As with many other original-minded mechanics, invention became a habit with him, and by study and labour he rarely failed in attaining the object which he had bent his mind upon accomplishing. Indeed, nothing pleased him better than to have what he called "a tough job;" as it stimulated his inventive faculty, in the exercise of which he took the highest pleasure. Hence mechanical schemers of all kinds were accustomed to resort to Clement for help when they had found an idea which they desired to embody in a machine. If there was any value in their idea, none could be more ready than he to recognise its merit, and to work it into shape; but if worthless, he spoke out his mind at once, dissuading the projector from wasting upon it further labour or expense.
One of the important branches of practical mechanics to which Clement continued through life to devote himself, was the improvement of self-acting tools, more especially of the slide-lathe. He introduced various improvements in its construction and arrangement, until in his hands it became as nearly perfect as it was possible to be. In 1818, he furnished the lathe with a slide rest twenty-two inches long, for the purpose of cutting screws, provided with the means of self-correction; and some years later, in 1827, the Society of Arts awarded him their gold Isis medal for his improved turning-lathe, which embodied many ingenious contrivances calculated to increase its precision and accuracy in large surface-turning.
The beautiful arrangements embodied in Mr. Clement's improved lathe can with difficulty be described in words; but its ingenuity may be inferred from a brief statement of the defects which it was invented to remedy, and which it successfully overcame. When the mandrill of a lathe, having a metal plate fixed to it, turns round with a uniform motion, and the slide rest which carries the cutter is moving from the circumference of the work to the centre, it will be obvious that the quantity of metal passing over the edge of the cutter at each revolution, and therefore at equal intervals of time, is continually diminishing, in exact proportion to the spiral line described by the cutter on the face of the work. But in turning metal plates it is found very in expedient to increase the speed of the work beyond a certain quantity; for when this happens, and the tool passes the work at too great a velocity, it heats, softens, and is ground away, the edge of the cutter becomes dull, and the surface of the plate is indented and burnished, instead of being turned. Hence loss of time on the part of the workman, and diminished work on the part of the tool, results which, considering the wages of the one and the capital expended on the construction of the other, are of no small importance; for the prime objects of all improvement of tools are, economy of time and economy of capital—to minimize labour and cost, and maximize result.
The defect to which we have referred was almost the only remaining imperfection in the lathe, and Mr. Clement overcame it by making the machine self-regulating; so that, whatever might be the situation of the cutter, equal quantities of metal should pass over it in equal times,—the speed at the centre not exceeding that suited to the work at the circumference,—while the workman was enabled to convert the varying rate of the mandrill into a uniform one whenever he chose. Thus the expedients of wheels, riggers, and drums, of different diameters, by which it had been endeavoured to alter the speed of the lathe-mandrill, according to the hardness of the metal and the diameter of the thing to be turned, were effectually disposed of. These, though answering very well where cylinders of equal diameter had to be bored, and a uniform motion was all that was required, were found very inefficient where a Plane surface had to be turned; and it was in such cases that Mr. Clement's lathe was found so valuable. By its means surfaces of unrivalled correctness were produced, and the slide-lathe, so improved, became recognised and adopted as the most accurate and extensively applicable of all machine-tools.
The year after Mr. Clement brought out his improved turning-lathe, he added to it his self-adjusting double driving centre-chuck, for which the Society of Arts awarded him their silver medal in 1828. In introducing this invention to the notice of the Society, Mr. Clement said, "Although I have been in the habit of turning and making turning-lathes and other machinery for upwards of thirty-five years, and have examined the best turning-lathes in the principal manufactories throughout Great Britain, I find it universally regretted by all practical men that they cannot turn anything perfectly true between the centres of the lathe." It was found by experience, that there was a degree of eccentricity, and consequently of imperfection, in the figure of any long cylinder turned while suspended between the centres of the lathe, and made to revolve by the action of a single driver. Under such circumstances the pressure of the tool tended to force the work out of the right line and to distribute the strain between the driver and the adjacent centre, so that one end of the cylinder became eccentric with respect to the other. By Mr. Clement's invention of the two-armed driver, which was self-adjusting, the strain was taken from the centre and divided between the two arms, which being equidistant from the centre, effectually corrected all eccentricity in the work. This invention was found of great importance in ensuring the true turning of large machinery, which before had been found a matter of considerable difficulty.
In the same year (1828) Mr. Clement began the making of fluted taps and dies, and he established a mechanical practice with reference to the pitch of the screw, which proved of the greatest importance in the economics of manufacture. Before his time, each mechanical engineer adopted a thread of his own; so that when a piece of work came under repair, the screw-hob had usually to be drilled out, and a new thread was introduced according to the usage which prevailed in the shop in which the work was executed. Mr. Clement saw a great waste of labour in this practice, and he promulgated the idea that every screw of a particular length ought to be furnished with its appointed number of threads of a settled pitch. Taking the inch as the basis of his calculations, he determined the number of threads in each case; and the practice thus initiated by him, recommended as it was by convenience and economy, was very shortly adopted throughout the trade. It may be mentioned that one of Clement's ablest journeymen, Mr. Whitworth, has, since his time, been mainly instrumental in establishing the settled practice; and Whitworth's thread (initiated by Clement) has become recognised throughout the mechanical world. To carry out his idea, Clement invented his screw-engine lathe, with gearing, mandrill, and sliding-table wheel-work, by means of which he first cut the inside screw-tools from the left-handed hobs—the reverse mode having before been adopted,—while in shaping machines he was the first to use the revolving cutter attached to the slide rest. Then, in 1828, he fluted the taps for the first time with a revolving cutter,—other makers having up to that time only notched them. Among his other inventions in screws may be mentioned his headless tap, which, according to Mr. Nasmyth, is so valuable an invention, that, "if he had done nothing else, it ought to immortalize him among mechanics. It passed right through the hole to be tapped, and was thus enabled to do the duty of three ordinary screws." By these improvements much greater precision was secured in the manufacture of tools and machinery, accompanied by a greatly reduced cost of production; the results of which are felt to this day.
Another of Mr. Clement's ingenious inventions was his Planing Machine, by means of which metal plates of large dimensions were planed with perfect truth and finished with beautiful accuracy. There is perhaps scarcely a machine about which there has been more controversy than this; and we do not pretend to be able to determine the respective merits of the many able mechanics who have had a hand in its invention. It is exceedingly probable that others besides Clement worked out the problem in their own way, by independent methods; and this is confirmed by the circumstance that though the results achieved by the respective inventors were the same, the methods employed by them were in many respects different. As regards Clement, we find that previous to the year 1820 he had a machine in regular use for planing the triangular bars of lathes and the sides of weaving-looms. This instrument was found so useful and so economical in its working, that Clement proceeded to elaborate a planing machine of a more complete kind, which he finished and set to work in the year 1825. He prepared no model of it, but made it direct from the working drawings; and it was so nicely constructed, that when put together it went without a hitch, and has continued steadily working for more than thirty years down to the present day.
Clement took out no patent for his invention, relying for protection mainly on his own and his workmen's skill in using it. We therefore find no specification of his machine at the Patent Office, as in the case of most other capital inventions; but a very complete account of it is to be found in the Transactions of the Society of Arts for 1832, as described by Mr. Varley. The practical value of the Planing Machine induced the Society to apply to Mr. Clement for liberty to publish a full description of it; and Mr. Varley's paper was the result.[3] It may be briefly stated that this engineer's plane differs greatly from the carpenter's plane, the cutter of which is only allowed to project so far as to admit of a thin shaving to be sliced off,—the plane working flat in proportion to the width of the tool, and its length and straightness preventing the cutter from descending into any hollows in the wood. The engineer's plane more resembles the turning-lathe, of which indeed it is but a modification, working up on the same principle, on flat surfaces. The tools or cutters in Clement's machine were similar to those used in the lathe, varying in like manner, but performing their work in right lines,—the tool being stationary and the work moving under it, the tool only travelling when making lateral cuts. To save time two cutters were mounted, one to cut the work while going, the other while returning, both being so arranged and held as to be presented to the work in the firmest manner, and with the least possible friction. The bed of the machine, on which the work was laid, passed under the cutters on perfectly true rollers or wheels, lodged and held in their bearings as accurately as the best mandrill could be, and having set-screws acting against their ends totally preventing all end-motion. The machine was bedded on a massive and solid foundation of masonry in heavy blocks, the support at all points being so complete as effectually to destroy all tendency to vibration, with the object of securing full, round, and quiet cuts. The rollers on which the planing-machine travelled were so true, that Clement himself used to say of them, "If you were to put but a paper shaving under one of the rollers, it would at once stop all the rest." Nor was this any exaggeration—the entire mechanism, notwithstanding its great size, being as true and accurate as that of a watch.
By an ingenious adaptation of the apparatus, which will also be found described in the Society of Arts paper, the planing machine might be fitted with a lathe-bed, either to hold two centres, or a head with a suitable mandrill. When so fitted, the machine was enabled to do the work of a turning-lathe, though in a different way, cutting cylinders or cones in their longitudinal direction perfectly straight, as well as solids or prisms of any angle, either by the longitudinal or lateral motion of the cutter; whilst by making the work revolve, it might be turned as in any other lathe. This ingenious machine, as contrived by Mr. Clement, therefore represented a complete union of the turning-lathe with the planing machine and dividing engine, by which turning of the most complicated kind might readily be executed. For ten years after it was set in motion, Clement's was the only machine of the sort available for planing large work; and being consequently very much in request, it was often kept going night and day,—the earnings by the planing machine alone during that time forming the principal income of its inventor. As it took in a piece of work six feet square, and as his charge for planing was three-halfpence the square inch, or eighteen shillings the square foot, he could thus earn by his machine alone some ten pounds for every day's work of twelve hours. We may add that since planing machines in various forms have become common in mechanical workshops, the cost of planing does not amount to more than three-halfpence the square foot.
The excellence of Mr. Clement's tools, and his well-known skill in designing and executing work requiring unusual accuracy and finish, led to his being employed by Mr. Babbage to make his celebrated Calculating or Difference Engine. The contrivance of a machine that should work out complicated sums in arithmetic with perfect precision, was, as may readily be imagined, one of the most difficult feats of the mechanical intellect. To do this was in an especial sense to stamp matter with the impress of mind, and render it subservient to the highest thinking faculty. Attempts had been made at an early period to perform arithmetical calculations by mechanical aids more rapidly and precisely than it was possible to do by the operations of the individual mind. The preparation of arithmetical tables of high numbers involved a vast deal of labour, and even with the greatest care errors were unavoidable and numerous. Thus in a multipltcation-table prepared by a man so eminent as Dr. Hutton for the Board of Longitude, no fewer than forty errors were discovered in a single page taken at random. In the tables of the Nautical Almanac, where the greatest possible precision was desirable and necessary, more than five hundred errors were detected by one person; and the Tables of the Board of Longitude were found equally incorrect. But such errors were impossible to be avoided so long as the ordinary modes of calculating, transcribing, and printing continued in use.