Whitemetal Casting for Beginners

Whitemetal Casting for Beginners Part 2 - Practice

Nigel Lawton 2,248 words

This is a continuation of a previous article ‘Whitemetal Casting for Beginners Part 1 – The Theory’ in which I described the process I have used to produce home-made whitemetal castings with minimal tools and equipment. To review the process is outline is:-

1. Make a master.

2. Make a silicone rubber mould around the master.

3. Reassemble the mould and fill with whitemetal to replicate the master.

The subject I chose for my first casting efforts was the humble V-tipper or ‘skip’ as my interests in NG modelling lean towards the industrial. There is only really one 009 kit available for a skip which we all know and love however compared to the wide variety of skip prototypes which exist this is not exactly a comprehensive covering of this very common type of rolling stock. Looking at prototype photographs skips found in industrial use not all were the usual ¾ cu yard ‘Rugga’ type with a flat rim, many are slightly larger ‘continental’ types with raised ends increasing their capacity somewhat. Also the frame and cradle arrangements used on such skips are completely different from the ‘Rugga’ type often using U channel frames with the rims facing out rather than in and inverted U channel cradles with a flat bracket on the skip rather than a flat cradle and U bracket on the skip as on the Rugga. A typical train of skips which might be seen running on an industrial line would normally include various types of skip and making a model based on a significantly different prototype gives the opportunity to move towards this non-uniform look. Another factor was significant in my thinking – that of weight. The commercially available Skip kit is extremely light and needs ballast to run well which makes it very difficult to model ‘empty’ skips. Producing skips in whitemetal makes them heavy enough to be robust in running but so long as wall thickness is kept down they need not be over-heavy.

You may ask ‘why cast this’ why not just scratch build?– well most industrial railways used a large number of skips and although I reckon I could scratch build skips I don’t think I have the mental resilience to scratch build 10 or 20 of them and it makes more sense to build one really well and copy it rather than make 20 mediocre models. A further reason is ease of working – to generate a silicone mould for casting you can make your masters from easily worked and joined plastic card and section which would be too light if used as rolling stock themselves but cast in whitemetal they are fine.

Having decided on the subject the next stage was to obtain photos and drawings of a prototype and decide how to make the masters. I have made much use of an article in the ‘Narrow Gauge and Industrial Modelling Review’ called ‘Vee type tipping wagons’ by Gordon Hatherill which illustrates several ‘continental’ skips and includes a drawing which covers several options from one supplier. As it seems typical of the type seen in other photographs I decided to try to reproduce a skip based on the W.G. Allen design shown in this article.

At this point if you are making 009 rolling stock for 2ft gauge prototypes you have to be prepared to compromise as the 9mm (rather than 8mm) gauge and over scale wheels (tyre too wide & wrong diameter) mean than your frames have to be a lot wider and with a different wheel base compared to the prototype. The smallest wheels available to my knowledge are 5.1mm (15¹/₃ ") whereas even the largest prototype skip shown in the article has 14" wheels and many are only 12". This results in all the frame dimensions needing to be distorted to allow standard wheels to be used and the spacing of the axles opened slightly to compensate for the wheels being oversize on their diameter. I make extensive use of a PC and generate drawings using Word – you can set dimensions etc to 0.1mm and once you have an outline scale drawing you can easily ‘stretch’ it in one dimension without affecting the others. I then print the plans on paper to use as templates and directly onto plasticard for the plastic sheet components using an inkjet printer. As a matter of interest I have AutoCAD on my PC and know how to use it but still prefer to use Word because I think it’s a lot quicker!

I decided to fabricate the hopper part of my Vee tipper using two sheets of plasticard laminated together with rivets embossed using an embossing riveting tool borrowed from a fellow modeller (thanks Nick). This allows rivet detail on the inside and outside of the hopper and gives the required minimum wall thickness of 0.7mm if 10 thou (0.25mm) and 20 thou (0.5mm) are used. Careful choice of which order to use these allows for stepped joins and minimum exposed edges – I used the 20 thou for the outside of the Vee part and inside of the two gussets and 10 thou for the inside of the Vee part and outside of the gussets. I marked out the shape of the parts using a PC and inkjet printer as noted above cutting them out with a sharp craft knife and embossing the rivets. The 20 thou Vee part was pre-formed using a simple wooden former, crepe bandage and boiling water (exposure time about 30 seconds). This technique is thanks to Stephen Sullivan in the April 2001 ‘009 News’. The 20 thou parts were glued together first with the gussets inside and flush with each end of the Vee. The inner Vee part and the outer gussets were then added. I added detail to the outside using more 10 thou sheet and some plastic section embossed with rivets. The ends of the support brackets were the most challenging and the final solution is insulation from fine wire (0.8mm outer diameter) superglued on and blended in with Milliput. The upper rim of the hopper was the cause of the failure or one would-be master as I tried to use 10 thou plasticard which is just too thin unsupported and curled badly – judging by the experience of the chassis/frame it would probably have cast OK. I think brass or some other metal would have been necessary to get the thinner wall thickness to work. I did it in 20 thou the second time and although still only 0.5mm wall thickness casts OK as its narrow. Shiny areas caused by the solvent glue I used to fasten the parts together were removed by careful use of a glass fibre pencil-brush (mind your eyes). When setting out to build this master I made some deliberate dummy attempts to check my ideas on how to do it and improve my technique – this is one of the things about plasticard – its so easy to work you can quickly dummy something up to try out an idea. The final master was my second real attempt following two deliberate dummies.

The chassis/frame was more challenging than the hopper as it is very open with little material or structure. There must also be a way of fitting wheels without bending and probably destroying the casting! After much consideration I decided to make a half chassis casting and put two together to make a complete chassis. Of course this is only possible with designs which show the type of mirror symmetry which is the case for my prototype. Two dissimilar half-chassis castings could be used for other prototypes. Actual skip chassis are fabricated from steel U channel which would be closely modelled by small plastic U section. However as the frame is a fairly complex shape and involves ‘bent’ corners it is difficult to use the plastic section as it does not ‘hold its own bend’ so I decided to use brass for this master. You can obtain suitably sized (1/16" x 1/32") brass U section, I had none to hand but had some 1/16" square cross-section tube which give a U channel the right sort of size if you cut one of the sides off. I bent up the frame using a PC generated template and filed and sanded it down to scale channel depth. The axle boxes I obtained as spares from Worsley Works – 1.5mm x 1.5mm brass bearings as used in their bogie kits. These are filed down to remove the section which is bigger that 1.5mm diameter and soldered in place on the frame with solder paint again using my PC generated template. The prototype support cradle for the hopper is, I think, 2" U section (not shown in the drawing I have) which I made using the normally hidden half of the new code 55 Peco N gauge track which has a dummy base then a real base (used for rail joiners) moulded into the sleepers. With careful filing this can be made to look like U section with a 0.66mm dimension! Two pieces of this material soldered together make up each of the two half-cradles and a third small offcut from the N gauge rail set into a slit in the appropriate U section forms the catch. A similar effect could be achieved by filing down 1/32" H section brass (which I did not have to hand). The buffer/couplings form the join in between the two halves of the frame and are made by filing down a spare 009 whitemetal coupler from my bits box and cutting it in half with a razor saw. I set this up to take ‘Greenwich’ coupler loops. The frame components were set up carefully using templates, mirror and set square and soldered together.

Masters for many items of rolling stock, line-side accessories etc could be produced using either or a combination of these methods.

All that remains is to produce moulds for these items and pour castings as described in part 1! The accompanying photos will hopefully act as an additional guide and evidence that it can be done! In fact I have found it relatively easy to pick up and very rewarding as an offshoot to my Narrow Gauge Modelling activities.

Notes to accompany pictures:-

WMCP Fig 1

The completed masters, on the left the half chassis/frame from brass, nickel-silver and whitemetal soldered together with both normal and low-melt solder. On the right the skip from styrene sheet & section and small diameter wire insulation.

WMCP Fig 2

The skip master on its bed of plasticine – it is stuck down with blue-tack (inside the skip) and the plasticine is built up to the rim of the skip on all sides.

WMCP Fig 3

The skip master with alignment pins and wall built around the plasticine slab.

WMCP Fig 4

The first half of the skip mould after pouring.

WMCP Fig 5

The skip master still embedded in the first half-mould after removal of the plasticine slab. Plastic masters such as the skip should be removed from the first half mould whilst it is cleaned and mould release is applied before pouring the second half mould.

WMCP Fig 6

The chassis/frame master embedded in its slab of plasticine. For a complex casting like the half-chassis its important to choose the split line between the two parts of the mould carefully. You need to consider firstly how you are going to get the two halves of the mould apart with the casting inside and secondly how you are going to get the casting out of the mould. The half-chassis mould is split so that the ‘female’ mould can be removed from the male plus casting with some flexing side to side to disengage the skip support cradles. The casting is then slid out of the mould along the plane of the split (‘horizontally’) to disengage the inboard part of the coupler then ‘vertically’ away from it.

WMCP Fig 7

The chassis/frame master with alignment pins and walls built up around its plasticine slab.

WMCP Fig 8

The first half of the chassis/frame mould after pouring.

WMCP Fig 9

The chassis/frame master still embedded in the first half-mould after removal of the plasticine slab. Brass and other non-plastic masters can be left in place and carefully cleaned around – this is generally better as it prevents any misalignment or reversal upon replacement or damage to a fragile master such as the half-chassis.

WMCP Fig 10

A mould after pouring showing clamp arrangement and elastic bands to hold the top together. I was too lazy to cut some clamping pieces which were big enough!