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Home , Parallel motion

The MUNCASTER . . ;& ”

steam-engine models Westbury ’ j 7-Entablature or table engines Continued from 2 May 1957. pages 634 to 636

N THE EARLY STAGES of its have the common feature of a flat acting type, having a sliding evolution, the steam-engine as- elevated table supported by four with bar slides. Both the baseplate I sumed various forms, some of (sometimes more) columns-compar- and the entablature are made from which, though now obsolete, are able in fact to the humble kitchen table. flat plate, the former being 1/4 in. thick Many of the classic examples of these with chamfered top edges, and the of great interest to the model engines had fluted Corinthian columns latter 1/8 in. The columns may be constructor. Design was influenced with decorated capitals and moulded built up, as indicated in the part by several factors, including ex- edges to the entablature. section, the ends being shouldered pediency or convenience in the down to form studs, with separate materials and methods of con- SIMPLE “ BASIC ” DESIGN capitals and pedestals fitted to them. struction available at the time; The engine illustrated in Fig. 34 This is economical with material, and also by traditional structural represents one of the simplest possible but I have a predilection for making . styles. designs in this class, being reduced things in one piece where this is I have already explained that the almost to the point of austerity, yet possible by straight-forward machining preferred position for the - fully in character. It is of the direct- and I think I should prefer to turn which was then usually the heaviest Fig. 34: A simple type of single-cylinder entablature engine single component-was on, the floor or bedplate; the difficulty of producing accurate straight slides, capable of resisting side thrust without undue friction, favoured the use of parallel motion for guiding the rod, or indirect action with long con- necting rods, such as in beam, return- and steeple engines. The class of engine known as the “ entablature ” or “ table ” engine made its appearance very early in the 1800s, but became most popular in the middle years of the century. Some very fine examples of these engines by Maudslay and other prominent makers , were shown at the 1851 Crystal Palace Exhibition; they varied a good deal in design, some being of the indirect- acting type, with the below the cylinder and the ex- tended upwards to a rather spidery crosshead from which motion was transmitted by side connecting rods to the crank. . Architectural term Others, such as the types illustrated here, had the cylinders mounted on the bedplate and the crankshaft rtl mounted on an elevated platform- probably the first attempt at what came to be known as “ direct-acting ” engines. In common with many other terms in , the word “entablature” is borrowed from architecture, being in fact a legacy from the classic Graeco-Roman era. Its definition (to quote a standard architectural text- book), is“ the horizontal member or members supported’ by the columns, and including the cornice, frieze and architrave.” All engines in this class, therefore,

MODEL ENGINEER 16 MAY 1957 * Fig. 35: Side view and motion-workplan of the double Fig. 36: End view and the entablature engine with parallel motion crosshead. cylinder plan of double engine them from 1/2in. square bar, leaving to the underside of the entablature, on both the an the flanges about 1/16 in. wide unmachined but the sliding surfaces must be eccentric rod; the crosshead is of H- at each end, with simple mouldings exactly vertical and parallel to the section with grooved faces to embrace adjacent to them and the rest of the cylinder axis both ways. It is probable the slide bars. Despite its simple shank tapered from 5/16 in. to 1/4 in. that these were intended to be forged construction, this design can be made dia. Needless to say, the length to shape, and machined or filed only into quite a handsome and dignified between flanges must be the same in on the working surfaces; but most model and an efficient worker. all cases, and not only must the flanges constructors will probably find it be square with the sides of the en- best to cut them from the solid. TWIN-CYLINDER OR “DOUBLE” tablature but the latter must also have The crankshaft, of the overhung ENGINES square corners, not rounded; as type, has a 1/4in. dia. main journal The two further examples of engines Muncaster says,“it is a sound rule and runs in plummer block bearings in this class, illustrated in Figs 35, 36 in architecture that no cylindrical mounted on the flat surface of the and 37, are both the “ double ” type; part appears about the square cap of entablature; the web or crank disc having overhung cranks at either end a column.” has a pin 5/32in. dia. fitted at 3/8in. of the shaft and a central flywheel; Brass is often used for the structural radius, either by screwing or pressing but the design could quite easily be parts of these steam-engine models in. A spoked flywheel, 3 in. dia., is adapted as a single-cylinder engine if on the grounds of appearance, or fitted and it may be observed that if desired. They are also much more avoidance of rust, but in the proto- character is to be as faithful as possible elaborate in design than the foregoing types nearly all parts were made of both the rim and spokes should be example and best suited to con- cast or wrought iron. The cylinder thinner than is usual in modern struction from castings, though many, is 3/4 in. x 3/4 in. , the design, practice. if not all, of the components could be including slide-, etc., following The eccentric is attached to the shaft produced by machining from solid or conventional practice. Piston and as close as possible to the main fabrication by brazing and soldering. valve rod glands have oval flanges bearing, thus serving as an end locat- The latter methods are often preferred and the sides of the stuffing-box on ing collar, and this should enable the by constructors who wish to obtain the cylinder cover have flat surfaces rod to be lined up with the valve rod the utmost accuracy in details such as for the attachment of the slide bars. without bending, which is always un- fluting and other forms of decoration, The latter are splayed outwards at sightly and frequently quite un- which was such an attractive feature the top, with horizontal lugs to fasten necessary. Forked ends are employed of these old engines. 16 MAY 1957 701 MODEL ENGINEER

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Very little descriptive matter was sides of the cylinders were used. crosshead bearings, the latter being furnished by Muncaster on these The use of a deep bedplate or forked. A belt-driven governor is engines; the drawings were considered plinth with the cylinder partly or fitted, operating a butterfly throttle to be self-explanatory, at least to those completely sunk into it, in conjunction on the steam supply line which readers who were sufficiently exper- with an equally deep entablature, not connects to the two cylinders by a ienced to be likely to take an interest only enhances the dignified appear- horizontal branch pipe. in their construction. Taken in con- ance of the engine, but by enabling When the drawings of these engines junction with previous examples of shorter columns to be used, increases were published one or two of the design and functional details, I the rigidity of the structure. details were mildly criticised by think that most of the essential in- In the two engines shown in Figs 35 meticulous students of period steam- formation will be found in the draw- to 37 it appears that two separate plinths engine design; for instance, it was ings. are employed,and also separate suggested that the flywheels had too The major difference between the entablatures in the form of box girders; great a radial depth of rim, and that engine shown in Figs 35 and 36, and but I should prefer to employ a four spokes should be used instead that in Fig. 37, is that the former was single plinth and a rectangular frame of six, also that the crankshaft should fitted with parallel motion to the entablature; even in an engine having be of square section, turned only on piston and the latter with only one cylinder this form of con- the journals, with the flywheel and slide bars; this would probably, but struction would give maximum eccentric sheaves staked on. not necessarily, be a guide to period, strength and simplify lining up. I have no doubt that the critics as the earlier engines were less likely Note that the columns are not were well informed, but apparently to be fitted with sliding crossheads. turned to a straight taper but are Muncaster made some concessions to In the particular type of parallel slightly convex or “ fish-bellied “; simplicity in castings and machining motion illustrated, the geometry is this is correct to architectural tradi- procedure-just as I do myself-and simple and obvious; it was used on tions and improves the appearance so if every example of a model purporting many types of engines, both hori- long as it is not overdone. In the to be a true period piece were as zontal and vertical, though in the details of column pedestals and correct as his drawings I for one should latter case the ends of the radius rods capitals on the right of Fig. 37, the be very well satisfied. Incidentally, the were more often anchored from exact shape of mouldings, etc., is drawings for Figs 35 and 36 were brackets fixed to the walls of the shown, most of the dimensions being made by my colleague, J. N. engine house than from columns; in. given m 32nds of an inch. The Maskelyne, and are a fine example of a few cases, however, short rods connecting rods have gib and cotter engineering draughtsmanship. anchored to lugs extended from the fixings for both the crankhead and l To be continued Fig. 37: Another double engine with sliding crossheads, showing details of columns

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MODEL ENGINEER 702 16 MAY 1957