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Aviation History
1920
1920 - 0963.PDF
SEPTEMBER 2, • 1920 MODEL AEROPD^S All communications to be addressed to the Model Editor. A stamp should be enclosed tor a postal reply area of this the ball race is to come. The cup to form theA Whirling Arm— Continued)THE accompanying drawings show the bearings on which the whirling arm rotates about the tubular steel shaft referred to last week. These details are all reproduced fairly large for convenience in taking accurate measurements. One of the most important tools needed to make these .bearings is a lathe, and if the worker does not possess one he should try and get access to one, with permission to do his work on it himself. By so doing the whole of the bearings will cost but a trifle. The lower bearing is perhaps the best to undertake first, being rather more simple than the top one. The first thing to do is to obtain a piece of steel cycle tubing, i£ in. outside diameter and 1 \ in. long, No. 16 gauge. One end of this should be turned off true. Next turn up two pieces of steel plate, circular, and an accurate fit within the tube. Out of the centre of these discs turn away the race should be made by hammering with a ball pane hammer,the point at which the cup is to be dished up being placed over a round hole in a blacksmith's swage block or otherodd piece of iron, the most suitable diameter hole being |-in. An old lathe face-plate, the end cf a piece of J-in.iron piping, or a bit of old boiler plate bored out are amongst the makeshift things which can be used. The plate to beembossed must, of course, be heated, and the hammering done when it is red hot. For this reason perhaps the bestthing to hammer on will be the end of a pipe, since it will not cool the thin plate so quickly. The process is made clearby the sketch which also shows the plate. After the boss is hammered up, the plate should be marked out and cutas shown, the parts at the four corners being cut away, leaving the central boss, with two long and two short 1 Imiltr/man &rotl of ttnort l Simon •m^tf-V* 1 n >, , ; metal, leaving them in the form of flat rings, the internal diameter being such that they make an easy fit over the main f-in. tubular upright shaft. The rings are now to be pushed into the trued end of the ij-in. tube, and sweated with solder into place, taking care that they are true with the turned end and with each other. The distance between them should be a full TVm- This space between the plates will, as can be gathered from the drawing, form the lower ball race. The upper part of the tube has now to be slit down with a fine hacksaw, making eight cuts. The metal between alternate cuts is then to be removed, and the bottom of the four slots thus formed filed away neatly to the four lugs shown in the illustration, which also indicates how the re- maining four lugs are to be turned back to take the arms and outriggers, c, d and g, respectively. The insertion of a row of ^-in. diameter steel bicycle balls completes this bearing. •The top bearing is to be made from a piece of steel rod for the fixed part, turned in the lathe to the shape shown in section in the lower drawing and in perspective in the small side sketch. It should be a tight fit in the top end of the main tubular shaft. Such bearings should properly be of either tempered steel or should be case-hardened, but in view of the small amount of wear likely to take place owing to little use, such hardening will not be really necessary. The other part of the bearing is to be made from steel plate. A piece of about No. 17 or 18-gauge should be taken, measuring 7 ins. .by 2| ins. Around the exact centre of the arms. It should then be mounted on the face-plate of a lathe, and the inner side of the cup turned and polished to remove hammer marks and make a smooth race for the balls. The hole in the centre of the cup should be bored in the lathe, after the cup is formed, and the two short arms turned up to carry the spindle on which the pulleys are mounted. The pulleys should now be made. These may be bought at the ironmonger's, but they will certainly require some attention before being used, as the average ironmonger's pulleys are generally abominably wobbley and out of truth. If you can get a pair fairly true so much the better, but they had better be put in a lathe and properly trued and balanced. The centres will require to be bushed with brass and re- drilled to' fit the spindle shown in plan about TVm- bare in diameter, the smaller compatible with strength the better, in order to reduce friction. The diameter over the groove in which the cord runs should be f-in. The spindle can very well be made from a piece of stout steel wire ; a bicycle spoke will do admirably, a collar being soldered on the wire near each pulley to keep them from running toward the centre, or the spindle can be turned down from a piece of •J-in. steel rod, as shown in the drawing. When the spindle is ready the pulleys should be slipped on, and the lugs forming the bearings standing up from the plate should be closed over the spindle ends, and the second bearing, when the fL-in. diameter draw balls are provided, is complete. , • (To be Continued) /'""'''' 965
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