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Aviation History
1971
1971 - 0079.PDF
74 to-Pioneer 6 measurement from the longer Earth-to-Pioneer 8 measurement. This means that ionospheric effects on the two sets of radio signals travelling an identical path between the Earth and Pioneer 6 cancel out. Any remain ing effects are caused entirely by solar wind phenomena in the space between the two craft. If only one spacecraft is used, measurements must be taken of the Earth's ionos phere using the geostationary ATS satellites, and these duly subtracted. Because the ionosphere varies rapidly, such a system is relatively inaccurate. Pioneer 6 was launched five years ago and will return FLIGHT International, 14 January 1971 to its solar orbit injection point next August (Flight, December 31). At its farthest distance when it was directly behind the Sun, the spacecraft was 182 million miles, 290 million km from Earth. Pioneer 8 was launched at the end of 1967. SOVIET DOUBLE GIANT A radiotelescope under construction in the Soviet Union will measure 1,970ft, 600m in diameter, according to a Novosti report last week. This is nearly twice the size of the present world record holder, the 1,000ft, 300m dish at Arecibo, Puerto Rico, built in 1963. It is being built at Zelenchuk in the North Caucasus, adjacent to the new 236in, 6m optical telescope, also a world record (Flight, October 15, page 607). Neither of the two radiotelescopes is steerable, Arecibo consisting of reflecting mesh laid in an excavated bowl while the Zelenchuk reflector appears to be suspended from a ring of pylons. Both telescopes of the Russian observatory are located some 7,000ft, 2,000m, a.s.l. and will be able to operate synchronously. HELICAL CARBIDES High-speed routing is a large part of the machining of many integral air frame components, where design re quirements to achieve minimum struc tural weight necessitate extensive pocketing and profiling operations. This subject is dealt with in some detail elsewhere in this issue in an article on the machining of Concorde parts at the Weybridge Division of the British Aircraft Corporation Ltd. For this kind of operation, straight- toothed routing cutters with tungsten- carbide tips have been, and still are, much used although, for this purpose, they are not ideal: severe shock-load ing is imposed as each tooth engages the work to the full depth of the cut, which must consequently be limited to avoid chipping or breaking the carbide tip. As is well known, helically toothed cutters have a much smoother cutting action. The cutting action of the teeth is continuous and more than one cutting edge can engage simul taneously. Both factors reduce the shock-loading on the teeth. Development of helically toothed cutters has been impeded by difficul ties inherent in the production of carbide inserts of a true and accurate helical form. Over the last two years, Marwin Cutting Tools Ltd, Rothley, Leicester, has developed a technique for this purpose. As a result, it is claimed that helical tips can be produced for cutters of from 12mm to 8in in diameter to any required helix- angle between 5° and 45° in lengths equivalent to more than three cutter diameters with consistency of form and helix within a maximum tolerance of O.Olin. The first application of these tips has been to routing tools, but the Suparouter cutter, in which they are embodied, is in fact designed to make optimum use of both carbide and high speed steel. These cutters have a high speed steel body with two or more helical flutes to which helical-carbide tips are brazed. From the outside diameter of the cutter towards the centre, the surface speed of the teeth on the end-face Left, two views of a tungsten-carbide tip for a Marwin Suparouter cutter, showing its true helical form. Right, tips of unequal width on the end-cutting teeth of a Suparouter cutter prevent the joint between carbide and high-speed steel from leaving "tracking" marks in the machined surface. A, Helical-carbide tip; B, High-speed steel reduces progressively becoming, in fact, zero at the centre. At and near the outside diameter of the cutter, the carbide tips can work with greatest efficiency at the maximum surface- cutting speed, which is arranged to fall within their optimum performance range. Over that portion of the end- face teeth between the tips and the centre of the cutter, the carbide would be underworked and inefficient, but here the high-speed steel, to which the tips are brazed, can perform quite adequately. On two-flute cutters, carbide tips of unequal width are used. With this arrangement, the paths of the joints between the tips and the high-speed steel do not coincide, with the result that "tracking" marks in the machined surface of the work are avoided (see illustration). £ These cutters can be used for both pocketing and profiling operations, so rendering two separate types unneces sary. In profiling operations they can, if required, be sunk straight in to the depth of cut and "ramping-down" is not necessary. High metal-removal rates are claimed for these cutters. In cutting aluminium on a Marwin Max-E-Trace machine, a cutter 2in in diameter has been operated consistently at a feed rate of lOOin/min on a cut lin in depth —a metal-removal rate of 200 cu in/ min. Removal rates as high as from three to eight times those of cutters previously used are claimed. An indication of the range of con figurations available is given by the fact that a cutter 6in in diameter with 20 flutes has been produced. Another type of cutter, the Maxeflow, is made in end-mill, shell- mill and roller-mill forms, and em bodies similar helical carbide tips^... Because the tips are mounted on the periphery of the cutter, the cutter body can be made of steel that is cheaper than the high-speed alloys normally required.
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