GWMark Posted October 28, 2013 Share Posted October 28, 2013 I am currently building a 4-4-0 locomotive (GWR Duke) and have the typical issue with such models, balancing the model to get enough of the weight on the drivers. I have yet to attach the dome to the boiler, this sits forward of the front drivers and is a large lump of white metal. Adding this is just going to make the balance issues even worse. So my thoughts are to create a lighter weight version of the dome. My first thought was to copy the white metal version and create a resin casting of such a device. Looking at various sources it looks like I will need to get some RTV mould making material, silicone release agent, and some resin - my first thought was mouldcraft range. It does seem like a lot of bits to just create a small component. Has anybody got an easier option? Having not resin cast anything previously I have no idea how hard this would be to do either. I guess one risker option might be to drill out the white metal version to make it lighter that way, but I'm not sure I fancy this - at least making a copy of less destructive if I get it wrong. Has anybody got any thoughts on this, or know of a supplier of lighter weight detailing components in 4mm? Thanks Mark Link to post Share on other sites More sharing options...
shortliner Posted October 28, 2013 Share Posted October 28, 2013 If it is not undercut - make a mould of the item from plasticine, and then use Davids Fasglas 2-part resin (used for fibreglass body repairs)from your local car shop - I have used this method to cast bogie sides successfully - Mix quantities and pour - it sets quickly but is exothermic (it gets HOT!) - when set it can be filed and drilled and is cheaper in the quantity you need. BTW use something cheap and cheerful for mixing in - and throw it away - you cant clean it! (Plastic pot and cocktail stick) Link to post Share on other sites More sharing options...
RMweb Premium uax6 Posted October 28, 2013 RMweb Premium Share Posted October 28, 2013 The silcon mould release can be replaced with Wilco household polish in a yellow can (test it by spraying on your hand, and you will find it's really slippy and almost pure silicon! Andy G Link to post Share on other sites More sharing options...
shortliner Posted October 28, 2013 Share Posted October 28, 2013 The silcon mould release can be replaced with Wilco household polish in a yellow can (test it by spraying on your hand, and you will find it's really slippy and almost pure silicon! Andy G ...also a spray-on cooking oil from Morrisons - I forget the name! Link to post Share on other sites More sharing options...
RMweb Premium uax6 Posted October 28, 2013 RMweb Premium Share Posted October 28, 2013 BTW I bought some RTV in small quantities (to try out) from Polysil via ebay. Quite cheap I thought. The resin came from http://www.nigellawton009.com/PayPalCasting.html Both products seem quite good, and you'll soon find an excuse to use it all! Andy G Link to post Share on other sites More sharing options...
black5f Posted October 28, 2013 Share Posted October 28, 2013 Hi I started with fast glass but it's very viscous and damages the moulds after a while as the previous poster said, gets very hot. Now I use this below, have also added a link to the RTV I use. http://www.mbfg.co.uk/liquid-plastics/sg2000.html http://www.mbfg.co.uk/rtv-silicone/gp-3481-f.html The sg2000 resin has a short pot life (3 minutes) but is very easy to mix and is about the same consistency as milk. Lipsil of vasalene make a good mould release for the master. For casting the resin I only use talc, just dusted with a brush, very paintable. I have no connnection with the company but they are very fast delivery, very freindly and have an ebay shop. Normally arrives next day. If it's just a one off, consider latex for the mould, painting on a layer at a time and allowing to dry. If I were you I wouldn't attempt a two part mould first. Make an open mould (just one cast piece of RTV) and use plasticine to build up a pillar that is slghtly less diameter then the base of the dome so the base rim is cast but comes out easily. When you pour in the resin, just tickle it with the handle end of a small brush to agitate out any trapped air. the talc will do the rest. Resin casting is quite easy, and very rewarding. You just need some cooking scales for measuring (sg2000 is 50:50 by mass) and I use old coke tins to mix in. Cut the tops off with scissors and then form a pouring spout. Regarding 4-4-0's etc there is an old technique of using the tender. On the tender you arrange the rear axle fixed as per usual. The front two axles sit in a bogie that is mounted not by a central pivot, but via beam pivoted at the bogie one end and under the rear wheels at the other rather like an old Hornby leading truck (but all hidden in between the frames). The tender then rests on a single pivot on the drawbar of the loco. This way you can fill the boiler with lead and counter that with lead in the tender, as much as you like. The tender being effectively a pony truck will also stop the engine crabbing as some 4 coupleds tend to do. Your Duke will out haul many Pacific's. If I haven't explained it well enough, let me know, I'll dip my spider in an ink well and attempt a drawing. The resins above are very good at picking out detail. Tom Link to post Share on other sites More sharing options...
RMweb Premium uax6 Posted October 28, 2013 RMweb Premium Share Posted October 28, 2013 I bought a cheap (£5 from ebay) set of gold scales, making sure they had a tare function. For the RTV I mix use plastic throwaway drinks glasses ( the Mrs had some in a cupboard so i purloined them), and mix with a screwdriver with a knacked point. For the resin I use 10cc syringes to measure out (ensures a proper 50-50 mix) and mix in either the drinks cups or waxed paper pill pots. You will also need a grasp of measuring volumes. This morning I made a mould (see my bodging thread) and measured the volume in cc (in this case 6cc). I then mixed up the same measure of rtv (6gm). Looking at the mould I was convinced that there wouldn't be enough, but decided to pour anyway, which was lucky as I had just about enough! I find this casting lark can be addictive. I've had quite a lot of failures, but now I'm using RTV the results are improving. BTW I only use the silicon spray on the master, I've not used it for the cast yet, as they always seem to come out. Andy G Link to post Share on other sites More sharing options...
GWMark Posted November 5, 2013 Author Share Posted November 5, 2013 Thanks for the advice everybody. I have order some small quantities of RTV and SG2000, just because I can't resist trying. I suspect I will end up hanging the tender on the rear of the loco to balance it. Having never tried casting I think I will give it a go as well, even if I end up using the original. Link to post Share on other sites More sharing options...
black5f Posted November 5, 2013 Share Posted November 5, 2013 Hey good luck. It's a lot of fun, quite addictive and very rewarding! Tom Link to post Share on other sites More sharing options...
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