A small six-coupled tank engine, 25 cm long, on two pieces of 45 mm gauge track. Everything under the running plate works the way it does on a real locomotive. Turn the wheels and the main rods drive the pistons in the cylinders, which have windows so you can watch them. The valves are moved by Walschaerts gear: a return crank on the driving wheel swings the curved expansion link, the radius rod picks up that swing from the die in the link, and the combination lever adds a little of the crosshead's motion, so the valve opens just before each stroke. The reversing lever in the cab works too. Through the reach rod and the weigh shaft it lifts both radius rods in their links: at the bottom the engine is in full forward gear, in the middle the valves hardly move, at the top it runs in reverse. The gear is set out like the real thing, with 0.4 mm lead in every gear and the right-hand cranks a quarter turn behind the left ones. The joints are short pieces of 1.75 mm filament, so you need no screws.
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One of the two main frames, 225 mm long, with the axle holes, the hole for the weigh shaft and slots for the stretcher. A tab at the front goes into the cylinder block, one at the back into the rear buffer beam.
Holds the two frames the right distance apart, behind the driving axle.
Both cylinders, both steam chests and the saddle between the frames in one part. Windows in the outer walls show the pistons and the piston valves, and you can see the steam ports at both ends of each cylinder.
Front cover of a cylinder, with a spigot that fits the bore.
Front cover of a steam chest.
With two buffers and the coupling hook. Two filament dowels fix it to the front of the cylinder block.
With two buffers and the coupling hook. The frames go into its two slots.
The running plate over the cylinders. It rests on the lugs of the cylinder block.
The running plate under the tanks and the cab. Underneath it carries the brackets for the two expansion links, the pivot for the reversing lever and the cab steps. Its front edge laps over the front part.
56 mm across the flange, with twelve spokes, a counterweight and a coned tread. The D-shaped holes for the axle and the crank pin only let it go on one way.
The same, with the crank a quarter turn behind the left one.
6 mm, D-shaped, through both frames. It turns in the frames; the wheels are glued on its ends.
For the front and rear wheels. Its head holds the coupling rod.
The same for the right side.
For the driving wheel: a collar for the coupling rod, a seat for the main rod and a square end for the return crank.
The same for the right side.
Joins the crank pins of all three wheels on one side, so they turn together.
From the crosshead to the main crank pin.
Slides along the slide bar. It holds the gudgeon pin for the main rod, the piston rod and, on its drop arm, the union link.
The same for the right side.
The crosshead's guide. A tab at the front is glued into the back of the cylinder.
Piston with its rod, which is glued into the crosshead.
Sits on the square end of the main crank pin, so it always points the right way. Its pin drives the eccentric rod.
From the return crank to the foot of the expansion link.
The curved link that rocks on its trunnion. The die at the end of the radius rod slides in the groove on its outer face: the lower the die, the further the valve moves.
The same for the right side.
Carries the die in the expansion link at the back and drives the top of the combination lever at the front.
Radius rod at the top, valve spindle in the middle, union link at the bottom. It mixes the swing of the link with the motion of the crosshead.
From the drop arm of the crosshead to the bottom of the combination lever.
Joins the valve spindle to the combination lever.
Two valve heads on a spindle. It slides in the steam chest and you see it through the window.
Crosses through both frames and carries the two lifting arms and the reach arm.
On the outer ends of the weigh shaft. It lifts the radius rod through the lifting link.
Short link from the lifting arm to the radius rod.
On the weigh shaft between the frames, for the reach rod.
From the reversing lever in the cab to the reach arm.
Comes up through the slot in the cab floor. A small peg on it catches in the quadrant.
Notched guide beside the slot in the cab floor. It holds the lever in forward, mid or back gear.
Glued on the end of a pin to keep the eccentric rods and the reach rod on.
Firebox, barrel and smokebox in one part, with the saddle, the boiler bands, the smokebox door and, at the back, the fire door and gauge glasses that you see in the cab.
Glued onto its flat seat on the smokebox.
Glued onto the barrel.
Glued onto the firebox in front of the cab.
Water tank beside the boiler, standing on the running plate.
The mirror image for the right side.
The cab with its windows and the coal bunker behind it, with the coal heaped on top.
Curved roof with rain strips. Two ribs underneath locate it between the cab walls.
150 mm of 45 mm gauge track on a base. A dovetail at one end fits the socket of the next piece.
For a 0.4 mm nozzle. Filament amounts are estimates for these settings.
Nothing needs supports. Print the small valve gear parts at 0.12 mm and the body at 0.2 mm. Clean the edges of every hole. A filament pin must turn freely in the plain holes and needs a firm push in the tight ones, where it gets glued; open a tight hole with a 1.8 mm drill if it is too tight.
Glue the two frames into the slots of the cylinder block and the rear buffer beam, with the stretcher between them. Check that the frames are square on a flat table while the glue sets. Glue two short pins into the holes in the front of the cylinder block and fit the front buffer beam onto them.
Push an axle through the frames and glue a wheel on each end, flange inwards. The D-shaped holes set the right-hand crank a quarter turn behind the left one. Do the same for all three axles, then glue the crank pins into the wheels: the short ones in the front and rear wheels, the main ones in the driving wheels, every flat facing the same way as the flat in the wheel.
Slide a piston into each cylinder from the front, rod first, through the gland in the back wall. Slide a valve into each steam chest the same way. Glue the cylinder covers and steam chest covers on, and glue the slide bars into the sockets in the backs of the cylinders.
Put the coupling rods on the crank pins. Slide each crosshead onto its slide bar from the back and glue the piston rod into it. Put the main rod on the main crank pin, fit its small end into the crosshead and join them with a pin glued in the crosshead. Then glue the return crank on the square end of the main crank pin: it holds the main rod on. Roll the engine: the wheels, rods and pistons must move without catching.
Glue the rear running plate onto the frames and the front one onto the cylinder lugs, with the rear part's front edge lapping over it.
Fit each expansion link to its bracket under the running plate with a pin glued in the link. Join the eccentric rod to the return crank and the foot of the link, with a washer on the return crank pin. Slide the die of the radius rod into the groove of the link. Pin the combination lever to the radius rod, the valve crosshead to the lever and the union link between the lever and the crosshead's drop arm, then glue the valve spindle into the valve crosshead.
Push the weigh shaft through the frames, threading the reach arm onto it between them, and glue the reach arm and a lifting arm on each end. Their flats make them all point the right way. Join each lifting arm to its radius rod with a lifting link. Put the reversing lever on its pivot, coming up through the slot, connect it to the reach arm with the reach rod and a washer, and glue the quadrant to the cab floor beside the slot.
Glue the boiler to the running plate, the chimney, dome and safety valves on their seats, the side tanks beside the boiler and the cab over the firebox. The roof just sits on, so you can take it off to reach the lever.
Put the track together and set the engine on it. Push it along in full forward gear and watch the valves move through the windows. Move the lever to the middle notch and the valves hardly move; move it to the top and the gear is set for running backwards.
Small parts and filament pins: keep them away from small children. It is a display model, not a toy to play rough with.
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