975CFd01.pdf

The MUNCASTER

steam-engine models

EDGAR T. WESTBURY glances back with a modern eye

toosome classic models of the past

N THE COURSE of the long history

Of MODEL ENGINEER-now, in-

cidentally, approaching 60

years-many notable designs and

descriptive articles have been pub-

lished which have established tradi-

tions or marked milestones of

progress in model engineering.

Not only are these remembered by

old readers but they are often the

subject of considerable discussion.

and requests for further information

about them are constantly encountered.

A few of the authors of these features

are still with us, and in one or two

cases continue to contribute articles;

but most of them have passed on and

are no longer available to provide

either new designs or guidance on

their earlier ones.

Many readers have suggested that

the M.E. should reprint some of these

earlier features, but while this might

be a good idea, from certain aspects

there are several reasons why the

policy has not been adopted by this

journal. In the first place, although

the designs for models do not neces-

sarily become outdated the mode of

treatment, including methods of con-

struction, is subject to certain changes

as workshop equipment and technique

improve.

In modern setting

To many modern readers, reprinting

of old articles or designs may seem

to be a policy of retrogression, or at

least stagnation;it may even give

the impression that there is a dearth

of new ideas in model engineering-

which is far from being the case.

Therefore the idea of verbatim re-

prints of articles is not considered

desirable, but there is much to be said

for the revival of old designs in a

modem setting.

There can be few model engineers

who have not heard of such pioneers

as Henry Greenly, C. S. Lake, Fred

Westmoreland, H. H. Groves, George

Gentry, or the traction engine special-

ist “ Frost-spike,” who have been

acknowledged masters in a very wide

and versatile field of design. Last

but not least, the name of H. Mun-

MODEL ENGINEER

fore, need despise the crude and

primitive types of models produced

by beginners, so long as they lead on to

the more realistic types which were

Muncaster’s speciality.

The simplest form of engine de-

scribed by Muncaster is one having a

single-acting oscillating cylinder (Fig.

1) and this will commend itself to

many readers, not only on account

of its simple construction, but also

because it can be built without castings.

It is of the type which would now be

classed as “ inverted ” vertical, having

the cylinder below the crankshaft,

though in the early days the practice

of locating the cylinder at a low level-

firmly bolted to the floor if possible-

was considered normal and orthodox.

caster is well remembered as a special-

ist in the design of all types of steam

engines, whose excellent drawings of

many types of stationary and marine

engines in early volumes of the M.E.,

and also in the handbook Model

Stationary Engines, published nearly

half a century ago, provided scope

for the talents of innumerable con-

structors.

H. Muncaster was a practical

draughtsman who not only had a

wide experience of steam-engine design

but also obviously had a love and

devotion to his craft, and to all

things mechanical. In the introduc-

tion to his book he pays due homage

1-A simple

oscillating

engine

THE PILLAR

The main structural component of

this engine is the pillar, shown in

Fig. 2, the lower portion of which is

of rectangular section, with extended

feet at the sides for mounting on the

flat square baseplate.At the top end,

the section is also rectangular and is

cross bored to form a housing for the

single main crankshaft bearing. .In

the centre, it is turned to circular

tapered form, with simple ornamenta-

tion in the form of a beading near the

lower end.

To save material in making this

part, the foot at the base may be

made separate and silver-soldered on;

or screwing and sweating would

probably be satisfactory. This should

be done before machining and I

suggest that the front and rear sides

should then be faced quite flat and

true by filing, or any other convenient

method, after which the two ends

may be marked out, exactly central

both ways, and centre-drilled so that

the part can be mounted between

centres for turning.

The cross holes for the main bearing

and the cylinder trunnion may now

be drilled, and it is essential that

these should be exactly square with

the pillar face, so it will be advisable,

after marking out their positions, to

set the pillar up on the faceplate of

the lathe for these operations.

An alternative to the pillar as the

21 FEBRUARY 1957

to the many early engineers and

inventors who contributed to the

development of the steam-engine,

and also gives a complete answer to

those who would condemn model

engineers for“living in the past.”

“For the purposes of the model

engineer,” he states, “it does not

follow that the most recent and perfect

engines are most suitable; on the

other hand, some of the older engines

form subjects better adapted and more

fitted as prototypes for models, being

more picturesque and providing better

object lessons.”

With which precepts I whole-

heartedly agree, and also with his

further comments that many of the

most popular so-called models “ have

no prototype in reality, but neverthe-

less may be useful in illustrating some

of the points of the steam-engine, as

well as providing a simple motor,

where only a small amount of power is

required.”No model engineer, there-

270

support for the crankshaft bearing is

given in Fig. 3. This consists of an

A-frame cut from sheet metal, with

the bearing housing at the apex,

either bushed or otherwise reinforced

to provide extra bearing surface. It

does not, however, incorporate the

port block or other cylinder mounting

and it is not explained how this should

be fitted. For this particular type of

engine, I do not consider it so elegant

in appearance as the pillar, neither

does it simplify construction.

CYLINDER

The designer suggests that the

cylinder (Fig. 4) may be made from a

piece of brass tube, with the flange,

end cap and portface soldered on,

These conditions can be assured by

machining, as the bore and flange

can be dealt with at one setting;

a D-bit is recommended for taking the

final cut in a blind bore, after which

it should be finished by lapping with

aluminium oxide or brick dust on

a short copper or aluminium lap-

not one which extends the full length

of the bore, as this will tend to make

it tapered or bell-mouthed.

If the cylinder is machined from the

solid the smallest diameter of bar

which can be used is 1 in. A good

deal of material will. be left around

the base, after turning as much as

possible of the outside, and this will

have to be filed or machined away,

leaving the portface to be faced flat.

working to the same index reading on

the topslide for each cut, the shape

may be made practically circular

and flush with the upper turned part,

needing only a clean-up with a smooth

file to take off the sub-angular corners,

and a final polish with emery cloth.

The trunnion is fitted to a tapped

hole in the face of the portblock,

and it is most essential that this

should be dead square with the cylin-

der axis. It could well be drilled and

tapped while the cylinder is set up

on the faceplate’, to ensure this; the

hole should not go right through into

the bore, though some constructors

may find difficulty in tapping a short

blind hole.

If it does go through, however,

The components of the engine

but in practice it will usually be found

just as easy to machine it from the

solid, as the manipulation of small

pieces, which have to be accurately

located and soldered simultaneously,

is not as simple as it looks.In either

case, however, it is essential that the

bore of the cylinder should be exactly

circular and parallel, the flange faced

square with it, and the portface dead

flat and parallel to the axis.

21 FEBRUAltY 1957

A very efficient way of doing this is

to make a short mandrel, of a size to

fit neatly in the cylinder, and fix this

in an angle-plate or a short piece of

angle iron, on the lathe faceplate.

Clamp the cylinder endwise on this,

checking it first to see that it is parallel

with the faceplate; it can then be

turned into any position to‘ machine

the portface of “nibble” away the

rest of the surplus material. By

271

make certain that the trunnion stud

does not project into the bore when

tightly screwed in and that there are

no burrs left on the inside to interfere

with the free movement of the piston.

It is an advantage to machine a shallow

recess around the tapped hole to

relieve the centre of the face; alter-

natively, this may be done on the

corresponding face of the pillar.

Little need be said about the cylinder

MODEL ENGINEER

Muncaster

that they are correctly located in

relation to each other,

First of all, the hole m the cylinder

is marked out as correctly as possible

and drilled undersize, say 5/64 in.

or No 48 drill, the hole being con-

tinued right through the ‘opposite

wall of the cylinder. The engine is

then assembled and the crankshaft

turned to swing the cylinder to

maximum angle in one direction,

where it is clamped in place by the

nut on the trunnion stud with a

suitable distance piece.

steam-engine

models . . .

MACHINED AWAY

cover (also shown in Fig. 4), as this

is a simple job which can be turned

at one setting. The spigot should fit

neatly in the cylinder bore, and the

hole drilled centrally to a working fit

for the piston rod. It is attached to

the cylinder flange by three 3/32in.

or 8 B.A. screws.The piston assembly

(Fig. 5) is built up in three pieces,

the rod, of 3/32 in. dia. bright mild-

steel, being screwed on each end to

take the solid piston at one end and

the crankhead bearing on the other,

k;&;Fse pieces bemg of brass or

In the drawing, the piston is shown

as a plain parallel disc, machined to

fit closely in the cylinder, but I strongly

recommend, at least to those with

little experience in these matters, that

a groove should be machined in it

for packing with graphited asbestos

or cotton yarn. The advice I have

given in articles on other engines,

that the final machining of the piston

should be done after it has been

screwed tightly on the rod, still holds

good.Final adjustment of the length

of the rod, so that the piston just

stops clear of the end of the bore at

the extremity of its stroke, can best

be done on assembly.

CRANKSHAFT

The crankshaft is built up with a

web made from rectangular brass bar,

into which the main journal and crank-

pin are screwed. As an alternative

form of construction a disc can be

LAPPING

By running the drill through the

hole in the cylinder the position of

the hole in the block may be spotted

or drilled to full depth, after which

the cylinder is shifted to the other

extreme position by turning the crank,

and the operation repeated. The

ports are then opened out to 3/32 in.

or No 42, and the hole in the outer

cylinder wall closed by a plug screwed

or soldered in.

Finally the two side holes in the

portblock, forming steam and ad-

mission connections, are drilled to

meet the ports and tapped to take

screwed pipes, the faces of both cylin-

der and portblock then being lapped

on a piece of plate glass to produce a

truly flat and smooth finish.

When finally assembled, a light

spring is fitted to the trunnion and

the locknuts are adjusted to hold the

cylinder against the block, but with

no more tension than is necessary_to

keep it in steamtight contact against

the working steam pressure. The

engine will run in either direction,

according to which of the two con-

necting pipes is connected to the

steam line, so that it could readily

be made reversible by fitting a change-

over cock.

If made according to directions and

carefully finished, this should not

only be a satisfactory working model,

but also a handsome and dignified

one.

Set up for rna;F&;g the cylinder

PORT LOCATION AND TIMING

The entire success of an oscillating

cylinder engine depends on the accur-

ate location of the steam-ports, and

this is where many constructors fail

to get the best results, as it is by no

means easy to mark out and drill

holes exactly in the right place.Both

the size and position of the two holes

in the stationary portblock are depend-

ent on their radius from the trunnion

centre, in conjunction with the maxi-

mum distance of swing at extreme

cylinder angularity-which, incident-

ally, is not the same thing as half the

piston stroke.

In this engine, the maximum dis-

tance of swing under these conditions

at 3/8 in. radius is 3/16 in., so the ports

should be drilled at 3/16 in. centre

distance apart, and as the blank space

between them should be exactly the

same as the port diameter, this dimen-

sion should be 3/32 in.; on no account

drill larger holes as this would only

result in steam wastage between the

ports.

Even with the utmost care in locat-

ing the holes in the portblock, how-

ever, there is still a possibility of error

in the position of the single hole in the

cylinder face, which may completely

nullify all efforts to produce a correctly

timed engine. I suggest, therefore,

adopting an unconventional method

of drilling-these holes, which not only

kills two birds with one stone,. as it

were, but also ensures positively

272

used, and this would not only improve

the appearance but could also be

balanced if desired. In either case,

however, it is essential that both the

tapped holes should be square with

To be continued.

-- --

the web and parallel with each other.

No details are given of the flywheel,

which is shown as a solid disc, but I

recommend that a spoked flywheel

with a heavy rim should be fitted.

The main bearing is in the form of

a plain bush, made to press tightly

in the cross hole at the top of the

pillar, and the centre hole in the end

of the latter is drilled through into the

bush to serve as an oil hole. It is

now in order to assemble the parts

temporarily, to ascertain that every-

thii works freely and smoothly,

without binding or tight spots, and

that the piston clears at both ends

of the cylinder.

MODEL ENGINEER

ADDITIONS TO THE LATHE

Instructions for making centring

devices ; chucking accessories; tool

holders and cutter bars; dividing

appliances.; simple milling attach-

ments; aids to screwcutting; and

steadymg appliances are to be found

in Edgar T. Westbury’s Lathe Acces-

sories.-

Priced 3s. 6d., postage 3d. (U.S.A.

and Canada $1.00), it can be obtained

from Percival Marshall and Co. Ltd,

19-20, Noel Street, London, W.1.

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