Great Progress in
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Steels for Tools
A Considerable Improvement in the Efficiency and Durability of Files as the Result of the Use of New Materials
THE numerous developments in steel manufacture, which have been recorded in previous articles of this series, have exercised an extraordinary influence on the design and production of tools made from steel. Some of these advances have already been discussed; the present article indicates other progress in simi
lar directions. .
_ The common file, one of the 'oldest _ tools known to Mankind, has probably uudergbne gfeater changes within the past decade then at any period since ' the transition from flint to metal. In .. _ „
the first place, there have been' numeroils alterations in the" compositionof
the steel for files. : , '
.T.Ip to recent years file steel was an ordinary, low-carbon material hard-. cued in a lead bath. , 'id-day, whilst a large number of files is still made of this material, alloy steels have been introdUe:ed ' for the ' purpose and are rapidly winning faVoin. ' Originally,what was known at the " high speed steel " file was not made of high-speed steel, hut of a steel to which a small percentage of the element tungsten had been added, to give increased cutting power.
High-speed Steel.
This steel is being ever more widely employed in file manufacture, owing to the improved results which it gives, these far outweighing the higher, cost. Another, metal which is, to some extent, replacing it is chromium steel.
In addition to improving the basic material of the files, there have been remarkable improvements in the design of the tools themselves. The angles of the cutting teeth, their shape and the treatment of the file in the processes of manufacture have all been scientifically studied, with interesting results.
Whilst no sensational all-round " best " form of tooth for every class of work has been designed, the closer attention paid to cutting angles and shape has resulted in greater performance capacity in the standard files, and the production of a number of special files for specific purposes. Among these must be numbered the file with half-moon teeth for dealing with plastic substances, such as readily clog the teeth of ordinary files; that with a specially milled tooth, in which a milling machine, and not a mechanically operated chisel, forms the teeth; the special files for brass, and others.
Circular files for machine filing cf special character, and the extremely small files for watch and clock makers, known as grobet or Swiss files, because previously they were obtainable only from Switzerland, have also been successfully manufactured in this country.
Circular saws for cutting wood and metal are another type of tool the development of which has been rapid and of great interest and importance. Originally but a circular steel plate, in the periphery of which teeth were cut, the modern circular metal-cutting saw is a very different tool. It is employed in an electrically driven sawing machine, and consists isf a humber of replaceable segments bolted together, each segment being provided with teeth" •
. Prior to this invention, saws with inserted teeth were tried. Whilst these were successful up to a point, there. was a great deal of difficulty and expense due to the fact that the inserted highspeed-steel teeth were apt, under heavy pressure of work, to rip out of the sockets. It was difficult • to find teeth which would stand up -to any and every kind of work that a circular saw was called upon to perform.
Furthermore, the steel of which these saws are made has changed. A large number of the old circular solid-steel saws is still being made in the cruciblecast steel on which their past reputation was based, but some of the newer saws are made from chrome-alloy and tungsten-alloy steels. These are claimed to give a cuttingpower so much higher than that of the ordinary steel saws that the slightly higher cost is speedily recovered.
Ingot-slicing Tools.
The rapid development of welded tools has been referred to in a previous article, but a later and valuable development has been the invention of ingot-slicing tools for cutting tip metal ingots, such tools being of a composite character, like the fuse-welded devices. In these the cutting steel ends with which the tools are provided are not of super-high-speed steel containing cobalt, but of 18 per cent. tungsten high-speed steel, which is excellent for the purpose, and likewise enables the tools to be sold at extremely low prices.
Hacksaws have improved out of all recognition. In some respects they have progressed on lines similar to those of the circular saws, fn that nee: steels have been used. But their teeth have been redesigned with far greater attention to scientific cutting capacity. The steels of which they are made contain high percentages ofs tungsten when the duty they have to do is extremely heavy, and even some makes of hand hacksaw blade are manufactured from high-speed steel.
The manufacture of composite twist drills was alluded to in the previous article of this series. In addition to this sensational change, other advances must be noted. The greater use of high-speed steels has led to the revival, in a measure, of the flat-twist drill.
This kind of drill has the advantage . that it needs a much smaller amount of high-speed steel, because the twisted flutes may be fuse-welded to alloy-steel
shanks, as with the ordinary drills. It requires much more power to drive, hut. it has great endurance and strength, and for heavy production in hard., metals, this extra power .cost is sometimes more than compensated by
the increased output per drill. • A great deal of research has been Carried out on the cutting angles, point thinning, lip clearance and other dements in the design of these tools, and this has led to the production of special types of twist drill for specific purposes. Thus, short, stubby drills of sturdy design are being manufactured ' for the hardest materials.
Cobalt-steel Drills.
Drills of a design different from the standard are also being supplied. for work on such substances as bake-. lite, brass, gold, aluminium, erinoid, copper and non-ferrous metals, Cobaltsteel drills for manganese steel and other exceptionally resistant materials are another improvement.
Some interesting claims have been made for chromium plating as applied to tools. Milling cutters, twist drills, files, etc., are all said to show improved _ • performance after chromium plating. In this connection, the writer suggests that caution be exercised before taking these claims at their face value. In the only instance with which he is familiar of the subjecting of chromiumplated tools to a proper independent test the result was far from 'convincing.
With chromium plating there is always the danger, furthermore, t f flaking off the plating. The surface hardening of certain tools by means of the nitriding process has, however, definitely given satisfactory results ; but the types of tool capable of being treated in this manner are limited.
An interesting tool process is the making of certain chisels by casting a high-grade cutting alloy to the desired shape, then hardening, tempering and polishing, to form a tool suitable for use. It is assetted that chisels manufactured by this method are not so hard on the surface as chisels forged from bars of steel, but have cutting edges that are durable and efficient.