After reading an article on narrow gauge locomotives that might be suitable to model in 2 1/2in. gauge I was sold on the idea of narrow gauge, giving a large engine in the gauge, and decided to make a simple quickie engine. It had to be as simple as possible to build using mostly stock material and castings that were already available.
The wheels, dome, and smokebox door are the same as Tich, and so are readily available. The eccentrics and cylinders are the same as Eagle.
Castings are available from trade suppliers.
Having looked at a number of NG engine outlines I took the best bits from each and the result is Toby, named after my son.
Long water tanks were chosen, although as we shall see they are not actually tanks at all. But they do add weight in the right place - over the driving wheels. An 0-4-2 layout was chosen to give more stability than 0-4-0.
The boiler is unusual in this gauge, it is a circular marine type. It is much easier to make than a conventional locomotive boiler, and uses stock tube sizes.
The locomotive has proven to be a really good runner, every bit as good as many small locomotives in 3 1/2in. gauge, and is a simple to drive as it is to build. And it should be a fraction of the cost. You can build it all on a small lathe, though those with a milling machine will find life a bit easier. If you do not have a mill or vertical slide for your lathe, it can all be done with a hacksaw and files, which can often be quicker, anyway.
So if you would like an engine that is simple, inexpensive and give pleasure on a large club track or a short line in the garden, take a look at Toby.
Here are the vital statistics:
Overall length: 15in.
Width: 6in.
Height: 12in.
Driving Wheel diameter: 2 1/16in. dia.
Trailing wheel: 1 1/2in. dia.
Cylinders: 3/4in. dia. bore x 1 1/8in. stroke
Valve gear: inside slip eccentric
Boiler: circular firebox type with radiant superheater
Boiler pressure: 100psi max
Grate size: 2 1/2 x 3 1/2in. approx.
Making a start
Main frames
Cut two lengths of mild steel 2 x 1/4 x 12 1/4in. plus an allowance to clean up. Square up one end of each. Mark out the cut-out for the axles only on both pieces and cut them out by chain drilling and sawing and remove the scrap.
If you use bright drawn mild steel, like me, then you will find that the frames will have bowed. This is the time to to straighten them, and the method is to use is to hold each one in a sturdy vice and whack it with large hammer until it is back into shape. Use a straight edge along the top edge of each frame to get them as straight as possible. These are the only cut outs likely to cause a problem, so there should be no further distortion of the frames.
Now the rest of the frames can be marked out, and the other pieces cut off to give the final shape. Clamp the two together and file all edges together. Take care to make sure that the axle box spaces are parallel, square and a decent fit on a piece of 3/4in. wide material. There are no horn blocks to be fitted as there is enough width in the frames themselves for the axle boxes to run in.
The cut out for the cylinder steam chest will also have to be chain drilled and filed unless you have suitable milling equipment. You may have to adjust this hole later to fit the cylinder.
The holes are all 4BA clearance size. I counterbored the holes and used cap head screws. Alternatively, you can countersink them and use countersunk screws.
Buffer beams
These are made from the same 2 x 1/4in. flat bar or MS sheet as the main frames. The front beam is very simple and has two location slots 1/16in. deep cut out in the back for the frames to slot into. These will need to be parallel and square and milled or cut with a file.
Mark out and drill the 8BA clearance holes and then position the buffer beam on the frame ends. Spot through these holes, and drill and tap the 8BA holes in the ends of the frames.
The rear buffer beam has a cut out at the top to allow removal of ash from the fire box. Two 4BA clearance holes are counterbored/sunk and will need to be spotted through to the trailing stretcher on assembly. The centre hole is drilled and tapped 2BA for the draw bar clevis. It can be drilled and tapped after fitting to the trailing stretcher so that the thread is in both pieces.
Trailing stretcher
This is a piece of 1 3/4 x 1/2in. section mild steel. Cut a piece 5 1/2in. long and square up both ends to leave it 5 7/16in. long. Cut the width down to 1 5/8in.
Clamp the frames and the rear buffer beam. Spot through the holes, remove the clamps and drill and tap the 4BA holes. Drill and tap the 2BA hole for the trailing frame pivot pin.
The large hole is for clearance for the blow down valve on the boiler. This can be drilled or bored now and the position transferred later to the boiler when that is made.
I have designed it so that the trailing stretcher is level with the edge of the frames and the cut out in the rear buffer beam, so that if the frame is erected on a flat surface, there will be no problem in getting everything square.
Pump stretcher
This is a piece of the same material 1 3/4 x 1/2in. cut off at 2in. plus enough to square up both ends to 2in. long. Take 1/8in. off the width to make it 1 5/8in. wide. Drill and tap the pump hole 1/2in x 40tpi. Mark out the slots for the eccentric rods and mill them or drill and file out. Locate the stretcher in the frames, and spot through the holes in the frame. If you scribe a line down the centre of the edges of the stretcher before you put it in the frames, then you can use this to line up the holes with the centre of the stay.
Now you have a bare chassis, all nice and square. Next time I will deal with the wheels, axle boxes, horn keeps and eccentrics, and you will have something that can be pushed up and down the bench.
