August 4, 1932. The Model Engineer and Practical Electrician. 103

1 A 2" inch , 1 inch ~troke, Model Described by W. W. MASON

HE little model engine about to be 14 gauge. From an examination of the sketch T described ,,,as kindly lent to me for this (Fig. I) it will be seen that the strap is purpose by Mr. S. VV. Simpson, to whom split in two places on the horizontal centre many member s of the Society of Model and line, and it can therefore be sprung open Experimental Engineers are indebted for sufficiently to allow its being slipped over into some very delightful clays spent at his house. the eccentric sheaf groove and then secured The model was made probably about the by a screw, No. 8 B .A. in this case. The same date as the " Planet" type clouble-action is worked on tht> slip-eccentric principle, o"cillating locomotive described by Mr. Gentry in Vol. 60 of the MODEL ENGINEER, and is therefore about fifty years old. I t is also about as inaccurate and lacking in de­ tails as the locomotive; nevertheless it makes q uite a pretty little working model. This engine has some rather unusual features: (A) the absence of the usual ; (B) the main bearings for the beam; (C) the eccentric rod and strap. Taking these three features in the order given: (A) The arrangement substituted for the usual .parallel motion is, of course, done to simplify con truction, and consists of a g uide for the rod placed just above the gland, and by connecting the rod to the beam end by means of a pair of flat links hinged The Beam Engine and simple Pot-Boller on the pins so that they can accom­ the sheaf being driven by a segmental-headed modate themselves to the arc described by the pin driven into the haft, so the engine beam end during its period of vibration. The wi ll work in either directi-an. Main Bearings. The main bearings for the crank­ shaft are split, and caps a re held down by screws in the usual way. The Bed Plate. The bed plate, or base, consists of a brass casting 5i in. in length by 2 5/ 16 in. in width and -k in. in height. lts thickness is 1/ 16 in., except at the corners, which are left thicker for strength. The is 3 7/ 16 in. diameter and i in. in width on the rim. The model (engine and ) is constructed entirely of brass, with the exceptions of the , beam pin, c rosshead and valve spindle. All screws were originally of brass, but some have been replaced by the 1" x 1" working Beam Engine present owner with steel ones. photograph shows this piston r-ad guide sup­ Cylinder. ported by two turned brass columns screwed The cylinder is ! in. bore by 1 in. ; into the bedplate. made fro m a casting, but is now fitted with Beam Trunnions. a liner of hard drawn brass tubing. I fancy (B) The two trunnions, their "caps," feet, the r eason for this is that a t so me time a and the square plate r esting on the column previous owner had the m isfortune to twist top, are all cast in o ne pi ece, there being no off one of the screws fixing the steam-chest remo,-able caps. The bearings a re simply co ,-e r, and in drilling it out the drill pene­ drilled .through, and a steel pin 3/ 32 in . t"ated the cy~i nd er wall, which 'i s very thin. driven in for the beam to ",,-ing upon . The pi ton, 3/ 16 in. in length, is of the Eccentric Rod. usual old type wi th a it in. g roove pac. ',,·d (C) The eccentric strap a nd keleton rod a re with cotton, ancl i scre" -ed and oldered to made in one piece fr-a m sheet brass, about X o. the h in . pi ton rocl. The upper end of piston 104 The Model Engineer and Practical Electrician. August 4, 1932. rod is turned down, screwed No. 6 B. A., to engine, but having an opening cut therein pass through crosshead, and secured by a nut. 31 in. by I t in., into which the spirit reservoir Crosshead. drops. The cross head is a piece of i in. round This re::ervoir is made of tinned steel sol dered up, and has a brass edging all round M. S. 5/ 16 in. in length turned down to ~ in. each end, forming two spigots, upon which it which rests upon the brass base, thus the the lower ends of the two brass links work, lamp is suspend'ed and does not rest on the . thus connecting the crosshead to the beam. table. The lid is flat and is p rovided with The links are made fro m 16 gauge brass strip three wick tubes of brass, i in. in diameter ; 3/I6,in. in width and t in. ce ntres. they stand up i in. from the Ji'd, but do not project below it more than ·enough to hold a SteaIn Ports. fill et of so lder. To return to the ·cylinder, it will be noticed The usual type of is fitted in that as the valve works at right angles to the the top of the " dome,'"" and a plug steam­ , the steam ports are not in the cock in side of same. ·' Vorking pressure is', I usual position. The sketch (Fig. 2) shows expect, about 15 lb. per sq'. in. The engine. the arrangen,lent. The ports are 1/ 16 in. works well with the aid of a cyc1'e , so diameter holes, steam and exhaust being alike. shou:<1 go \\'ell by steam. The right hand port leads to the top of the cylinder, the left hand to the bottom, and the centre (exhaust) is also drilled up from belO\\', and then plugged up to where the exhau: t , , passage passes out at the side; this is ! • ' i to take a piece of 5/32 ill. copper pipe. The is of hard drawn brass, ancl has 5/32 in. travel and a full 1/32 in. steam lap, so ports are opened to steam for about half their width only.

Sketch showing arrangement of steam-ports

Split eccentric strap sprung open to pass over the sheave In my opinion this little model could be General DiInensions. improved considerably by making the follow­ H eight of beam centre from bedplate = ing alterations. The beam should be raised by a t least one inch by means of a longer 3 1/ 16 in. L ength of beam between centres =3 11 / 16 in. column; at the same time the main bearing ' Vidth across beam trunnions = 111 in. standards should be lowered by half an inch. Width of beam = 5/32 in. These a lterations would ,permit of a longer Length of crankshaft = 3 in. being used and also longer . Diameter of crankshaft = i in. links between piston rod and beam. The ~ .Crankpin, length 3/ 16 in., diamete:- piston rod guide could be raised, say, half an inch, and thus be more effective in steadyi ng = 3/ 16 ill . L ength of connecting rod (centres) = 2n in. the piston rod when at the top of its stroke. r ,H eight of crankshaft bea rings from bed- The beam might be lengthened with advan­ plate = I in. tage without altering the positio n of the cylinder or crankshaft. B,y ha ving the beam Width of bearings = 3/ 16 in. Diameter of valve spindle = 3/32 in . of such a length that the connecting links The connecting rod is a casting, fl at and assume a vertical' position ,,(hen piston is at with the flu tes cast in, and has a forked to p­ the bottom of the cylinder, less side strain end. Big-end split, wi th cap. "'ould be put on the piston rod and gland, and therefore less friction set up. A larger and The Boiler heavier flywheel would make for smooth and The boiler consists of a piece of braos slow wo rking; this would entail lengthening tubing 2 in. in diameter and of about No. 2C the feet of the base to' keep fl ywheel clear of gauge, h aving the domed ends spun over and the g round level, unless the wheel worked in soldered in.. The overall length is 5 in. The a "pit. " present o wner has augmented the heating sur­ The base could be mad·e up as a tank to face by fitting ten brass screws in the boiler hold water, and a pump' fitted therein worked barrel o n the underside, and he tells me th a~ from the beam to pump the feed water into its steaming properties have been improved the boiler. This would form a realistic and immensely thereby. Mr. Crebbin tried out use ful addition. The exhaust steam might be this dodge some years ago on a locomotive discharged into the tank, thus partly con­ boiler and described the results in the MODEL densing and warming the feed water. . ENGINEER. A model constructed on these lines would The boiler rests upon two brass slings sup­ prove an interesting j-ob, and would also look ported by four turned brass columns which are well when working. It would be wo rthy of screwed into a base sim ilar to that of the a better type of boiler tham that described.