It might not appear to be such a big challenge at first sight, but I’ve come to believe that one of the more challenging types of rolling stock to build in the hobby of railway modelling are passenger vehicles. I can think of a number of instances where I’ve been caught out working on passenger cars. One of the first kits I assembled in HO, many years ago, was a passenger carriage and the exercise turned out to be far more challenging than I’d expected. I have vivid memories of struggling to get the sides assembled straight and true, the floor was slightly warped so that the wheels wouldn’t sit level on the track and finally, I’ll never forget the challenge of trying to get a thin piece of decal spaghetti to sit straight along the side after the carriage had finally been painted.
In spite of all of these challenges I feel that, in retrospect, I made only one real mistake: I blamed my modelling skills rather than the kit I was building. I’ve since come to realise that most of the problems were in the production methods used to produce the kit and the way these were applied to such a long vehicle. The kit in question was injection molded styrene, however I’ve come to believe that it’s not so much the materials as the process of casting itself that often presents the problems with long vehicles such as passenger stock. In approaching the assembly of long passenger stock I start from the assumption that, if it’s cast, it’s likely to be warped in some way. As such I will have to address and overcome the issues this throws up as I assemble it. I’m sure there is a mathematical formula to cover this but I’d wager good money that there’s a strong correlation between the length of a casting and the likelihood of it being warped.
I recently offered to help a friend out by assembling a couple of passenger vehicles he had agreed to build for a client. These were two carriages from the R car series by the Australian company O-Aust. As I had encountered problems with passenger stock kits in the past this may encourage you to question my sanity in agreeing to build passenger kits in O where everything is twice as long. However I have a couple of these kits in my own collection so I figured if I was going to mess something up, I may as well practice making a mess on someone else’s model rather than my own 🙂
I’ve spent about 3 weeks dragging my heals and taking my time preparing the castings for assembly and I’ve only just assembled the sides to the ends and fitted the floor. The kits main body and roof components are of cast polyurethane and thus far I’ve encountered little or no warping. However this is not to suggest that there have been no challenges in assembly. I’ve found that cast parts that emerge from RTV rubber moulds are rarely of a consistent thickness and this has to be adjusted for in the assembly by a bit of judicious scraping, sanding and filing. After I had cleaned up the castings of flash I took a good look at the floor and realised that, while it wasn’t warped, that I wasn’t happy with the rough edges of the casting. The edges form the main lower support for the sides and sighting down the edge, much as you do when purchasing timber, it was pretty clear I was going to have trouble getting the sides to sit straight when the floors edge looked about as straight as a dog’s hind leg. This looked like an opportunity to give my new milling machine a test drive.
The first thing you learn when you’re working with precision milling machines is that you need to start with a datum point: namely an edge or a point that you can rely on. With a casting that has wandering edges this means that you need to work out the centre-line and use it because you can’t rely on the edges. What I wanted to do was mill both ends of the floor casting down to a depth of approximately 5mm and I also wanted to mill accurately along the sides to give me a square and true casting that I could use to assemble the body around.
I started this operation by making up a 12mm think MDF base from two piece of 6mm MDF that I cut and glued together. I made the bottom layer of this sandwich about 3mm wider than the floor casting and about the same length. The top layer was about 5mm narrower so that when they were glued together I had a small step along one edge to give me a slot to mill in without MDF flying about. I marked a centre-line down the length of the casting and marked a similar line down the centre of the MDF support base. When these lines were matched up, one edge of the casting sat out over the slot allowing for easy milling. I drilled three holes in the floor casting and carefully attached it to the MDF base.
I clamped the workpiece on the mill’s table only to discover that it’s travel wouldn’t allow me to mill the full length of the casting in one go. This meant that, after going to all the trouble of making sure the casting was held exactly parallel to the cutting tool, I would have to do half the job and then un-clamp and move it. This is a recipe for making mistakes. Anyway, to cut a long story short, the operation went quite well and I now have a casting that is square and true and sits neatly into the assembled carriage body.
When I purchased the mill several months ago I had visions of turning out scratch built locomotives and shaping metal: thus far the jobs I’ve used it for have been mainly confined to adjusting kit parts and modifying castings during run of the mill (pun intended) jobs I do around the workshop. In spite of this reality check I’ve already come to rely on the mill and I am starting to wonder how I ever got along without it. I’ll post a photo of the carriage when I’ve made a little more progress on it.