Although there are still a few bits to be done on the S15 and C2X (not to mention the on-going saga of the Dean Goods) I felt sufficiently flushed with success to press on to the next "big" project, a pair of GWR long prairies. I have three RTR ones - an Airfix era model which is no longer a runner, and has a somewhat damaged body, plus two later Hornby versions, neither of which I would rate as being particularly smooth performers. However, after seeing a real one at the Great Central Railway some twelve years ago, moving smoothly over pointwork with barely a hiss of sound, I was smitten with the sense of power inherent in this beautiful tank loco. A "decent" 61xx has long been on my want list.

The plan here is to build two engines - one using the Comet chassis under the Airfix/Hornby body, and the other to be built from the SE Finecast brass and white metal kit. Both models will be driven using the same DJH motor/gearbox combinations, so it should be interesting to compare their relative performance. All being well, they should be very similar ... but time will tell. The chassis design is a little different, with the SE Finecast one in effect being a 2-8-0, with a fixed rear pony truck, and the Comet one using a pony truck at either end.

I felt like tackling the Comet project first, as this was the one with the least work involved. I'd acquired the frames and motion parts a few years ago from another RMwebber, only having to buy the wheels separately. I ordered the wheels some while ago from Comet and put them in the kit box until it was time to begin the construction.

That time was last night. In preparation, I tidied my work bench:

There. Nice and tidy.

I soldered up the frames in rigid fashion, using Comet jigs to aid assembly. Personally, while being very appreciative of the Comet range, I don't like the lack of locating tabs for the frame spacers. The philosophy is supposedly to allow the modeller maximum flexibility in where they place the spacers, but I bet 90% of modellers just put them where Comet suggest - I do, anyway. For my money the lack of locating tabs does open some scope for misalignment of the frames, although in practise I've managed to correct any such errors before getting too far with the soldering. The moral is to tack the spacers and frames together very gradually, constantly checking for squareness, parallel-ness and so on, before committing to soldering everything up solidly. Incidentally I solder half the spacers onto one frame, half onto the other.

With the frames assembled, I began to test fit the wheels. On the Comet chassis, I'm using a Markits wheelset, whereas the SE Finecast one will have the new plastic wheels from Scalelink. My intention was to fit crank pins and test the coupling rods for free running, and if that was going well I might have progressed to fitting pickups. That's where things got interesting!

Fitting the outer wheelsets was no problem. The axle bushes just need a little tweak with the reamer to get smoothly turning wheels.

When I began to fit the middle wheelset, though, I noticed something ... odd.

Can you spot the deliberate error?

One of the six wheels has the right diameter, but the wrong crankpin throw. It's not even a mismatched wheelset - it's just one out of six wheels. So that's an end to that, for now, until I can obtain a new wheel, which may not be as simple as that given the supply difficulties with Markits. I have no doubt that Comet would have supplied a replacement, but the firm has now changed ownership and I wouldn't think it fair to pass this issue on to the new owner. Perhaps I should have spotted the error at the time? That said, who really checks wheels until it's time to fit them to a chassis?