Just wondering if anyone here has used molds to make resin parts etc.
What im wanting to do is make some parts for some of the fire models im converting by making molds of existing parts from other models etc (the parts will mainly be things like the lightbars/beacons, ladders etc.
I read it is possible - only problem is that they are in the US so the stuff they use isnt over here (well it proberly is but indr a different name)
If anyone has has anyone got any tips on doing it, or any links to any model places in the UK that supply the stuff needed to make it.
I'm not sure about the part you need, but if these are relatively small and thin parts (sure sounds that way), you might get away with using disolved sprue instead of resin. Presumably, thin plastic cement and old sprue are easy to come by, so that would eliminate the need to track down a supplier for PU resin. A fellow modeller has also had considerable success with epoxy resin instead of the more common PU resin, so that too might be an option. Whatever you use, you will need to make the moulds, preferable from sillicone rubber. Keep in mind that the characteristics of the mould depent in part on what material you intend to put in them, so don't start making them untill you have located and chosen your medium.
I think the trick is not to search by brand name, but by product specs. RTV (Room Temperature Vulcanising) rubber is also used for making tin soldiers and the like, so you might want to check on that scene. Unless I'm seriously mistaken, there are several cottage industry aftermarket producers in the UK; you might drop them a line. With any luck, they can point you to a supplier of rubber and resin. Also, around here at least, it can be ordered through arts suppliers.
I would stay clear of the polystyrene resin sold at DIY or car supplyers; in my experience it doesn't work well in small amounts, and sticks to your moulds with disasterous results.
I could dig up some addresses here in The Netherlands, but I suspect those would be useless to you as well, unless they do mailorder. Let me know if this will be of any help. Also, I'm fairly certain I could find an address in Germany that will at least supply the sillicone rubber you need.
I had an article in Fine Scale Modeling about a year and a half ago on the subject. There is also an article in the current issue, that I have not had time to read yet. The subject has been kicked around on this group several times in the past.
You will find the community split into two views. First group says you must use pressure or vacuum. Second group says those are nice but not really essential. I am a member of the second group. I occasionally get a few small bubbles, but not enough to make castings unusable.
Design of molds takes a bit of thought. Pouring sprue should be J-shaped, entering mold cavity from bottom, NOT top. Top part of cavity should have vent tube. Any local high spots in complex mold must also have such vent tubes. Think like an air bubble wanting to escape from mold cavity to prevent being drowned by incoming resin. Where you like to see escape tubes? Resin entering bottom of cavity should be able to easily push air out top.
I also design molds to be predominately vertical, with top of pour sprue tube at least one inch above the highest point in mold cavity to provide a small amount of hydrostatic pressure down sprue.
They have quite alot of different casting products but im not too shure which would be the best.
The marks im making i already have the master parts to make a mold from. As they will be parts i have taken from existing models to duplicated for used on custom or converted models.
Most of the parts will be small parts like ladders, lighting reels etc (mainly equipemnt seen on roof of UK fire appliances. So the likes of them the colour dosent matter as they will be sprayed.
But for the likes of the light bars both the 2 websites have a clear resin which can be tinted with the color tints they have to give a transparent colour so for the lights im making would be the transpartent blue.
Would the resin/mold making solutions on those sites be the stuff im after.
I just took a peek at the trylon site. The quickcast resin on this
page is the polyurethane resin used most often for scale modelling. If you plan to use this material, be advised that once the cans are opened the material begins to deteriorate; after a few months it will no longer be useful. I'd suggest you prepare your masters, and your first moulds, but do not start casting until you expect to have plenty of time over the next month.
The silicone rubber you need is also on their site on this
page. The rubber has a much longer shelf life when opened (up to a few years), and is used in much greater quantities than resin, so if you can afford it, I'd recommend getting the 2kg package.
The hobbicraft site also has rubber that looks suitable (and cheaper!), but the descriptions on the resins offered there are unfamiliar to me. These might, of might not do the job.
Incidently, if you should buy the rubber at hobbicraft, you'll have to choose between rubber intended for metal casting or rubber casting. I've never had to make that choice myself, but in my experience, rubber intended for metal casting works just as well with resin (although the way it is used must be slightly different), and has the benefit of being useful for metal casting as well. I'd say that it never hurts to be versatile..
Don Stauffer has already pointed out most of the relevant bits about making the moulds. Personally, I tend towards somewhat higher sprues, but I guess we all use what our particular experience has shown to work well. If you have difficulties digging out the info on the basic process of mould making, feel free to ask.