Having rebuilt the tram engine (our first season's only locomotive), then built an 0-4-0PH to augment this, the time came to build a 'proper' (steam) locomotive. In a perfect world, I would have liked to have built a model of Linda of the Festiniog Railway: a beautiful, large narrow gauge engine, with (as I remember her in the early 1980's) an open-backed tender ideal for driving from. Unfortunately, there are no plans or castings available for this commercially. So, as I do not have much steam locomotive building experience, I decided to got for something with plans and castings. Maybe next time, though......
The Alice class of Hunslets are almost perfect for me - it builds to be quite a large locomotive (36-48" long, depending on scale, and about the same power and weight as the two current petrol-hydraulics so fits into our stable well), and is relatively simple. Commercially, there are four designs of something like this available:
The first two designs are really Alice look-alikes which were designed for serious passenger hauling, whereas the latter two are much truer-to-scale designs. These will (of course) take longer to build, and some parts may not be as strong than on the first two. Of course, it depends what you want something good to look at or something which will haul well.
On the basis of talking to each of the suppliers, posting queries on the web, and reading the responses, I decided to go for the Milner design, but with some simplification/strengthening to aid longevity (e.g. oilite bushes or roller bearings wherever possible to make replacement simple). The Milner design is not of any particular locomotive, of which there are several variants. Mine is also of no specific locomotive, with features from both early (frame shape) and later (frame cutout shape) Alice class engines, as well as some to Milners design (reverser etc.).
I decided to make her a metric engine wherever possible - so many off-the-shelf components are either only available in metric, or are so expensive in imperial, that it's not a difficult decision to take. Therefore most threads will be M6/M8 instead of 1/4 BSW and 5/16 BSW, the oilite bushes are metric, as is most of the platework.
I also decided to go for a copper boiler. Steel would have been cheaper (about 1/2 the price) but because I will only get to use the engine intermittently, copper will last longer with less maintenance. It also has the advantage that it conducts heat better (so will steam better). A talk to someone who'd done the same suggested that John Ellis would be a good person to do it - he has built copper boilers for this type of engine ever since John Milner first designed it, so I guess there isn't much he doesn't know about it. He offered a lead time of about 9 months.
I decided not to go with the cab as drawn. In their days in the quarry, the full-size engines never had cabs, and, personally, I believe that they look better like this. There is a slight prblem with this - the cab helps hide the fact that the fittings are somewhat overscale - but, having seen pictures of others where people have done the same it looks fine. I was also worried that you'd forever be hitting your head on the back of the cab roof - painful, to say the least.