Test Etches for SR Moguls

Hollow Boiler for DCC Decoder and Speaker

Last updated: 6 June 2006

This etch replaces the firebox front, boiler and smokebox end plates from the David Andrews kit for the SR/BR U class 2-6-0 so that a brass tube can be used as a basis for the structure. There is space enough in the tube for a DCC speaker mounted in a plastic tube. It is expected that the sound decoder will be housed in the tender.

The next picture shows the rear of the smokebox and boiler with new end plates in place.

... and this shows the front with the smokebox door in place. Note the tube in both pictures which will contain a plastic tube and speaker.

... and this shows the full assembly with smokebox in position.

The holes in the main frames of the David Andrews kit need to be opened up to take 1/8" bearings and then slotted downwards so that the bearings can move up and down. If the slots are extended to the bottom of the frames and the springs removed then the whole compensation system together with the wheels can be dropped out of the chassis. The following view shows the left hand frame unmodified, the right hand frame ready for the beam to be attached and the right hand beam.

The following view shows the left hand frame unmodified and the right hand frame with beam attached.

There are 2 sets of inner beams, one for each side of the chassis. The washers are soldered to the inner end of the bearings to hold the beams in place. The tabs on the beams are folded down and locate in the slots in the washers to stop the bearings from turning. It is intended that the rear axle will be fixed. The tabs on the middle and front bearings are designed to act as keepers for a spring wire which is passed through a chassis cross member and bears on the top of the bearings. It is hoped that this arrangement will provide the benefits of conventional beam compensation and springing. Note that axle movement is downwards only so that splasher clearances are not compromised. Driving wheel springs hung from the compensation beams are provided to replace those in the David Andrews kit.

This is the test etch. A number of changes are planned as described below.

The next picture shows various stages of assembly of the springs and beams. The spring leaves are assembled on to a 0.3mm wire held in a pin chuck being careful to keep the side of the leaves which were tabbed to the fret to the back of the spring. The second wire is added using another pin chuck and then both pin chucks removed. The leaves are closed up with tweezers and a dab of solder at top and bottom secures the

wires. The ends of the wires are clipped and cleaned up. The remains of the tabs at the back of the leaves are removed with a file and the slots at front and back are cleaned up to take the hasp. The beam at the top is viewed from the back with a completed spring assembly on the right and, on the left, a hasp assembled to the beam with 0.3mm wires awaiting the spring leaves to be inserted. The hasp is folded round the

spring and secured with a 0.5mm (or maybe 0.45mm) wire through the hole at the top. The completed beam at the bottom is viewed from the front.

The risers are 0.45mm nickel silver wires reduced to 0.3mm where they locate in the half etched slots in the beams. <A HREF="hintsandtips.htm">Hints and Tips</A> shows the reduction of small wires.

Here is the completed assembly installed in the chassis. The spring steel wires pass through a tube soldered into a piece of 3.5mm x 3.5mm channel. The channel is screwed to the horizontal chassis spacer. The tension can be adjusted by changing the diameter of the spring wires and by adding shim between the channel and the spacer. Graham Shirley has scratch built a similar system but he has captured the screw so that the channel can be adjusted using the screw from above. I intend to try that next.

A plate is installed between the motor and the top of the Branchlines gearbox. This plate is screwed to the chassis so that the whole beam, gearbox and motor assembly can be dropped out of the chassis by releasing the screws holding the gearbox and the channel.

Several changes are planned for the next version of this etch including:

- a pair of 0.3mm holes near the middle of all spring leaves to assist assembly with wires. Only one set includes these holes on the test etch and the assembly of this set is much easier.

- the holes in the ends of the top 3 spring leaves were etched assuming 0.3mm wires for the risers. They will be increased to take 0.45mm wire. This produces a stronger result and is closer to prototype, which seems to be slightly tapered. The wires will need to be reduced to 0.3mm where they locate in the slots in the beams.

- a second rectangular pad, nuts and washers will be added to the etch for inclusion on the risers. The test etch has been assembled using pads from unused leaves and 0.3mm washers drilled out to 0.45mm. They look better than nothing but purpose etched nuts and washers should look better still.

- alternative hasps (is that what they are called?) will include the bottom spring leaf. This should make assembly easier and removes the need for removing the awkward tab holding the bottom leaf to the etch.

Jig for Removal of Boss from Stapleton Wheels

Last updated: 6 June 2006

The boss on the front of the Stapleton wheels, available from the

3mm Society, causes clearance problems between the slidebars of the U chassis. This jig holds an 18mm wheel to facilitate the reduction of the boss to 0.005", 0.010" or 0.015" as required.