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

A 1 2" inch bore, 1

Beam inch ~troke, Engine

Model

Described by W. W. MASON

T HE little model engin e abou t to be described ,,,as kindl y lent to me for this

purpose by Mr. S. VV. Simpson, to whom man y member s of the Society of Model and Expe rim ental Engineers are indebted for some very delightful clays spent at his house.

The m odel was made probably about the same date as the " Planet" typ e clouble-action o"cillating cylinder locomotive described by Mr. Gentry in Vol. 60 of the MODEL ENGINEER, and is therefore about fifty years old . I t is a lso about as inaccurate and lacking in de­tai l s as th e locomotive; nevertheless it makes q uite a pretty little working mod el.

This engine has some rather unusua l features: (A) the absence of the usual parallel motion; (B) the main bearings for the beam; (C) the eccentric rod and strap.

Taking these three features in the order given: (A) The arrangement substitu ted for the usual .parall el motion is, of course, done to simplify con truction, and consists of a g uid e for the pi ston rod placed just above the g land, and by connecting the rod to the beam end by m eans of a pair of flat links hinged on the crosshead pins so that they can accom­modate themselves to the arc described by the beam end during its period of vibration. The

1" x 1" working Beam Engine

photograph shows this piston r-ad gu ide sup­ported by two turned brass columns screwed in to the bedplate.

Beam Trunnions. (B) The two trunnions, their "caps," feet,

and the square p late r estin g on th e column top, are a ll cast in o ne pi ece, there being no remo ,-abl e caps. The bearings a re simply drill ed .through, and a steel pi n 3/ 32 in . driven in for the beam to ",,-ing upon .

Eccentric Rod. (C) The eccentric s trap a nd keleton rod a re

mad e in one pi ece fr-a m sheet brass, abou t X o.

14 gauge. From an examination of the sketch (Fig. I) it will be seen that the strap is split in two places on the horizontal centre line, and it can therefore be sprung open sufficiently to allow its being s lipped over into the eccentric sheaf groove and then secured by a screw, No. 8 B .A. in thi s case. The va lve is worked on tht> slip-eccentr ic principle,

The Beam Engine and simple Pot-Boller

the sheaf being driven by a segmental-headed pin driven into the crank haft, so the engine 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 flywheel is 3 7/ 16 in. diameter and i in. in width on the rim.

The model (engine and boiler) is constructed entirely of brass, with the exceptions of the crankshaft, beam pin, c rosshead and valve spindle. All screws were originally of brass, but some have been replaced by the present owner with steel ones.

Cylinder. The cylinder is ! in. bore by 1 in. stroke;

made fro m a casting, but is now fitt ed with a liner of hard drawn brass tubing. I fancy the r eason for this is that a t some time a previous owner had the m isfortune to twist off one of the screws fixing the steam-chest co ,-e r, and in drilling it out t he drill pene­t"ated the cy~i nd er wall , which 'is very thin . The pi ton, 3/ 16 in. in length, is of the usua l o ld type wi th a it in. g roove pac. ',,·d with cotton, ancl i scre" -ed and oldered to th e 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 pass through crosshead, and secured by a nut.

Crosshead. The cross head is a piece of i in. round

M. S. 5/ 16 in. in l ength turned down to ~ in. each end, forming two spigots, upon which the lower ends of the two brass links work,

. thus connecting the crosshead to the beam. The links are made fro m 16 gauge brass strip 3/I6 ,in. in width and t in. ce ntres.

SteaIn Ports. To return to the ·cylinder, it will be noticed

that as the val ve works at ri ght angles to th e p iston rod, the steam ports are not in the usual position. The sketch (Fig. 2) shows the arrangen,lent. The ports are 1/ 16 in . diameter holes, steam and exhaust being alike. The right hand port leads to the top of the cylinder, the l eft hand to the bottom, and the cen tre (exhaust) is also drilled up from belO\\', and then plugged up to where the exhau: t passage passes out a t the side; this is tappet! to take a piece of 5/32 ill. copper pipe.

The slide valve is of hard drawn brass, ancl has 5/32 in. travel and a full 1/32 in. steam lap, so port s are opened to steam for about half their width only.

Split eccentric strap sprung open to pass over the sheave

General DiInensions. H eight of beam centre from bedpl ate =

3 1/ 16 in. L ength of beam between centres =3 11 / 16 in. ' Vidth across beam trunnions = 111 in. Width of beam = 5/32 in. L ength of crankshaft = 3 in.

. Diameter of crankshaft = i in. ~ .Crankpin , length 3/ 16 in., diam ete:-

= 3/ 16 ill . L ength of connecting rod (centres) = 2n in.

r ,H eight o f crankshaft bea rings from bed-plate = I in.

Width of bearings = 3/ 16 in. Diameter of valve spindle = 3/32 in . The connecting rod is a casting , fl at and

with the flu tes cast in, and has a forked to p­end. Big-end split, wi th cap.

The Boiler The boiler consists of a piece of braos

tubing 2 in. in diameter and of about No. 2C gauge, h aving the domed ends spun over and soldered in.. The overall length is 5 in. The present o wner has augmented the heating sur­face by fitting ten brass screws in the boil er barrel o n the und erside, and he tell s me th a~ its steamin g properties have been improved immensely thereby. Mr. Crebbin tried out this dodge som e years ago on a locomotive boiler and described the results in the MODEL ENGINEER.

The boiler res ts upon two brass slings sup­ported by four turned brass column s which are screwed into a base sim ilar to that of the

engine, but having an opening cut therein 31 in. by I t in . , into which the spiri t reservoir drops.

This re::ervoir is made of tinned steel sol dered up, and has a brass edging all round it which res t s upon the brass base, thus the lamp is suspend'ed and does not rest on the table. The lid is flat and is p rovid ed with three wick tubes of brass, i in. in diameter ; they stand up i in. from the Ji'd, but do not project below it more than ·enough to ho ld a fill et of so lder.

The usual type of safety valve is fit ted in the top of the " dome,'"" and a plug steam ­cock in side of same. ·' Vorking pressure is', I expect, about 15 lb. per sq'. in. The engine. works well with the ai d of a cyc1'e pump, so shou :<1 go \\'ell by steam.

, , • ' i

Sketch showing arrangement of steam-ports

In my opinion this little mode l could be improved considerably by making the follow­ing al terations. The beam should be raised by a t least one inch by means of a longer column; at the same time the main bearing standards should be lowered by half an inch. These a lterations would ,permit of a longer connec tin g rod being used and a lso longer links between piston rod and beam. The piston rod guide could be raised, say, half an inch, and thus be more effective in stead ying th e piston rod when a t the top of its stroke.

The beam might be lengthened with advan­tage without altering the positio n of the cy linder or crankshaft. B,y ha ving the beam of such a length that the connecting links assume a vertical' position ,,(hen pi ston is at th e bottom of the cylinder, less side strain "'ould be put on the piston rod and g land, and therefore less friction set up. A larger and heavier flywheel would make for smooth and slow wo rking; this would entail lengthening the feet of the base to' keep flywheel clear of the g round level, unless the wheel worked in a "pit. "

The base could be mad·e up as a tank to hol d water, and a pump' fitted therein worked from the beam to pump the feed water into the boiler. This would form a realistic and use ful addition . The exhaust steam might be di scharged into the tank, thus partly con­densing and warming the feed water. .

A model constructed on these lines would prove an interest ing j-ob, and would also look well when working. It would be wo rthy of a better type of boiler tham that described.