When working in HO what height to set your couplers is not something you really have to think about. I was a pretty dedicated HO modeller for something like 15 years and I can never remember having a serious discussion with anyone in the hobby about whether couplers should be some height other than that which was normally accepted, namely the height of a KD coupler height gauge. I have no idea whether this gauge is set at a prototypical height for NSWR practice, the topic just never came up. And why would it? Everyone that I knew set their couplers at that height, including manufacturers, that was that!
The situation could hardly be further from this happy state of affairs for those of us working in 1:43.5, but following the NSWR as a prototype. KD height gauges might work ok for those following Victorian and Queensland outline, as these modellers work in the same scale as those in the US. For this reason the height of the O-scale version of the KD gauge comes out at something similar to the height of couplers in these states. However if those of us who work in 7mm (1:43.5) were to use these gauges the couplers would come out a couple of millimeters too low because of the difference in scale. So what’s the answer?
I won’t go into the arcane reasons why there are no recognised standards for coupler heights for 1:43.5 modellers following NSWR practice: it might be a topic that fascinates some but it really doesn’t fascinate me. However I do think it might be worthwhile explaining the method I have settled on to set the height of the couplers I use and perhaps take a quick look at some of the reasoning behind this.
The first thing you need to determine the height of the couplers on your rolling stock and locos is a way of reliably determining the height of the coupler above rail head height. I started by laying a length of flextrack on a section of ply and then laying a small piece of thinner ply at one end of this with the height of the top surface of this small piece of ply very carefully set at the same height as the rail head of the flex track. I got close with a piece of 6mm ply and then raised this with some thin card. I attached the ply rectangle with countersuck screws.
After you have a place to set your rolling stock so as to reliably compare the coupler heights above the rail head you need some way of measuring the height and I carry this out with a woodworking saw blade height gauge. These can be had at retailers such as Hare and Forbes and McJing and from many other sources. The reason I use this particular piece of equipment is first and foremost because I already owned one and secondly because it is perfectly suited to this task. If you so desired you could make up a gauge from styrene or metal but the ability to move the saw gauge to whatever height you want is a great advantage.
After getting these pieces of equipment arranged it’s easy to work out whether your couplers are too high or low. For the record I work to the prototype dimension used by the NSWR to set my couplers. The NSWR used a height of 2’11” between the top of the rail head and the centre of the coupler head as its standard and I use the same. This dimension works out at 20.4mm in 1:43.5. I use a set of digital calipers to set the height of the gauge (I don’t rely on the dimensions printed on the gauge itself) and then place this on the wooden block. I place the rolling stock or loco on the track to determine whether the coupler needs to be lowered or raised.
Ok so we’ve got a way of checking the height of the couplers, how do I go about getting the couplers the height I want them if the gauge indicates things are too low or high. Well I fiddle about with packing and milling out bits of the coupler pad until I get it close to where I want it. It’s a bit of a pain really but then it was the same when I worked in HO so these’s no advantage or disadvantage working in one scale rather than another.