Part one

Brian Podmore

To create a working Travelling Post Office, (TPO), for my O gauge railway seemed a daunting task. I have the ubiquitous TPO coach on a Hornby Dublo 3-rail railway and that really was the inspiration for this project in 7mm.

My Travelling Post Office is based essentially on the one at Didcot. Sourcing the body and chassis for it was straightforward. Using Allen Doherty’s Worsley Works etching facility, he was able to provide a 7mm etch of the GWR coach body. The roof, chassis and coach apparatus came from a BR Mk1 TPO sold by JLTRT, (perfect for my needs). As this was to be a fully working model some research was necessary into practice and procedures and the usual books and internet searches took place. There are also mail days run at Didcot Railway Centre and Nene Valley Railway amongst others and with videos on YouTube, this was enormously helpful in putting my project together and more importantly making it work. I have provided a book list and list of suppliers I used at the end of this article.

The coach, which is of brass and whitemetal construction, has internal workings to activate the catching net and traductors by using servos. As my railway is DCC controlled, a PCB controller board from ESU, (the Loksound 4 XL), is resident in the coach and drives the servos, interior lights and a warning bell. I wanted to organise the coach just as if it were a real TPO and as such, it can drop and collect mailbags from ground apparatus set between a road bridge and a tunnel on my layout. The coach is heavy, (it has to be, to avoid damage when working), and the paint finish was achieved with U-Pol etch primer followed by Railmatch aerosols with Fox and HMRS transfers, (the finished model is shown above). A more thorough explanation of the project is on my website at www.bpodmore.co.uk, just search for TPO or look for links in the projects section.

I’m going to split the description of this project into three main parts. This first part involves the building and testing of the coach. The second part deals with the developing and testing of the ground apparatus and the third in the setting up and testing of the control equipment in the coach using DCC. I will try to keep descriptions as straightforward as possible and deal with the technical bits in a nontechnical way.

Building and testing the coach

I constructed the bogies and chassis from JLTRT first. The bogies I was supplied with are white metal and very heavy, (a bonus in my case because they have serious work to do keeping the coach on the tracks with a low centre of gravity when the bags are dropped and picked up).

Fig.1 shows a close-up of one of the bogies. Electrical pick-up for DCC control is achieved through the wheels of both bogies.

Figure 1

You can see where I have soldered a phosphor bronze strip on the axle and the rim of two wheels on one side only. By doing this on each bogie and having them alternately left and right hand rail connected, the circuit is made. All that needs to be done is to isolate the body of the coach from the bogies so that each bogie supplies feed from one or other rail of the track.

Figure 2

Using the brass floor gave a much stronger build to the whole body, (fig 2). JLTRT also supplied the traductors and net framing as brass castings as well as the roof of the coach and various fittings. Some of these required modification but more on that later.

Figure 3

Initially, I used the resin chassis floor from JLTRT (fig 3), but I found that for me it had a couple of issues. First it was a little too thick to fit inside the brass floor of the coach and second it is designed to be integral with the Mk1 body and has slits to attach the latter to it. These slits weaken the resin chassis if not used as intended and as my body would not fit, I decided to use just the sections above the bogies as insulation and after sanding down fitted them into the brass floor that formed part of the body etches.

The coach body parts were well produced and fitted together with very little alteration. Allen calculated the correct size from measurements of the coach roof (fig 4).

Figure 4

All that was required of the roof was to remove the rain strips and cut out the recess required for the top of the net door. The result was a well-fitting roof (fig 5).

Figure 5

It just shows how you can bring together two independent companies to work together to create what you need and in this respect I am delighted with the result.

As mentioned before, the brass floor sits on parts of the resin chassis over each bogie. It fits exactly after rubbing down the chassis parts to remove rivet detail and reduce the thickness of the pieces. The BR coach body is narrower than the GWR coach so this enabled me to get the proportions correct and support the body solidly. It also created that important electrical isolation barrier between the bogies and the coach body. Where DCC is concerned this is crucial, short circuiting chips can be expensive and often means they have to be replaced.

Fig. 6 show the TPO catching net framework in original condition as supplied by JLTRT. Although the pieces are quite small and seemingly fragile, because they are cast bronze they do stand up to a fair amount of bashing and with care I was able to modify them and make them work.

Figure 6

The net arrangement needed to be hinged in two places as shown in Fig. 7, and the joints therefore would need to be drilled out. Not an easy job. This took a whole morning and necessitated the removal of cosmetic rods, drilling out bearing holes and replacing with brass wire. This having been accomplished I painted the arrangement with matt black paint as shown. It will now fold flat against the coach side when not in use and can be extended when necessary to catch the mail bags.

Figure 7

The traductors are solid castings (fig 8) but in practice the arms rotated out and down from the carriage body. To make this work, a rebuild would be necessary. I had four castings two for each door and they were ‘handed’. I ground out the solid arm extensions on two of them to be replaced by moving ones.

Figure 8

This was accomplished by drilling a hole in the bottom of the main bar to add in a small piece of rod on which the arm could rotate (fig 9).

Figure 9

A small washer was soldered onto the end of the bar to help retain the arm on the rod. Here they are with one arm in the down position and the other in the up position. The traductors were then soldered in position on the coach sides on either side of the door openings. The arms shown here were replaced by longer ones later on when testing started. There were changes to how the mail bags were attached to the arms as well, the end result is shown in Fig. 9a.

Figure 9a

The net was added and sewn onto the frame (fig 10). Inspection of drawings of this part of the equipment showed that heavy rope and chains were strung across the net to guide the bags into the coach on impact. The frame was soldered to the coach body as was the vertical net rib on the right hand side of the door that held the net to the body of the coach. After fixing all was painted matt black and tested for movement. You can also see the ‘fixed’ traductors either side of the door next to the net. I decided that the front two would be enough.

Figure 10

The traductors arms were connected to a sliding platform inside the coach (fig 11).

Figure 11

Thin wire from the arms was fed through a tube connected to this platform to allow for the rise and fall of the arms. The ‘rails’ that the platform travels along are small brass tubes soldered to the insides of the coach. The right hand traductor has now been set properly as it was suffering from early testing collisions with apparatus and tunnel walls! In the real world, accidents included loss of life, damage to track and ground apparatus as well as to coach sides. As the forces created when collecting and dropping bags was fierce, even the track was moved and skewed by the side of the ground apparatus.

Having devised the ways in which the traductors and net would be deployed, it was necessary to find the best (not necessarily the cheapest) way of achieving control of these parts of the coach. In the next instalment of this project I will relate how the ground equipment was put together and placed alongside the track and in the final part I will endeavour to explain in simple terms how I tied everything together with DCC control.

Booklist

An illustrated History of the TPO by Peter Johnson

Great Western Railway Travelling Post Offices by J.G. Hosegood

Mail trains by Julian Stray

TPO. A History of the Travelling Post Offices of Great Britain by H.S. Wilson

Suppliers: Just Like The Real Thing, Worsley Works, Invertrain

Other support: Didcot Railway Centre, Nene Valley Railway, Great Central Railway, Google Images, Royal Mail web site