[wombat_tree]

Hello guys. Recently I have been looking into making moulds and casts of some of my scratch built models. Today I have started to look at how I would go about doing this.

I have found a great tutorial on how to make the mould and casts here. The only problem is that I have no idea what sort of rubber and plastic mixes I need. Because I live in Adelaide the products need to be readily accessible to me so I found this website. The only problem is that it is kind of unclear as to what I should use to make a plastic mould and then the platic to make the cast.

This looks like it could work for the casting aspect but I have no idea as to what I would use to make the mould and what I should use for a release agent. There is also the question of is there anything else I need to do this.

Hopefully some one can give me some useful help on the subject.

EDIT: Okay, this and this look like they could be quite good for my purposes but I don't know which one to choose and I don't even know for sure if this even is what I need.

 

[chromedog]

Hello guys. Recently I have been looking into making moulds and casts of some of my scratch built models. Today I have started to look at how I would go about doing this.

I have found a great tutorial on how to make the mould and casts here. The only problem is that I have no idea what sort of rubber and plastic mixes I need. Because I live in Adelaide the products need to be readily accessible to me so I found this website. The only problem is that it is kind of unclear as to what I should use to make a plastic mould and then the platic to make the cast.

This looks like it could work for the casting aspect but I have no idea as to what I would use to make the mould and what I should use for a release agent. There is also the question of is there anything else I need to do this.

Hopefully some one can give me some useful help on the subject.

EDIT: Okay, this and this look like they could be quite good for my purposes but I don't know which one to choose and I don't even know for sure if this even is what I need.

Firstly: You don't use plastic to make the moulds OR the cast. You use a silicon RTV for the mould and usually a Polyurethane resin for the cast.
Both are available from AMC.
Try this resin: Easycast. http://www.amcsupplies.com.au/index.php?main_page=index&cPath=19_495_273. It will come with mixing instructions.
Try here for the silicon rtv rubber: http://www.amcsupplies.com.au/index.php?main_page=index&cPath=23. Pinkysil or ultrasil are ones I've used and can recommend.

The guide you linked should do you fine (how to).
Get yourself some unscented talcum powder as well (works well as a mould release).

Plan your mould. You will need at least one area for the resin to go in, and at least one for the air inside the mould to escape (generally at the extremities like gun barrels, points, etc) and be prepared to stuff up the first couple of casts.

 

[wombat_tree]

Thank you for your response Cromedog. You said that you would recommend Pinkysil and Ultrasil, but which do you prefer?

EDIT: The Easycast says that it sets in about 10-30 minutes but the Pinkysil and Ultrasil don't specify how long they take to set. Perhaps you could enlighten me.

 

[chromedog]

Depends a lot on catalyst ratios.

6-12 hours according to the datasheet I have (I generally leave it overnight anyway). When I do casting, it takes around 3-4 days to make the mould and then the same for the first cast to getting ready for secondary casts.

Be careful with PVA glues around some RTV silicones as they can have a tendency to bond permanently to the pva.

 

[wombat_tree]

3-4 days for a single mould! Why does it take that long? Why does it take just as long to make a single cast?

 

[chromedog]

Because I don't rush things. Rushing into this is just going to cost you money - there are no ctrl-Zs in casting resin. No takebacks. If you stuff up the mould, you HAVE to start again. Resin casting isn't cheap to start with, no sense in making it cost any more than it has to.

Patience is a virtue. One of my few and one in scarce supply in most people under the age of 30, ime.
I like to make sure the rubber is cured (6-12 is optimal time, temperature and weather changes can change this).
I CAN go straight on to the first cast in 24 hours if I want to - but, this is the stage where I plan where extra vents will go (if they are needed) and when I carve them in. Also when I figure out how many casts I will need to do to break even.

I like the resin to fully cure before I extract it from the mould, minimises issues.
Ever bought FW resin?
That stuff is still outgassing when they ship it (bad enough that some of the chemical tells are too close to some plastic explosives) and it reeks.

 

[wombat_tree]

The tutorial that I listed said that the plastic will probably harden in a few minutes. Why is it that you use resin instead of whatever plastic a company like Games Workshop would use?

EDIT: How is resin casting expensive? As far as I can see all you need is the RTV silicone and the Easycast resin which makes for a total of about 50$. Am I missing something?

EDIT 2: I understand that the mould will take a while to make, I just don't get why it takes so long to make a cast

 

[rob12763]

Wombat tree the injection molds GW and other plastics companies use are filled with molten plastic that cools and hardens not a mix of resins and hardeners.Listen to Chrome dog,once your molds are made and vents cut and you made a good cast or two then it gets faster as your experiance grows.I like the translucent rubbers as they let you see the part and also if your resin is filled.Rob

 

[chromedog]

The tutorial that I listed said that the plastic will probably harden in a few minutes. Why is it that you use resin instead of whatever plastic a company like Games Workshop would use?

Because GW use an expensive (around $100,000) industrial Injection moulding system with $10,000-30,000 steel trap dies and manufactures on the scales where this is viable. You can't just melt plastic and pour into a mould (without risking serious burns and/or respiratory issues). Any room-temperature 'plastic' compound for casting with is not the same 'plastic' used in kits.

Reply to Edit 1: Yes, $50 to get the necessaries to make your first mould (plus whatever it cost you for whatever you are copying) Which you will no doubt screw up anyway (as most first timers do. It's inevitable. All of us have done it.)
If you don't make the mould right, you will have to redo it.
Even when you do have it right, not all of your castings will be good ones.

Reply to Edit 2: You're not getting that it's a game of patience? Take the time to get it right and you don't have to worry about do-overs. I like my pieces to fully cure before extraction. This can and does take a few days. You don't HAVE to wait that long, but I loathe the smell of outgassing resin - and it can irritate the lungs.

 

[wombat_tree]

Thank you for your response, sorry if I sounded snappy in my earlier post.

 

[chromedog]

You wanted answers and I've come to expect a lack of patience from the younger gaming crowd - you've grown up with pretty much an "instant" lifestyle. Stuff is more or less available whenever, so why wait?

Still, learning patience will go a long way towards getting people of MY generation to share what we do know.