Harold’s article about the Wirral railway in the November 2020 Gazette provoked much interest in how he laid his tighter radius curves. Here he explains the method in more detail

MY PARTICULAR BEE IN THE BONNET concerns minimum radius. I have made posts on the Guild Forum showing that it is possible to get large main line locomotives to negotiate 3ft radius curves and still have a model with flanges on all wheels, brake gear and sand pipes, etc. Given the increasing availability of good quality RTR models able to go round tight radius curves, I feel that more should be done to show just what can be done in a small space. A single line curve can be fitted in a baseboard width of just seven feet; add an extra seven inches and you can fit a double track. All my stock will negotiate a 3ft radius curve. This includes: a 9F 2-10-0, a West Country 4-6-2 pacific, sundry 2-8-0s, 4-6-0s, a 2-6-4T, and a 2-6-2T. There does appear to be a general view that layouts with a minimum six-foot radius are the only feasible home for our 4-6-2 locomotives and that anything less than 4ft 6in. is for small branch line locomotives only.

The Guild’s track standards manual is not very informative; I suspect a lack of knowledge of minimum radius amongst its members! People moving up from 4mm are used to fitting quite a large layout into what we think is a small space, and when they ask for help in planning their new layout are met with all the old chestnuts concerning what can and can’t be done.

I enjoyed the Virtual Exhibition, and I watched with interest the video by Geoffrey Goddin concerning the ‘Train Set’ and the use of RTR stock, concentrated on the branch line. I apologise for mentioning this, as I realise that this is the best use of his available space, but I feel that for newcomers to O gauge, we need to do more than just embrace RTR but fully explore all the possibilities that modern technology has to offer.

Right, having banged away, here is how I have achieved this in my 7ft 7in. wide shed. For demonstration purposes, I have used off cuts from my baseboards to represent the 8 x 4ft sheet of MDF that I used. Your materials and dimensions may vary, the principles remain the same.

When I started, I wanted a double track main line in my 16 x 8ft shed. These dimensions are nominal. The first task was to identify the constraints involved in persuading large locos to go round small corners. After much experimentation I arrived at the following requirements:

• A single-piece flat baseboard to provide continuous level support to the curved track
• New track, so the rail would slide smoothly in the chairs, thus avoiding any tension which could lead to kinks or derailments later
• The use of laser-cut track templates to ensure a smooth dogleg free curve.

I also found that gauge widening and super elevation were not required. There is sufficient tolerance in finescale standards without gauge widening, and super elevation may look nice, but it introduces twisting of the track which, with a tight radius, just leads to derailments. As most of my curves are either hidden by platforms or in tunnels the omission is not noticeable.

Now, to start. I cut the 8 x 4ft board to 7ft 7in. length to form one of the end baseboards. My baseboards are 2ft 6in. wide, so I cut a piece out of the inside edge 18in. x 2ft 7in. to match the central operating well.

As we are laying a double track curve, we need to measure its width, including the ¾in. clearance. This distance is 6½in. Next, I mark out the centre of the 7ft 7in. baseboard. This marks the end of the first quadrant and then I mark 6½in. in, to show where the end of the inside track sleeper should finish.

I begin with the inner track; this is the most critical as it is the tightest radius and will be used as the template to set the outer track. Using the track templates, I start with the 4ft radius just for a couple of inches. This gives a gentle lead into the curve, followed by the 3ft 6in. radius for a bit longer (no complicated formula here!) then by the 3ft radius.

I use PECO track, so use PECO rail joiners (inset). These are about half an inch long and introduce an element of straightening of the rail at the join – hence the possibility of a dog leg, so, I cut the fishplates into two parts and use the longer of the pieces. Again, I do not have any set number of track pins per foot, just knock a nail in where I think it is required.

The aim is to finish the first quadrant of the curve at the point we have marked, with a smooth, flat and kink-free curve. Adjustment are made by varying the length of the 3ft 6in. radius template until the track meets the target point. I use the 6ft track centre position of the Railwood gauge to set the outer track in position and gently slide it along, knocking in track pins as I go. You should finish with a curved double track with transition curves at both ends.

Please be aware that stock clearances will be minimal and that some adjustment may be required. I had problems when I fitted door handles to my Lima coaches. The solution is to re-lay the inner track, maintaining the same radius, but starting the curve ½in. or so earlier. This will give increased clearances, without reducing the overall radius of the inner track. The outer track will not be affected. As these tight radius curves are partially hidden by platforms and completely by tunnels, the appearance is not affected.

Next, Editor permitting, I will show how I addressed the perceived problems of buffer locking and getting large locomotives round bends without butchery.