-drawn—ED.] which may help readers to understand how the work was carried Mt."