ICI Bogie Hoppers
ICI Hopper Wagons
There is no point in looking for evidence that the famous ICI Limestone hoppers ever worked through Exeter Central...they didn't. They have however been one of my favourite items of rolling stock for years and I've scratch built several examples in both 2mm and 7mm scales. At some point I'm going to need several LSWR/SR/BR 40t ballast hoppers so I thought I'd resurrect my interest and build a rake of Limestone hoppers 'as practice' for the ballast hoppers.
The Chassis
I had scratch built a prototype to work out how to do it so now I embarked upon a batch of 5. These were based on some old damaged Tri-ang bogie tank wagon chassis. I first cleaned off all the top detail and the cross members before cutting the chassis in half and adding extensions to put the bogies in the correct place. The buffer beam also had to be brought back so right distance to the headstock is maintained. The bogie sides were modified with glued on plastic overlays as shown here in the 'Manufacturing techniques' section.
One drawback of keeping the Tri-ang couplings is too large a gap between what would be close coupled rakes of wagons. I decided the simplicity of leaving these alone was preferable to devising an alternative coupling.
Being plastic the Hoppers are quite light so I 'Trialled and errored' to find the right amount of lead to add for good running but was faced with the problem of where to hide it. The chassis are quite open and any lumps would be seen. I build a couple of 'model' weights from plastic which could be fitted to the central chassis member to mimic some of the cross bearers and had a tapered profile to hide behind the side girders. I used the 'models' as masters to sand cast 7 weights which were cleaned up and glued to the underside of the chassis. See the 'Making castings' section.
The body
The main body was cut from 0.75mm plastic on the CNC mill as per the 'Manufacturing techniques' section. The great thing about this is all the parts are consistent and accurate in size so gluing them together was a doddle. The body fold line was filled and rubbed smooth and the strapping was from various sizes of microstrip.
The body was fitted to the chassis and glued in place before the triangular side supports were attached. The step plates on each end were hand cut from 0.25mm plastic and attached before the end support plates were fitted.
ICI hopper parts on Freecad.pdfI turned a batch of 16 vacuum cylinders from mild steel and these were glued into position on the end with short plastic support brackets securing them to the chassis. The prominent angle supports for each end of the body were from 1.2mm 'T' section softened in the appropriate place with solvent before being bent to shape in a simple jig. They were then attached between the body and the buffer beam and allowed to set firmly. The last piece to fit was the vacuum pipe running between the two cylinders, through the holes in the body supports on one side. This was made in two halves bent from 0.5mm brass wire, including the coupling pipe (a piece of PVC tube) and passed through the holes from each end to meet in the middle. The joint was hidden inside one of the triangular supports and all was held by superglue.
Once the bodies were built I needed to find a way to represent the slightly raised lettering made on the originals from plafe cut steel plate. Painted letters would have been lost under the rail dirt but having a slight depth meant the letters were slightly visible, especially at certain angles and light conditions...that's what I wanted to recreate.
When I bought the CNC mill I also bought a small laser. I used this to cut out the letters 'ICI' from a design drawn to scale in Inkscape. Using a manilla envelope I had something 0.15mm thick which was attached to the side by flooding solvent through the paper to bond it to the plastic side.
This picture shows the finished bodies painted mid grey with the raised lettering picked out by hand in white. The insides were to be finished empty but in reality they were anything but empty. Wet limestone is just like concrete and sticks well to the steel so I sprayed a base of matt black inside the body in preparation for detailing at the end.
The prototypes were notoriously filthy with a thick brown rail dirt covering the whole vehicle. This is how I wanted to present them so I mixed my own version of this brown muck and sprayed several thin coats on all the wagons, varying a few to try and find that elusive 'semi transparent' quality that hinted at the ex-works grey hidden underneath. Once dry, I attacked the inside with a mix of off whites/greys and browns and a slurry of plaster/PVA to represent the layers of hardened limestone adhering to the platework. I left a space at the top of the wagon and fitted a dummy load consisting of two layers of card sandwiching a piece of tinplate. By using a magnet I can remove the load represented by 'O' gauge limestone ballast
