Railway Ballast Cleaning Train - Part 4

Having spent ages scrutinising photographs of the prototype I think I have finally worked out the principal of operation and how the ballast was handled within the machine. Initially I thought ballast cleaning meant the ballast was picked up, washed and put back down. Not the case at all! The principle of machine operation is simple; ballast is excavated from beneath the track and conveyed to a vibrating sieve where anything smaller than the 'rocks' falls through the sieve and is either conveyed to open wagons stationed alongside or, spewed onto the adjoining landscape. The remaining 'cleaned rocks' are returned to the track bed. The complication comes in understanding how materials are moved through the machine.

Having made the chassis for the model I decided to populate it from bottom up. The most significant addition is the 'ballast distribution conveyor'. In the photograph it is the long thing with holes beneath the chassis. Either side of the holes are rollers for the conveyor belt (not in the model of course - here they are a crude representation). 

This conveyor is the last process in the cleaning operation. It is shown on the model stored for transportation. In operation it is pivoted down and manually swung side to side to distribute the cleaned ballast to the track bed.

Why does ballast need cleaning? Over time the content of the track bed is corrupted with dirt and other particles that could lead to destabilisation of the track bed, meaning the natural locking of the ballast rocks is disturbed.

I have also completed the cab that sat at one end of the machine. I do not know what was inside. I guess it contained controls. 

The paint finish I made up from yellow and brown acrylics to get as close as I can to the 'grubby' yellow used by BR for these machines in the late 1950s to early 60s.

The design of these models goes beyond mirroring the prototype. I also have to take into account the foibles of the FDM 3D print machine. I intended to print the cab as one piece but that would have shown the layers of plastic requiring much sanding down (in fact the first photo above shows the effect). In the end each side and roof were printed separately with the outside faces being the first plastic layer set down on the smooth printer bed. The lines of plastic are much less visible this way. Not the case for the roof where the corrugated effect due to plastic layering was covered in superglue and bicarbonate of soda sprinkles and then sanded smooth.

I have been spoiled by the incredible finish and details of current ready to run models from the trade. My 'scratch build' is rough but, possibly acceptable at normal viewing distances. Reminds me of RTR proprietary models from the 40s and 50s, which were also a bit naïve!

To Part 5.

To Part 1.