Document 22: Henry B Allen -- Improvements in Steels for Woodcutting Saws and Knives 1930

Henry B Allen Improvements in Steels for Wood-Cutting Saws and Knives 1930 WDI-53-5

Note to readers: My motive for uploading this document is to help illustrate the background for the introduction of carbide-tipped saw blades for woodworking. That this metallurgy traces back to the 1920s comes as a surprise for me, and in that light, assumed that others who share a curiosity about where, when, how, why such developments occur would also like to have access to this important information. 



Improvements in Steels for Wood-Cutting Saws and Knives


Chief Metallurgist, Henry Disston Sons

Paper presented at the

Fifth National Wood Industries Meeting, New York, N. Y.,

Oct. 16 and 17, 1930, of the American Society Mechanical Engineers


(NOTE: Statements and opinions advanced in papers are to be understood as individual expressions of their authors; and not those of the Society.

ACKNOWLEDGMENT: The author expresses his appreciation and thanks to Mr. S. Horace Disston, Vice-President, Henry Disston & Sons, Inc., for suggestions which have been most helpful in the preparation of this paper.)

The box below contains the "teaser" for Allen's paper:


The important factors in a review of saw steels are the blade which carries the teeth and the teeth themselves. There is little in sight to promise further marked improvements in the solid-tooth type of saw. The next logical step is to use inserted teeth made from materials known to be well adapted to the function of cutting wood. The same forward step was taken years ago in metal cutting.


The two important factors in a review of steels used for sees are the blade which carries the teeth and the teeth themselves. The steel for the blade, after heat treatment, should combine high elastic limit, good ductility, resistance to fatigue cracking, resistance to impact, and uniformity. There is little in sight to promise further marked improvements in the solid-tooth type of saw. The next logical step is to use inserted teeth made front materials known to be well adapted to the function of cutting wood. This same forward step was taken years ago in metal cutting. Future changes in design, so as to put to use metallurgical discoveries, will require the best. thought of saw user, machine builder, and saw maker. Research and untiring effort alone lead the way to accomplishment.

The saw is a venerable tool. It dates bark to prehistoric time. The first saw consisted of serrations along the thin edge of a piece of stone or hone. As bronze and, later, iron were discovered, the same scheme was followed, only with the greater refinements made possible by the malleability of the metals.

When steel came into civilization, still further improvements were possible. Here was a materiel which could not only be forged into shape, but subsequently could be made hard and springy.

It is interesting to note that at this stage of development Western practice very probably branched off from that of the East. The bronze or iron saw, because of its lack of springiness, could be used only to full advantage when pulled through the material being cut. The Oriental still operates his hand saws in this fashion. The West, however, finding that a tempered blade enough spring to prevent buckling, decided to do his cutting on the push stroke.

Civilization has always been slow to change. This conservatism has applied with full force in the field of the mechanic arts. Great changes, however, are taking place in our day; the teachings of science are more widely accepted and applied than ever before. if a curve were plotted between time and the application of progressive ideas in the field of mechanics, we would see


it long, slowly rising line, with here and there an up or down trend, until a comparatively few years ago, when the curve started up the present rapidly increasing slope.
The saw maker and user have, in the past, been no exceptions to the general law of human conservatism. The manufacture of saws has been an art acquired by years of first-hand experience. Specialized knowledge and equipment have been required. The manufacture has therefore been retained in the hands of comparatively few. Probably for these reasons there is a remarkable scarcity of published information about the steels used.

Simplicity is a consideration of prime importance in any device. The saw has been a good exponent of this principle. Even today the greater number are made from a single piece of steel, the blade and teeth integral and of the same temper. The advantage of this design is mainly simplicity of manufacture, hence low cost. The disadvantage is that the steel forming the blade must also serve for the teeth: The blade, as we shall see later, requires properties which do not coincide with those hest suited to a cutting edge.

The obvious way to eliminate these shortcomings of the solid-tooth saw is to provide separate teeth which can be mechanically attached to the blade. Thus each part of the saw can be made out of a material best suited to its respective function. Inserted-tooth saws have been used to some extent for many years, although not primarily for the reason just stated. In the past they have found their place mainly because of the ease of keeping them in running order and also that they hold to their original diameter. More attention has been lately paid, however, to their great usefulness in providing the means of applying a more efficient cutting medium for the teeth: The discovery of new steels and materials which display valuable properties for cutting wood, but which cannot be used for the blade, must result in the further development of. the inserted-tooth saw.

There are therefore two general types of saws, the solid tooth and the inserted tooth, to he included -in a discussion of the steels used. Inasmuch as the problems of today are concerned mostly with power-operated tools, the paper. will be confined to that type.
There are two equally important factors which must be considered in a review of steels used for saws; namely, the blade which carries the teeth, and the teeth themselves. Both are of equal importance to the success of the saw: The subject of saw steels will therefore be taken up under the two headings. Knives also can be treated in the same way, although the problems offered by the knife back or blade, as distinct from the cutting edge, do not offer the same difficulty.

The Blade

Most tools can be made with as heavy a shank or body as is necessary for rigidly supporting the cutting edge. The saw, however, is an exception. By its very nature it is a thin tool. The policy of conservation in the wood industries is increasing the tendency toward greater thinness. While the saw blade has strength and rigidity in a direction truly normal to its thickness, it is weak and flexible under side strain. The rigidity of a saw has a direct bearing on the accuracy and smoothness of the cut produced. and on the rate of cutting, which are considerations of first importance. An increase in the blade thickness is the direct way to produce greater stiffness, but this method is prohibited by the equally important consideration of wood wasted. A material having a higher modulus of elasticity would give greater stiffness to bending, but there is no relief in sight. We have to be content with the 29,000,000 elastic modulus of steel.

The speed of a revolving circular saw and the static tension applied to a band saw furnish a stiffening effect which compensates in part for the flexibility of the disk or band.

A circular saw revolving at wood-cutting speeds involves the complicated mechanics of centrifugal stresses and also vibrations. The stresses set up by centrifugal force are low as compared with the strength of steel. A 16-in. saw revolving at 3600 r.p.m. has a maximum stress from centrifugal force of about 6000 lb. per sq. in., and this occurs at the center hole. But while this stress is not high, it does produce some stretch in the blade, which is not uniform from center to rim. These strains in turn, if uncompensated, result not. only in added lack of stiffness, but even in an actual fluttering of the rim.

To counteract the stretching from centrifugal force, the circular saw blade is given a prestraining operation called tensioning. This may be done by hammering, roiling, or otherwise, and results in a saw which will be "stiff" when up to speed. The stretching of the saw rim in work due to frictional heat is compensated for in the same manner. While the stresses set up by centrifugal forces are low, those induced by the pre-straining treatment are high.

The steel for the blade, after heat treatment, should combine: (1) High elastic limit, (2) good ductility, (3) resistance to fatigue cracking, (4) resistance to impact, and (5) uniformity. And because most saws in use today are of the solid-tooth variety, there is an additional qualification; namely, (6) satisfactory edge holding.

It is self-evident that the steel and its fabrication into saws must not be too costly. Another consideration that is becoming increasingly important is that the steel weld readily.

(1) High Elastic Limit. The saw blade shout behave as nearly as possible as a perfect spring.- Operating strains, due to centrifugal force, frictional heating, or other o al causes, should produce as little permanent distortion as possible. If a blade-is strained beyond the elastic limit, it will be stretched or distorted, and the saw will have lost its tension or have become uneven and lumpy. In any event, it will not rim true, and so will produce a poor cut and not stand up under heavy feed.

Plain carbon-tool steel, formerly used for all saws, could not be heat treated to the high elastic limits found desirable for the more modern production rates without an over-sacrifice of other essential properties. For instance, a high elastic limit would be accompanied by brittleness. The usual carbon content of the steels used was 0.85 per cent, although it might range as low as 0.70 per cent up to 1.10 per cent. The carbon content used depended there on the edge-holding requirements of the teeth, although high carbon was 'often selected for a thick plate so as to get better hardening.

Nickel was the first alloy used to any extent in saw steel. The object was to produce a stronger blade without sacrificing toughness. The nickel content ranged between 1.25 to .3.5 per cent, with carbon between 0.60 and 1.00 per cent, depending on the use of the saw. The plain nickel steel constituted a real advance in saw steels, and it is still used to some ex-tent. One objection to this steel is its tendency toward a. striated, crystalline structure which may result in spalling teeth. Another difficulty encountered in the use of this steel is sluggishness in tempering, some of the hardened steel structure remaining, with consequent brittleness. These objections are more often with when the nickel and carbon contents are on the high side. However, when on the low side the amount of benefit derived is open to question. The compositions shown in Table. 1, (a), (b), and. (e), are types still used to some extent.

The properties of nickel steels were so interesting that the next developments of alloy saw steels were mostly made with the view of eliminating its weak points by the use of one or more additional alloys. Following other alloy-steel developments, chromium was tried and found to give very high elastic limits, but at some sacrifice in ductility. The steel showed a tendency to be "brash," as the old sawmaker calls it when the steel will not stand considerable cold swaging without checking. Vanadium was added with the object of overcoming this "brash" condition, but without more than a partial cure. It does, how-ever, produce a marked increase in toughness. Nickel-chrome steels are used today for many saws where the ductility requirements are not severe. Typical compositions are shown in Table 1, (c), (d), (f), and (j). Chromium is an inexpensive alloy and in some compositions can be obtained from the scrap metal charged into the steel melting furnace. Chromium, too, in small amounts, enhances the hardening power of nickel steels and so aids the sew manufacturer in hardening the thicker saws.

Another attempt to obtain high strength, together with high values for the other essential properties, has resulted in nickel-molybdenum steels, both elements being present in small amounts. (Table 1 (g) shows a typical composition used very largely and with good results. The elastic limit can he made high without. sacrificing ductility and toughness. The types shown under (j) and (k) are very good steels where no cutting edge is involved.

(2) Ductility. The elastic properties of steel, together with its ductility, make possible the tensioning. or prestraining treatment essential to a hand or circular saw. Mechanical tensioning is done by hammering or cold-rolling selected areas of the saw. The raid working elastically expands the steel adjacent to the spots where the force is applied, the latter spots being permanently stretched. A steel low in ductility can be given but little deformation by the cold working without dangerously approaching the breaking point.
A phase of ductility, the ability to he cold-worked without. rupture, is an essential property of solid-tooth saws whose teeth are swaged for clearance.

The property of ductility is dependent, to a large degree, upon, the inherent quality of the steel as determined by the method, of manufacture and the quality of raw materials used. No alloy will compensate for inferior steel-melting practice.

As noted previously, chromium does not assist in developing ductility in saw steel. Nickel does help, and the combination with molybdenum, Table 1, (g), gives particularly good ductility with high elastic limit. Alloy steels have eliminated most of the body cracks which were fairly common in carbon-steel saws.

(3) Resistance to Fatigue Cracking. The high speeds and feeds at which production saws are now run have introduced new problems. Among these is the matter of gullet cracking, due to repeated stress below the elastic limit of the steel. Cracks of . this type can usually be identified by the lines of progressive growth on the adjacent surfaces of the fracture. Sharp angles or corners should never be allowed where there is repeated stress, but the saw user Alen allows this condition to exist. Gullet cracks sometimes occur which cannot be traced to any such self-evident cause. Those who have made extensive studies of the-phenomenon of fatigue cracking are generally agreed that the strength of steel to resist this type of failure bears a direct relationship to the ultimate! strength; also that the freedom of the steel from dirt and other inclusions halt a direct bearing on its resistance. If such is the case with saws, the present-day alloy steels, when clean and well made, should possess remarkable resistance. This is not always true, and there is reason to believe that fatigue cracks in band and circular saws may be caused by complicated stresses which are aggravated rather than relieved by high physical properties. Good ductility in the steel is a valuable asset, however.

Special measures can be used to largely prevent fatigue cracks from forming. Properly designed and spaced rim slots is one means often used. Another method frequently practiced, in band-saw mills, is to cold-work the bottoms of the gullets, thus stretching the metal at those points. Keeping the saw sharp and preserving well-rounded gullets and even tension are self-evident and worth-while precautions.

(4) Resistance to Impact. A saw in service is subjected to repeated blows. If the teeth are sharp and the saw is in good shape, the normal impacts of the teeth in the wood are not excessive. But other shocks incidental or accidental to service may be heavy. One form of accident often met with is striking a piece of steel in the cut. The old-type carbon-steel saw would be apt to crack under such treatment, or at least he put badly out of shape. A good alloy-steel saw will either cut through the steel or will have teeth sheared off, the blade itself being left in fair condition. Side shocks which would distort a low-elastic-limit carbon saw will have little effect on the alloy blade.

(5) Uniformity. A saw which has not uniform physical properties will never be a satisfactory tool. If the blade has hard or soft spots, it can only he made fiat with difficulty, it can-not be tensioned evenly, and it will not retain its trueness or tension in service. Lack of uniformity can be due to variations in steel composition or to faulty heat treatment. The first-mentioned cause is most apt to occur from failure to remove any decarbonized skin that may have been on the steel sheet. Faulty heat treatment is the usual reason for ununiformity and may result from poor heat-treating practice or by reason that the steel composition is unsuited to good hardening.

On account of the physical dimensions, saws must be hardened in a comparatively slow quenching medium such as oil. Carbon steels will not harden thoroughly in oil unless the piece is thin or unless it has been overheated, which is of course bad practice. . Carbon steels, therefore, cannot be considered as suitable for saws to meet present high standards unless they are of light gage.

The judicious use of small amounts of alloy will give the steel suitable hardening properties. For this reason many saws that are to be used only for work of the lighter so are made from low-priced alloy steels. Chromium is an alloy often used in this way, such as the composition shown in Table I, (h). Where a slightly, tougher steel is wanted composition (i) is a good choice.

Little need be said about the properties of the steel vacs m machine knives. Sufficient toughness is of course necessary, together with stiffness. Some types of knives, such as the hog and chipper, are subject to heavy impacts and pressures, and therefore the steel must possess more toughness than is needed for other kinds. The planer or finishing knife, on the other hand, will have sufficient strength if made out of a less tough material such as high-speed steel. Some typical compositions of solid knives are given in Table 2.

The Cutting Edge

The cutting action of a saw and of most knives is similar to that of other cutting tools. The wood is parted by a wedging action, and the power required is therefore a function of the cohesive strength of the material. When the wood is gummy, an additional factor of increased friction is introduced. No variety of wood is very strong as compared with metals, and therefore wood is said to be easy to cut.

There is, however, another and more vital factor than strength that enters into the cutting of wood, namely, abrasion. comparatively little power is required to sever the fibers of any wood while the tool is sharp. The condition may he short-lived, how-ever. The abrasive action starts at once to polish away the keen edge until, sooner or later, dullness results, enough to. cause poor cutting and excessive power consumption. The saw maker and user have not sufficiently appreciated the relation between sharpness and smoothness of cut. A saw tooth is ordinarily considered sharp if. it appears so to the naked eye, as it is left by a file or medium-grit abrasive wheel.

The abrasiveness of different woods varies very widely, even though their other properties may not be greatly different. An example of this difference is given by the test results shown in Table 3. The test was made with a 9-in, circular saw, electrically driven and with a positive feed, the wood being rip-cut.

Abrasion is a complicated phenomenon about which little is really known. The type of abrasion met with in wood cutting can be pictured as a buffing action, the abrasive being cellulose and mineral salts, including silica. To make a particular steel more resistant to abrasion, the first thought would be to make the tool harder. But here enters one of the curious features about abrasion, at, least under conditions met with in wood cutting. When the saw speed is very low, as in hand operations, greater saw hardness may result in increasing by several times the life of the edge. When the saw speed is high, however, as with a power tool, there is little difference in life between the harder and the softer tool. To obtain a marked improvement in edge-holding with fast-running tools it is necessary to change the steel composition.

The difference in tool life with change in tool speed and tool hardness, but with the same composition steel, is shown in Table 4. Although the material out was a wood substitute, the comparison will hold for wood. The saws were made of 0.901 carbon-tool steel.

It will be noted that at low speeds the increased life brought about by the greater hardness was 350 per cent, whereas at high speed the increase was only 20 per cent.

Another example of the effect of tool hardness on the edge-holding properties is shown in Table 5. The tool was a knife used in an automatic handle-turning lathe and made from 0.60 carbon-tool steel. The wood cut was maple, finishing 1 1/4 in. in diameter. The speed was 3200 r.p.m.

It is interesting to compare the results shown in Table 5 with those of Table 4. The increase of 12 to 14 points in Rock-well hardness between the 48 and the 62 hardness tools resulted in both cases in an increased. tool life of 20 per cent. It is seen from Table 5 that the extreme difference in tool hardness between the hardest, which was tempered at 350 deg. fahr. and file hard, and the softest, which was tempered at 90(1 deg. fahr. and easily filed, resulted in a difference in tool life of only 22 per cent.

The effect of changing the composition of the steel is shown in Table 6. The tools were operating on the same job as that' illustrated in Table ,5, except that the wood cut was cherry.

Their compositions are shown in Table 7.

It will be seen from Table 6 that the increase of carbon content, the, hardness being the same, in the plain carbon steels (a), (b), and (c) resulted in a consistent increase in tool life, up to 100 per cent. Also that the medium-nickel-low-chromium vanadium steel (d) gave about the same results as did the plain carbon steel (b) of like carbon content. The fact that the low-nickel-low-molybdenum steel (e) with comparatively low carbon; 0.76 per cent, had the same life as the higher carbon steel (d), is . interesting. It would indicate that a steel of greater toughness, resulting from the lower carbon, can be had with no sacrifice in cutting life. The high-speed steel tool (f) had an unusually low life for this kind of steel, most saw and knife applications showing about a 10 to 1 ratio in its favor as compared with carbon-tool steel

A significant point indicated by the foregoing tests is the far greater effect produced by a difference in carbon, as shown in Table 6, than by a difference in hardness, as reported in Table 5. The difference in hardness between high and low temper gave only. a 22 per cent variation in tool life, whereas difference in carbon between high and low gave 100 per cent.

It must be borne in mind that the conditions under which the saw or knife is operating may have a mark .l influence on the comparative performance of different steels. In certain applications a carbon or-low-alloy tool steel will give no service. Where the temperature developed in cutting is really high, only a material (as high-speed steel, for example) which remains hardat these temperatures will do the work. For some classes of work a. steel having a tungsten content of from 2 to 8 per cent will give better service than without the addition, although not so good results as will high-speed steel. It can be taken as axiomatic that the better a steel resists softening at elevated temperatures and also the type of abrasive wear met with in wood cutting, the better service it will give.

We can make use of the improved properties of the steels in either of two ways: to obtain longer tool life under the same conditions of operation, or to maintain the same tool life but at a substantially higher rate of production. In either case, to effect a major change in tool performance, our present-day steels all fell into either one of two classes, high-speed steels and all other tool steels.

For wood as well as for metal cutting, high-speed steel is the best type known today. It is enough superior to warrant wider application to wood sawing than is now the case. The wood-working industry should profit more from the example set by the metal-working industry and establish, by fundamental research, more data about cutting its product. If the results of such studies were at hand, we would not only be making more use of the best steels we now possess, but we also would be better' prepared for new developments in tool materials.

The recently developed cemented tungsten-carbide tool material will effect profound changes in wood cutting. It possesses toughness, together with hardness and resistance to abrasion, such that cutting speeds and quality of cut heretofore impossible will be obtained. A typical example of the results-being obtained with this material operating on a machine designed for high-speed steel tools is given in Table 8. The job was planning, tonguing, and grooving fireproofed oak flooring. The 10-in. cutter head was operating at a speed of 3600 r.p.m. with a feed of 80 f.p.m.


Other applications of cemented tungsten-carbide knives and also saws are -giving results similar to those indicated. The possibilities of such new materials cannot be ignored and can hardly be overestimated by the wood-cutting industry.


To one who has been in close touch with the recent developments of saw steels there is little in sight to premise further marked improvements in the solid-tooth type of saw. The two conflicting requirements for the one steel for the blade and for the cutting edge would seem to take us for further advances beyond the nature of this metal.

Up to 15 years ago, or thereabouts, the saw maker for a hundred years had spent an unbelievable amount of effort and ingenuity in effecting the best compromise possible with carbon steels. The next step was the development of an alloy-steel saw, with the object of producing a stronger blade and also to effect all possible improvement in edge-holding. A much better blade resulted, but even with the aid of. modem laboratories and metallurgical knowledge, there was little improvement in edge-holding properties, far from keeping pace with the potentialities of the new blade.

The next logical step is therefore to depart from the old-type saw sad use inserted teeth made from materials known to be well adapted for the function of cutting wood. In the field of metal cutting this same step forward was made years ago.

Future changes in saw design, so as to put to use metallurgical discoveries, will require the best thought of saw user, machine builder, and saw -maker. Research and untiring effort form the only road today to accomplishment, but the benefits in store for the woodworking industry are worth the struggle.


J. P. Potter (American Woodworking Company, New York, N. Y.): Most of the experience that the Writer has had in the woodworking field has been with saws and cutters. He has seen it pass from the old carbon steel to the high-tungsten steels and come on through to the cemented tungsten-carbide steel. A great many woodworking tools are made today without due regard to the safety of the swinging of steel and knives and saws, especially of the high frequency machine. When you go up to the neighborhood of 7200 to 9000, the centrifugal strains become very great. So far as is known, there has not been anything put on the market that offers absolute safety. The internal head or the solid-back head which was invented some 20 years ago comes the nearest to it, but it. will not support a cutter projecting more than three-quarters or one inch.

Speaking primarily about saws, the prepared paper seems to be a very elaborate proposition. It needs very little addition.

The things noticed in practice regarding saws are the extreme misunderstanding on the part of those using the steel in knowing what strengths are required from it.

The matter of Preparing steel for the shop is a subject which needs a lot of discussion. The stock patterns can be prepared in manufacturing plants far distant and remote from the point of manufacture and can be shipped in due time for ordinary purposes.

In plans for individuals, oftentimes one little house requires enough steel' to write off the cost of the manufacture. The use of cemented tungsten-carbide steel is also costly. The writer h found that on stock runs the steel costs relatively little in proportion to the amount of wood run. It will range somewhere from 2 to 4 cents per 1000 ft. On an ordinary mold of 3 in. width, it will run with about 5 or 6 in. of eel with a 6-knife equipment all around. Those 60 in. of steel will run about 4,000,000 lineal feet of molding before they are completely worn out. That has been proved in soft woods along the Pacific Coast.

With the higher priced steel, it becomes a question. By the per cent of this paper, the steel will run so much longer than the ordinary carbon-tool steel that perhaps there would be no limit to the wear of the cuts. That brings up another problem of using this steel properly supported in very thin sections.


The points brought out by Mr. Potter are of real practical interest. The present-day use of saws and knives at higher speeds is no exception to the modern trend, and, as Mr. Potter indicates, the necessary safety precautions must be taken, not only in the design of the tool, but also in its. use. A point in this connection may well be discussed briefly. An inserted-tooth saw or cutter head is usually refitted many times by the user. He must see to it that. the blade or head is not only properly refitted, but also that it is maintained-in good mechanical condition and balance. With higher speeds, the machine also must he kept in better shape than formerly was necessary.

In calculating the effect of centrifugal forces in rapidly revolving sews and knives, the subject should he considered from two angles. A revolving disk will have maximum stresses from centrifugal forces set up, not at the rim, but at the center hole. The stresses at the rim will he comparatively small. For ex-ample, a 16-in. blade with a 1-in. center hole revolving at 3600 r.p.m. will have stresses set up amounting to about 6000 lb. per sq. in. at the center hole and 1500 lb. per sq. in. at the rim. A 10-in. disk running at 7200 r.p.m. will result in about 9000 and 2000 lb. per sq. in. at the center and rim, respectively. These stresses are well within the factor of safety for a good steel and in themselves far from dangerous.

 Excessive rim-strains set up by poor tooth or cutter-edge clamping methods vibrations, and accidental strains in operation are far more dangerous than those from centrifugal forces. The added danger from centrifugal forces as speeds increase does not come about as much through the greater possibility of a well-made and properly operated tool being broken by these forces as by reason of the much greater damage done if breakage occurs. The energy of a piece flying off the rim of a saw or cutter in-creases as the square of the r.p.m. of the tool. Thus doubling the speed of the rim increases the energy by, four times, and protective measures must be bettered correspondingly.

Mr. Potter properly raises the question of economy in using expensive steels or tool materials for working-ordinary-woods. The relative tool costs must always be considered. An extreme case where a cheap steel is clearly good enough is where short runs of special molding shapes are made from soft wood with no particular requirement for surface finish. It would be poor economy to make an expensive tool only to discard it after a few hours' run. Special material like cemented tungsten carbide for woodworking is finding its first applications to production jobs where the wood is particularly abrasive and where machine down time or other-factors are important. Users are, however, beginning to. see its possibilities for more of their regular production work on common woods whose accuracy or smooth finish is desired. Its' use will grow as experience indicates its proper applications.