DaveArkley Posted April 4, 2011 Share Posted April 4, 2011 I have a detailed plaster casting of a stone retaining wall (in 2mm) which I'd like to reproduce. What's best practice for creating a mould and what are appropriate materials to use for casting to ensure that the fine detail is retained? Many thanks Dave Link to post Share on other sites More sharing options...
RMweb Gold Jonboy Posted April 4, 2011 RMweb Gold Share Posted April 4, 2011 Personally I would use a two part silicon moulding compound for any detailed molding work - we use it for making moulds of finger prints at work. There may be cheaper methods out there though so I would hang on a while for advice. clicky As ever when working with plaster (recommend herculite 2) remember it is exothermic and can cause burns if you heavily encase fingers etc. whilst it sets. Link to post Share on other sites More sharing options...
musketter Posted April 10, 2011 Share Posted April 10, 2011 Try gelflex, easy to melt and reusable again and again. Local hobby shops sell it for about £6 for 1/2 a kilo which should be more than you need. Please remember this can be reused ! Example http://cgi.ebay.co.uk/Gelflex-Remeltable-Moulding-Rubber-1Kg-Flexible-/230598081991?pt=UK_Crafts_Other_Crafts_EH&hash=item35b0b77dc7#ht_1340wt_905 If you Google it, you will find lots of instructions on how to use it . I just use normal casting plaster to make the items. Keith Link to post Share on other sites More sharing options...
bertiedog Posted April 10, 2011 Share Posted April 10, 2011 Agree with previous, same material, different name, Vinamould, various grades are done, completely re usable, makes "sheet" or "slab" moulds to be pressed in to plaster for set stones and paving, etc, or proper moulds for poured plaster for say cliff sections and cast building parts. I would use cheap ordinary plaster, nor expensive specials for scenery. Reserve the specials and dental plasters for fine detail building parts. It also takes resin casting materials, (use a good mould release like wax). Any master can be used that is non porous, and can take about 150c , this excludes polystyrene masters, and low melt metal masters. Card etc is OK, or plaster itself, or any metal master part. All plaster masters should be very thoroughly waxed to render them non porous, heat them and rub in furniture wax till it is polished and non stick. Vinamould and equivalent can handle massive undercuts on the master, it is very, very flexible indeed in thinner sections. If hard grade Vinamould is used then more strict engineering casts can be made, and Vinamould itself can have Talc powder mixed in when it is liquid, to stiffen the mould material. 40% talc by weight can be added at most, usually about 25% will give a "stiff"mould. This method can cast very accurately, resin parts, like sideframes and even wagon sides, but keep undercuts to a minimum. The moulds will last only a few castings though, strictly low production, but you can just repeat with a new mould from the same material. Hope this helps, I used the stuff for museum diorama work and gained a lot of experience with the stuff, Stephen. Link to post Share on other sites More sharing options...
bertiedog Posted April 10, 2011 Share Posted April 10, 2011 Also for Garden Railway enthusiasts, Vinamould works perfectly with a strong Portland cement mix for concrete mouldings like arches and stone bridge parts, almost indestructible!. Stephen. Link to post Share on other sites More sharing options...
DaveArkley Posted April 12, 2011 Author Share Posted April 12, 2011 Excellent advice guys, thank you so much. I've ordered some Gelflex to give it a try. On a related, but different question, is there any way to cast something at half size. I have some 4mm plaster casts I'd like to reduce to 2mm. I can't think of any mecahnical way to achieve this. Cheers Dave Link to post Share on other sites More sharing options...
bertiedog Posted April 14, 2011 Share Posted April 14, 2011 Excellent advice guys, thank you so much. I've ordered some Gelflex to give it a try. On a related, but different question, is there any way to cast something at half size. I have some 4mm plaster casts I'd like to reduce to 2mm. I can't think of any mecahnical way to achieve this. Cheers Dave Not by direct casting, a master can be reduced, mechanically or by CNC machining. The new CNC "3D "cast" sculpture machines being developed could do it easily, but these are expensive to own, or expensive to get contract work done on , but it is getting cheaper, and the resolution, (the number of layers), is getting better. The object is made in layers of ABS plastic, generated by precision spraying molten dots onto the work to generate a solid object when set. Size scaling is only limited by the machines capacity, or the resolution on small objects, when scaled down. A 2D reduction is easier, a pantograph driven engraver is used, which can do 3d surfaces to a minor degree. It looks a bit like a letter engraver, where only one sized master is used for all the required sizes, the pantograph takes care of the size increase or decrease. TTH (Taylor Taylor and Hobson) made such engravers, lovely machines used by engravers and artists. They can reduce large masters for coins and medals down to the die size. Very expensive, even in smaller workshop sizes, Stephen Link to post Share on other sites More sharing options...
St. Simon Posted April 14, 2011 Share Posted April 14, 2011 Hi, Just to add, what ever you do, don't use Dental plaster, it's heavy as anything and quite fragile. Hope this helps! Simon Link to post Share on other sites More sharing options...
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