A couple of years ago, I made a somewhat abortive start on a 2FS scratch built loco. I had got to the stage of a rolling chassis, and a body that consisted of footplate, valances, buffer beams and a cab bunker. Where I had failed was getting the chassis to actually run happily. In the end, I decided to shelve the project and move onto my 1854 Saddle Tank that has been documented previously that used one of the 2mm Association etched chassis kits.
Now that I have proved to myself that I can construct coaches, track work (and most importantly get a loco to run well) in 2FS, I have decided to resurrect my Metro Tank project. A look at what I had already built prompted me to discard the chassis - not because it is unsalvageable, but rather because with such a small 2-4-0 engine I feel that weight will be key to getting a successful outcome - the original chassis was constructed traditionally with 0.25mm phosphor bronze frames held together/apart with PCB.
Initially, I had intended to use one of Nigel Lawton's small 6mm diameter motors driving the leading drivers (an earlier iteration of the chassis tried to drive the rear drivers with the compromise that some of the gearing would be visible in the cab), but on this re-work, I have decided to utilise a Nigel Lawton 8mm diameter motor along the boiler into the smokebox (again driving the leading drivers).
A diagram was drawn up in Inkscape to verify that everything would fit in this new arrangement :
The first thing to produce was a set of coupling rods, these were fretted and filed out of a sheet of 0.028" nickel silver (the pair soldered together until complete) :
Once finished, the pair were separated giving these :
To provide as much weight as possible in this version of the chassis, I have decided to construct a solid brass chassis comprising a 6mm square main block, and a 6mm x 1mm strip alongside. Initially the pair were double-sided taped together while a pair of 1mm holes were drilled outside the finished frame ends which were then tapped 12BA to allow the pair to be kept together for the remaining machining. 3 further 1mm holes were drilled in the chassis proper clear of the wheels and gears to allow the chassis to be held together once the chassis is cut to it's finished size. These holes in the main block were opened out to 2.5mm, then subsequently plugged with milliput which once dry and hard were re-drilled 1mm (using the outer frame as a jig) and tapped 12BA too.
A 0.4mm hole was drilled in the chassis block on the centre of the rear drivers (0.4mm because I couldn't find any 0.5mm drills!), which allowed one of the previously made coupling rods to be "pinned" in place so that it could be used as a jig to drill a further 0.4mm hole for the leading drivers.
Once the coupling rod jig was removed, the axle holes were opened up to the axle size of 1.5mm (later opened up again to 1.6mm as the stub axles on the wheels I have wouldn't fit in the holes).
The two chassis parts were separated, and the axle holes in the main block milled out to accommodate the "muffs" used in 2FS to hold the 2 stub axles together (leaving a 1mm deep axle hole on the outside edge of the main block). The area where the gears will be was also milled away :
A trial fit of the wheels and gears has shown that I need to remove a little more of the main block to accommodate the worm gear, and I also need to remove some from the top of the chassis to house the gear box which will also be milled from solid - the cross shaft of the gear wheel is too close to the top of the block so was never intended to be in the main block (it will also allow easier set up of the quartering,etc if it isn't locked solid be the worm)
Once the above has been done, the lower part of the chassis ahead of the leading wheels, and behind the trailing drivers will be removed to give a better looking chassis profile (the area between the leading wheels and the leading drivers will also be removed).
Hopefully, the brass for the gearbox and the 0.5mm drills will appear in the next few days to allow further progress.