firefly9 Posted May 26, 2012 Share Posted May 26, 2012 I PM'd another member on here with regards to making my own moulds and casting my own plastic for a project i'm on with. he suggested making a casting box from lego and using clay as the medium for creating the mould but he was not sure about what sort of clay to use as there is a specific type. He also was not sure of what Resin/plastic to use. could anyone advise me on both the clay required and the correct plastic/resin i need. Rich Link to post Share on other sites More sharing options...
bertiedog Posted May 26, 2012 Share Posted May 26, 2012 It all depends on what the final items are to be, and what the master is made from. Is it for very accurate parts for stock, or more for building parts or scenery? Clay moulds work for one off's unless hardened, and proper allowance for removal must be made. For very accurate work a silicon flexible mould is cast over the master, and then it can take resin to make several copies. For simpler casts like building parts, then Vinamold vinyl can be poured over the master and copies made in resin or plaster etc, cheap and versatile as the mould can be re-used by melting. There is lots on casting on the net, but ask here with far more details of the work, the master parts, and the final use and standard required. Stephen. Link to post Share on other sites More sharing options...
firefly9 Posted May 27, 2012 Author Share Posted May 27, 2012 Its to make a scale length jib for the Hornby 75 tonne breakdown crane. I'd like to make several sets as i want to convert more than one. Link to post Share on other sites More sharing options...
JeffP Posted May 27, 2012 Share Posted May 27, 2012 Might be a bit brittle cast in resin over that length. Can you not make one up from brass? Link to post Share on other sites More sharing options...
firefly9 Posted May 28, 2012 Author Share Posted May 28, 2012 i was wanting to be able to make a small batch of them hence the casting of some resin ones. i may not have the patience for brass making and soldering isn't my strong point. Link to post Share on other sites More sharing options...
Castle Posted May 28, 2012 Share Posted May 28, 2012 Hi All, With modern casting resins, you should be alright with the jibs. I would recommend using a silicone mould making material and a polyurethane casting resing. Fast cast is one of the trade name of the stuff I have worked with in the past. Alec Tirantis (on line - Google and contact them and they will give you the exact grades of silicone and resin to use - it has been a good few years since I did this) are a well known supplier and do it in reasonable size batches. Make sure you have a lot of masters and castings ready to do as the stuff isn't cheap and has a shelf life especially when opened. The use of the cold cast silicone over the hot Vinamould means you can make styrene masters. The hot Vinamould would melt these of course... I have used thick styrene sheet before to make mould boxes but you could even get some budget Tupperware or similar of some sort of take away type foil container or anything with sufficient wall thickness / stength so it doesn't bow & bend, thus causing a leak of your precious silicone! Remember that you will have to stick your master down to the bottom of the mould box to stop it floating and any cyanoacrylate (super) glue you use should be allowed to vent off for an hour or so before pouring the silicone in. Remember also that Lego may not be entirely water tight... A couple of tips when working with silicone. Firstly, it is worth buying a coloured dye to go with the silicone you buy as if you put a SMALL bit in with the catalyst, you can tell when it is all thoroughly mixed (the catalyst is clear!). Really, really, really mix it thoroughly! There is nothing worse than going to the trouble of making a master that the silicone never sets on - that is something only the bin has a use for... Buy a cheap paint brush that you will throw away afterwards and use this to carefully paint a thin layer of silicone onto the master from your pot as this prevents air bubbles in your mould. Pour it slowly and finally, NEVER scrape the last dregs from the bottom and sides of the pot as this is where the non catalysed silicone likes to hide and can cause problems. Similar care will be needed with the resin. Work in a well ventilated area as the fumes from this stuff are in what I heard the other day described as the 'well naughty' category (!). Thorough mixing and slow, careful pouring again are key to good casts and don't be surprised if the first cast out of a new mould looks poor. It usually is due to the gunk and grease off the masters. The next one is always better. That lot should get you started... All the best, Castle Link to post Share on other sites More sharing options...
jonhall Posted May 29, 2012 Share Posted May 29, 2012 The design of the mould will be critical - I'd be very surprised it you could achieve a single piece jib like the Hornby crane, and I'm not quite sure how many breakdown cranes one person would actually need? Jon Link to post Share on other sites More sharing options...
Castle Posted May 30, 2012 Share Posted May 30, 2012 Hi All, I agree with Jon about the mould design. One way to approach it would be to build the master for the sides, top and bottom of the jib, as far as possible, flat, out of sheet styrene on a relatively thick (3mm ish) sheet of styrene or acrylic. If you then make the mould about 25mm / 1" thick and (important this bit) ensure that it is dead level as it cures, you will then find you can make some pretty thin castings. The trick there is to put the resin in with the mould dead level too, use a straight edged piece of something to scrape off and excess and then put a further sheet of thick acrylic or styrene (the thicker the better and get some spray release agent to go on it when you get your casting materials) on top with a weight (not too heavy or you will compress and distort the mould). Wait for the resin to cure and then pull out your awesome castings! Remember to ensure that the resin gets into all the nooks and crannies and a bit of wire for poking and prodding the air bubbles out purposes is a great idea here. Make sure you keep the acrylic top bit clean and work fast. This is not a technique for hot weather as the resin cures quicker in the warm. As soon as it starts to go misty, you have had it... If it is hot and you absolutely HAVE to do it then get the air moving with fans to cool stuff down. Gloves at all times when working with resin (latex or similar disposable type are best as you retain an element of 'feel') are a must. All the best, Castle P.S. How many cranes can one man use Jon? Perhaps Rich wants to become Cowans & Sheldon (Miniature Department) Ltd.? Cowan and Sheldon Works - the layout? Each to his own, life's rich (excuse pun!) tapestry... Link to post Share on other sites More sharing options...
Horsetan Posted May 30, 2012 Share Posted May 30, 2012 .....P.S. How many cranes can one man use..... Enough not to have to pay eBay prices for D&S kits. Link to post Share on other sites More sharing options...
RMweb Premium Neil Posted May 30, 2012 RMweb Premium Share Posted May 30, 2012 I'll put in a plug for Sylmasta who offer a complete* starter kit. I've found them to be very helpful. Before I started to dip my toes into the world of resin casting I read up lots and talked to friends who had already trodden that path but there was no substitute for getting stuck in, making mistakes and trying again. I'm still no expert, but I'm getting better at getting better, repeatable, results. * disposable pipettes and party cups are not included in the kit, but are very useful for measuring out the small quantities of the moulding rubber activator and for mixing in. I also use protective goggles and latex gloves whilst working with both rubber and resin. Link to post Share on other sites More sharing options...
N15class Posted May 30, 2012 Share Posted May 30, 2012 I know very little of casting resin. But would it be possible to lay a couple of brass or nickle wires in as you are casting? This would help with the stength as it is going to be quite long. Link to post Share on other sites More sharing options...
firefly9 Posted May 30, 2012 Author Share Posted May 30, 2012 cheers for the info guys i'll be comsidering my options carefully and there are some good how to clips on youtube. i am planning on converting the Hornby cranes to something more realistic and then hopefully selling them to anyone that might be interested in having a scale size crane on their layout. This is very early days though as there are other considerations such as the crane superstructure and how to make a correct scale jib runner. Rich Link to post Share on other sites More sharing options...
Castle Posted May 30, 2012 Share Posted May 30, 2012 Hi Rich, You could do the same as above and cast your crane superstructure and runner bits too. As I said, get as big a batch of masters together as possible at one time so that you conserve and get the best out of your materials. Why not draw them up using something like Google Sketchup first to check that it will all go together? All the best, Castle Link to post Share on other sites More sharing options...
jonhall Posted May 30, 2012 Share Posted May 30, 2012 I agree with Jon about the mould design. One way to approach it would be to build the master for the sides, top and bottom of the jib, as far as possible, flat, out of sheet styrene on a relatively thick (3mm ish) sheet of styrene or acrylic. If you then make the mould about 25mm / 1" thick and (important this bit) ensure that it is dead level as it cures, you will then find you can make some pretty thin castings. All the best, P.S. How many cranes can one man use Jon? Perhaps Rich wants to become Cowans & Sheldon (Miniature Department) Ltd.? Cowan and Sheldon Works - the layout? Each to his own, life's rich (excuse pun!) tapestry... and if you follow Castle's advice you would end up with a) master stuck to a piece of plasticard, b ) a flat rubber mould c) lots of Cowans Sheldon 75T jibs. I couldn't find the old forum thread with my photo's, but eventually tracked them down on my hard drive... J Link to post Share on other sites More sharing options...
Castle Posted May 30, 2012 Share Posted May 30, 2012 Yeah Jon, I guess it would look at least a bit like that... I thought I remembered admiring something like that in the back of my mind on the old RM WEB, in the dim and distant pre me posting and taking up the mantle of Castle! Very nice indeed! All the best, Castle Link to post Share on other sites More sharing options...
firefly9 Posted May 30, 2012 Author Share Posted May 30, 2012 i have seen those pics on a thread by matt angell saying how he converted the Hornby crane. someone posted those pics on there. Link to post Share on other sites More sharing options...
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