Reed 8: From iron to steel

Working of iron was still by primitive means for the various parts of a locomotive through the decade when George Stephenson was holding the fort alone, and for years thereafter. Eventually manufacture and machining of wrought, rolled and cast irons were brought near perfection, but by then the production of steel had become technically and commerically sound, and the gradual change from iron to steel as the basic material transformed the structure of the locomotive and permitted the increase in size and power required by the growing industrialisation of the country.

Increased tensile and shearing strengths were the main reasons for the change to steel, enabling greater loads to be taken through the same scantlings, and permitting increase in size and power without proportionate thickening of the material. Where ductility or wearing qualities were needed, iron was given up slowly, and Low Moor iron boilers, wrought iron wheel centres and cast iron axleboxes and guides continued to be made until the 1890s. Rolled steel for most purposes was higher in first cost than iron until a decided cheapening through 1881-5. Cast steel was always higher in price per ton than cast iron, but its greater strength and resistance in all aspects except wear, permitted economic replacement of complex iron and steel forgings where the number off was sufficient to cover the cost of patterns.

Cogitation on the hand-made taps and dies used by George Stephenson at Killingworth, displayed at York, will give some idea of what many early locomotive constructors had to contend with, remembering that for an appreciable part of annual working hours such tools were used by candle light and dim natural light. Stephenson probably made those taps himself; they were not of Maudslay's triple-pass type that later became standard.

Though better facilties were denied Stephenson, concurrently Henry Maudslay was approaching the zenith of his powers at his new Lambeth factory. With him began the science of precise engineering measurement and the use of metals and machines that could repeat the precisions. He developed the first accurate plane surfaces for machine tools, the first accurate lathes with iron beds, and the first precision power-driven screw-cutting lathes with slide rests and in which threads of any pitch could be cut by a combination of gear wheels and a changeable lead screw. He evolved standard nuts and bolts for use in his own factory, made the first iron floor cranes, and trained up in high-quality production a succession of leading engineers, two of whom directly (Richard Roberts and James Nasmyth) and one indirectly (Joseph Whitworth) profoundly influenced locomotive manufacture. The Maudslay works remained in business with a high reputation until 1899, and in them was trained Collett, the penultimate chief mechanical engineer of the GWR, who made notable advances in Swindon shop practice and equipment.

Machine tools of the quality and accuracy of Maudslay's did not spread widely through industry as it then was, but after 1836 methods in locomotive factories developed to suit the increasing demand. In the late 1830s skilled and forward engineers such as Richard Roberts and Daniel Gooch were using templates to ensure the same leading dimensions through a batch of hand-made locomotives, in Gooch's case for engines built at several widely-separated works. More accurate manufacture was helped by the limited adoption of gauges for the measurement of certain details. Roberts introduced this in 1825 for textile machinery and used it to some extent in locomotives before 1840 and more widely thereafter. McConnell of the Southern Division of the LNWR recorded in the late 1840s that a few years before he had received from Sharp Roberts a spare cylinder that needed no fitting up and went into its place exactly, and spoke of this as altogether exceptional.

General closer tolerances and more accurate measurement and machining as a matter of daily practice on a wide scale could not come until Joseph Whitworth's introduction of 'master' plane surfaces, 'go and not go' gauges, and standard sizes and threads for nuts and bolts, the germ for all of which he had gathered in his time at Maudslay's works, where small 'plane tables' were used for workers to test the smoothness of their work. Before 1848-50 every bolt was made up as an individual piece from a rough bar or forging, and innumerable thread pitches and forms existed. Many bolts, and even other small forgings, were made up to sketches prepared by the erecting charge-hand when he found just what he needed for the work in hand.

Growing availability of rolled iron plates up to the maximum needed for locomotives from around 1855-60 brought possibilities of considerable im- provement in locomotive construction. Inside and outside frame plates hitherto had been built up of sections forge-welded together, and either cut by hand or trimmed up and surfaced by hand after sim- ple drilling and slotting of part of the profile. Big advances in machine tools were made through the 1850s, but no planing machine could deal at one pass with the flat top edge of a locomotive frame 20ft or more in length. Items such as cylinder flanges and faces and motion plates were only partly machined, and 'shaping' was still by hand chisel, file and scraper, and individually fitted by the same tools, though frame slotters were in use from the 1840s.

These manufacturing methods, the crude shops, primitive lighting, and under-developed power supplies and drives enforced the adjustable bearings and other details that were universal. Wedge and gib-and-cotter adjustments for big and small ends and for coupling rod ends enabled service wear in the brasses to be taken up, but their primary purpose was to cover inaccuracies in machining and first erection. Not uncommon works records of those times could read 1/16in or tin short in distance between driving and trailing wheels, tin long between driving and front wheels, and 1/16in or more out of square between one side and the other. Shop drawings of connecting and coupling rods often gave no centre-to-centre length, this being ad- justed by the forge-men to the requirements of the charge-hand erector. One of the first things Ramsbottom had to do on taking charge of Crewe works in August 1857 was to have added to each drawing a note 'Work to dimensions'.

Richard Roberts devised a simple planer in 1817 for small general work, but a big step forward did not come until 1842 when Whitworth began produc- tion of his reversible-toolbox planer that could cut in each direction. Gradually these and rugged shapers (developed much by Nasmyth), si otters, drills and screw-cutting lathes of greater range and accuracy found their way into locomotive shops, and though they did not approach the thousandth of an inch standards of modern times, or even the one sixty-fourth of the 1920s, they served their purpose. Indeed, they sometimes served more than their pur- pose; simple and robust shapers and slotters bought in 1847 were still in use at Crewe works at the time of the 1923 Grouping. They were samples of an ob- solescence that enforced the complete reorganisation and re-equipment of that plant over the years 1924-28 by the new owner, the LMS.

Principal practical defect of the steam locomotive was that by the whole nature of the reciprocating direct drive, and the way the chassis developed, it became the most effective wear-producer known, engendering friction in a hundred flat and cylin- drical metal-to-metal surfaces throughout the length and breadth of engine and tender, moving over each other all the time, and some of them subject to no lubrication from one year's end to another. Added to this friction were constant shocks from the reciprocating drive and from the movement over the  track. In the driving mechanism alone, for example, a GNR Atlantic on a journey from London to York experienced 95,000 reversals of stress, plus 25,000 separate uncushioned shocks on each wheel-and- axle pair through rail joints and points which had to be taken up by springs to prevent transfer in toto to the rest of the machine.

All this required constant maintenance and periodic heavy repair and renewal, involving high wages costs, great capital investment, and substan- tial continuous expenditure on spares, machine tools and plant. Yet directors were generally reluctant to sanction expenditure, particularly of new capital, on machinery or works extensions.

From the time of the SDR railways established their own works for locomotive major repairs, but with growth in mileage, traffic and engine stock the original works could not always be extended. As early as 1840 the GJR had to consider moving its works from Edge Hill, Liverpool, to a more commodious site, and at this juncture Joseph Locke, as chief engineer, proposed that future locomotives should be built at the new factory. This was largely because Locke was being forced to the idea of a new standard locomotive to replace the troublesome Patentees from several makers with which the GJR had been worked since 1837. The result was Crewe works, which completed its first new locomotive in 1843.

Other railways gradually followed suit in one degree or another. Opposition could not be raised by private builders at that time because the quite un- developed industry was rarely keeping pace in design or in quality of construction, though certain builders such as Step hens on and Sharp Roberts in- fluenced general design from the outset. In 1850 Locke gave 43 the construction cost of locomotives built at Crewe as less by the 20 per cent profit he presumed was made by private builders. Robert Stephenson at once refuted this by saying that on the last œ240,000 worth of machinery built at the Newcastle factory there had been a loss of £1,200, and he quoted figures from the LMR to show that the claimed cheaper cost of railway-built locomotives, said to be £400 less than bought-in locomotives, did not include all materials, or any allowance for coal, power, capital, rent, rates or taxes.

This remained a contentious point to the end of steam. Naturally financial overheads per new locomotive would tend to be smaller in a works whose main business was the steady overhaul of 10 to 20 times the number of new locomotives built than they could be in a factory devoted to new con- struction with a fluctuating demand, and one in which locomotive building was the sole or main source of profit instead of a working expense.

Midland Kirtley outside-frame 2-4-0 of the 1860s, as No 1 58A in the M R duplicate list. Some of these engines lasted into LMSR days and this one has been preserved.

Following in the wake of the great Maudslay- trained engineers a generation of locomotive works engineers arose in the 1850s that revolutionised the standards and equipment of manufacture and materials. Prominent were Charles Beyer, Henry Dubs and John Ramsbottom, each of whom had spent a time when young at the Manchester works of Sharp Roberts and must have been influenced directly by the mechanical genius of Richard Roberts.

In later years Beyer (1854-5) and Dubs (1863) were able to plan and erect complete locomotive- building plants of their own in which maximum use was made of the latest machine tools, gauges and templates, and in which provision was made for sub- sequent works extensions as part of a planned whole and without upsetting the nucleus or the work flow,

Beyer, as chief engineer of Sharp Bros, had appreciated Whitworth's standardising and measuring work, and from the beginning Gorton Foundry production was based on true plane surfaces, stan- dard threads, plug gauges, and the use of the so- called graduating machine, which in essence was a screw-cutting lathe with precision-made lead screw and a measuring attachment on the slide rest to mark pieces for machining, and to make other measuring items, such as patternmakers' rules, for distribution through the shops. Beyer, who had a name for elegance in design, believed in robust con- struction before appearance in order to maintain for as long as possible in service the accurate centre lines and squareness he had taken some trouble to achieve, and from Gorton Foundry beginnings he used lin main frames whenever he could on six- wheelers of 20 to 30 tons, and some of which lasted from 1860 to 1920.

Ramsbottom's main task from 1857 was the com- plete reorganisation of Crewe works from a factory with 'hand-made' productions in which startling departures from marked dimensions were permitted, to a works whose products were based on accurately made standardised components and capable of handling about 1000 heavy repairs a year con- trasted with 400 14 years earlier. Ramsbottom was an unusual combination of good organiser, compe- tent administrator, and practical engineer. From the 1850s there was wide acceptance of his inventions of the split piston ring, safety valve, double-beat regulator, screw reverse, cylinder lubricator, feed pump regulation, and, after his death, of the water pick-up he had invented and applied on the LNWR in 1860. At Longsight and Crewe from 1842 to 1871 he was constantly devising new machines and processes to do work more accurately and cheaply.

Matthew Kirtley, locomotive superintendent of the Midland from 1847 to 1873, was an engineer to whom little credit has been given for his works practice and administration. As a designer he was noted for robustness, rather than for innovation, though from 1862-3 he combined both in 0-6-0s with frames slotted from rectangular rolled plates that gave greater support round the horns. He had final responsibility for the brick arch and firehole deflector development outlined in Chapter 7; he pushed the development of welded iron boilers into the strongest of the time in the late 1850s and 1860s; and under him was initiated at Derby works over the years 1858-63 what was probably the first attempt at a limits-and-fits system of gauging in a railway-owned works.

This last-named activity was based primarily on Whitworth's practice and the development of his plane surface into a marking-off table for details nd a more accurate procedure in setting up frames in the erecting shop. Precision (for the time) moulding was also introduced in the foundry, particularly for cylinder castings, this at a time when high quality, toughness and wearing properties of cast iron were being achieved. By 1855-8 the shrinkage in iron castings was only half what it had been 15 to 20 years earlier. This helped precision, and also changed the patternmakers' and moulders' arts; and to historians it also illuminates some of the difficulties of the early builders in getting sound cylinders and locomotives.

North Eastern long-boiler 0-6-0 of the early 1860s. Sandwich frame flitching plates still with rivetted horn plates; dome 35 per cent of boiler diameter.

From the 1820s rolled iron plates around tin thick suitable for locomotive boilers could be ob- tained from Longridge's Bedlington Ironworks, but until the mid-1830s they rarely exceeded 4ft square; by 1837-8 4ft plates of 7ft to 8ft length were available. A Planet locomotive with a boiler barrel 3ft dia by 5ft long and a 4ft by 2ft 6in outer firebox required 22 plates, which was not much improvement over the 28 to 36 plates in the Wylam locomotives 15 years before. Joints throughout were of the lap type, and everyone was liable to leak for neither the accuracy of surface nor the skill in hand rivetting, lapping and caulking was high. The butt strap and joint were later developments, and in locomotive work seem to have come first at the works of Sharp Bros around 1847.

Available plate sizes grew slowly, and for years the larger sizes were adopted reluctantly because homogenity could not be guaranteed, particularly when thickness got above tin. Even in 1847 the firebox wrapper of the broad-gauge Iron Duke, then the largest locomotive boiler in the kingdom, was made up of five separate lap-jointed plates. By that time Yorkshire iron had gained its reputation for boiler plates, largely because William Fairbairn's tests of 1838 showed it to have an ultimate tensile strength some 10 per cent above the Derbyshire, Staffordshire and Shropshire brands, and with superior homogenity.

Early domes were small in size, being limited by boiler plate dimensions. The huge domes of the 1840s and 1850s were practicable structurally only when a barrel ring could be obtained in one plate. Those great domes helped the dry pipe to function more in accordance with its name, but were a source of weakness as the diameter of some was 35 per cent of the barrel diameter. No early solution was found to the method of water-sealing the firebox at the bottom or at the firehole.

Hand rivetting was universal until the 1860s and the results given by early power rivetters were not always superior in tightness or speed of work. Rivet holes were punched, not drilled, through the plates until the 1870s, and even then punching was often preferred for iron boilers as giving slightly conical holes that were better filled by the hot hand-driven rivets. Punching and shearing machines came into use in the 1840s, but only with steel boilers did drill- ing of rivet holes become general. Power flanging over blocks was unknown until the mid-1850s; before that square corners joined by angle irons were not uncommon for outer fireboxes.

Because of low barrel pitch quite a number of boilers from 1835 to 1855 were made two or three inches oval with the shorter axis across the barrel, in order to get in the maximum number oftubes, and had a row of stays across the minor axis.

The amount of handwork needed for quarter of a century on barrel and firebox plates well warranted the term boilersmiths. It also helped to limit boiler pressures, and the 120psi adopted for the Jenny Linds in 1847 needed exceptional care in boiler making. A dozen years later pressure still normally did not exceed 1201b, but by then boiler manufac- ture was more accurate and under greater control, and double-rivetted butt straps were in more general use for longitudinal seams. Pressures above 150psi could scarcely be used until double-strap butt joints, steel plates and drilled holes came into vogue. Longitudinal lap seams were always a source of weakness as long cracks tended to develop close to them where the shape departed from the truly cir- cular and two plate thicknesses became one. This started the path to many of the boiler explosions that occurred until the mid-1880s though the final cause was usually the lack of inspection of the boiler interior. The go-as-you-please policy of the time, which in locomotive departments reached its peak on the NER under Edward Fletcher, gave that com- pany 10 out of the 16 locomotive boiler explosions recorded over the years 1875-80. Board of Trade enquiries often showed a complete lack of internal inspection. The many fewer boiler explosions of the 20th Century were nearly always due to running with low water, resulting in a collapsed firebox crown rather than a rupture of the shell, though a notable exception was the 1922 Buxton explosion of an LNWR 0-8-0 due to safety-valve binding.

In the late 1850s the Midland developed forge-welded boiler rings, with each ring united to the next by a lOin wide shrunk-on external hoop double rivetted, and with the front of the first ring thickened for flanging outwards to take a flat tubeplate. By 1866 there were 19 such boilers at work in which the centre shrunk-on ring also form- ed the dome base. Manufacturing cost was said to be œ465 against the œ415 for the structure of a normal lap-rivetted boiler 4ft dia by 11ft barrel length. 44 The system was to be adopted permanently, but seems to have died out with the change in superintendents in 1873.

In 1859 The Engineer stressed: 'Steel in locomotive construction must largely replace iron,' and in that year odd applications to boiler shells were made on the GNR and in 1862-3 on the GWR. By 1862 Krupp was prepared to roll steel plates in widths up to 15ft, which made possible single-ring barrels, but many years elapsed before that feature was established, first in Gresley's 2-6-0 No 1000 on the GNR in 1920. Possession of a Bessemer steel rolling mill from 1866, plus Webb's experience in the steel industry 1866-70, led the LNWR to pioneer the consistent manufacture of steel boilers from 1872, but Webb was then following a policy in- itiated by his predecessor, Ramsbottom, and his suggestion of all future boilers in steel put to the directors in January 1872 was based specifically on the condition of a prototype steel boiler built in 1865.

Several Planet and Bury engines on the LMR had iron inside fireboxes, as had the American Norris engines on the Birmingham & Gloucester 1839-42, and there were always a few locomotives running about with iron inside boxes until the 1870s. Steel fireboxes were tried on the Maryport & Carlisle and Scottish Central in 1862-4 and on the Caledonian in 1870-1, all these being good water lines, and on the North London in 1873-7, but only the two first named had any success. The NLR boxes had to be withdrawn after less than 100,000 miles.

Despite the efforts of Webb on the LNWR steel never caught on in Britain for inside fireboxes until Bulleid began to apply them on the SR in 1941, though there was the mass application to the Railway Operating Division (ROD) 2-8-0s in 1917-19, but when those engines came back on to British railways many of the steel boxes were re- placed by copper.

Reluctance to use steel fireboxes was not because British steel was inferior. Many boxes of English and Scottish plates were put into export orders and gave satisfaction; but no persevering attempt was made on a British railway despite the potential saving in weight and cost, partly, in this century, because with large locomotives working under high load factor and watered at widely separated points, water softening was needed. In his experiments Webb set out to do more than get a steel box; he sought to eliminate side stays and reduce others, and to prevent super rigidity that might bring cracks. He also put in water bottoms, combustion chambers and other novelties, and so in the end he achieved unsatisfactory results in 1888-90 with both his square corrugated box and his figure-8 shape.

The thin-spoked one-piece cast iron wheels of the Killingworth and early SDR engines were almost the weakest part of the locomotive, partly because the crankpin was attached crudely to one of the spokes and breakages were incessant. The cast iron two-piece plug wheels used on the SDR from 1826-7 (see Chapter 3) even by 1845 had practical applications limited to a top speed of 15mph in com- bination with a maximum axle load of 8 to 10 tons. Tyre developments on these and other early wheels have been mentioned in Chapter 3. The first separate tyres at Killingworth and Hetton, and probably the first few of those on the SDR, were hand forged and had variations in thickness and from the true circular shape, but by 1830 Bedlington had begun to roll flanged tyres, though of course the final weld had still to be made before shrinkage on the rim.

Richard Roberts patented in 1832 a wheel with wrought iron spokes having T -heads at the outer ends rivetted to wrought iron rims, but the Sharp Roberts engines for the Dublin & Kingstown in 1834-5 had cast iron wheels with the same spoke section. Bury's early 2-2-0s and 0-4-0s generally had wheels akin to those of the Roberts 1832 patent. Robert Stephenson's 1833 patent." for cast iron naves and wrought iron rims connected by malleable iron gas pipes set at alternate slopes was the last, and not very successful, endeavour before acceptance of wrought iron spokes and rims as the only method giving sufficient strength and reliability. Occasional fully wrought wheels were known from 1836-7, but until around 1850 with a few ex- ceptions the cast iron hub was retained and various methods adopted for the connection to it of wrought iron spokes.

Through the late 1830s and 1840s forging of wheel centres was entirely by hand. One spoke was forged to one curved rim section and each end of the section forged to the next. At Sharp Roberts three or four spokes were forged to a flat rim section, and then these flat assemblies were forged into one and the whole bent hot round a cast iron centre former that had projections to determine the spoke position; finally an iron hub was cast round the inner ends of the spokes. Despite the labour and expense in forging this procedure was economic because the wheels of Sharpie 2-2-2s were standard over considerable numbers, and as they were for inside-cylinder single drivers they had not the complication of a crank arm. Some tender wheels of this Sharpie construc- tion lasted on Hayling Island into this century, and the tyres were observed to be fastened by deeply countersunk bolts passing right through tyre and rim, a method used on occasion into the 1860s.

Spokes as a rule were either circular or rec- tangular in section, tending towards the latter. A few ECR 2-2-2s of 1844 had driving and carrying wheels in which the major axes of adjacent spokes were at right angles to each other. From 1844 to 1849 Stephenson long-boiler and other engines had spokes and rims formed of T-angles, two of which were set back to back to give a cruciform spoke sec- tion; by this means the cost of a full forging was ob- viated. Well over 1000 such wheels were made for English-built long-boiler engines. Many Hawthorn engines for slow-speed service from 1847 to 1851 had solid iron wheels, both coupled and carrying, as had some earlier machines by Shepherd & Todd. These were cheaper than forgings but had a limited range and were noisy.

Nasmyth's steam hammer, invented 1842, came into more general use from around 1850 and helped the whole wheel-making process, which then remained much the same until wrought wheels were replaced gradually by steel castings from 1884-6. From 1855-6 Beyer Peacock forged each spoke solid with a segment of the hub; the several sections were connected at the hub through keys of green iron driven into diamond-section keyways and this iron being more easily fused than the steel of the hub formed a sort of flux that helped the hammer welding.

Some of the finest specimens of wrought iron were the 7ft 9in centres of the Conner 8ft 2in 2-2-2s on the Caledonian and the 7ft 8in centres of the Stirling 8-footers. The former had 28 spokes and for the first time crescent balance weights were forged integral with the rim; the latter had 24 spokes and square-ended balance weights. Cast steel wheels were used for the Stirlings from 1887. This material was introduced first in 1884 on GER 2-4-2Ts for driving and coupled wheels and from the previous year in carrying wheels. Long before this, at the London exhibition of 1862, several crucible cast steel wheels were shown, including a wheel-and- crank-axle set by Naylor with 7ft corrugated disc centres, the corrugations being not primarily for transverse strength but to facilitate pouring. Stamped wheels, also, were introduced at that time by Owen of Rotherham, but they seem to have been confined to rolling stock.

Cast iron centres were used often for industrial shunters and also in the late Victorian period for shunters and local mineral engines on the GWR, GER and one or two Scottish railways. Webb applied cast iron driving and coupled wheel centres with H-section spokes to about 1400 coal and shunting engines with 4ft 3tin tread diameter from 1872 to 1900 and they gave excellent service. The last great application of cast iron wheel centres was to the Austerity 0-6-0ST shunters of World War II, when cast steel was in short supply and the locomotives themselves were stipulated to be capable of four or five years of arduous work and then could go for scrap. In fact most of them were in service for a score of years without any wheel troubles, and a few more were built for the NCB in post-war years.

In November 1840 Daniel Gooch took out a pa- tent for putting a steel wearing surface on iron tyres, and such tyres were used on GWR engines through Gooch's time at Swindon, and a grinding machine was devised to true the hard surface. From 1856 crucible cast steel tyres were in limited use on the NLR, ECR and LNWR largely through the sales efforts of Longsdon, the English representative of Krupp, and only the high cost retarded a much wider adoption.

The first Krupp set went on to one of the NLR four-coupled tanks in 1856; by May 1859 it had run 64,280 miles for a tread wear of 0.3in, said to be one-third the wear of a normal tyre but with a purchase price eight times greater. This wear rate was equalled on the ECR on which a set of Krupp tyres introduced in April 1857 showed no need for a re-turning after 80,000 miles. The NLR had another 12 engines equipped 1857-8 and when they had reached 44,000 miles no turning was needed, whereas a comparison set in Yorkshire iron had to be removed after 34,000 miles and two re-turnings. Several sets of Krupp tyres were fitted by the LNWR in 1858.

From 1860 crucible cast steel tyres became more general, but after the LNWR opened its Bessemer steel plant in 1866, rolled steel tyres replaced the crucible cast type and soon a thousand a year were being made at Crewe on a method evolved by Ramsbottom making use of powerful horizontal duplex steam hammers to get the ingot ready for the rolling mill.

The steam hammer in locomotive factories accelerated and consolidated the manufacture of such large constituents as axles and reversing shafts, and lighter hammers eased the rapid production of innumerable smaller items like intermediate valve spindles, eccentric rods, crankpins, brake hangers and draw hooks, and were of great utility when steel began to be used for such parts in the 1860s. In particular, the manufacture of wrought iron crank ax- les was improved and the reliability of the material enhanced because the cranks could be forged by bending and the fibre of the iron maintained through the axle uninterruptedly. From the 1830s forging had had to be done laboriously with three or four separate pieces forge-welded together to form half an axle, and then the two halves were lapped together over the centre section for the final forging into one piece.

Krupp steel axles came into limited use from 1859. The LNWR ordered a double-throw four-bearing axle for one of McConnell's big 18in outside-frame 2-2-2s of the 300-class in 1859 at a cost of œ231 but only on the condition that the maker would replace it free on any defect or rupture except one due to a derailment. At the same time one axle of Lancashire steel and two from Sheffield were bought at a cheaper price. Sheffield forged steel crank axles came first in 1866 with trials on two or three railways, but crank axles of that type did not supersede wrought iron for another 20 years or so except at Crewe.

Perfection of forging processes and improvement in steel increased the number of inside-cylinder locomotives in the late Victorian age until in 1897 there was scarcely a railway building outside- cylinder locomotives when only two cylinders were used; but with the larger engines constructed from 1899-1900 increasing cylinder diameters and piston thrusts caused a reversion to outside cylinders or the adoption of multi-cylinder propulsion, because when cylinders were increased above 19tin dia space could not be found for adequate axle and crankpin journals and web widths plus four eccentrics.

With the increasing stresses doubt also arose as to crank axle steel characteristics, some lines like the Midland favouring a 'soft' steel of low tensile strength and great ductility while others like the NER preferred harder steels of 38-40 tons/sq in ultimate strength. To get full advantage of the latter, and to ease the whole manufacture, built-up crank axles were introduced on some railways. They were made practicable by the higher standard of shop methods, and here again Webb was a pioneer for he introduced the first one in the late 1890s and is believed to have used a low nickel steel. Large rolled iron plates transformed main frame design, strength and manufacture principally because numerous bolted and rivetted connections along the side plates could be eliminated and no working could occur between individual frame and horn plates. In this aspect the plate frame was ahead of the bar frame, for not until the casting of a whole side frame in one piece in the 20th Century could a main bolted joint at a highly stressed location be eliminated from bar frame construction.

By the 1860s single rolled iron plates to suit 2-4-0s and 0-6-0s were available though not in general use, but by then in the larger works the old type of sectional frame was being welded up under l0cwt steam hammers. Advantage was sometimes taken of the sectional method to enlarge the area round driving and coupled axleboxes to get the box central in the frames, and even, as in the Met tanks at a width of 5in, to act as the axlebox guide thrust face. In some designs this thickened section was used to change the distance between frames fore and aft of it to get an extra two or three inches firebox width or to suit cylinder spacing. By the time of these developments frame conditions themselves had eased through the elimination of the frame-firebox tie-in and the substitution of expansion brackets, so that despite greater locomotive size and power the frames from the 1860s were a far more rigid and better maintenance proposition than those of the 1840s and 1850s.

With the increase in size of rolled plates, progressive steps had to be made in machine tools that could handle them, but probably not until the Smith & Beecroft machine introduced 1858-9 was there a frame slotter of accuracy able to take more than one set of frame plates. For long years thereafter the method of frame contouring remained awkward. From the rectangular plate the contour was shaped roughly by punching or drilling overlapping holes round a template, annealing and straightening to remove any strains caused by punching, and then putting six to 10 plates together on a slotter for the final machining, after which the plater and his mate with large hammers gave a final straightening to individual plates laid on large cast iron slabs.

Steel plates without any thickening over iron permitted higher piston loads to be absorbed and greater weight supported, but in the 20th Century with larger 4-4-2, 4-6-0 and 4-6-2 locomotives the almost standard 1in was thickened whenever weight permitted to 1tin and even 1tin; so small an addition as 1/16in was appreciated by some designers. Cross staying was the weak point, though alleviated by the use of steel castings for inside motion plates. Some of these castings, as on GCR 4-4-2, 4-6-0, 2-8-0 and 2-6-4T classes, were used to give great support at the location where the frame plates were set in at the front to clear the side movement of guiding wheels.

Only in the twilight of steam were horizontal or racking stays adopted to any extent. They were difficult to apply with inside cylinders or inside motion, and an advantage of outside-cylinders with outside valves and motion was always the possible stronger frame structure – if designers were so minded. They were not always so minded, because long decades of inside cylinders and motion and flabby frames brought designers to a self-defensive postulate that frames ought to be made deliberately with a little lateral flexibility. So frames became the weak point in large 20th Century multi-cylinder locomotives such as the GWR four-cylinder types and the LMS Royal Scots. By 1939 not one of the 79 Gresley 180lb and 220lb three-cylinder Pacifies of 1922-34 was still running with its original frames," and rate of Royal Scot frame cracks had more than quadrupled in six years.

Not until the Bulleid Pacifies of 1941 did a designer show how ample horizontal bracing could be provided with an inside cylinder, crank throw and motion. The later BR two-cylinder 4-6-2s and 2-10-0s with clear space between the frames also had full racking stays. In all three classes just mentioned was revived the old Beyer-Met practice of the frame centred above the axleboxes; and the BR types also followed the practice evolved on the LMS of link-and-pin cross tie-rods between the frames at the horns, and manganese steel liners for boxes and horns that greatly reduced the wear.

Towards the end of steam the composition of the usual 26/30-ton mild steel for frames was adjusted to suit oxy-acetylene flame cutting, for that process reduced considerably the time taken in preparation and machining. Then steel suitable for welding was introduced with small quantities of copper, chromium and manganese, and ultimate strengths up to 35-40 tons/sq in. By this means many bolted and rivetted connections could be obviated and the whole frame structure made up as one piece, an idea foreshadowed in England in 1869 when Webb had proposed that 'the frames, cross stays and back carriages are cast in steel with the necessary hornblocks enclosed and fixed in one piece'. Undeveloped foundry and machining techniques at that time prevented practical application.

From 1920 alloy steels were used increasingly for driving parts partly to cope with rising piston thrusts but mainly to reduce the weight of reciprocating and revolving parts that had to be balanced by weights in the wheels, and to decrease hammer blow. Only the GWR retained carbon steel for these constituents, but by heat treatment increased the strength to 38-40 tons/sq in. This railway also kept to rectangular sections for coupl- ing rods. Other Group lines used 3 per cent nickel steel and nickel-chrome-molybdenum steels up to 60-65 tons/sq in ultimate strength, and favoured pronounced l-sections for connecting and coupling rods, sometimes with webs only tin thick. To reduce weight and eliminate joints Gresley forged the piston and rod in one piece of nickel steel, a practice tried by Hackworth in 1849 and by McConnell in the 1850s with wrought iron.

Efforts to balance revolving weights are believed to have been made late in 1837 by Dawson, running foreman on the London & Southampton at Nine Elms with a panel between two spokes opposite the crank, and this was noted and adopted by Sharp Roberts in 1838 but with weights in the rims. In the latter year Heaton, who had been balancing stationary engines from 1810-12, made suggestions for balance weights in the wheels and some Bury four-wheelers on the London & Birmingham were so treated. Working independently, Hunt on the North Union in 1839-40 fitted weights to the driv- ing wheels of Bury 2-2-0s primarily to try and ease pronounced fore-and-aft surging that was breaking intermediate drawbars. In 1844 Gray balanced the wheels of his large 0-6-0s on the Hull & Selby. From this time the practice of adding weights to the wheel rims or boss opposite the crank arm grew slowly.

The early efforts related only to revolving weights. The first man to suggest balance of reciprocating parts was]. G. Bodmer in a patent of 1834 for an opposed-piston engine, and in the 1840s two or three of his locomotives were tried on the London & Brighton and South Eastern railways but with an ingenious arrangement that brought the drive from both pistons out of the back end of the cylinders. First to make the compromise of balancing reciprocating parts by revolving weights in the wheels was ]. Fernihough, ex-Bury locomotive superintendent of the Eastern Counties in 1844. He may have been led to this by a letter from T. R. Crampton to The Railway Times in 1843 drawing attention to the 'unbalance' arising from reciprocating parts but offering no suggestions. The practice of balancing reciprocating parts really ex- tended only after the publication in 1855 of D. K. Clark's Railway Machinery in which he gave the rules and proportions to be observed.

Clark's recommendation that two-thirds of the reciprocating weights should be balanced in the wheels derived from his experience with 2-2-2s, 2-4-0s, 0-4-2s and 0-6-0s of 20 to 30 tons weight, but was largely perpetuated in Britain until after World War I, no more understanding of the com- promise principle having been attained than in the case of slide valves and valve motions. The LMS class 5 4-6-0s with 6ft wheels and 66 per cent of the reciprocating weights balanced in the wheels showed a clear wheel lift of 2in at speed of 7.8 revs/sec, cor- responding to 100mph, and of course the wheel came down with a corresponding blow.

Only the investigations of the Bridge Stress Committee in the early 1920s showed this proportion to be needlessly high in the large engines of the time and could be reduced without deleteriously affecting the riding and with benefit to the bridges, because at 5 revs/sec the hammer blow from driving wheels of some of the engines tested was 50 per cent more than the static axle load. An immediate result was that civil engineers raised from 20 to 22 tons the permissible axle load for carefully balanced multi-cylinder locomotives, but close attention had to be paid to low hammer blow per wheel, per axle, per rail and per engine.

To ease the wear on axleboxes and guides resulting from the different angles of drives and coupling rods on the two sides, Stroudley (LBSCR), Dean (GWR), Hill (GER) and others from time toú time on inside-cylinder locomotives put the driving crank and coupling rod crank on each side at the same angle. This practice brought a bigger balance weight in the wheel but did not increase the hammer blow. It was followed as late as 1928 in the two-cylinder ex-GER type 4-6-0s built by Beyer Peacock for the LNER. Partial balance of inside-cylinder locomotives could be achieved by prolonging the crank webs, more conveniently with built-up crank axles, though Bury is credited with beginning the practice in forged axles on the London & Bir- mingham by 1845. Only Drummond on LSWR 4-4-0 and 0-4-4T locomotives from 1903 to 1911, beginning with the 395-dass 4-4-0 seems to have carried this idea to the pitch where weights in the wheels were considered unnecessary, crankweb prolongations countering both revolving and reciprocating masses.

Four-cylinder locomotives with 180° cranks had almost self-balancing reciprocating masses. However, after Wilson's engine of 1825 no four-cylinder non-articulated locomotives saw service in this country until the conversion of NBR 4-4-0 No 224 to a tandem compound in 1885 and of two similar arrangements on the GWR in 1886, but all these were two-crank engines. The first four- cylinder engines with both inside and outside cranks were Webb's compound 4-4-0s on the LNWR and the Manson simple-expansion 4-4-0 on the GSWR, both in 1897. Manson's object may have been better balance, though the existing inside-cylinder 4-4-0s on the GSWR rode as well as any inside-cylinder 4-4-0s. Four-cylinder engines with the 135° crank setting to get a more even torque and more equable blast on the fire (North Stafford 0-6-0T of 1922 and SR Lord Nelson 4-6-0 in 1926) could be balanced satisfactorily.

Like four-cylinder types, three-cylinder engines were better balanced in regard to longitudinal forces than two-cylinder forms, so much so that Bulleid did not balance any portion of the reciprocating weight in his SR Pacifies and the engines did not suffer thereby at any speed up to the 95-100mph they reached occasionally. It was the balancing aspect, and not more even torque or greater power, that led to the first three-cylinder locomotives, built in 1847 at Newcastle in accordance with the Stephenson-Howe patent No 11086 of 1846. Here the two outside cylinders had cranks on the same centre line, with the inside crank at right angles to them. These two locomotives were long-boiler 2-2-2-0s for the York, Newcastle & Berwick, but one of them made some trips on the Southern Division of the LNWR in 1847. The idea behind this was tried also on a two-cylinder engine with cranks at the same angle by Sinclair on the ECR in 1856, but the uncertain starting and uneven torque made the experiment brief.

Next three-cylinder engine was a mineral 0-6-0 built in the shops of the Blyth & Tyne Railway in 1868 under John Kendal, but here the reason was to get greater power and more even torque, for the cylinders were of normal diameter whereas the three cylinders of the 1847 engines had a combined volume scarcely more than that of the standard two-cylinder long-boiler 2-2-2-0s of the time. For home use three-cylinder simple-expansion propulsion was not applied again until the end of 1902, in the GER 0-10-0T, which was a very definite attempt to get even torque and high accelerative capacity, but three-cylinder compounds of Webb type were running from 1882.

Fig 17 Welded steel inside and outside fireboxes of the SR Merchant Navy Pacifies, showing location of the two thermic syphons. Inner firebox plates tin thick. Net volume of inner firebox and combustion chamber about 275 cu ft. Firedoor was steam operated