James Nasmyth: Engineer; an autobiography Part 34

In order to obviate this inconvenience, I designed an arrangement of a key-groove mortising machine. It was capable of operating upon wheels of any diameter, having no limit to it capacity in that respect.

It was, at the same time, possessed in respect of the principle on which it was arranged, of the power of taking a much deeper cut, there being an entire absence of any source of springing or elasticity in its structure. This not only enabled the machine to perform its work with more rapidity, but also with more precision. Besides, it occupied much less s.p.a.ce in the workshop, and did not cost above one-third of the machines formerly in use. It gave the highest satisfaction to those who availed themselves of its effective Services.

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A comparison of Fig. 1--which represents the general arrangement of the machine in use previous to the introduction of mine--with that of Fig. 2, may serve to convey some idea of their relative sizes. Fig. 1 shows a limit to the admission of wheels exceeding 6 feet diameter, Fig. 2 shows an unlimited capability in that respect.

1836. An Instrument for finding and marking the Centres of Cylindrical Rods or Bolts about to be turned on the Lathe.

One of the most numerous details in the structure of all cla.s.ses of machines is the bolts which serve to hold the various parts together.

As it is most important that each bolt fits perfectly the hole it belongs to, it is requisite that each bolt should, by the process of turning, be made perfectly cylindrical. In preparing such bolts, as they come from the forge, in order to undergo the process of turning, they have to be "centred;" that is, each end has to receive a hollow conical indent, which must agree with the axis of the bolt.

To find this in the usual mode, by trial and frequent error, is a most tedious process, and consumes much valuable time of the workman as well as his lathe.

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In order to obviate the necessity for this costly process, I devised the simple instrument, a drawing of which is annexed. The use of this enabled any boy to find and mark with absolute exactness and rapidity the centres of each end of bolts, or suchlike objects. All that was required was to place the body of the bolt in the V-shaped supports, and to gently cause it to revolve, pressing it longitudinally against the steel-pointed marker, which scratched a neat small circle in the true centre or axis of the bolt. This small circle had its centre easily marked by the indent of a punch, and the work was thus ready for the lathe. This humble but really important process was accomplished with ease, rapidity, and great economy.

1836. Improvement in Steam-Engine Pistons, and in Water and Air-Pump Buckets, so as to lessen Friction and dispense with Packing.

The desire to make the pistons of steam-engines and air-pump buckets of condensing engines perfectly steam and water tight has led to the contrivance of many complex and costly constructions for the purpose of packing them. When we take a commonsense view of the subject, we find that in most cases the loss of power resulting from the extra friction neutralises the expected saving. This is especially the case with the air-pump bucket of a condensing steam-engine, as it is in reality much more a water than an air pump. But when it is constructed with a deep well-fitted bucket, entirely without packing, the loss sustained by such an insignificant amount of leakage as may occur from the want of packing is more than compensated by the saving of power resulting from the total absence of friction.

The first condensing steam-engine to which I applied an air-pump bucket, entirely without packing, was the forty horsepower engine, which I constructed for the Bridgewater Foundry. It answered its purpose so well that, after twenty years' constant working, the air-pump cover was taken off, out of curiosity, to examine the bucket, when it was found in perfect order. This system, in which I dispensed with the packing for air-pump buckets of condensing steam-engines, I have also applied to the pistons of the steam cylinders, especially those of high-pressure engines of the smaller vertical construction, the stroke of which is generally short and rapid. Provided the cylinder is bored true, and the piston is carefully fitted, and of a considerable depth in proportion to its diameter, such pistons will be found to perform perfectly all their functions, and with a total absence of friction as a direct result of the absence of packing. By the aid of our improved machine tools, cylinders can now be bored with such perfect accuracy, and the pistons be fitted to them with such absolute exactness, that the small quant.i.ty of water which the steam always deposits on the upper side of the piston, not only serves as a frictionless packing, but also serves as a lubricant of the most appropriate kind. I have applied the same kind of piston to ordinary water-pumps, with similar excellent results. In most cases of right packed pistons we spend a shilling--to save sixpence-- a not unfrequent result of "so-called" refined improvements.

1836. An instantaneous Mode of producing graceful Curves, suitable for designing Vases and other graceful objects in Pottery and Gla.s.s.

The mode referred to consists in giving a rapid "switch" motion to a pencil upon a piece of paper, or a cardboard, or a smooth metal plate; and then cutting out the curve so produced, and employing it as a pattern or "template," to enable copies to be traced from it.

When placed at equal distances, and at equal angles on each side of a central line, so as to secure perfect symmetry of form according to the nature of the required design, the beauty of these "instantaneous"

curves, as I term them, arises from the entire absence of any sudden variation in their course. This is due to the momentum of the hand when "switching" the pencil at a high velocity over the paper.

By such simple means was the beautiful curve produced, which is given on the following page. It was produced "in a twinkling," if I may use the term to express the rapidity with which it was "switched."

The chief source of the gracefulness of these curves consists in the almost imperceptible manner in which they pa.s.s in their course from one degree of curvature into another. I have had the pleasure of showing this simple mode of producing graceful curves to several potters, who have turned the idea to good account. The ill.u.s.trative figures on the next page have all been drawn from "templates" whose curves were "switched" in the manner of Fig. A.

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1836. A Machine for planing the smaller or detail parts of Machinery, whether Flat or Cylindrical.

Although the introduction of the planing machine into the workshops of mechanical engineers yielded results of the highest importance in perfecting and economising the production of machinery generally, yet, as the employment of these valuable machine tools was chiefly intended to a.s.sist in the execution of the larger parts of machine manufacture, a very considerable proportion of the detail parts still continued to be executed by hand labour, in which the chisel and the file were the chief instruments employed. The results were consequently very unsatisfactory, both as regards inaccuracy and costliness.

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With the desire of rendering the valuable services of the Planing Machine applicable to the smallest detail parts of machine manufacture, I designed a simple and compact modification of it, such as should enable any attentive lad to execute all the detail parts of the machines in so unerring and perfect a manner as not only to rival the hand work of the most skilful mechanic, but also at such a reduced cost as to place the most active hand workman far into the background.

The contrivance I refer to is usually known as "Nasmyth's Steam Arm."

None but those who have had ample opportunities of watching the process of executing the detail parts of machines, can form a correct idea of the great amount of time that is practically wasted and unproductive, even when highly-skilled and careful workmen are employed. They have so frequently to stop working, in order to examine the work in hand, to use the straight edge, the square, or the calipers, to ascertain whether they are "working correctly." During that interval, the work is making no progress: and the loss of time on this account is not less than one-sixth of the working hours, and sometimes much more; though all this lost time is fully paid for in wages.

[Image] Apparatus for enabling the machine to execute segmented work

But by the employment of such a machine as I describe, even when placed under the superintendence of well-selected intelligent lads, in whom the faculty of good sight and nicety of handling is naturally in a high state of perfection, any deficiency in their physical strength is amply compensated by these self-acting machines. The factory engine supplies the labour or the element of Force, while the machines perform their work with practical perfection. The details of machinery are thus turned out with geometrical accuracy, and are in the highest sense fitted to perform their intended purposes.

1837. Solar Ray Origin of the form of the Egyptian Pyramids, Obelisks, etc.

This will be found described summarily in the next and final chapter.

1837. Method of reversing the action of Slide Lathes.

In the employment of Slide Turning Lathes, it is of great advantage to be able to reverse the motion of the Slide so as to enable the turning tool to cut towards the Head of the Lathe or away from it, and also to be able to arrest the motion of the Slide altogether, while all the other functions of the lathe are continued in action. All these objects are attained by the simple contrivance represented in the annexed ill.u.s.tration.

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It consists of a lever E, moving on a stud-pin S, attached to the back of the head stock of the lathe T. This lever carries two wheels of equal diameter marked B and G. These wheels can pitch into a corresponding wheel A, fixed on the back end of the lay spindle.

When the handle of the lever E is depressed (as seen in the drawing) the wheel B is in gear with wheel A. while C is in gear with the slidescrew wheel D, and so moves the slide (say from the Head Stock of the lathe). On the other hand, when the lever E is elevated in position E", wheel B is taken out of gear with A, while G is put in gear with A, and B is put in gear with D; and thus the Slide is caused to move towards the Head Stock of the lathe. Again, where it is desired to arrest the motion of the Slide altogether, or for a time, as occasion may require, the lever handle is put into the intermediate position E', which entirely severs the communication between A and D, and so arrests the motion of the slide. This simple contrivance effectually served all its purposes, and was adopted by many machine tool-makers and engineers.

1838. Self-adjusting Bearings for the Shafts of Machinery

A frequent cause of undue friction and heating of rapidly rotating machinery arises from some inaccuracy or want of due parallelism between the rotating shaft or spindle and its bearing. This is occasioned in most cases by some accidental change in the level of the supports of the bearings. Many of the bearings are situated in dark places, and cannot be seen. There are others that are difficult of access--as in the case of bearings of screw-propeller shafts.

Serious mischief may result before the heating of the bearing proclaims its dangerous condition. In some cases the timber work is set on fire, which may result in serious consequences.

In order to remove the cause of such serious mischief, I designed an arrangement of bearing, which enabled it, and the shaft working in it, to mutually accommodate themselves to each other under all circ.u.mstances, and thus to avoid the danger of a want of due and mutual parallelism in their respective axes. This arrangement consisted in giving to the exterior of the bearing a spherical form, so as, within moderate limits, to allow it to accommodate itself to any such changes in regard to mutual parallelism, as above referred to. In other cases, I employed what I may call Rocking centres, on which the Pedestal or "Plumber Block" rested; and thus supplied a self-adjusting means for obviating the evils resulting from any accidental change in the proper relative position of the shaft and its bearing. In all cases in which I introduced this arrangement, the results were most satisfactory.

In the case of the bearings of Blowing Fans, in which the rate of rotation is naturally excessive, a spherical resting-place for the bearings enabled them to keep perfectly cool at the highest speed.

This was also the case in the driving apparatus for machine tools, which is generally fixed at a considerable height above the machine.

These spherical or self-adjusting bearings were found of great service.

The apparatus, being generally out of convenient reach, is apt to get out of order unless duly attended to. But, whether or not, the saving of friction is in itself a reason for the adoption of such bearings.

This may appear a trifling technical matter of detail; but its great practical value must be my excuse for mentioning it.

1838. Invention of Safety Foundry Ladle.

The safety ladle is described in the text, p. 202.

1838. Invention of the Steam Ram

My invention was made at this early date, long before the attack by the steam-ram Merrimac upon the c.u.mberland, and other ships, in Hampton Roads, United States. I brought my plans and drawings under the notice of the Admiralty in 1845; but nothing was done for many years. Much had been accomplished in rendering our ships shot-proof by the application of iron plates; but it appeared to me that not one of them could exist above water after receiving on its side a single blow from an iron-plated steam-ram of 2000 tons. I said, in a letter to the Times, "As the grand object of naval warfare is the destruction by the most speedy mode of the ships of the enemy, why should we continue to attempt to attain this object by making small holes in the hull of the enemy when, by one single masterly crashing blow from a steam ram, we can crush in the side of any armour-plated ship, and let the water rush in through a hole, 'not perhaps as wide as a church door or as deep as a well, but 'twill serve'; and be certain to send her below water in a few minutes.*

[footnote...

In these days of armour-clad warships, when plates of enormous thickness are relied on as invulnerable, our Naval Constructors appear to forget that the actual structural strength of such ships depends on the backing of the plates, which, be it ever so thick, would yield to the cramming blow of a moderate-sized Ram.

I published my description of the steam ram and its apparatus in the Times of January 1853, and again addressed the Editor on the subject in April 1862. General Sir John Burgoyne took up the subject, and addressed me in the note at the foot of this page.*

[footnote...

The following is the letter of General Sir John Burgoyne:

WAR OFFICE, PALL MALL, LONDON, 8th April 1862.

"General Sir John Burgoyne presents his compliments to Mr. Nasmyth, and was much pleased to find, by Mr. Nasmyth's letter in the Times of this day, certain impressions that he has held for some time confirmed by so good an authority. "A difficulty seems to be antic.i.p.ated by many that a steamer used as a ram with high velocity, if impelled upon a heavy ship, would, by the revulsion of the sudden shock, be liable to have much of her gear thrown entirely out of order, parts displaced, and perhaps the boilers burst. Some judgment, however, may be formed on this point by a knowledge of whether such circ.u.mstances have occurred on ships suddenly grounding; and even so, it may be a question whether so great a velocity is necessary. "An accident occurred some twenty years ago, within Sir John Burgoyne's immediate cognisance, that has led him particularly to consider the great power of a ship acting as a ram. A somewhat heavy steamer went, by accident or mismanagement, end on to a very substantial wharf wall in Kingstown Harbour, Dublin Bay.