leo charron (no login) from IP address 65.92.176.11
Somewhere in the past there was an entry on using silicon bathroom caulking to make casting moulds. Anybody use this method, or have any info? How deep (or thick) can the mould be made, ie. how thick can a layer be to cure properly and how long would curing time be? Does it need to be poured in 1/4" increments and left to cure before adding another layer? Wouldn't want to try to make a mould an inch deep, for instance, and the next day finding out the silicon was poured too deep to cure all the way through, leaving a gooey sticky mess, and ruining the master too. How well does silicon caulking fill small recesses and detail? This method sounds cheaper and less messy than using RTV; is it?
Leo, check out the Bare Metal Foil Company's website (can't think of it off-hand). There are cheaper types of RTV that are very easy to work with. I used to use some of their stuff quite some time ago.
Bob
Bob and Steve
Top Gun Military/IRON DIVISON Resins
http:www.topgunmilitary.com
Yes, what Bob said. The bathroom stuff is OK in thin sections, ie a few millimetres, but a large mass will take for ever to cure right through. The cure is triggered by moisture in the atmosphere, and as soon as it starts to set if forms a skin which slows down the penetration of more moisture. It will cure eventually, and it gives off acetic acid in the process (hence the vinegar smell) but unless it is very small things, packs, rifles, that sort of thing, it won't be stable enough to mould from for weeks.
You would be much better off getting a couple of lbs (kilo) of proper RTV moulding material. There are loads of sources for this, just look for a local craft shop. Keep it well sealed and it will last for ever. Be aware there are two types of RTV moulding rubbers, ADDITION cure and CONDENSATION cure. The first are usually translucent or even clear, while the condensation ones are usually white, or end up coloured by the catalyst being blue or green. Sometimes there are fillers added to the mix to improved tear or heat resistance, or to stiffen them up a bit. I use the clear stuff, because it is very useful to be able to see the master inside the cured block while you cut it out. Resistance to the nasties in polyurethane vary greatly as well, but if you only want a few castings for yourself, this won't matter too much, using a whiff of aerosol release agent on the moulds will extend the number of shots you get, but remember you will need to clean the castings very thouroughly to remove the release agent, otherwise the paint won't adhere very well.
Depending on the shape of the part you are casting, the hardness of the rubber is worth considering too. For a big, 'engineered' piece without any undercuts, a stiffer rubber, about grade 40 Shore A will be good. For a more detailed, sculpted shape, figures perhaps, a softer material, 25 Shore A might be better. But the softer RTVs can sag a bit under their own weight, so don't be too mean with them. You will need perhaps 3/4s of an inch (20mm) at least around your part, to be safe.
One other thing, don't mix your RTV types. The catalyst in the condensation types is a powerful inhibitor of the addition curing rtvs, and if you make a mould over a master with the first, then try and make another mould with the addition cure type, it won't cure off!! There are some plastics, vinyls, and some glues which have the same effect. And, strangely, onion and garlic!
Casting resins. Unless you have access to a vacuum chamber, get the runniest resin you can. There are several 'packs' available for hobby use, and while they are expensive per kilo, if you only want a few parts, it is the best way to go. Once the bottles are opened, the B component will degrade quite quickly, so it doesn't make sense to buy 10 kilos to get a good price, then end up binning most of it because it has gone off! If you have time, brush resin into the detail to prevent bubbles, or if the mould is open-backed, look through the resin and poke out any bubble with a toothpick, before it starts to gel. Depending on the resin you are using, you might only have 30 seconds or so to do this!
Finally, be warned. Have a go at this, think to yourself "Oh, I could make a few more and sell these, Hm, get a website, sort out Paypal, I'm in business!" and at that point, kiss goodbye to your hobby!! I know! I haven't put any paint on a model for nearly 3 years.....
PS, Oh, one other thing. If you are making copies of existing kit parts, do your sums first. By the time you have bought the original, the rubber, the resin, the time involved, the frustration of faild moulds, and so on, it might JUST be better to simply buy another kit and cannibalise it. Plastic kits are not sacrisanct, they are just a box of bits. I've got several HobbyBoss M4s JUST for the running gear, for example. So what if the hulls get ditched? Still WAAAAAY cheaper than moulding and casting bogies and wheels.
Now, make a master part of something that doesn't exist in a plastic kit, well, that is horse of a different colour! Cast on!
This message has been edited by wunwinglow from IP address 82.45.21.118 on May 12, 2008 5:15 AM
I've been working with RTV moulds and resin pouring for years -as an amateur, of course- and I have got mixed results. I've bought several brands in my hometown (Madrid, Spain) and abroad, but it seems that I haven't found the right one.
I mean, do you know which brand of RTV and resin is used by manufacturers like Quickboost or Aires? Besides the industrial processes that I will never be able to replicate in my home (vacuum chambers and so on), I think that the parts from these manufacturers look more like styrene than polyurethane. I still can not judge your own resin parts (I have just ordered some track sets from your site).
I've been working with RTV moulds and resin pouring for years -as an amateur, of course- and I have got mixed results. I've bought several brands in my hometown (Madrid, Spain) and abroad, but it seems that I haven't found the right one.
I mean, do you know which brand of RTV and resin is used by manufacturers like Quickboost or Aires? Besides the industrial processes that I will never be able to replicate in my home (vacuum chambers and so on), I think that the parts from these manufacturers look more like styrene than polyurethane. I still can not judge your own resin parts (I have just ordered some track sets from your site).
I've been involved in model making for years and done my fair share of cold cure moulds and agree that the the RTV stuff is best!
however I'm a bit of a tight git now I've got to pay for the stuff myself and as a result put some effort into bathroom sealant especially as I can get a tube for a £1 at Lidl!
I found that if its applied in a thin layer to the pattern and allowed to dry thoroughly you can then apply many slightly thicker layers in quicker succesion until quite a thick mould is produced only rule really is to allow each layer to dry a bit before going on to the next allowing the mould a couple of days to finally cure helps
Oh yes and I give all my patterns a quick rub with a release agent I did use silicon spray till I ran out then I used vaseline and parafin mix applied sparingly(me being cheap again) if you wipe the pattern clean after application there will still be enough to stop sticking and it will allow you to apply the first layer of silicon!
I've used many moulds from the radio in the universal carrier, the spare wheel on my daimler, flimsey cans and even the ends of a nissan hut which I hope to finish soon
My advice is give it a go just dont go to fast!
Please note I was referring to using this stuff for reproducing very small or low relief parts, like casting numbers and symbols, you wanted to add to your Tamiya kits, which have none. As Tim said, deeper molds most likely would be much better done using RTV silicone rubber. This is a good way to get your feet wet (actually, no - this means you've used way too much.... ) in molding your own parts. I admit I have not had much luck with the Alumilite resins, but I'm trying to find a really liquid type that will flow very easily into all the nooks and crannies. For casting numbers and symbols, filler putty is still a good way to go, as the final details will be only a fraction of a mm high.
Well, there are, quite literally, thousands of different polyurethane formulations!! It is an unsung hero chemical family, without which our consumerist lives would be much the poorer. In my day job I regularly deal with 4 suppliers, and we see probably a dozen or more reps a year from other companies trying to sell us their wares. They are all aimed at industrial users however, and usually require fast mixing, pouring under a vacuum, and curing at elevated temperatures, apart from only being supplied in packages that need a pallet to lift them! They don't seem to see the hobby market as a viable one to tackle, and yes, I have suggested it to them all! Most of the resins have a fairly short shelf life, especially in small containers, so I can understand their reluctance to go that way. Carriage too is an issue, because the chemicals in the resin often require all sorts of paperwork safety and disposal, hazard warnings and so on, again making them unsuitable for mail order. Alumilite is the only stuff I have seen aimed at the hobbyist, here in the UK we can get it from EMA in Feltham, Middlesex. I've tried it once, but it is too quick for me! I prefer something with a longer pot life, so I have time to fill the mould resevoirs, get the lid on the vacuum chamber, let the pump get down to vacuum, boil off for a minute or so, vent the tank, then unload it. Takes at least 10 minutes, and the resin should be fully liquid for at least 8 of them. Alumilite was hard enough to demould in that time!
However, a quick google search for polyurethane resins will turn up a supplier near you. Explain what you want to achieve, simulate ABS/polystyrene parts using an rtv mould, hand mix so the mixed resin is as runny as possible, (low mixed viscosity) and they should be able to point you in the right direction. But don't be surprised if they aren't interested in only supplying a kilo; try somewhere else.
Hope this helps,
Tim
www.fighting48th.com
This message has been edited by wunwinglow from IP address 82.45.21.118 on May 12, 2008 5:47 PM
Thanks for all your advice. I should have elaborated on my purpose. In the past I have used RTV and Alumalite for making resin parts, etc, but I have no vacuum so results were hit or miss with air bubbles. This time I want to make hydrocal castings of building sections and walls. I just need to make a flat mould with low relief detail of the wall face and the sides of the mould will be built up with Lego blocks. I've used RTV moulds in this way in the past with satisfactory results, but wanted the opinion on using silicon caulking as it's much cheaper than RTV. Since the moulds I want to make are flat with no sides or lip ( they will fit snugly into the Lego box) they only have to be maybe 5mm or 1/4" thick.
Leo, perhaps you could take a slightly different route. Box around the master, and lay up the first layer of your mould with your caulking rtv, then while it is still liquid, embed some thin cloth, a J-cloth, or heavy kitchen paper, into it, to reinforce it. Lay up another layer of rtv so you end up with a thin, but reinforced layer of rubber. Allow to dry. Then back this up with some plaster of paris, again let it set. Disassemble, removing the master. The rubber mould layer will now be free to come off the master AND the plaster block, but to use the mould drop the rtv skin back into your plaster block, which, being exactly the same shape as the back of your mould, will support it perfectly while you pour in your casting material.
Just another thought, for buildings, walls and so on, there are acrylic casting plasters which are much easier to use, bing water based, can be coloured with acrylic or poster paints, and don't attack the rtv; your mould will last indefinitely. The cast plaster isn't quite as strong as PU, but for big structural things, it is probably easier to handle than PU, and way less expensive. No smell, either! Not that I can smell anything nowadays....
Tim
www.fighting48th.com
This message has been edited by wunwinglow from IP address 82.45.21.118 on May 12, 2008 5:46 PM This message has been edited by wunwinglow from IP address 82.45.21.118 on May 12, 2008 5:45 PM
I did some moulding and parts making not long back, so beforehand I looked over a lot of offerings online. What I eventually settled on was product from a company called Smooth-On. I got an RTV kit of OOMOO 30 (yes, funny name, but...), and a kit of Smooth-On 322 casting resin. The two kits were a good deal, there was more than enough material to do what I needed, and it was about $60 if I remember right. I followed the instructions to the letter, but I do have a work background in composite construction of airplanes, so I've played with a lot of resins and moulding techniques, and know trouble when I see it.
I'm not into endorsing products, especially to say that "this is your answer!", but this system did exactly what it advertised, and well. I did go with the slower set on both the mould material and the casting resin, and I'm glad I did. This set-up did what I needed, with no vac equipment or any of the fancy stuff. I made some one-piece moulds and a two-piece one that "keys" together, and still have not worn them out after 20+ parts. Your mileage, of course, may vary.
about Smooth-On products, and will probably try it for my ICM '222 project, as I want to add some details to the suspension units. Thanks for the information.
