Railway Ballast Cleaning Train - Part 5

Now it is beginning to look like something interesting albeit bizarre! 

The long sloping down arm is the excavator in its 'parked' position. There is another one on the other side. These were lowered and pulled out to the ballast shoulder. First though the ballast must be cleared manually (I assume) from between two sleepers down to the substrate because the two excavators are joined at their base by a removable section that goes under the rails. Contained in the arms is a continuous chain driven series of blades that collect and push the ballast to and up the furthest arm as the vehicle moves slowly along the track. I'll explain later how that was done as the machine is not self powered. At the apex of the arms the ballast falls onto a conveyor (the sloping up piece) that moves it to the sieve (not yet modelled).

I am pleased how well the 3D printer created the chain driven blades. I designed these as separate components with their blades attached to a thin wall (the chain), the flexibility of which allowed it to be bent around the curve at the base of the excavator arms.

The  excavator 'motor' is positioned high up and pokes above the girder frame. Understanding its shape and fixings was extremely difficult to glean from photographs as it is not clearly detailed but, eventually I got the drift and whilst not totally correct to prototype (there is a mass of girders etc. up there that are not modelled) it looks ok and gives the impression it could work. 

The conveyor belt came out well. The printer decided to give it a slight ripple in places that gives the impression of a floating, flexible belt. Colouring of this was done with black pastel scrapes.

This was an intense design period so, I'll return to the simpler Power Generator wagon next for a mental break.

In fact, there are another two more intense design periods for the ballast cleaning wagon before it is done. These being the sieve mechanics and spoil expulsion.

To Part 6

To Part 1.

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.

Railway Ballast Cleaning Train - Part 3

Why did I pause the ballast cleaning wagon design and build to start its associated power generator wagon? Well, the design of the former is intense and potentially exhausting. At the end of it would I then be motivated to start all over again with the power generator wagon? By turning attention now to the latter is refreshing and seeing both develop together reminds me that the two wagons are inseparable in practice.

The power generator wagon has fixed wheel sets located in axle boxes hung from the chassis together with leaf springs. These include quite detailed parts; very small in 4mm scale that FDM (fused deposition modelling) printing cannot reproduce well. Fortunately, I had available a scrapped kit built wagon with detailed injection molded parts precisely matching the prototype. These, including a portion of sole bar they were fixed to, were cut from the donated wagon and inserted in the sole bar of the power generator wagon. BTW, brake blocks were also reclaimed.

Inserted axle box - final

Now, the sole bar of the donated wagon is not as tall as the new wagons so, the axle box etc. had to be offset in the new sole bar to be flush with its base. When I placed the new wagon on the track the buffer line was at least 1 mm higher than other wagons! This is not much, but glaringly wrong. Here we go again, 2 steps forward and one back. The parts had to be cut from the new sole bar and its height reduced to match before replacing them. Razor saw cuts were filled with superglue and bicarbonate of soda sprinkles to give a solid infill then filed smooth.

Weathering was applied with brown pastel scrapes (appears grey in photo)

I am impressed with the levers and hangers that printed better than expected. Vacuum pipes were made from solid copper wire with thinner wire wound around.

I'll return to the other wagon design and build next.

To Part 4

To Part 1