DUBS A

But I did want an NZR locomotive to complement my existing Model T and Fiat railcars.

A search of New Zealand Railway Steam Locomotive Classes soon revealed the 'A', 0-4-0T, at the head of the list.

Wanting a new G gauge project, live steam posed a suitable challenge.

The Australian Model Engineer’s Edwin project was a good place to start.

The provision of dimensioned elevation drawings by a fellow modeller was all I needed to make a start. Using free drawing software, I traced over scanned images of the side and end elevations. This is a technique that I have used on my two previous models. Having scaled them to 1:24, I determined that the loco was only 228mm over the buffers!

Believing that the boiler and burner were probably easier to construct than the engine, I began working on them. Also, I needed to establish that they would raise sufficient steam.

Already having pieces of brass sheet, (ex scrap metal yards), I started by making the side frames and end beams. The four wheels were turned from bronze stock, coming from another modeller’s workshop. I was quite pleased when I managed to get the assembled coupling rods and wheels turning freely. And yes, there had to be some inbuilt slack.

The boiler, which is 120mm long x 40mm diameter, only 100cc, complete with safety valve and Goodall filler valve. It has been pressure tested. So too has the butane gas tank. The two bungs at the end were to be for a sight glass. This never did eventuate.

The butane gas tank with tapped hole

for the Ronson filler valve and the

poker burner without a gas jet.

The finished burner with Ronson

valve and jet assembly.

With the boiler and burner complete, I was able to raise steam, hopefully in sufficient quantity. Time would tell.

Another necessary part of construcion

was the displacement oiler,

with filler bung and water drain.

Cylinder and steam valve construction.

Originally I intended using a piston valve, since I thought this would be easier to make than a slide valve. The cylinder is made from a purchased ½ inch bore bronze bush. This was faced on one side and pinned together with two brass plates and the valve block. The whole assembly was soft soldered together.

Unfortunately I could not make the piston valve with sufficient accuracy.

I removed most of the valve block, back to the white line, and proceeded to make a slide valve assembly. The two contact surfaces were faced using cutting paste on a

piece of glass.

Slide valve and steam ports.

And fully assembled.

The parts disassembled.

The bolts are all 10BA and made to suit. At this time there are no piston O rings. I expected that performance would be improved with them.

I had decided to make the engine reversible, with radio control, so had to make expansion links, fiddly work, and radius arms.

Eccentrics and expansion links in place.

Construction well advanced. Radius arm lifting levers in place. These will be moved using a radio control servo located in the left side tank.

By this stage I had run the engine satisfacturally on compressed air, in reverse too.

A test run with the loco on wooden blocks. Boiler, burner, oiler in place.

Mounting boiler, and start of cab construction.

Cab with removeable roof and back.

The side tanks are made from plywood

with MDF ends and spacers.

The reversing servo is hidden in the

left side tank.

The smoke box, complete with

opening door.

Smoke box, funnel and exhaust manifold.

I have now fitted O rings to the pistons. They were slightly over size. After a calculation, using diameters and circumferences, I cut out a small section to reduce their diameters. This also helped with fitting them into the grooves in the pistons.

The driver was 3D printed by another modeller for me. The brimmed hat was added.

The cow catcher is fabricated from brass rod and sheet, all soft soldered together. I will not make another one for the rear.

Fire box door has a catch.

Under view showing white styrene packers/insulators under the boiler, and the throttle servo connector. The coupling rods are not fitted here. Hence the angle on the connecting rods.