In this article I will describe how I set about making my own models of dockside container cranes and associated railroad cars in 1/1200 scale. As casting white metal in hand-held moulds is involved, with the potential for serious burns and other injuries if mistakes are made, this is most definitely NOT a project for an inexperienced model maker or a beginner. However, by adhering to the supplier’s guidance on Health and Safety in the use of the materials, the techniques described and processes used should be within the skill set of any experienced model maker. I live in England and obtain the silicone rubber and white metal used from Alec Tiranti - visit www.tiranti.co.uk for information on products. Modellers elsewhere should be able to locate local suppliers through a Google search for silicone rubber and white metal. There are several different styles of crane in use and after some difficulty in sourcing accurate plans I decided to make a ‘generic’ model that embodied all of the key elements of this type of crane. As I intended to display the cranes in a dockside setting (using Tri-ang Minic quays) I also decided to make some railroad equipment to give some ‘life’ to the display. I was provided with some information from fellow collectors via the 1250 Board and gratefully acknowledge the help provided.
2. Making a ‘Master’- The first stage in the production of cast models is to make a ‘master’ or ‘pattern’ to be used in the mould-making process. Dockside container cranes can be ‘broken down’ into a handful of key components to enable simple, two-part moulds to be created that avoid ‘undercuts’ that would otherwise require more sophisticated, multi-part moulds to produce usable castings. It is essential that each master is made as accurately as possible – any fault will be replicated on every subsequent casting. The masters for the crane were made from plastic card, cut to shape and formed up square on a flat working surface. Each part was ‘dry-fitted’ to the rest as each was made. The full set of components was taped together to ensure the fit was true.
3. Making a Mould – ‘First Half’ - To create a mould from the master, embed each component carefully in plasticene (re-usable modelling clay) and leave approximately half of the master exposed. It is essential not to distort the master during the embedding process otherwise a distorted casting will result. Ensure that the joint between master and plasticene is 100% ‘sharp’ and there are no gaps around it. After embedding the master, build a ‘box’ around it approximately 1" deep. At least half an inch of rubber is needed in the smallest of moulds to ensure that the mould is stable when filled with metal and that it does not distort from the heat. A deeper fill of rubber is needed for bigger section casting. Experience will quickly show what is best. I use balsa wood to make the ‘box’ and ensure that each joint is glued securely. (Some people use Lego bricks for this!) Insert a plasticene ‘runner’ shape into the mould to provide for the mould filler neck. The surface of the plasticene left exposed can be lightly coated with ‘Vaseline’ to aid separation later from the silicone rubber. Do not get any Vaseline on the master as this will result in the marks of the Vaseline being replicated on every casting. The next stage is to mix the silicone rubber with its catalyst and pour this into the mould. The big issue here is unwanted air bubbles that can spoil the mould and cause voids which will fill with metal during the casting process. The way to avoid bubbles is to use a vacuum chamber to extract them. I do not have one of these so I rely on careful application of the rubber to the master and prick any bubble that appears during the pouring process. It is quite simple to lay down a thin ‘skin’ of rubber on each master before filling the mould completely with rubber. Leave the rubber to cure for at least 48 hours. When it is cured it will be firm to the touch with no soft spots.
4. Making a Mould – ‘Second Half’- To make the second half of the mould the first half must first be released from the casting box and cleaned up. This entails trimming off all unwanted bits of rubber eg the meniscus all around the edge of the rubber block as well as around the edge of the master. Take great care when trimming the meniscus off the master not to scratch the master as this will, again, show up on every casting made from that mould. When all the trimming has been done cut some location ‘cones’ into the surface of the rubber. When the second half of the mould is made the rubber will fill each of these and provide for 100% accurate alignment of each part of the mould during the casting process. Add another ‘runner shape’ to match the shape embedded in the first half of the mould. Build another balsa wood box around the rubber block and ensure that at least half an inch or more depth is available for the rubber to fill. Before any rubber is poured it is VITAL that the exposed rubber of the first half is protected with a thin coat of Vaseline. This includes the location cones cut into the surface. Particular attention should be paid the joint between the master and the rubber to ensure this is as clean as possible. If you do not protect the surface of the rubber you will never get the two halves of the mould apart without cutting them to pieces! Silicone rubber is amazing stuff and will only stick to itself – and this it does fantastically well! Leave the completed mould for around 48 hours to allow it to cure fully – with each part exposed to the air. Trim off any unwanted bits of rubber and prepare the mould for casting by cutting out the filler neck carefully to join it up to the casting void. Cut as little as possible here and allow for any unusual characteristics in the mould – for example several small items in one mould where multiple fillers will be needed.
5. Making Castings - SAFETY NOTES: Casting hot metal must be done in accordance with suppliers’ instructions. The wearing of a durable apron, heavy leather gloves and eye protection is strongly recommended. Do not wear shorts or beach shoes of any kind when using hot metal – splashes can hurt and be dangerous! Melt the metal in a well ventilated room and also wear a face mask to protect against fumes. Do not get any moisture near the mould – moisture will cause the metal to spit back at you and this can be very dangerous.
When hot metal enters a mould it pushes air ahead of it. When the metal reaches a ‘dead end’ it will be prevented from filling the void by the air that is now compressed into that space. To avoid this and to ensure that all voids are filled – particularly where square corners are involved – air vents need to be cut into the surface of each half of the mould. This should be done very carefully to provide small ‘v’ shaped vents. It is best not to run these cuts to the outside edge of the mould as hot metal could find its way along them and out of the mould during casting. Where the dead end does not allow for a vent to be cut it will be necessary to drill through the mould with a very small drill bit to ensure that it is vented adequately. Make sure any rubber ‘swarf’ is cleaned away if a drill is used. Experience has a part to play here and there could be some ‘trial and error’ involved. Avoid making deep cuts into the surface of the rubber – deep cuts can trigger tears when the mould is in use and that could destroy it. Before casting the mould should be ‘dusted’ with French chalk, or failing that, talcum powder to assist metal flow and leave castings with a smooth surface finish. It is also best to warm the mould to help the hot metal flow when you start to cast -corners furthest away from the filler neck needs warming most. I warm the mould by pouring a small amount of the hot metal onto it and leaving it to stand for a few minutes. The mould will heat up quickly during casting and it is important not to get it over-heated as this will damage the mould and result in castings with rough surfaces finishes. I melt the metal in small ladles obtained from the supplier. It is poured into the mould held in a gloved hand between two pieces of wood cut to size to allow firm pressure all round the mould. It is important that no metal escapes from the sides of the mould during casting. In case of this event I pour the metal above a special board provided with an edge all around that will capture any spills. The excess metal can be poured back into the melting ladle after a few seconds, leaving the casting in place inside the mould. Experience will show you how to judge this moment. Even with small moulds, great care should be exercised when opening the mould after casting. The cast model will be very susceptible to cracking if it is exposed to cold air too quickly, or if it is put under strain by removing it from the mould too soon. Again, experience will teach you the technique here. Handle all new castings with care – even small ones will burn an un-gloved hand. It is prudent to keep a full bowl of water to hand to drop each casting into as it is removed from the mould. With practice castings can be turned out quite quickly – small items such as the railroad cars featured here can be cast one at a time very rapidly.
6. Cleaning up the Castings - No casting is usable ‘straight from the mould’ – each one will need washing – to remove any traces of French chalk and grease from handling, as well as ‘fettling’ to remove the casting neck, ventilation tag ends and any flash. Be wary of misalignment that creates ‘steps’ in the casting. This can be caused by careless handling of the mould during casting, or by over heating of the mould through too much casting. ‘Steps’ cannot be cleaned up and the casting will need to be put back in the pot. When the castings are all cleaned up they are ready for assembly – that’s all there is to it! This photo features the master, casting and mould for 3 crane components. At left is the jib – a long piece that is at the limit of safe hand-held casting. Centre is the master, casting and mould for the main front and rear crane structures; and at right the master, casting and mould for the machinery platform unit that fits on the rear of the main structure. Note the location ‘cones’ and air vents cuts in each mould and the wide casting neck in the crane structure mould – this ensures efficient metal flow during casting. Sufficient castings for around 6 cranes shown with some cast container stacks, cast in the way described in this article. The wooden tray contains cast jibs and aluminium rodding used for the crane hoists; the multi-compartment box has the crane front, rear and side structures at left; centre top there are railroad cars and locomotives; centre lower there are machinery platforms; right top has the container lifting fittings; lower right contains the crane header, square rodding locators and gantry fittings. These are crane gantry units shown with part-assembled container lifting fittings. The lifting fittings have been made to allow for either a long (53’) container or short (30’) container to be held. The part is simply trimmed to length and redundant features cleaned off. Paper clips to represent the hoist cables have been glued to the lifting fittings. In due course these will be glued to the gantry fittings which are then glued to the underside of the jib in whatever position is required. Here are some part-built cranes with a completed model alongside finished in white primer. One of the part-built cranes illustrates the ‘raised jib’ option that can be selected by simply cutting and bending the jib (very carefully!) to the appropriate angle. The rodding joining this to the structure has to be reduced in length as appropriate. The part-built cranes comprise 5 components at this stage – front / rear/ left / right and jib. The side pieces are ‘handed’ to fit left or right and have a rebated face to overlap the corner of the front and rear pieces to provide a strong joint. Two cranes at a more advanced stage of construction – These have the rodding ‘location squares’ fitted to enable the construction of the main superstructure and header components. A completed container crane finished in white primer. Note the full set of rodding, that represents the various hoists involved, coming together at the header piece, the gantry installed on the underside of the jib with brass shim cut and folded to suit to represent the communications and power loop and the cross-bracing rodding installed from front to back at the top of the basic crane structure. Six completed cranes finished in a selection of colour schemes. Five views of a busy container port, that shows model ships by Tri-ang Minic, CM and Herpa, with cranes, container stacks and railroad cars modelled, cast and finished by myself with all parts made in accordance with the steps outlined in this article.
Other Castings - A clutch of home-cast Zeros made around 1970 – cast in lead in a Plaster of Paris mould. These were made for a Superior ‘Akagi’ which had just been acquired. Condors, B25s and a part-formed Corsair all dating from around 1971, cast in lead in Plaster of Paris. The Condors and B25s looked good when fettled and painted. Masters from around 1990 for a dockside crane and lock gates, built from plastic card. This is a recent white metal model of a stone quay cast in silicone rubber, with a repainted Tri-ang tugboat. A model of the Japanese ‘Shimakaze’ cast in white metal in a silicone rubber mould – showing how flash can arise with a mould that is held too loosely during casting. In this case the flash can be removed quite easily and will not spoil the model.