I spent a few days thinking about what I wanted to do about the LCH wagon I wrote about in my previous post Jigs. It was apparent from the moment I placed the wagon on the track that deliberately incorporating a twist in the chassis to solve the problem of the axle bearings riding at different heights wasn’t going to be satisfactory. Things like this niggle at the back of my brain and bug me till I do something about them. While I spent a couple of days pondering a better approach I’ve been reading emails from friends and others who have replied to questions I’ve been posting on the 7mmAusmodelling Yahoo! group and this blog. I’ve done some basic research and have decided that I’m going to scratch build a 12 1/2 ton wagon similar to those in the prototype picture I posted in my last post. This wagon will be a close match to one of the wagons common to the Muswellbrook Colliery. These wagons were longer and heavier than the prototype the kit from O-Aust represents and if I feel I can build multiples I’m going to make more than one down the track. I’ll be using a plan I’ve scanned from the book Coal, Railways and Mines by Brian Robert Andrews. This is a fantastic resource if you’re interested in the coal mining industry and associated railways of the Hunter Valley and Newcastle, NSW. There are a couple of foldout pages in the back of the book with plans of a range of items and there is one for a 12 1/2 tin hopper labelled for the Pelaw Main colliery that I feel is a pretty close match for the hopper I plan to scratch build.
After considering the problem with the wheels on the O-Aust hopper I felt that the only solution was to dismantle it and re-drill the holes for the brass bearings in slightly different locations. The difference between the ride heights of each axle bearing was approximately .5mm. I didn’t want to drop or raise one of the holes by this amount: the ideal would be to raise one by half the required amount and lower the other the same. So this evening I bit the bullet and set to wrestling the joints apart with soldering iron and brute force. I got the wheels out first, cracked the joints on the four braces and then pushed till these parts came away. I then worried the corners while holding the soldering iron in a critical spot and managed to get the corners apart. Once I’d managed to get the parts broken down I drilled out the old brass bearings and essentially had the kit back the way it had started. The only real damage was that I had to drill right through the axle boxes to get the remnants of the old brass bearings out.
The reason I needed to re-drill the bearing holes was to address a problem: I needed two holes at exactly the same height above the rail head so that when the brass bearings are installed the axles are parallel to each other front and back. If they’re not then only three of the four wheels will ever be in contact with the railhead, resulting in poor running. I’ve tried to ignore this problem in the past on wagons I’ve built and it has never proved a successful strategy. The wagon always runs poorly and is far more liable to derail than a wagon that has all four wheels in contact with the rails. The “cast in” drilling dimples on the rear of the axle-boxes, when they came out of the box, were different heights and I drilled them out using these to guide the location of the holes, trusting that they had been manufactured in the correct location. They weren’t. After getting out my trusty calculator and I carefully installed a datum rail at the required distance on my pillar drill. By pushing the white metal side frame installed in the stryrene jig I posted a photo of in the last post I could easily drill both holes at exactly the same height in relation to the model rail head. It would be more accurate to say that I drilled an elongation in both holes: I elongated one hole .22mm up and the other was elongated .22mm on the lower lip of the original hole. I then glued new brass bearings into these holes and pushed them hard up against the tops and bottoms on the new holes. If you look very carefully at the photo above you can see a very small crescent moon shaped gap below and above the brass bearings showing through the holes in the axle boxes. The one on the right is a little off to the upper left but the solution still worked. I lightly soldered the frame back together with the wheels installed and the wagon now sits on the track square and level with all four wheels in contact with the rails. A tiny dab of putty in the holes and no one will ever notice they were there after the wagon is painted.