By RUDY KOUHOUPT

AS A PRIME MOVER, the steam en-gine came into existence over two

centuries ago. From its humble begin-nings, James Watt improved upon the op-eration of the steam engine until he raisedit to the position of a great industrial andeconomic force. One of his innovations,the parallel link motion, functions in thiscaptivating miniature just as Watt speci-fied in his patent of 1784.

Briefly, this is how it works: Steam,regulated by the valve, drives the pistonup and down in the cylinder in a vertical,straight line. The piston rod, likewise,travels in a straight line but is connected

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Technical Art by Fred Wolff

to one end of the beam. This is where theparallel link motion comes in. It is inter-posed between the piston rod and thebeam. There it converts the linear motionof the piston rod into the radial motionnecessary for the beam to oscillate, orwalk, about its midpoint. At the oppositeend of the beam, the connecting rod dropsto the crank to impart a rotary motion tothe crankshaft. An eccentric mounted onthe crankshaft controls the valve so thatsteam is admitted to and exhausted fromthe cylinder in the proper sequence ofevents. The cylinder is double action.

Begin construction of your miniature

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engine by cutting out the wood base andthen mark out the bedplate on 1/8-in. Duraland drill the holes for the mounting screwsand column. Two wood screws, throughthe holes in diagonal corners, hold thebedplate to the base.

The complete column assembly is com-posed of the column, the two column ends,and the entablature. Machine the columnfirst, then the ends for an exact fit. Whenall parts are finished, pass a ¼ x 5-in. boltthrough them and anchor the assembly tothe bedplate with a nut on the underside.

Next, mark out the outline and holecenters of one spring beam on 1/32-in. sheetmetal. Drill it and use it as a guide whendrilling the second piece. Bolt the twopieces together with 2-56 screws throughthe smaller holes and cut out both parts atthe same time with a fine hacksaw. Finishto the mark by filing. Attach one to eitherside of the entablature with two 2-56screws. Now make the stretcher andplace it between the spring beam ends.

Next, make the gudgeon which spansthe spring beams and acts as the mainpivot for the beam. Four nuts on thethreaded ends of the gudgeon hold it inplace; one nut goes on each side of eachspring beam. Make the two link gudgeonsnext. Screw one into each spring beamand add a locknut.

Follow the same basic procedure on thebeam side members as you did on thespring beams. Assemble the beam by put-ting the shouldered ends of the centerspacer through the 5/16-in. holes in thebeam sides. Put the other spacers in place,AUGUST 1969

TWO PARALLEL LINKS go between the back and mainlinks and two more between back link and gudgeons

BRASS TUBING is sweat-soldered into an elbowflange to form the exhaust fitting for the cylinder

using 2-56 machine screws through thesides. The 1/8-in. openings are for the pinson which the connecting rod and linksmove. Mount the beam on the column bypassing the gudgeon through the spacer.

Shape the main and back links as shownand install with pins made from 13/16-in.lengths of 1/8-in. steel rod. The top screwsin the links will hold the pins in place. As-semble the four parallel links on a simplejig to insure that all will be exactly thesame length. The jig consists of two 1/8-in.steel pins accurately placed l¼ in. apartin a wooden block. Cut eight pieces of

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THIN SHEET METAL is rolled in a sleeve to form aninsulating lagging or cover around the cylinder

1/8-in. i. d. brass tubing, each 3/32 in. long, toform the eyes of the links. Put one overeach pin in the jig, and cut a length of3/32-in. brass rod to go between. Solder thetwo eyes and the rod together. Removefrom jig, and repeat until all links are done.

Cut 17/32-in. and ¾-in. lengths of 1/8-in.steel rod to form the lower pins in theback and main links, respectively. Spacersabout 1/8 in. long must be placed betweenthe parallel links on the lower pin of theback link. Exact size of the spacers andsetting of the link gudgeons must be de-termined individually so the beam willswing freely and evenly.

Cut a 3 5/8-in. length of 1/8-in. steel rodfor the crankshaft connecting rod and addthe big and small ends. After assemblingthe three parts, install the assembly in thebeam by passing a pin through the beamand the transverse hole in the big end.The pin is a 13/16-in. length of 1/8-in steelrod.

Shape the crankshaft bearing blocks asshown, and mount them on the bedplatewith 4-40 screws from the underside. Usebronze bearing stock for the crankshaftbearings which should be a light press fitin the blocks. Pass a 1/4-in. reamer throughthe bearings after mounting to be surethat all is well aligned.

Turn the crankshaft between centersfor the best job, then make the crank andcrankpin and mount them on the crank-shaft. Put the crankpin through the smallend of the connecting rod and adjust itslength by the setscrews.

Its length must be such that the beam ishorizontal when the crank is at mid-stroke. The beam ends must move sym-metrically, 5/8 in. above and below thehorizontal, when the crank is at eitherend of the stroke.

Use a block of ¾-in. square brass forthe cylinder. Set it up in a four-jawchuck, face the ends to bring it to lengthand mark the center of the ends. Start thebore with twist drills, bringing it up toabout 7/16 in. The bore can be finished inseveral ways, including the use of a sharpparallel reamer. My favorite method is touse a between-centers boring bar withthe cylinder mounted on the lathe saddle.Block the cylinder up and clamp it so itscenter coincides with the axis of the lathe.Feed the work slowly on power feed, in-creasing the bore a little at a time. Thismethod will produce a cylinder in which

AUGUST 1969

the walls are absolutely parallel through-out their entire length.

With the boring complete, mark out thetwo steam passages on the midline, 39/64 in.from either end. Drill these punch marks3/64 in. deep with drill No. 52. Mark theends of the cylinder where the steam pas-sages come out half way between the cyl-inder bore and outer wall. Drill 5/8 in. deepfrom either end with drill No. 52 to formthe complete passages which will be L-shaped at this point. Use a small file orend mill to remove about 1/32-in. of thewall between the end of each passage andthe bore to give free entry of steam.

Mark the locations of the four screwswhich will hold the port face to the cyl-inder, then drill 3/16 in. deep, and tap 2-56.

Cut a 1-in. square of ¼-in. brass forthe port face. Accurately locate the centeras a reference point. Working from thecenter, locate the four steam ports. Thetwo ports on the vertical centerline aredrilled No. 52 right through to meet thepassages in the cylinder wall. The twoports on the horizontal centerline aredrilled No. 52 to a depth of 1/8 in.

Connecting passages are drilled on thehorizontal centerline from each side toserve as steam inlet and exhaust. Markout and drill locations of the four mount-ing screws, then counterbore to form re-

(Please turn to page 202)

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THE ECCENTRIC STRAP must be a good running fiton eccentric with retaining screw loose in the groove

added the steam inlet flange and exhaustfitting to the port face, you are ready totackle the valve and its associated parts.

Make up the valve pivot first and screwit right into position in the port face. Markout the valve on a piece of 3/16-in. brassand work from the pivot center as yourreference point. Steam grooves in thevalve face are best formed by end-millingwith a 1/16-in. dental burr. Set up a falsepivot by mounting a 3/16-in. rod horizon-tally on the lathe saddle. Mount the valveon the pivot with its face toward theheadstock and the mill gripped in a chuck.Set the pivot 19/64 in. off center to corre-spond to the radius of curvature of thegroove. Feed the work in slowly, rotatingthe valve manually on the pivot throughthe proper angle. Lap the valve face andport face with jeweler's rouge to makethe joint steam tight. Mount the valve onthe pivot, holding it against the port facewith a light spring and nut.

Chuck a piece of brass for the eccentric,and machine the o. d. and the groove forthe retaining screw which prevents theeccentric strap from moving sideways.Then sever with a parting tool. Use thecenter mark from parting off as a refer-ence point to locate the crankshaft open-ing. The setscrew must pass through thebroad part of the eccentric.

Put a locknut on each end of the eccen-tric rod for length of adjustment. Use ashouldered screw for connecting the ec-centric rod's small end to the valve.

Making final assembly

Mount the eccentric on the crankshaftin any position for now and hook up thevalve through the eccentric strap and rod.Adjust the length of the eccentric rod sothat the division between the steamgrooves in the valve face will move equaldistances back and forth across the portson the vertical centerline of the port faceas the crankshaft is rotated. The last ad-justment is the eccentric position relativeto the crank. The eccentric should forman angle of about 165° to the crankpin.Adjust it so that the valve will be juststarting to admit steam to the appropriateport when the piston is at the end of itsstroke and is about to change direction.

My lathe is not big enough to handle theflywheel, so I hunted around and foundthe old gear which serves admirably. Witha heavy flywheel and long stroke, the en-gine runs very smoothly on either air orsteam. The proper operating speed for abeam engine is 50 to 60 rpm.

Complete plans detailing each part ofthe model can be obtained for $3.50 fromBeam Engine Plans, 691 Garretson Road,Somerville, N. J. 28876. ***

POPULAR MECHANICS

MODEL WALKING-BEAM ENGINE(Continued from page 159)

cesses for the screwheads. Now drillthrough the center reference point and tap10-32 for the valve pivot. Put a gasket be-tween the port face and cylinder side.

Machine the upper and lower cylindercovers from Dural. Use the cylinder as aring gauge to check the register diame-ters. Drill the covers for the mountingscrews, then spot the cylinder ends fromthe covers and drill and tap for themounting screws.

Chuck a piece of Dural for the piston,drill through for the piston rod and ma-chine the packing groove. Bring the o. d. toabout. 0002 in. oversize. Make the pistonrod and mount the piston on it. The pistonis held in place by a thin nut (3/64-in. ) oneither side. Next, chuck the piston rodwith the piston on it and, with a very sharptool, skim the piston to finish diameter.

Pack the piston with graphite-asbestosstring rolled into the groove. Use com-mercial packing split down fine. Assemblethe cylinder and covers with the piston inplace and gaskets under the covers. Putsome packing into the stuffing box andscrew in the gland.

Fit the piston-rod eye to the rod with alocknut on the rod. You can now mountthe cylinder on the bedplate by means of4-40 screws through the big holes in thelower cover. Connect the piston-rod eyeto the main link by its lower pin. Gentlyrotate the crankshaft to adjust the pistonrod in the eye. Its length must be suchthat the piston will not contact the coversat the ends of the stroke. When you have

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REAR SIDE OF ENGINE shows exhaust outlet along-side cylinder. Gear serving as flywheel in originalmodel could be lathe-turned disc of brass or steel