Model Steam EngineSIMPLIFIED FOR BEGINNERS

The finished engine and a small boiler installed in a model boat18 in. long. The engine itself is only a trifle over 3 in. high

Can be built without a lathe if necessary, andwithout castings if you have brazing equipment

HIS model steam engine has beendesigned as a miniature powerunit that can be built with thefacilities of an ordinary home

workshop. As built originally, it calls for alathe and castings, but as explained later,it can be built up from stock materials,and with nothing more elaborate than or-dinary hand tools.

The engine stands a little over 3 in.high, has a base of 1 by 1½ in., a bore of½ in., and a stroke of ¾ in. It will op-erate satisfactorily on either a pot or aflash boiler and has sufficient power todrive a fair-sized model boat.

The base and cylinder are brass orbronze castings, which any brass foundryshould supply from your patterns at avery moderate cost. White pine or ma-hogany may be used in making the pat-terns, with fillets of wax. Allow 1/16 in.

for machining on surfaces that are to befinished.

To make the cylinder pattern, turn thecylinder from solid stock. Then turn adisk of wood 1 5/16 in. in diameter by¼ in. thick. (This thickness includes the1/16-in. allowance for machining.) Thesetwo pieces are fitted together as shown inthe drawing of the finished cylinder assem-bly. The 1 5/16-in. disk forms the slidingsurface on which the cylinder oscillates.

The pattern for the enginebase and frame can be built upof several pieces and filleted withwax.

The cylinder may be cast solidand drilled out to 3/8 in. on apower drill press, then bored tofinished size on the lathe, or coreprints may be put on the patternand the casting made with a 3/8-

Above: Close-up of engineand how end of cylinder isfaced. Below: Completeparts ready for assembly

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in. core. Having obtained your cast-ings, proceed as follows:

Cylinder. Mount in four-jaw chuckor on angle plate bolted to faceplateas shown so that center line of cylin-der bore is in line with lathe centers.Face off one end of cylinder. Thecasting may then be turned end forend. If the finished end is buttedagainst face of chuck, the oppositeend will be parallel and can be facedoff.

To finish surface of disk that formsback of cylinder assembly, the castingmay be mounted in the four-jawchuck or on an angle plate fastened tothe faceplate. The second method ispreferable. If the angle plate is used,placing one finished end of cylinder onit will insure that cylinder is at rightangles to lathe bed. It is then neces-sary only to adjust the casting untilsurface of disk to be finished is atright angles to a line between lathecenters. This can be done by mount-ing a scriber in tool post.

After surface of disk has been fin-ished flat, take a 1/32-in. cut acrossthe center, leaving a 3/16-in. rim atedge to reduce bearing.

circular portion at top, against which cyl-inder oscillates, is at right angles to lathebed with its center coinciding with a linebetween lathe centers. Turn this face flat,then recess the center portion like disk atback of cylinder. While casting is still inposition, drill a 1/8-in. hole through centerof this circular por-tion for bearing boltthat supports cylinder.

By turning lathe atslow speed and takinglight cuts, the frontend of shaft bearingcan be faced off at thistime. Change positionof casting so thatshaft bearing is in linewith the lathe centers.Using a surface gageresting on lathe bed,adjust so that the disksurface just finished isat right angles to linebetween lathe centers.Using chuck in tail-stock, drill and reamshaft bearing with a1/8-in. hole. Reversecasting and square offother end of shaftbearing. Dri l l steamports with hand drillor drill press. (Thephotos show a rec-tangular piece at toporiginally intended forattaching an exhauststack, but found un-necessary and there-fore omitted from thedrawings.)

To bore cylinder, mount it on an angleplate with one finished end flat against thesurface of faceplate. Adjust until a line be-tween lathe centers coincides with centerline of cylinder bore. With boring tool,bore cylinder to finished size. The last cutshould be fine, with a slow feed. The cyl-inder will be lapped in after piston hasbeen made.

Drill steam ports as shown. Holes forcylinder-head bolts may be drilled andtapped to suit your convenience. Use 0-80hexagon-head machine screws if you canget them. Cylinder heads may be of 1/8-in.sheet brass.

For the stuffing box, thread a piece ofbrass rod ¼ in. in diameter. Turn it intoa threaded hole in center of lower cylinderhead and cut off to required length. Thendrill a 1/8 -in. hole through center for pistonrod. This hole should be drilled a trifleundersize and finished with a 1/8-in. straightreamer. The stuffing-box cap can be madefrom a piece of ½-in. round brass stock.

Base and Frame. File bottom of baseflat. Mount on faceplate. Block up until

Assembly. The cylinder is held againstengine frame by a 1/8-in. bearing stud,screwed into a hole tapped in rear of cylin-der. A coil spring holds cylinder againstframe. The tension should insure a closefit, but should not interfere with free os-cillation of the cylinder. Cylinder and en-gine-frame surfaces should be lapped to-gether with fine valve-grinding compound.The piston should also be carefully lappedinto the cylinder. The flywheel is turnedfrom brass and keyed to shaft, or may bea driving fit.

Alternative Construction. By making afew changes in design, it is possible to con-struct an engine of this type without alathe. The cylinder may be made from apiece of heavy brass tubing or from a brassbushing of suitable size and bore. A diskof heavy brass can be sweated to one sideand filed flat. Then the surface should be

Piston. Turn from steel rod. The shaftis 1/8-in. drill rod or cold-rolled steel,threaded at one end and screwed into ahole tapped in center of piston. If cylinderis carefully bored and piston is lapped in,no piston ring is necessary. The groovein piston will hold oil and prevent undueleakage. If desired, however, a split ringcan be made.

Crankshaft. Build up from 1/8-in. cold-rolled steel.

The general set-up, sectional drawing of boiler, and the safety valve

10?MODEL MAKING

The boiler and cocoa-can housing assembledpreparatory to covering them with asbestos

Complete power unit readyfor use and, above, brazingthe tubes with silver solder

Underside of boiler.The tube in center isthe superheater tube

The general set-up, sectional drawing of boiler, and the safety valve.

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HOW ENGINE IS CONSTRUCTEDDetail drawings of all principal parts—the baseand frame, cylinder, piston and rod, and crank-shaft—and two assembly views, one being partlybroken away to show the construction. The boreis ½ in., stroke ¾ in. While not complicated,the model w i l l give an amateur mechanic excel-lent practice in pattern making and machine work

106 AMATEUR CRAFTSMAN'S CYCLOPEDIA

Boring cylinder with small boring attachment

scraped down so that only a small areaaround the steam ports is in contact withthe bearing surface of the engine frame.Other surfaces can be filed smooth. In fin-ishing the engine frame, file the surfaceagainst which the cylinder oscillates as flatas possible; then scrape down all but asmall area around the steam ports.

F brazing equipment is available, nocastings need be made. The engine

frame can be of heavy sheet brass sweatedtogether.

Action. Steam is led to engine throughbrass tubing which enters both inlet ports,one at top, the other at bottom. Checkports so that connection is made with prop-er holes. When piston is at top, the port incylinder should be in line with inlet portin engine frame. The lower inlet port inframe will then be covered by the cylinder,while the hole in lower end of cylinderwill be in line with lower exhaust port inframe. When piston is driven downward,steam is driven out of lower exhaust port.

The boiler, although designed especiallyfor this engine, is suitable for use withany small steam power plant. It is par-ticularly suitable for installation in modelsteamboats of the slower type where ahigh-pressure flash steam system is not re-quired. Among its advantages are sim-plicity of construction, low cost of mate-rials, a unique and efficient heating unit,and safety.

Materials. One piece seamless brass tub-ing 2½ in. in diameter by 6 in. long. Sixfeet seamless brass tubing of 1/8-in. insidediameter. One piece copper or brass tubing½ in. in diameter by 6 in. long. One piece1/32 in. thick sheet brass, 6 by 8 in. forboiler ends and fuel tank. One 1-lb. cocoatin of the type shown for boiler housing,¼ lb. plastic asbestos, and a little asbestoswool. The safety valve, filler plug, andother small parts can be made from scrapmaterial.

Making Boiler. Square and smooth endsof 6-in. length of 2½-in. brass tubing. Cuttwo disks of heavy sheet brass to fit snuglyin ends.

NNEAL 1/8-in. tubing by heating to adull red and quenching in water. Take

the entire length of tubing and, leavingenough stock to hold onto with a pair ofpliers, make the first bend. Then, usingthe hands only to hold the tubing, makethe second bend the proper distance fromthe first to form one of the water tubes.Saw off and trim to exact length.

As shown in cross section of boiler, thesuper-heater tube has its open end insideboiler about ¼ in. from the top. The tube

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pressure, a careful job of soft solderingwill serve.

EXT solder in the end plates, whichshould fit closely. First spot-solder

them at three or four points around theedge, placing them about Ms in. in fromends of boiler. Using light hammer blowswhile rotating the boiler on an anvil oriron block, carefully turn ends of boiler inover end plates.

Filler Plug and Safety Valve. The fillerplug is simply a screw plug, seated in ashort length of drilled and tapped brassrod soldered in top of boiler. If you donot care to buy a safety valve, a simpleone can be made of scrap brass as shown.By varying tension of spring, the valvecan be adjusted to pop at the desired pres-sure. The adjustment can be made at anyfilling station having an air pump that canbe set to deliver air at different pressures.

Housing. The 1-lb. cocoa can is exactlythe right size, but light gauge sheet ironcan be used if desired. Carefully cut outone entire side of the cocoa tin. Then,with ¾-in. strips of tin or light brass, formstraps to support boiler so that it dropshalf way into can. It will be found thatthe can is ½ in. longer than the boiler.This space is left at the rear and serves asan opening for the stack, which is formedof tin. The stack should run from bottomof boiler to any desired height.

Strips of brass or tin may then befastened to bottom of boiler housing formounting purposes. Next rivet in placethe clips or supports for burner as shown.

After assembling boiler, stack, and hous-ing, bind boiler firmly in place with copperwire. Then cover entire assembly with a¼-in. layer of plastic asbestos.

Burner. Take a piece of ½-in. brass orcopper tubing and with a hack saw make,eighteen cuts ¼ in. apart, each halfwaythrough the tube. Close one end of tube

Turning recess in disk at rear of cylinder

then passes down through bottom of boilerand along underside between the watertubes, enters boiler again at opposite end,and passes up through top.

After all tubes have been formed andends filed square and smooth, spot the tenholes on bottom of boiler into which thetubes are to be soldered. Dri l l holes a trifleundersize and file ends of tubes to a snugfit. Ends of water tubes should projectinto boiler about 1/32 in. Put tubes inplace and bind securely with iron wire.If you have access to a brazing torch, thesoldering should be done with silver solder.However, since the boiler operates at low

with a plug. Cut a plug to fit other endand drill a hole through plug to receive apiece of 1/8-in. brass tubing. Take a pieceof 1/8-in. tubing about 10 in. long and,starting at one end, drill sixteen or eighteenholes ¼ in. apart with a No. 60 drill. In-sert this fuel supply tube in burner tube asfar as it will go; then pack unit withasbestos wool. Slip plug over protrudingend of fuel supply tube, slide it into place,and crimp burner tube over plug. With apin, pull a portion of the asbestos woolout through each of the slits in burnertube to form wicks. These wicks shouldbe about Mi in. long. The burner tube isheld in position by the bracket and clipshown.

The fuel tank is simply a small sheetbrass tank or a can of suitable size. Inserta small shut-off cock between fuel tank andburner.

Operation. Open shut-off valve, allowingthe fuel, which is alcohol, to run down intothe burner. The size of the flame may beregulated by the valve.

If used in a boat, the fuel tank may belocated in any convenient place so long asit is higher than the burner. Boiler andengine should be so placed as to make thedistance from the boiler steam outlet tothe engine as short as possible. A smallglobe steam valve should be inserted insteam line between boiler and engine. Thephoto of the entire power unit shows theengine connected to the boiler by a length

The ½-in. burner tube with wick slots, the1/8-in. feed tube, and tank for holding fuel

of rubber tubing. At 25-lb. pressure thisis entirely satisfactory where flexibility isdesired in making tests and adjustmentsand in experimenting with the unit. Thick-walled rubber tubing of the type used onauto windshield cleaners is satisfactory.

This type of boiler can be altered slightlyfor high-pressure use in a speed boat onshort runs by adding a water gauge andsubstituting a gasoline burner of the blow-torch type. By a few experiments withthe throttle wide open, it can be deter-mined just how much fuel can be used atone filling without exhausting the watersupply.

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