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For DRIVERS, MECHANICS & FOREMEN.

6th September 1917
Page 23
Page 23, 6th September 1917 — For DRIVERS, MECHANICS & FOREMEN.
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Which of the following most accurately describes the problem?

A PRIZE OF TEN SHILLINGS is awarded each week to the sender of the best letter which we publifii on thi page ; all others arc paid for at the rate of a penny a line, with an allowance for photographs, All notes' are edited before bang 2n1Wiehed. Mention your employer's name, in " confidence, as evidence bf good faith. Address D., Al, and F., The

Compiercial Motor," 715, Rosebery Avenue, London, , '

Lamps Alight—

Light your lamps at 8.2 in London, 8.49 in Edinburgh, 8.12 in Newcastle, 8.15 in Liverpool, 8.10 in -Birmingham, 8.12 in Bristol, and 9.0 in Dublin.

A Repair-shop, Method of Cutting Special Gears.

The sender of the following comm'unication has • been awarded the 108. prize this week.

[1777] " V.W.C." (Dulwich) writes :—" I have been for some years a constant reader of your useful and instructive journal, and find much of particular interest to me in your 'D., M. and F.' page. It occurs to me that, in return for the many hints and tips which I have myself obtained from that page, I cannot do

better than try to help other readers in a similar position to mine by relating the following method of cutting the teeth on the smaller of a pair of sliding gears of the pattern, illustrated by the sketch which I enclose. [We have had this sketch redrawn, and it is reproduced herewith.—ED.1

'The cutting of the teeth on the larger of the two gears is a simple matter ; it may easily be accomplished on any milling machine, if the blank be held between centres. The smaller one cannot be ' so treated, however, as there is not, as a rule, room forthe milling cutter to travel the full 'width without its fouling the larger gear and damaging it. At one time we used to slot the small gear, using a single-toothed. tool, after it had been roughed out...on the milling machine. This method did not, however, always give the best results, although a good workman could generally produce a fairly accurate gear by these means. The following method proved, in actual use, to be much better, and all such gears are now so formed.

" After -the large gear has been cut in the usual manner, the small one is then divided up and roughed out in the milling machine so far as possible. It is then secured to the top of the slotting machine table by a central bolt on which it can revolve, care being taken that it is quite centrally placed on the table. If necessary, a bush or collet may be utilized to ensure it being accurately located in this respect. "The tool used, of which I also enclose a sketch, is carried on a piece of mild-steel bar, 12 ins, long and

11ins, diameter, which is turned down at the end for the purpose. The latter is cut from mild steel also ; I find that this material, if carefully case-hardened, stands up to this class of work as well as tool steel.

he cutter is really another gearwheel, having any convenient number of teeth of the same pitch as those of the gear which is to -be cut. The tool-bar, with its revolving cutter, is secured in the ram of the slotter, and the stroke of the machine so adjusted that, when the ram is at the top of its lift, the teeth of the cutter are still -engaged to the extent of ie in. with those of the gear it is cutting.

"When everything is adjusted, the machine is set in motion, and the table also caused to revolve ; this in turn revolves the cutter. The cross-feed of the tool is adjusted little by little until the required depth of tooth is reached and the gear finished."

A Simple Emergency Valve Repair.

[1778] " T.G.," (Chesterfield) writes :—" A short time ago, while I was on an important journey and was.conveying goods, the immediate delivery of which was of national importance, one, of the valves of the engine I was driving .broke of on a level with the underside-of the cotter. I was some miles from the end of my journey, and the remainder of the road which had still to be-traversed contained many stiff gradients. I knew, therefore, that it was useless for me to try and hobble home to the garage on three cylinders.

"The broken valve was of the'type which utilizes a cotter of horseshoe shape to holdup the spring collar, the said cotter resting in a groove which is turned in the stem of the .valve. This circumstance proved-to be a fortunate one, and I was able to effect a temporary repair by drawing out the broken valve, as shown on the sketch which I enclose. [We have had this redrawn and it is reproduced herewith.-7--ED.] When the stem had been lengthened to the required extent, it only remained to file a groove to receive the cotter and the job was completed.

"If any other of your readers is placed in a similar predicament, he must be careful, when heating the

valve stem, that he does not raise it to too high a temperature, or it will be burned. A. red-heat is quite sufficient for the purpose. Further, allow enough of the untouched stem to bear in the guide, otherwise the valve will bind in its guide. I may add that I now carry the old repaired valve as a spare one in case of emergency."


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