"Six Year Old's 4F"
The simple edition in 2½-in. gauge, of a L.M.S. class "4F" 0-6-0
suitable for operation by a six-year-old child, has aroused sufficient
interest among followers of these notes to warrant publication of a very
brief description and drawings ; so by kind permission of our friend
the K.B.P., here they are.
The locomotive is frankly a toy, but a very powerful and realistic toy ;
and given reasonable workmanship, it is quite capable of giving its
young owner-driver a ride on a simple four-wheel ball-bearing flat car,
provided he - or she, for that matter ! - can sit still "whilst the
train is running." Any child who can strike a match without setting
itself alight can operate the engine entirely unaided.
Also "dad" needs very little time, material, and even skill, to turn out
something that would have driven young Curly into a frenzy of delight.
There is, of course, no obligation to stick to the outline of the L.M.S.
"4F" engine ; the "top works" can be made to represent any locomotive
having this wheel arrangement. Also, sizes of wheels and other parts can
be varied to suit material in hand.
The main frames, shown by the heavy lines, can be cut from sheet
metal of any thickness from 13 to 16-gauge; no hornblocks are needed.
The axleboxes are made from 3/16-in. brass, and have a 1/16-in. slot either side, to slide in the frame openings.
The hornstays are made from angle-brass.
The buffer and drag beams are ¾ in. by 13-gauge strip metal,
the frames being attached to the angles by riveting only, riveting and
soldering, or silver-soldering.
The six-coupled wheels are 2½ in. diameter on tread, but anything slightly larger or smaller can be worked in.
Coupling-rods can be filed up from 3/16-in. by ½-in. steel, and
as the axles are sprung, should have the usual knuckle-joint behind the
driving crankpin; but this can be left out if ultra-simplicity is
The axles are made from 3/8-in. round steel shouldered at the
ends, if greatest strength is needed; otherwise they might be only ¼-in.
diameter, pressed into bare ¼-in. holes in the wheels, to save turning
The crank axle is built up same as "Mollyette's"; and if the
holes in the webs are drilled a press fit for axle and crankpin, no
brazing or pinning will be needed. The webs are made from ½-in. by
3/16-in. steel, and are 1¼ in. long.
The single cylinder is ¾-in. bore and 1_1/8-in. stroke, and if
no casting is handy, can be made from a bit of solid bar 1_5/16 in. by
1_1/8 in., chucked in the four-jaw for drilling to size and reaming.
The steam-chest is made from two pieces of ½-in. by 3/16-in.
brass rod for the sides, and ½-in. by ¼-in. for the ends,
silver-soldered together to form a rectangle.
The cover is a piece of 1/8-in. brass plate.
The crosshead is shaped like the letter " L," and can be filed
up from a piece of brass. The vertical part is drilled No. 30 to slide
on the single guide-bar, which is made from 1/8-in. round silver-steel
screwed into the gland boss. The outer end is supported in a plain hole
drilled in the cross-stay which takes the place of the usual
motion-plate. The horizontal part is slotted to take the little end of
the connecting-rod, and cross-drilled No. 30-for a 1/8-in. gudgeon or
The connecting-rod has a marine-type big end, and is filed up
from ¾-in. by 3/16-in. steel ; or it can be built up from 3/16-in. by
5/16-in. steel, with the cross piece for holding the brasses brazed on
to it. The brasses are made from two pieces of ¼-in. by ¾-in. brass -rod
placed side by side screwed to the cross piece on the rod, and then
drilled 3/8-in. clearing on the joint line.
The slide valve is operated by a loose eccentric controlled by a
stop collar ; and as there is only one pin joint between the eccentric
and the valve, there is nothing to get slack or out of order, and the
engine will retain the correct setting indefinitely.
The eccentric is turned from 1-in. steel bar, and has a- flange
on one side only. Care should be taken to get the hole through truly.
The stop pin is 3/32-in. silver-steel, pressed in. The strap can be made
up from a casting, or even a ring cut from 3/16-in. brass plate would
do, the eccentric rod being silver-soldered to it. The strap, if solid,
is placed over the eccentric before assembly, and there is no need to
take it off any more.
The driving collar is easily turned up from 1-in. brass rod ;
and a piece filed or milled out of it, leaves the two shoulders which
catch and drive the pin.
The valve setting is my usual ; the port should just crack as
the main crank comes on to the dead centre, and close at approximately
70 per cent. of the stroke.
The boiler is a plain water-tuber, with no more complication
than an ordinary toy "pot" boiler. The casing is 9¼ in. long and 2¾ in.
diameter, and can be rolled up from a bit of 1/32-in. sheet iron or
steel; even a good stout cocoa or coffee tin could be used for the
casing, if one of the right size, or near it, is available. The inside
barrel should be either a thin copper tube 9 in. long and 1¾ in.
diameter, or a piece of 24-gauge-sheet rolled up and silver-soldered at
the joint. Special to beginners: thick tube or sheet won't do, under
Fittings consist merely of safety-valve, regulator, test cock,
and blower. Safety valve is plain ball type, and screws into a bush
silver-soldered to the boiler barrel. The regulator is a screw-down
valve with a crank handle, see illustration ; the steam pipe from the
union underneath, goes along the bottom of the boiler barrel to the
cylinder. Blower valve is a smaller screwdown valve fitted as high as
possible, and the pipe from the union passes along inside the casing,
terminating in a little nipple pointing up the chimney liner. The test
cock may be either a plain plug cock of the commercial pattern, or a
screw-down valve without gland, fixed on the backhead at the centre line
of the inside barrel, so that if opened, water runs out when the boiler
is half full.
The boiler is fired by a four-burner spirit lamp, the wick
tubes being ½-in. diameter, 1_7/8 in. long, mounted on two ¼-in. feed
The superstructure requires little comment.
I don‘t think there is any need to go into further detail for a "toy"; as
to the tender, this is merely an "ornament," and can be made from sheet steel,
or even stout tin, in three or four evenings. All being well, I will give an
outline drawing of it soon.
The one-off article appeared in the 7th December 1944 issue of The Model Engineer.
The Association can supply a photocopy of the 5 page article.
This page was last changed on 06/05/2016