Monday, January 24, 2011

Step 2 Planning the Model

Silo bin roof showing conveyor, bin roof and silo roof vents.

Top conveyor with electrical box, motor/gearbox drive, walkway and handrails.
Conveyor with walkway, conveyor cover sections, ladder and walkway down to silo bin roofs.
Short end of walkway with grain feed chute to bin No1, note that the corrugated iron has 3in corrugations which allows the measurement of other parts such as the door width and vent width.
Outloader type on centre of elevator, with lighting
Outloader on No 1 Bin
400 tonne outloader on bins 2 and 3
Front of silo showing corrugated iron, outside of hopper bin, silo rings and centre outloader.
Rear view of silo elevator, with louvred vents and silo rings and top of wagon shed.

Vent for base of silo left hand end.
Vent for base of silo right hand end, concrete sections to be prototyped.
Partitions and wagon shed support footings with grate.
Partitions and wagon shed support foundations, with grate.

The first question that comes to mind when planning to build a large structure such as a silo, is , what is available commercially. By this I mean what size are the silo bins, and what commercial conduit is readily available to suit. Luckily the bin diameter for the Merriwa S052 Silo worked out to be 30ft with a wall thickness of 7.5 in. The total dimension being 31ft 3in, in HO scale, this relates to 109.375mm. Well blow me down if 100mm sewer conduit is 110mm o/s diameter, how lucky was I? So the plans will need to be adjusted to suit the conduit, and everything that comes in contact with the conduit is varied to suit. This will mean very little change from the plans.

Now that that we have the bins covered, we need to know the height of the silo, and luckily for me, I was able to get access to a few plans which give the levels from the base to various levels. This ensured that the silo looks correct and the aspect is kept to the prototype. There will, no doubt, be certain items that may to be adjusted to suit, but at the end of the day, if anyone wants to put a vernier gauge over the silo just tell them to nick off. I have a simple philosophy, with model building: “while the model should be accurate to the prototype, more importantly it has to look right”.

I needed to work out the materials that certain parts of the silo need to be made from. From the base all the way through to the roof of the elevator. So the logical starting point is the base or foundation. I always build models on a craftwood sub-base, using T-nuts to screw it into a full base that forms the base of the storage box that the model is delivered in.

The actual base of the silo is naturally set up from rail height and the base will be built up using laser cut acrylic that has had holes, laser cut to suit the inclusion of all the parts that build up from the base. The partitions in the wagon shed will all be prototyped from Shapeways in the Netherlands, as will the footings for all the wagon shed supports. These can include the holes for the wagon shed supports and the nut/bolt detail if required. The footings can then be located directly into the holes in the base, which makes the model more accurate in assembly. The grates in the wagon shed are photo etched brass, to suit the holes that they fit into.

The internals of the wagon shed are scratch built over paper plans using special shapes brass profiles and soldered together. Small angle can be substituted with small square section to allow easier construction and making the silo cheaper to construct. Corrugated iron is used to clad both the wagon shed and the workhouse and elevator. I prefer to use Campbell’s Corrugated Aluminium. This material comes in packets in sizes from 4 scale feet to 12 scale feet. I suggest that the most economical packets to use are the 12 feet ones. You can cut smaller lengths from the longer sections.

There are 18 louvered vents, and various doors that will need to be prototyped in the finest material possible, and designed to simply press into the holes after the corrugated aluminium has been fitted. The shed in the wagon shed is laser cut, tabbed, glued and clad, with prototyped doors windows and vent.

Possible the hardest job on this particular silo will be the locating of the rings on the bins. Locating the starting point was as simple as measuring from the base, and then testing what looks correct when doing the drawings. The rings can be Evergreen styrene strips (6in - scale). An important part of any silo are the drains, and in this silo the drainage surrounds the entire silo, and can easily be made from laser cut acrylic and tabbed into the acrylic base. Other parts that will be prototyped and scratch built include the vents at both ends of the silo and the various outloading chutes .

The elevator and bin roofs will be made in laser cut acrylic, which can then be clad in aluminium. The hopper bin will be scratch built from brass section. The bin roofs will be built up from acrylic sections that are tabbed and glued so that they fit the 100mm conduit neatly. Pipes will be located into the centre of the roof builds so that the top conveyor and walkway can be located easily and accurately. I believe that models with the external parts needing to be attached can be plugged into the base structure, allowing painting off the model, and then touch up to blend the part to the model when installed.

The conveyor and walkway will need to be scratch built. The closed conveyor can be prototyped in sections and glued together. The walkway will be etched and the handrail supports are all scratch built with jigs to keep them uniform. The roof vents will be prototyped, and then have etched brass detail added.

So, as you can gather, there are many parts to the construction of a silo, and if you plan it correctly the construction method will flow easily. Of course, the whole planning method revolves around 3D drawings of the sections, which then allow the correct fitting of parts , and sub parts, this method of 3D CAD construction is time consuming but saves time overall, in that you only need to do it once, and correct any mistakes as you go. If you use the trial and error method in the actual building process, it would be more costly at the end of the project. The other advantage to using CAD , is that all the prototyped parts need to be drawn in 3D anyway.

So the next posting, we will discuss the foundations and acrylic base, until then BYE for now.