PADDLES

E D G A R T . WESTBURY

describes a set of engines suit-

able for powering a 6 ft. paddle

steamer

THE POWER UNIT described is adevelopment of an earlierdesign published in response

to the requests of many readersfor information on engines of asuitable type for the propulsion ofworking model paddle steamers.So far as can be gathered, this wasthe first time a complete design ofa specific type for such a purposehad been published and, previousto the issue of proper information,many builders of this popular andpicturesque class of model steam-shiv had installed engines of quiteuncharacteristic design.

There are, however, some notableexamples of paddle boats with enginesof correct type, one of the best knownbeing Mr. Eltridge’s Royal Sovereign.

Diagonal engine advantagesThe diagonal arrangement of steam

engines was employed extensively inpaddle steamers of all types from aboutthe middle of last century onwardsand may be regarded as a definitemilestone in the development ofmarine engines, following up the veryearly types such as the sidelever andthe oscillating cylinder engine. Itsprincipal advantages over the latterwere that it overcame its drasticlimitations in length of stroke, affordedbetter accessibility and allowed theengine weight to be distributed over agreater area of the hull.

For engines intended to produce ahigh torque at low speed, a longstroke in relation to bore is mechani-cally desirable as it increases theleverage applied to the crank withoutimposing abnormal bearing loads.

MODEL ENGINEER

So reliable and efficient did this type ofengine prove for its purpose that itwas universally favoured in GreatBritain for all types of paddle steamers,including small tugs, harbour tenders,passenger boats and ferries, up to atleast the first 20 years of this century.

The later examples were usually ofthe compound type, with two ormore cranks and, particularly in thecase of tugs, engines in two self-contained halves were used, with aclutch in the centre of the shaft so

that the port and starboard enginescould be uncoupled and manoeuvredseparately to facilitate steering.

The design featured here is notclaimed to be a true scale model ofany particular full-sized prototype, butis intended as a practical power unitfor a working model steamer, ofgenerally correct character, with avoid-ance of features which would bedefinitely out of place in a marineinstallation of this type. I make thisclear in order to forestall any possible

General view of the engines

732 17 NOVEMBER 1955

criticism from the purists who mayfind that I have omitted a few minordetails or made the bolts and nuts outof scale !

There is a definite distinction be-tween true scale models of engines andthose intended to perform a full-timejob of work. but that is no excuse formaking the latter crude in appearanceor completely out of character. Theengine room of a model steamer, eventhough it may lack complete fidelityin every detail, can be made to producethe authentic atmosphere and in nocase is this more marked than in apaddle steamer.

Made on the premisesThe set of engines illustrated (in-

cidentally, I would point out that inmarine terminology engines are al-ways referred to in the plural-not“ an engine.” but “ a set of engines “)has been constructed in the M.E:workshops under my supervision byJ. Message with a view to provingthe practical merits of the design andthe working out of all machining andfitting operations.

In the course of building the set ofengines, a number of minor modifica-tions have been found desirable andthese have been incorporated in thedrawings so that these differ in detailfrom the design published in ModelShips and Power Boats and also theblueprints subsequently issued. This

does not render the latter obsolete, asmany of the details are optional and,in common with most of my enginedesigns, are capable of adaptation tosuit the varying requirements of con-structors, or application to differenttypes of hulls.

In the matter of dimensions, it mayperhaps be considered by some readersthat the engine is on the large side forpopular demand, but my experienceleads me to the conclusion that themost successful prototype model boats,from the navigational aspect, arethose of fairly large size and a 6 ft.boat does not look very big when it isout in the middle of the pond.

Scaling-down suggestionIt is, of course, quite possible to

build the engines to a smaller scaleand I suggest that for those who wishto install them in a smaller hull, say4 ft., all the dimensions could bereduced in scale proportion to two-thirds, giving a bore and stroke of1/2 in. by 1 in.

If made much smaller than this,however, some of the operations wouldbe rather finicky and it would bedifficult to preserve scale proportionsthroughout while ensuring robustnessof the working parts. Marine enginesof all kinds lead a very strenuous lifeand must be sound in wind and limb.

Unlike locomotives, in which byfar the greater stresses and strains

are encountered when starting fromrest and the load is considerablydecreased when running at full speed,ships engines, whether driving paddlesor screws, meet very little resistancewhen starting, but heavy collar workwhen under way.

General designIn the general arrangement draw-

ings. the side elevation shows thecylinder and the crosshead of one“ engine ” in section. The obliqueplan, also in part section, viewed fromsquare-on to the cylinder centre line,shows half the complete set, as theother half is identical, though mirror-reversed.

The two cylinders are inclineddownward at an angle of 20 deg.to the horizontal driving on to separ-ate but permanently coupled single-throw cranks, which may be madeintegral with the actual paddle shaftsor connected by flange couplings.(Some engines, it may be noted, havebeen spur geared to the paddle shaftsand it is possible to incorporate thisfeature if desired.)

The simple or single-expansion typeof engine is used because it is not onlvless complicated but also generallyfound more satisfactory than thecompound engine in small sizes-theadvantages of the latter could hardlybe realised at all without the additionof an efficient condenser.

17 NOVEMBER 1955 733 MODEL ENGINEER

1

I

In the structure of the engine.steel plates are used, mainly in theinterests of simplicity. Althoughmost large paddle engines employedmore o r less complex structuralcastings, often incorporating a surfacecondenser and other working parts,the use of plate frames was by nomeans unknown in the smaller andless elaborately-equipped engines.

The main bearings are of the splittype, rectangular in external shapeand carried in hornblocks attached tothe top of the frame plates. In thisand several other features there is asimilarity to locomotive practice sothere will be little difficulty in buildingthe components. Not many castingsare necessary and those that are usedare of simple and straightforwardnature.

Temporary arrangementsIn the photographs of the engine,

which were taken when it was firstset up for running in and testing, itwill be seen that in place of the centrecoupling, a flywheel has been fittedto the middle of the shaft. This is a

Reversing gearWhile it is not absolutely necessary

to provide means of reversing modelmarine engines, since nearly all activerunning of the boat on the pond canbe confined to one direction-fullahead-it is a great convenience,besides adding to realism, if it canmanoeuvre in either direction.

This is particularly important if theboat is radio-controlled, which isquite practicable in a model steamerof the size specified, though the onlyradio-controlled paddle boats I haveseen have been electrically propelled.There are, however, an increasingnumber of constructors who seek toescape the limitations of electricpower and are tackling the problemof remote control on steam and petrol-driven boats.

The great majority of marine steamengines, of all types, are fitted withStephenson’s link reversing gear, andit would be very difficult to improveupon it for this particular purpose.Alternative forms of valve gear, suchas Joy, Hackworth and Marshall, etc.,are by no means unknown on marine

temporary fitting, intended not onlyto provide some momentum in theabsence of the paddle wheels, butalso to serve as a brake drum toenable the engine to work under load.

Another temporary feature is thelever fitted to the weigh shaft formoving the links to reverse rotation.

Castings and parts for the construc-tion of these engines are obtainablefrom Messrs. A. J. Reeves of

MODEL ENGINEER

engines, however, and may haveadvantages in certain cases.

The “Eagle” class of Thames paddlesteamers had Walschaerts gear, which,so far as my experience goes, is veryunusual in marine practice and it issignificant that in a well-known marineengineering text-book, known collo-quially as “the greaser’s Bible,” allthe above gears except the Walschaertswere described. While it is possible toring the changes and adapt other

734

forms of valve gear to this set ofengines, therefore, there seems littleto be gained by doing so.

The launch linkThe type of link used in these

engines is appropriate to marinepractice and is generally termed the“ launch ” link. It gives the maximumvalve travel for a given eccentricthrow, but is somewhat more liableto errors in timing, due to die slip, thanthe original link used by Stephenson.

These links do not show in the sideelevation of’ the engine and are onlyseen from the top edge in the half-plan, but will, of course, be fullydetailed in a later issue.

They are controlled by a weighshaft which runs right across the topof the engine and is connected to thereversing control, as mentioned, bysuitable linkage, according to theposition found most convenient for thelatter.

Before commencing the construc-tion of the engine (assuming that it isto be fitted to a hull) the space avail-able for its accommodation, and themeans of installation, should becarefully considered. In most cases itis possible to provide a flat surface onthe floor of the hull so that the twoflat soleplates shown on the drawingscan be firmly screwed down to providea true and rigid foundation.

Alternative mountingIf, however, a flat surface is not

available, some alternative method ofmounting which will enable theframes to be equally well secured,with no stresses tending to twist themout of line, must be built into the hullstructure. It is obviously desirable tokeep the engine fixings as simple aspossible so that it can be installedand dismounted without undue diffi-culty.

Location will, of course, be deter-mined by the shaft position, as laidout in the hull design and the correctdepth of immersion of the paddleshas an important influence on theirefficiency so that the displacementdepth of the hull, fully loaded, mustbe taken into account.

The fore-and-aft position of thepaddle shaft is also subject to varia-tions in hull design; generally it is asnear amidships as possible and theengines may be either forward or aft,as may be most convenient. To obtaina compact layout of the steam plant,the boiler will need to be placed asclose to the engines as possible, at theshaft end and it is generally possibleto adjust the trim of the hull by shift-ing auxiliary gear as required.

If the hull design allows, the crank-shafts may be extended outwards sothat the paddle wheels may be mounted

17 NOVEMBER 1955

illustration on

directly on them, but more often thannot it will be found necessary to fitseparate paddle shafts, with flangecouplings to line up with the engineshafts.

AN ELECTRIC

The arrangement of the engine and the width of the complete set isshown, with the cylinders on the out- also adjustable to suit hulls of varyingside and valve gear on the inside, will beam.generally be found best for access- l Further details of the engine willibility, but may be reversed if desired, be given in the issue of December 1.

(Continued from page 731)CLOCK

Before any further work can be carried out on thecoil assembly, the frame itself must be accuratelylocated on its pivots between the plates. The bestway to do this is to secure the three columns to back

I plate and insert the bottom pivot of coil frame intoits bearing hole. Place front plate into position,and secure it with three 6 B.A. screws. The longstaff extension now projects through the 7/16 in. crutchboss hole. Now, place the cock-piece into position,with outer pivot in its appropriate hole. Slide cock-piece to the left; until the upper right hand corner isalmost in line with the edge of plate. Lightly clampit in this position, using a watchmaker’s hand vicefor the purpose.

Juggle the cock about until coil staff is exactly

I vertical and the frame swings freely on its pivotsat which point mark off the cock anchorage screwposition through the hole already drilled and removethe cock-piece. Drill and tap the hole 6 B.A. and

. replace the cock, slewing in slightly here and there toattain true alignment of the pivots, when the coil

I frame should swing quite freely. Lock the screw tightly.Drill the two 3/64 in. steady pin holes and remove

cock-piece. Slightly chamfer edges of holes onunderside and remove the burred edge. File twopins slightly tapering forcing each into its repectivehole, leaving about 1/16 in. protruding from the under-side. Round both tips and file down surplus untilflush with outside surface. Finish to light grain.

Slightly broach the pin holes in plate until the pinon cock-piece can just be forced in. Make sure thatthe pivot is in its bearing and lock clamping screwtightly. If insufficient end-play now exists, removecock and counterdrill the pivot hole slightly. Thecoil must be quite free, with about l/64 in. end-playwhen all screws are tightly locked. The plates can

now be separated and the coil frame removed inreadiness for winding and assembling to pendulumcrutch.

Before winding is attempted the space betweenflanges of coil must be effectively insulated. Thisalso applies to both protruding ends of the axis staff,that is, over the length covered by winding. Thisprepriration must not be rushed through, but everycare taken to ensure all surfaces are absolutely flatso that a maximum number of turns can be wound on,without any probability of a short circuit betweenturns and frames.

Attach to the finishing end of coil, about 3 in.of thicker wire of about 36 S.W.G., double silk orcotton covered, and make one complete turn roundthat space between the lower flange and winding.It can now be bound tightly to the front staff exten-sion, over insulating sheath, with fine thread. Varnishthe binding and the loop. The loop can then begently pressed in to clear the flange. Trim off allsurplus sheathing from staff projection, leaving 5/16 in.clear for crutch attachment and 3/32 in. at lower pivot.

Pendulum crutchConstruct this to measurements as indicated in

Fig. 10. Finish both faces after bending, also burnishthe edge. Turn crutch attachment collet from 5/16 in.brass rod after-drilling through. Taper off the pipeon the left hand side from 1/8 in. to 1/16 in. ; this mustnow be slit with a very fine saw to form a frictiongrip on the staff. Polish all edges and finish theremaining surfaces to a light grain. The short hair-spring collet boss must fit fairly tightly into the colletof a standard spring and that taken from a ” Crown ”Ingersoll will be found just right for the job.

Attach the collet to crutch with the long extensionfacing inwards, by burring over the 3/16 in. dia. spigot,after inserting it through the appropriate hole.

l Next week the author will conclude the article.

17 NOVEMBER 1955 735 MODEL ENGINEER

MAIN FRAMECONSTRUCTION

EDGARRT. WESTBURY gives instruc-tions for making the engine frame platesand main bearings in this instalment ofbuilding diagonal paddle engines for a

6 ft. model ship

THE ENGINE FRAME plates are cut from 1/8 in.mild steel plate, which “should be quiteflat and true but not necessarily bright,

as the surface will need to be painted eventually-if only in order to protect it from corrosion.

It is hardly practicable to keep every part of theengines clean and bright in the confined space of amodel boat hull and the smaller the number of surfaceswhich have to be wiped down and oiled after everyrun, the better. Black steel is quite satisfactory andis generally less liable to buckle or distort than cold-rolled bright steel. Pitting or patches of mill scalemust be avoided, at least in the part of the main

Milling grooves in bronze stick to make main bearings

Outer frame plate mounted on faceplate to serve as a jig forboring bearings

frames on which the cylinder and steam chest aremounted. It is necessary to make a steam joint onboth sides of the plate here, so a true surface is mostessential.

Methods of cutting the plates to shape will dependon the equipment available. no doubt most con-structors will have to rely upon sawing, drilling andfiling The use of a hammer and chisel should heavoided, or kept to the bare minimum necessary forbreaking out closely-spaced holes, as it is liable tocause distortion.

Exact outside contour is not highly important butobviously pairs of frames must be identical and holescommon t o the complete set of frames must becorrectly aligned. One of the main frames, aftermarking out and drilling undersize holes, may beused as a jig for drilling the other plates, one at atime. They should not be clamped all together ina stack, as it is possible that in drilling through 1/2 in.thickness the drill point may wander an appreciableamount. The four plates should, however, be boltedtogether, in their relative positions (mark them 1, 2,3, 4) for filing or milling the hornblock seatings towithin about l/64 in. of finished size. A trepanningtool or tank cutter is useful for formmg the lightening

Hornblocks of 1/4 in. mild steel plate are next cutout and attached to the plates by riveting andsweating, the object of the latter process being toensure that a perfectly rigid joint is obtained withoutusing a large number of rivets or hammering them upso tightly as to distort the plates. Solder is not reliedupon for mechanical strength but will definitelyprevent the first tendency to that microscopic move-ment often detected in bolted or riveted joints.

Note that the hornblocks and also the anglebrackets at the feet of the plates are fitted to alternatesides (outer side of inner frames and inner side of

1 DECEMBER 1955

holes.

View of engine illustrating frame assembly

Right: Details of outer main frame

outer frames) producing right-hand and left-handframes, which face towards each other. This arrange-ment can be seen in the photograph of the framesset up temporarily for aligning the homblock seatings,with the aid of a test bar made from 5/8 in. silversteel bar.

Fixing the angle bracketsThe angle brackets may also be riveted and sweated

(unless it is found more convenient to make themdetachable to suit the method of mounting the plantin the hull). in which case 6 B.A. or 1/8 Whit. boltsmay be used. Snap-head rivets are recommended forfixing the angle brackets but projecting heads areundesirable in the homblocks, so that countersunkrivets, tiled flush, are advised. In all cases, the rivetsare 3/32 in. dia.

It should not be taken for granted that commercialangle steel is necessarily true or square on the faces,when it is obtained. This should be checked andcorrected by filing or machining if found necessary.The best way to locate the brackets correctly is toclamp them in place with toolmaker’s clamps at eachend, while resting on a flat surface, so that they aretruly aligned with the edge of the frame plate, and jigdrill them from the plates while thus secured.

Castings supplierFor constructors who do not wish to go to the

trouble of building up the frames in this way, Messrs.A. J. Reeves can now supply castings in light alloywhich incorporate both the hornblocks and themounting feet. These differ slightly from the detaildrawings in that they are reinforced by means ofraised edges, but this makes no difference to essentialdimensions and, if anything, the appearance isimproved. Had they been available when the set

illustrated was built, they would certainly have beenused.

Main bearingsThere are several ways of machining and fitting

the main bearings and some readers may prefer tomake them singly, fitting the external surfaces in-dividually to the hornblocks. In this form of engineconstruction, the use of solid (non-split) bearings,like locomotive axleboxes, would be practicable, asthe use of single-throw crankshafts enables them tobe threaded over the ends, but the split bearings aremore convenient for lining up and assembly.

The method employed in this case was to machinea rectangular piece of bronze cast stick on the foursides bv facing in the lathe and. after checking itssquareness, holding it in a Myford machine viceclamped on the vertical-slide for end-milling thegrooves in the two sides with a home-made flatcutter. This set-up is clearly seen in the photograph.If a vertical slide i s not available, the operation canbe carried out by vackinn the work up exactly tocentre height in the toolpost.

The dimensions were left on the full side and thewidth of the groove slightly tight for final fitting tothe homblocks, after which the stick was held in thetoolpost and sawn into lengths with a circular sawin the lathe, leaving them true and parallel on theend faces.

Before boring the split bearings, they should becarefully fitted to the homblock seatings, the align-ment of which must be checked after. the frames aremounted on the soleplates, or other bearing surfaceand held in their proper location by temporary tie-bolts, which may be extemporised out of pieces oftubing and a length of fin. screwed rod, pendingproduction of the permanent stays. A piece of 5/8 in.square steel rod is useful as an alignment gauge and

1 DECEMBER 1955 821 MODEL ENGINEER

Frame plates set up in assembly position, showing the useof a test bar for aligning hornblocks

may be smeared with marking colour to indicate anyhigh spots in the seatings.

When fitted, the bearings should bed firmly in thebottom of the seatings and the halves against eachother, the top surface being very slightly proud of thehornblock faces. The keep plates are then made andholes drilled to take the securing studs, which fittapped holes in the hornblocks. While clamped inposition, the half-bearings are numbered to indicatetheir mating and location.

Boring the bearingsIt is now necessary to bore the beatings accurately

so that they line up when assembled. Setting themup individually would be extremely difficult and themethod employed, therefore, entailed the use of ajig to ensure that uniformity in the bore position,relative to the hornblock surfaces, was obtained.Construction of a special jig, however, was not neces-sary, as the purpose was admirably served by usingone of the outer frame plates.

Main bearing clamped on pin mandrel for facing the reverseside

Inner and outer frame plates, and hornblocks, after cattingout, and before attaching the latter

This was mounted on the faceplate with a parallelpacking piece behind it and with one pair of half-bearings in place, and was set up so that the exactcentre point of the bearings was coincident with thelathe axis. After boring and facing one pair. it wasremoved, and the other three, in turn, placed inposition and similarly dealt with, the position of thejig remaining unchanged. Take care that the bearingsare all the same way round and, if the markings areremoved by the facing operation, re-mark thembefore there is any chance of mixing them up.

A second operation on the outer face of the bearingscould possibly be done in the same way but a simplermethod is to clamp them together on a pin mandrelby means of a small toolmaker’s clamp as shown inthe photograph. Only a very light skim is requiredto true the bearing face and produce a relief on theouter part of the face. The ends of the bore shouldhave a slight radius to prevent riding on the journalfillets.

I regret that an error was detected in the drawingof the stay bolts too late for correction. Only twoouter and one inner stay bolts are required as shown ;the other inner stay, fitted above the cylinders, shouldbe made with male ends like the outer stay, but toa length of 2-3/4 in. between shoulders.

Bedding-in the bearingsFinal bedding-in and lining up may be done with

a scraper, with the bearings in position? using a3/8 in. test bar, and marking to show up high spots,but very little treatment of this kind should benecessary.

The permanent stay bolts shown in this drawingare turned from mild-steel bar, all work being donebetween centres except drilling and tapping the holesin the centre bolts. The shanks of the studs shouldbe a close fit in the holes in the frame plates to assistin maintaining true alignment.

Several readers have already expressed theirappreciation of the design of this engine, as informa-tion on paddle boat engines has long been in demand.A few others, while welcoming any contribution to

MODEL ENGINEER 822 1 DECEMBER 1955

TAP?6~

INCLINED 20 DEG.

INNER MAIN FRAME 2 OFF ‘/e” M.S. PLATE

Details of inner main frame

model marine engineering, suggest that it would havebeen more appropriate to have described a set ofengines for screw-propelled boats, which are by farthe more popular, and they are of the opinion thatfew constructors wish to build paddle steamers.

This is a question which always arises when any-thing a little way off the beaten track is described,but my experience has been that popularity does notalways depend on sticking to well-known lines ofdesign. When I introduced designs for a petroldriven road roller, for instance, some readers saidthis would never attract constructors-but howwrong they were !

What really matters, however, is not whether alarge proportion of readers will rush to build aparticular type of model, but how much the designcontributes to general knowledge of design andmethods of tackling constructional operations. Ifsome of the components or processes introducespecial problems which have to be tackled by theconstructor, the information on these details willinvariably be found valuable to readers who en-counter comparable problems, even though they mayoccur in machinery of a vastly different type.

l Further details of this engine will be given in ourDecember 15 issue.

1 DECEMBER 1955

Main bearings, keep plates and stay bolts

823 MODEL ENGINEER

,

THE CYLINDERS

EDGAR T. WESTBURY con-tinues his description of a set ofengines for a model paddle boat

Right: First operation on the cylinder casting-boring and facing one end

Below: Second operation with the cylindercasting mounted for facing the reverse end

IN THE DESCRIPTION of the main frames, noreference was made to the rectangular aper-tures to which the cylinders are fitted. These

should be roughed out by drilling and filing, butshould be left undersize for final fitting after thecylinders are machined. The drilling of theholes around this frame, to take the fixing studs,should also be left till a later stage.

A great deal has been written about the machiningof cylinders for steam engines in previous issues andas these particular cylinders are similar in mostessential respects to those usually fitted to locomotivesand other conventional types, I do not propose tolay down the law as to the methods to be employed,or the particular sequence of operations.

Readers who have already built engines and aresatisfied with the results obtained may use the methodsto which they are accustomed. I shall, however,describe how the job was tackled in the case of theengines actually constructed, with illustrations of theset-ups at each stage.

It will be seen that alternative materials for the cylin-der castings are specified; no doubt most constructorswillprefer bronze because of its resistance tocorrosion,but there is much to be said in favour of cast iron inrespect of durability under hard working conditions.Contrary to common opinion I do not find the lattermaterial more difficult to machine if the quality ofthe metal is good, but it generally calls for slowermachining speeds unless special tools are employed,

1 MODEL ENGINEER

POWER BY

the expense of which is hardly justified by theirusefulness in general model work.

The first operation on the castings. was boring andend facing, for which purpose they were set up in thefour-jaw chuck as shown. Here it may be mentionedthat when a cylinder of any kind is held by radialpressure for machining the bore there is always a riskof distorting it, so that when subsequently released itsprings out of true circular shape. This risk, of course,is greatest with thin-walled cylinders and in thepresent case, the stress is taken on a flange of heavysection, so that with reasonable discretion in applyingchuck pressure no trouble in this respect need beanticipated.

An alternative method of mounting the cylinder isto an angle plate on the faceplate, after roughmachining or filing the valve port face to ensureflatness. The usual practice of using a strap and twobolts to clamp it to the plate may impose worse stressesthan the four-way pressure of the chuck jaws inmany ways.

Setting up the cylindersHaving regard to the fact that the cylinder bore

governs the location of other machined surfaces,care must be taken in setting up so that its relationto these surfaces can be properly maintained. It isnot sufficient to set up to the cored hole in the bore,as cores may be, and often are, inaccurately locatedin the mould. In a large casting, careful marking-outwill enable the position of all surfaces to be correctlylocated, but this is by no means so easy in small work,where the thickness of a line may be sufficient tointroduce error.

I always set up castings by reference to the surfaceswhich cannot or do not have to be machined, subjectto allowing sufficient metal for cleaning up the

b

Third operation. The cylinder is mounted on the angle platefor machining the valve face

machined surfaces. In the present case, the cylinderbarrel and the edges of the flanges should be set torun as truly as possible, both concentrically and onthe face.

After cleaning up the end flange with a facing tool,the cylinder bore is machined with a single-pointboring tool to within about 0.002 in. of finished size,the final cut being taken with the tool honed to a keenedge and several passes made without applying feed,to eliminate all spring and leave as smooth a surfaceas possible.

To face the other cylinder flange, it is advisable tomount the castings on a mandrel. As the bore isstill undersize at this stage, a piece of 3/4 in. stock barmay be used, set up to run truly in the chuck andreduced by skimming or filing to a wringing fit forthe cylinder bore. The end face of the bar should becentre-drilled for tailstock support.

Left: Fourth operation. The angle plate has been trans-ferred to the vertical-slideBelow: Fifth operation. Cutting three parts at once in thtvalve face

MODEL ENGINEER 922 15 DECEMBER 1955

Next operation is the machining of the cylinder portface, the casting being mounted on an angle plate bya bolt through the bore and disc or plate across theopen end, with paper interposed between surfacesat both ends to prevent bruising and improve the grip.After setting the port face parallel to the faceplate,the surface is machined to within a few thou. offinished dimensions, measured from the cylinderbore centre. While thus mounted, it is a goodpolicy to machine top and bottom edges of portfaces and flanges, but swinging the casting round 90degrees each way in turn and squaring off from theport face. These operations are not absolutely neces-sary, but they clean up the casting and produceaccurate reference planes parallel to the cylinder bore.

Mounting the cylinder castingThe surface by which the cylinder casting is mounted

on the frame plate is set back 3/16 in. from the port faceand must obviously be quite flat and true to producea steam-tight joint. This can best be machined by amilling operation unless a shaper or planer is avail-able, or if one has more than ordinary skill in filing-the latter method will certainly not be found easy bythe novice ! In the example illustrated, the angleplate was transferred to the vertical slide, and ahome-made end mill, running in the chuck, employedto machine both the rebated face and the four edgesof the port face, as shown, thus producing at once atrue joint face and a true rectangular register to fitthe aperture in the frame plate. The simple two-

bladed cutter shown is easily made from silver steel andworks, if anything, better than an expensive ready-made end mill.

Now comes a vital and critical operation on whichthe entire success and efficiency of a steam enginelargely depend. There are many ways of formingthese ports, all of which have been described in pastissues and I am aware that there are differences ofopinion as to the advantages of the methods I employ.Readers may, of course, use any alternative machiningor hand-forming process they please.

It involves the production of a special cutter-not avery big job really-but it is worth while, as this canbe adapted to many other jobs and it produces cleansquare-cut ports, automatically located. If the gangmilling cutter is considered too complicated, a simplercutter to deal with one port at a time can be used, butmeasurement of the distance between ports is easier toapply to the cutter than the cylinder.

The mounting of the cylinder for this operation isvery simple, as the use of a vertical slide, though help-ful, is not a necessity and an angle plate on the crossslide can be employed quite satisfactorily. Actualmachining time is only a matter of seconds, the majorwork being the setting-up operations, but to thosewho grudge the time “ wasted ” in all the preliminarywork of this nature, I can only say that it is the normalroutine of nearly every workshop in which one-offor prototype work is undertaken.

The next instalment in this series will be published onDecember 29

I-I

‘ E D b L A .3” _I SIX HOLES TAPPED 6 B.A.,

‘. SIX HOLES 6 B.A. CLEAR,O N 1-3/16" P.C.D.

TAPPED FOR DRAIN COCKS THREE HOLES 3/32 D I A.INCLlNED 30 DEG.

“i:l-ir;==jj- ~lN;;jNiF OR =.,, INNER & 0UTER:“:iz;cif,;

2 OFF EACH

Details of the cylinder with the inner and outer covers

15 DECEMBER 1955 923 MODEL ENGlNEER

C Y L I N D E R C O V E R S AND S T E A M C H E S TEDGAR T. WESTBURY continues his instructions

for building engines for a paddle power boat

FINALL OPERATIONS ON the cylin-der castings consist mainlyof drilling and tapping holes

for the fixing studs, but this canbe deferred for the present, as itis best to spot them off from thecovers and steam chest after thesehave been dri l led, ra ther thanmark off and drill the componentsindividually, which is more likelyto introduce errors.

Drilling passages from the ends ofthe cylinders into the ports is anequally important operation, in which,I am informed, several constructorscome to grief. There is no reason whythis should be so, however, and certainsuccess can be assured by correctmethods. There are some who candrill these passages by gripping thecylinder in the vice and getting towork with a hand brace, but the skillrequired to point the drill at the correctangle is, in my opinion, uncommonand I would not rely on it unless noother means were available.

A drilling machine with some formof angular adjustment fixture for the

. Right : Details of the steam chest

work is much better, but the photo-graph shows how it can be done inthe lathe, with the aid of the vertical-slide and machine vice and with muchgreater certainty of success.

The work can be set to the correctangle for drilling by swivelling theslide, using a protractor or othermeans to measure the angle, and afurther check is possible by loweringthe slide so that the drill can besighted over the top face. Beforedrilling, the chamfer at the lip of thecylinder bore can be end-milled, thejob being adjusted exactly to centreheight for this operation and, whilein position, a small centre-drill maybe used to start the first hole.

For the other two, the slide israised or lowered the required amountand the centre-drill is used again. Inthis way no marking out or centre-punching is necessary and there is noquestion of the drill being sprung outof line. Use all the lathe speed youhave and do not force the pace of thefeed. This provided, the passages willcome out in the ports-in the wordsof the famous few-“ bang on.”

An aIternative method, to attainthe same end, would be to use a drillspindle on the vertical-slide, with thework set over to the required angle ona suitable faceplate fixture.

The exhaust passage from the topsurface of the cylinder to the centralport is drilled at a suitable angle tobreak fairly into the port. The angleis not critical and demands no specialsetting arrangements, but it will befound easier to start the h o l e bysinking a 1/4 in. drill squarely into theface for about 1/16 in. This may bedrilled deeper for 1/4 in. tapping holeto take a screwed pipe connection,but a flange joint is better.

Drain cocksDrain cocks are not a necessity,

but they assist in clearing condensatewhen starting, and the inverted detaildrawing of the cylinder shows theirposition. The smallest available draincocks, obtainable from Bond’s, arescrewed 5/32 in. x 40 t.p.i.

Finally, the cylinder bores should belapped, using a solid or expandinglap, with a not-too-fierce abrasive

Below: Tapping the hole for the gland in the cylinder cover

MODEL ENGINEER 994 29 DECEMBER 1955

Drilling the steam passages in the cylinder

such as aluminium oxide or brickdust, followed by tripoli or metalpolish, to produce a high finish. Notethat the bores should be finishedbefore fitting the covers, the spigotsof which should register closely,especially those at the packing glandend.

Cylinder coversThe cylinder covers are quite

simple to machine, especially in thecase of the outer covers where it ispossible to provide a chucking pieceWhich will enable all essential opera-tions to be carried out at one setting.The inner covers, which incorporatethe tapped recess for the packinggland, call for somewhat differenttreatment and I prefer, after roughmachining the rear surface, to mountthem boss outwards for drilling, coun-terboring, and tapping, taking great

care to maintain concentricity in allcases.

For machining the joint face andspigot, a piece of bar is held in thechuck, turned to size with a pilot tofit closely in the piston rod guide andscrewed accurately to fit the tappedhole. This serves as a screw chuck tohold the cover truly and ensures. thatthe flange and spigot are true with thegland in both planes.

Stud-hole drillingDrilling the stud holes in the cover

flanges can be facilitated by the useof a drilling spindle, in conjunctionwith indexing of the lathe headstock,a centre-drill being used to start theholes in all cases-this ensures per-fectly accurate location of the holeswithout the need for marking-out.Finally the flat faces on the oppositesides of the gland boss, for mounting

the ends of the slide bars, must bemachined or filed dead flat and parallelto the axis, also equidistant fromthe centre. This is another job whichis much simplified by using a millingcutter in the spindle while the job isset up in the lathe chuck.

Steam chestThe usual “ picture frame ” type

of steam chest is used as, although it isnot in conformity with orthodox full-size practice (at least,in so far as marineengines are concerned), it simplifiesmachining and makes very littledifference to external appearancewhen assembled.

Both sides of the steam chestcasting are first machined flat byholding in the four-jaw chuck andapplying a facing tool. Centering isnot highly important, but the twosides must be exactly parallel toeach other and the amount of metalremoved each side must be so adjustedthat the gland boss is properly located.As there is machining allowance onthe latter, this dimension is notcritical, but should not be disregarded.

After facing one side, the steamchest casting may be gripped by theinside of the frame and the machinedside pressed firmly against the step ofthe jaws, to ensure that it will finishparallel. Other methods of obtainingpositive accuracy in this respect areto use a parallel packing block alittle smaller both ways than the steamchest and thick enough to hold it clearof the jaws when placed behind it;or to mount it on a “solder chuck”-this will be referred to Iater.

The thickness of the steam chestmay be left a few thou. oversize for final lapping of the joint surfaces.It is not practicable to machine theinside surface of the steam chest,but this should be filed to fit neatly

Left: Dimensions and details of the slide valve

Below: The cylinder cover held o n a screwed mandrel for makingthe joint face and drilling bolt holes

29 DECEMBER 1955 995 MODEL ENGINEER

POWER BY PADDLES . . . .

over the raised port face of thecylinder.

Sett ing upAfter checking the distance of the

gland boss centre from the inner jointface (nearest the cylinder) this shouldbe centre-punched as a guide to settingup. It is possible to use the four-jawchuck to hold the casting for boringthe gland recess, but the use of anangle-plate on the faceplate is prefer-able, to ensure positive accuracy andavoid risk of bruising the finishedsurfaces.

A single bolt and a flat plate withprotective paper packing will sufficeto hold the casting (as shown in thephotograph) and before attempting tocentre the boss, the sides should be

squared off from the faceplate asaccurately as possible. The angle-plate is then shifted as required tobring the centre-punch mark on theboss exactly central for centre drilling,boring. tappine and external machin-ing, after which the sides and backmay be faced by swinging the jobround to the required positions.

To complete the machining on thesteam chest, the design specified atail end guide for the valve rod,. andwhile this is not a necessity it is,in fact the exception rather than therule in small engines-the avoidanceof side movement which it providestakes a good deal of wear and tearoff the gland, and it is generallypreferable to an external front guidebearing in this respect, as the latter

Right: Details of the glands for the piston rod, tail rod,valve rod and slide valveBelow: Facing the sides of the steam chest

is often difficult to line up accurately.In the original design of this engine.

a boss was provided on the back-endof the steam chest casting for thisguide, but this must be drilled fromthe front end and it is difficult toensure that the long drill, after passingright through the gland recess, willstart truly on the inner surface of theframe to ensure accurate alignmentof the rod. It is therefore, preferableto make the tall rod guide separateand screw it into the back face of thesteam chest.

To ensure that it is properly located.the casting may b e mounted on ascrewed mandrel enabling the backface to be accurately centre-drilledthen drilled and tapped for the tailrod guide, which is turned fromhexagonal brass rod, as shown in thedetail drawing.

l The next part of this serial will bepublished on January 12.

MODEL ENGINEER 996 29 DECEMBER 1955

stages in the constructionmodel paddle steamer

By EDGAR T. WESTBURY

The slide valve set up for milling the slots in the back, show-ing the use of a solder chuck for mounting on the faceplate

HE NEXT COMPONENTS to beT made for the paddle boatare the piston and valve

rod glands; here the purists mayfind some grounds for criticismin the matter of fidelity, as theseare not of the orthodox flangedand studded type. Screwed pistonrod and valve rod glands would notbe used on a ful l-s ize marineengine, but they are advisable hereon the score of accessibility, andholes for a tommy bar as shownwill be more convenient for ad-justment than the use of a spanneron a hexagonal head.

Both glands should be machinedwith due care to ensure concentricityof the bore and the screwed externalsurface so that they do not bind orthrow the rods out of alignment.The internal bevel of the glands, andalso that of the recesses in cover andsteam chest, may be formed with anordinary drill, as the angle is notcritical, but a special piloted cutterfor these jobs will. produce a moreaccurate finish.

Improving accuracy and appearanceIn the case of the steam chest cover,

only the inner surface is really im-portant, but the rim of the outer faceshould be sk immed up, not only toimprove appearance, but also toprovide an accurate seating for thefixing nuts. That the faces are parallelis not vitally important, but they maybe made so by the same methods asmentioned above. It is advisable to

MODEL ENGINEER

mark out and drill the stud holes inthe steam chest, and use this as a jigfor drilling the clearing holes in thecover, the main frame plate and thetapping holes in the cylinder casting.Make sure that in each case the matingparts are the right way round and thatproper identification marks are pro-vided for future assembly.

Locating holesWhen spotting the holes in the

frame plate, the cylinder castingshould be put in position, so that thesteam chest is registered on the portface, and a. clamp may be applied tohold the assembly together duringthis operation. Alignment of thecylinder bore with the main centre-line may be facilitated by the use of atest bar long enough to extend to theshaft centre, and the aperture in theframe should be fitted to the cylinderport face so as to locate it positively

in this position before drilling thestud holes.

The slide valve is of conventional,design, though the method of operat-ing it from the valve rod is slightly_modified to enable the latter to beextended into the tail guide. A castingis provided for this item, but it couldbe made from the solid, or fabricated;apart from making sure that theworking face is perfectly flat, it isequally important to ensure that thedimensions-of the exhaust cavity andthe controlling edges at the two endsare correct.

In the casting, the cavity is cast in-it should not need to be touched buta check should be made to see thatit exactly spans the inner edges of the 4cylinder ports at each end.. This isbecause when working, these portsare alternately open to exhausf, each for 180 degrees of crank movement.The outer edges of the valve, which

. I

Details of the piston and rod. These are made of stainless steel

-

MACHINEDIN SITU

PISTON & ROD 2 OFF STAINLESS STEEL72 12 JANUARY 1956

I

. .

t

Left: , ’Steam chest mounted on ascrewed chucking, piece for drilling andlapping the rear face

control steam admission, are longerthan the distance between the outeredges of the cylinder ports, to producea certain amount of “lap,” whichmeans that the valve must travelsome distance from its central position

before either of the cylinder portsopen to steam; the dimensions given(13/16 in.) give l/32 in. lap at each end.

In the original design, a greateramount of lap was allowed, but while

this is good for steam economy ithas been found that the engines run

more smoothly, at the low speed forwhich they are designed, by reducingthe amount of lap.

Holding the valveThe valve may be held in the four-

jaw chuck for facing the workingsurface, and while set up the controledges may be milled, though filing issatisfactory if due care is exercised;the important point is that theseshould be square and symmetrical,measured from the exhaust cavity.

For machining the slots across theback of the valve, it is necessary tomount it in the reverse position, butit is rather difficult to hold properlyby orthodox methods. A somewhatunorthodox device was thereforeemployed, namely a “ solder chuck,”consisting of a flat brass plate about1/8in. thick: a circular brass blankhappened to be available (it could beof any shape so long as it is flat, ofeven thickness and capable of beingclamped to the faceplate). The surfaceof this was tinned and the valvetemporarily sweated to it underpressure (to ensure that it is notmisplaced by an excessively thicksolder film); it was then allowed tocool down.

The back of the valve can then befaced off to correct thickness and theslots milled. In this case the entire

operation was carried out on the face-plate using a rotary milling spindlebut if one is not available the jobcould be transferred to the verticalslide and the milling done by a cutterheld in the chuck. The narrow slotmerely serves as a clearance for thevalve rod (be sure that this is locatedon the axis of valve motion), and thewider slot receives the “ buckle ” bywhich the valve is driven; the lattermust be a free working fit but withno perceptible play. If no tail guideis used the more usual rectangularnut screwed on the end of the rodmay be fitted instead of the buckle.Finally, the working face of the valveand the cylinder port face are care-fully lapped to exact flatness.

Stainless steel is specified for thepiston and piston rods; this avoidsthe risk of corrosion but, mind you,many small steam engines have beenin use for years with mild-steel pistonrods. Stainless steel, cast-iron orbronze may be used for the piston.The rod may be turned betweencentres and, if it can be chuckedaccurately for centre-drilling, it neednot be touched on the parallel portion.Concentric truth of the threaded endsis most essential and the threads mustbe a good fit, that on the piston endmust be definitely on the tight sideand only screwed part of the way.

Dimensions of the slide bar which is made of mild-steel, four of these are required

SLIDE BAR 4 OFF M . S .12 JANUARY 1956 73 MODEL ENGINEER

After roughing out the piston, thecentre is drilled and tapped, half thelength of the hole is bored out toregister closely on the diameter ofthe latter part, allowing it to screwright home against the shoulder; itis then screwed on tightly and per-manently. If desired, the end of therod may be burred over, or swelledby means of a blunt-ended centre-punch in the previously drilled centrehole, but if this is done great caremust be taken to avoid distortion andputting the piston out of truth.

The assembly is now mountedeither between centres or. in a per-fectly true collet chuck for machiningthe outside of the piston, includingthe packing groove and the twolands., which should be a close butnot tight fit in the cylinder bore.

Piston rings are optionalPiston rings may be fitted if desired,

in which case two narrow and shallowgrooves will be called for instead ofone large groove; from the practicalpoint of view, however, soft packingusually gives the best results in smallsteam engines working at moderatepressure and, unless made to extremelyfine limits of accuracy, piston ringsare worse than useless. The holes inthe end face of the piston are usefulto enable the assembly to be screwedinto the crosshead, with the aid of asimple pin spanner.

The slide bars are simply lengths offlat mild-steel bar, 3/8 in. by 1/8in. section. If dead straight bars withtrue edges can be obtained, no moretreatment than a rub on a strip offine emery cloth will be needed. Ifit is necessary to correct inaccuracies,this may be done with a file andscraper. At the inner end, the barsare attached to the flat faces on thetop and bottom of the cylinder coverboss by means of 6 B.A. set-screws(hex. head preferred) and at the outerend, to the jaws of a bracket mountedon the side of the main frame, with

A set of components for thecylinder group assembly

similar set-screws. It is advisable toleave the drilling and tapping of theseholes until the bracket is fitted, incase of any possible discrepancies inlocation.

The projecting ends of the bars arechamfered on the inside to give ampleclearance for the connecting rod and,near the centre of the top bar only,provision is made for lubrication,preferably by fitting a small oil cup,though only a plain countersunk holeis provided in the engine illustrated.

The cylinder assemblyIn the assembly of the cylinder and

its attendant parts, it should be notedthat alignment with other workingparts is affected by the thickness ofany packing material employed. Itshould not be necessary, however, touse thick packing anywhere to ensuresteam-tightness of the joints, nrovidedthat the surfaces are accuratelymachined. For steam joints, wheresaturated steam or moderate super-heat is employed, I have found thattracing linen makes excellent jointingmaterial; it is tough and resilient,resists oil and water, and is onlyabout 0.005 in. thick when com-pressed. With carefully lapped jointfaces not even this thickness is neces-sary and it is possible to obtain aperfect seal with a smear of jointing

. Alignment e r r o r s , if n o texcessive, can be corrected by shim-ming but it is better to avoid the needfor this if possible.

The piston and valve rod glands,as well as the groove of the piston,are packed with graphite-impregnatedasbestos yam, and for gland packingI have obtained the best results bvplaiting individual strands of thismaterial and cutting it into lengthsjust sufficient to make one turn in theannular recess of the stuffing box. Asmany of these turns as will fill the

MODEL ENGINEER

space are used and the joints arestaggered; a piece of tube can beused to press them into place.

For the piston packing, on the otherhand, the texture of the yam should befairly loose, so that it will packsmoothly when wound in a continuouslength into the groove. Incidentally, Ihad a spot of bother with somegraphited yam which did not beddown and produced excessive friction,despite careful running in. When thepiston was removed after a period ofrunning, the cylinder bore showedominous-looking scratches, thoughthey were not deep enough to bereally serious.. I suspected grit inthe packing but on examination it wasfound that there was a hard brasswire running through the strands,which had broken up and scratchedthe bore. A sample of packing fromanother source proved to be wire-free, and has been quite satisfactory.

Men, models and methodsIn the course of recent correspond-

ence, not to mention lectures anddiscussions at several club meetings Ihave attended, some pertinent com-ments have arisen regarding themethods of construction I have re-commended for these engines andothers I have described. There are,I find, many constructors-not neces-sarily all of the old do-it-bv-handbrigade-who “ don’t hold with gad-gets,” and question whether all thismessing about with vertical-slides,milling spindles, jigs and such arereally necessary. The answer is thatof course they are not necessary-1have never claimed. that they were;but they provide a means of obtainingaccurate results with absolute cer-tainty, and also, in my opinion, cutout a good deal of tedious and un-interesting work.

Every man to his method-there

74

are always many ways of attainingthe same end, and the methods I haveillustrated show how operations haveactually been carried out in particularcases, with complete success; but farbe it from me to dictate to any modelengineer how he should tackle hisown machining or fitting problems.One of the unique attractions ofmodel engineering is that one canmake anything he pleases, in anyway he pleases, and at his ownconvenience. So long as the methodsI employ produce satisfactory results,I feel iustifled in passing them on toreaders, but if anyone can show mehow to improve upon them, I shallbe more than grateful.

Time factorThe time taken to set up attachments

or to make simple jigs may be grudged,but they usually save time in the end,as I have often vroved: and in anvcase, the interest obtained f romactually doing the job is a greaterincentive to most model engineersthan beating the clock in obtainingultimate, results.

To produce by hand fitting, or bythe minimum of machining resultscomparable to those which can beobtained by exploiting the inherentaccuracy of slides, indices and spindlesin machine tools demands a mostunusual degree of manual skill;certainly more than I possess at anyrate. When I wish to produce a flator circular surface, a definite measuredangle, or to devide a circle into anequal number of parts, I use machinemethods where possible, and shallcontinue to do so unless and untilsomeone convinces me of the errorof my ways.

In his next instalment the authorwill deal with the crossheads andconnecting rods.

12 JANUARY 1956

*--

i

Machining crossheads i

i

and connecting rods !

THE C R O S S H E A D S are of thebuilt-up “ box ” type, some-what similar to those em-

ployed in certain types of locomo-tives. This is not, strictly speaking,correct marine epgine practice,though such crossheads have beenused on paddle engines in one orI two cases. The main reason fortheir adoption here, however, isto simplify construction by avoid-ing the need for forked connectingrods, which some constructors finddifficult to machine.

For the main central portion of thecrosshead, rectangular mild-steel baris used and, if clean and accurate1 in. by 3/8 in. bar can be obtained, itneed not be machined on the sidesand edges. In such cases, however,the utmost care must be taken insetting the bar up in the four-jawchuck in order to ensure that theboss and the tapped hole for thepiston rod are exactly central bothways.

EDGAR T. WEST-BURY continues “I

The use of a dial test indicator willvery much simplify setting up but inits absence, a check on accuracy maybe made by taking a light cut overthe edges at the end of the bar beforeturning down to form the boss. Ifthe setting is correct, the same amountwill be removed from each of thefour corners, and if not, due correctioncan be made. The witness marks,if not taken too far along the bar, areremoved when the boss is turned down.

MODEL ENGINEER

his article onmaking a set ofengines for a 6 ft. t

The usual care must be taken to drill all identical in outline but differ in theand tap the hole dead truly. drilling, as indicated on the drawing.

Completing the forkA hole 9/16 in. dia. is drilled through

the centre of the crosshead-this issimply a clearance for the little endof the connecting rod and does notcall for critical accuracy in size orlocation. It will. however. be foundadvisable to set the crosshead upcrosswise in the four-jaw chuck, witha protecting pad over the face of theboss, and bore this hole after drillingit undersize. The fork is then sawnout and finished by filing or machiningto join the hole tangentially.

The cheek plates are made from1/16 in. or 16 s.w.g. sheet steel and are

Above: The slide bar bracket setup for millingthe seatings

Right: Turningthe spherical endof connecting rod

In the example shown in the photo-graph, hexagon-headed set screws areused to secure the plates on eitherside of the crosshead, but alternativelycountersunk screws could be fitted,or the assembly riveted up permanentlyusing flush-sunk 3/32 in. rivets.

Sweating or silver-soldering is alsoquite practicable but excess of soldershould be avoided, or the cleaning-upof the bearing faces and retainingstrips will become a major operation.

Oil holes, at least as large as thescrews or rivets which intersect them,are drilled through the top and bottombearing faces and the oil groovesshown, though not absolutely essential,

148 26 JANUARY 1956

are desirable to distribute oil all over the faces. Thev should not extendright to the corners. A scorper, orhand engraving tool, is the simplestmeans of cutting oil grooves for thosewho know how to manipulate it, butthey can be produced by milling orshaping methods in the lathe.

The crosshead pin is a straightfor-ward machining job which can beproduced from steel bar at one settingand parted off, then faced on the head.Note that this pin must be a closefit in the outer cheek of the cross-head, the screwed end passing throughthe smaller hole in the inner cheekwhere it is firmly secured by a 2 B.A.nut. In normal practice, pivot pinsof this type would have a “ snug”key under the head to prevent themturning and I have shown, in previousarticles, a simple method of fittingsuch keys. They may be dispensedwith if the pins are made a tight pushfit in the plates, and the nuts runfreely on the threads.

Do not slot the heads of the pins toenable them to be held while screwingup the nuts. All pivot pins may, withadvantage, be case-hardened to give

-maximum resistance to wear, butthe risk of distortion in this process isvery difficult to avoid and deters manyconstructors from attempting it.

Slide bar bracketThe slide bar bracket can also be

made from 1 in. by 3/8 in. flat bar andthe work entailed consists mainly ofsawing and filing; there is not muchadvantage obtainable from milling

A close-up of thecrossheadslide bars

and

or other machining processes, exceptpossibly in forming the slide barseatings. I understand that Messrs.A. J. Reeves have produced castingsfor the brackets which will undoubtedlysimplify their production, but up tothe time of writing, I have not seen asample and therefore cannot saymore about them.

It is most important that the loca-tion of the seatings for the slide barsshould produce correct alignment withthe cylinder centre line in both planes.The distance of the centre from themain frame plate should be verycarefully checked, in case of anydiscrepancy in cylinder dimensionsor to allow for the thickness of packing.

The width between the seating facesin the jaws of the bracket can be

Dimensions of the connecting rod, crossheadand pin, slide bar bracket and cheek plates

26 JANUARY 1956 149

checked by measurement, or by usingthe actual crosshead plus both barsas a gauge. In the event of error, it ispossible to fit shims to make up correctalignment, but if the need for themcan be avoided, so much the better.

The photograph shows how theseatings were machined by means ofa milling cutter in the lathe. Aftercutting the bracket to shape and sizeon its main contours, it was heldhorizontally in a Myford machinevice mounted on the vertical slideand the two seatings in turn milled bytraversing the slide in a verticaldirection. Note that the traverseshould be upwards when working onthe front seating and downwards onthe further seating (assuming normaldirection of cutter rotation) to avoidsnatching and digging in.

The cutter used was only half thewidth of the seating, so that more thanone “ bit ” was necessary to producethe full width. but this is an advantagerather than otherwise as wide cuttersdo not work very well in the lathe, dueto the heavy cutting stress they imposeon the work.

Fixing the bracketsWhen fitting the brackets to the

main frames. thev mav be clampedtemporari ly in position (so thatalignments may be checked) byscrewing the piston rods into thecrossheads and sliding them over thefull length of the stroke ‘to makecertain that they work smoothly andwith no tendency to deflect the rodto either side. Having ascertained theproper location, the holes in the backface of the brackets can be spottedfrom the frame plate, then drilled andtapped.

The sequence of operations re-commended for making the connectingrod may appear unusual, but they arebased on experience. It has often beenfound that what appear to be orthodoxor logical methods of machiningcertain components may lead one into

MODEL ENGINEER

POWER BY PADDLES . . . .

a blind alley where no positive meansof locating the work for an importantoperation can be contrived. In suchcases, the remedy is to get such opera-tions done at an early stage in themachining before essential markingsor reference surfaces are lost.

The rod is machined from solidmild-steel round bar (this will usuallybe found easier and quicker thanfabricating it) and the first operationis to produce a parallel cylindricalbar with accurate centres at each end.It is unlikely that bar of 15/16in. dia.will be available, so a skim over a1 in. bar after centring will be calledfor.

Do not drill the centre too large ordeep at the end which will be reducedin size instead a 3/16 in. recess isdrilled at the other end and slightlycountersunk. The bar is now chuckedaccurately and the ball end of the rodturned to finished size.

Although spherical accuracy is notof critical importance, the use of asimple ball-turning tool, such as thatshown in the photograph, will verymuch facilitate this operation. Theneck immediately behind the ballshould be reduced to finished size(or very near it) but only the minimum1eng th of bar turned down at thisstage. Check the length of the bar,measuring from the’ball centre, andcorrect if necessary.

The next operation consists ofcross-drilling the ball ex actly at rightangles for the crosshead pin bearings-this is by no means so easy as it looks,

Details of cross-dr i l l ing theconnecting rod

The final taper turning of the connecting rod

if one relies on marking out anddrilling in the usual way.. It can,however, be carried out with perfectaccuracy by mounting the bar hori-zontally in the vertical slide, set atright angles to the lathe axis andadjusted to centre position by thecross and vertical feed screws’.

Accurate settingIf a light facing cut with an end

mill is taken over the side of the ball,it will very much facilitate accuratesetting for starting the drilling opera-tion with a centre-drill. Any in-accuracy in this respect, when thedrill first contacts the work, will beseen and can be corrected before pro-ceeding further. Drill the holeundersize, as shown in the photo-graph, and finish with a reamer orD-bit ; bushing is optional, but iscertainly advisable unless the cross-head pin is case-hardened.

MODEL ENGINEER 150

Before removing the bar from thevertical slide, a centre line should bemarked out on the other end face,at right angles to the cross hole,using a square set up on the lathebed or any other convenient method.This will enable the positions of thecrankhead belts to be marked outand these may, with advantage bedrilled, as they provide a means ofdriving the bar for the final operationof turning away the surplus metaland finishing the taper shank betweencentres, leaving the flange at the footend.

An alternative method of drivingthe rod is to fit a bolt in the little endeye and work from the other end,;both methods have been tried, but itseems more natural to carry outturning operations from right toleft where possible.

l The next instalment of “Powerby Paddles ” will appear in the issuefor February 2.

SEVENTEENTH CENTURY RIGGINGBy R. C. Anderson. Published byPercival Marshall & Co. Ltd., London.Price 25s.

Seventeenth century ships havealways been popular with ship model-lers. Probably one reason is that theylook more like normal ships-shipsthat really would sail-then thegalleons and caravels which precededthem. But perhaps the principalreason is the magnificence of thecarved and gilded decoration whichthey carried. A well detailed model ofsuch a ship is indeed something to beproud of. But the only book whichgave authentic information about therigging of ships of this period wentout of print some years ago andsecond-hand copies reached a fantasticfigure. The book under review is arevision by the author of the originalbook.

26 JANUARY 1956