Now I switch from a mainly plastic body to a mainly photo-etched brass underframe as an upgrade on the one included in the Peco Parkside kit.
No surprises here: one the the major factors in my enthusiasm for returning to 4mm wagon modelling and the adoption of Scalefour standards was my discovery of the amazing Rumney Models photo-etched brass underframe kits. Among their many virtues are the extraordinarily detailed instructions that Justin Newitt makes available as downloadable PDFs. I’m not going to repeat the details of the instructions and their practical tips here. Instead I’ll focus on where I’ve applied my own techniques or where I’ve deviated from the instructions (mainly because I’ve opted to do things in a different order at some points).
In this case, the appropriate Rumney Models underframe kit is Ref. No. B.21. Once you’ve built a few of these, you realise that there is a high degree of consistency to their design and their construction approach. So, as usual, things begin with a part called the chassis top plate. And, already, I’m going to do something much earlier than the instructions state: before even removing the chassis top plate from the fret, I’m going to take the opportunity to solder in place the coupling pockets on the two headstocks. Justin’s instructions tackle this modest task much later in the assembly but I’ve decided to do it now because these are such tiny, fragile parts, it’s easier to secure them in place before the headstocks are folded at right angles to the rest of the chassis top plate.
This kit is designed to cover underframes for multiple types of mineral wagon, so it includes options for traditional bolted-on coupling pockets and the more austere welded ones. The latter are appropriate for 24.5-ton mineral wagons. So, before removing any parts from the fret, I began by cleaning the two coupling pockets and the headstocks with a fibreglass brush. Then I applied some La-Co flux to the rear of the coupling pockets and tinned them with a tiny amount of solder. While I was tinning these parts, I also took the opportunity to clean, flux and tin the rear of the four heavy duty axleguard overlays.
Then I removed coupling pockets from the fret, tidied them up and mounted them on the end of a cocktail stick which I had carved into a suitable rectangular profile. This enabled me to hold them in the correct position over the slots in the headstocks which I had painted with some more flux to solder them in place. This is broadly similar to the technique described in the instructions however I found that these parts are so tiny that tinning their rears didn’t really provide sufficient solder for a strong bond, so I switched to tinning part of the headstocks and made a second, much more successful, attempt.
Next I removed the chassis top plate from the fret. Note that voids in this part have been used etch a number a number of very small parts that are needed later. So I removed those and put them in a small ziplock bag to keep them safe. I bent the headstocks to shape using a “hold-and-fold” tool and checked that they were accurately folded through 90-degrees. Note that you can ignore the half-etched holes on the rear of the headstocks – they are there for punching out rivets for other types of mineral wagon that do not have fully welded underframes.
The next major part to work on is the axleguard assembly. This part provides eight half-etched holes on the plate axleguards so now is the time to examine some photographs of your chosen prototype to see which (if any) of these holes need to be drilled out fully with a 0.85mm diameter drill bit. It’s best to drill these holes before removing the part from the fret and I used a simple hand-held pin vise for the job. There are also some parts in the void in the middle of the axleguard assembly, so remove those at the same time as you remove the main piece from the fret and keep them safe. In fact, some of those parts (the heavy duty axleguard overlays which I tinned earlier) are needed next so I removed them from the sub-fret.
These overlays needed to be soldered in place on the rear (outside) of the axleguard assembly before doing any folding work. I set up a simple jig with a 2mm hole drilled in a plywood offcut and a cocktail stick to ensure that I positioned the overlays accurately before soldering. This makes it easier to keep the part in place by pressing down on it with something like the tip of another cocktail stick when introducing the hot iron to secure the pre-tinned parts. Before I forget, I should mention again that I cleaned the axleguards with a fibreglass brush and painted on some flux before soldering. The La-Co flux I use is a slightly sticky substance that actually helps to hold parts in place. Once all four overlays were securely fixed in place, I folded up the axleguard assembly as per the instructions. Again, getting the 90-degree angles right is important.
Now is the time to fit the axleguard assembly to the chassis top plate. Both parts have four 1mm diameter alignment holes which the instructions explain how to use with some brass rod and a simple jig to ensure the parts are fitted together accurately. I cleaned and fluxed both parts and followed the instructions. The result is something that pleasingly starts to look like a real underframe.
Onwards to the solebars: I removed both of these from the fret, cleaned them up and folded the flange with the aid of the ubiquitous “hold-and-fold” tool. The top tip here is to clamp the narrower flange side in the tool and fold-up the wider solebar side – it’s just easier to achieve a neat outcome this way round. Next came the task that I always find the most fiddly on these underframe kits – the solebar overlays…
The first thing to say is that the kit offers two different pairs of overlays – one for two door springs per side door and one for one door spring per door. In my case, for a Diagram 1/115 wagon, the latter was the correct choice. So if you’re building one of these 24.5-ton mineral wagons, pay close attention to select the correct pair of overlays for your chosen Diagram. The second thing to mention is that these parts are fragile so handle them with care! And the final point to note is that the overlays have tiny slots in them that are intended to align with slots in the solebars for fitting parts like the door springs, brake lever guards and support brackets. This means that it is really important to position the overlays accurately before soldering them in place and to avoid excess solder from clogging up these slots.
My technique for dealing with this challenge has evolved over several attempted builds of Rumney Models underframes. The first step is to clean, flux and lightly tin a few key locations on the solebars. In the case of this particular kit, I did this for the area immediately around each of the five tabs along the top edge of each solebar – this has the twin virtues of giving a good distribution of fixing points and staying away from the slots that we don’t want clogged up with solder. The second step was to test fit the overlays (they have tabs that fit in slots along the flange edge of the solebars to locate them correctly) and, once I was happy, I used some narrow strips of Tamiya masking tape to temporarily hold the overlays tightly in position. It is worth making the effort to re-align the overlays as many times as necessary to get this right. I found holding the parts up to the light to see the slots clearly was a good way to check alignment. Only when I was completely satisfied, did I apply the hot iron – working from the centre-most tinned areas outwards to the ones at either end of the solebars.
There are a few detail parts to fit to the solebars – label clips, “wooden” blocks and number plates. It’s a good idea to look at some prototype photographs to work out which of these you need and where to position them before wielding the soldering iron. Having done that, I cleaned, fluxed and tinned the rear of these tiny parts before removing them from the fret. Then I fluxed them again and eased each one into place taking advantage of the stickiness of the La-Co flux to aid positioning. Then I introduced the hot iron while pressing each piece down with the end of a cocktail stick. I also find on helps to tape the solebar down to the work surface (in my case a plywood offcut) to stop things from moving around. Rinsing and repeating this process for several incy-wincy parts calls for a little patience, so I’ve found having a bullet-proof process helps reduce stress.
At this point I deviated from the assembly order in the instructions again and jumped ahead slightly to fit the spring stops. The reason being that it’s less fiddly to do this now before the solebars are secured in place and reduces the risk of accidental damage. This is another detail where prototype photos can come in handy. These wagons were fitted with either traditional U-shaped spring stops or simple stubs of steel rod. The kit fret provides parts to fold up to make the former; if you want to model the latter then some 1mm diameter brass rod is required. I fitted the latter on this build and used the method described in the instructions. The solebar flanges have handy small dimples in them to indicate the correct positions for the spring stops.
With preparation of the solebars complete, they can now be soldered into position on the underframe. I dry fitted them in place using the tabs and slots provided and tightly secured them with masking tape before soldering at the tab/slot joints from the upper face of the chassis top plate.
The final job for this session was to add the support brackets. There are six on each side so you get a dozen chances to practice and improve! I started by fluxing and lightly tinning the underside of the spurs on the chassis top plate that form the horizontal part of the support brackets. Then the recipe I followed for each bracket was: remove from fret, tidy up with a fine file, test fit in place and fettle if needed, apply flux, fit again (making using of the stickiness of the La-Co flux to retain the bracket in position) and zap with the hot iron (from the upper side of the chassis top plate to eliminate the risk of accidentally knocking the bracket out of position with the tip of the iron). There’s a reassuring sizzle of melting flux as the solder flashes along each joint. After doing that twelve times over, I was ready to end this modelling session and take a break.
Next time I’ll go through fabrication of the tiebars and spring carriers plus test fitting of the Exactoscale axles and wheels.
Every Wagon Tells A Story 