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So I've made a few scratch built models, some larger (like land dreadnought to land raider size) and some smaller (space marine size), as well as bits like custom shoulder guards. What I'd like to do is cast the original in a basic block mold of silicon and then make duplicates with resin. What I'd like is some suggestions as what types/ weights of resin to use as well as as casting lubricant (ease) to make for easy removal. I've found some good tutorials and suggestions online but figured I'd come here for any tips since this will be for WH40K.

http://www.dakkadakka.com/dakkaforum/posts/list/307451.page

that is all you need to know.

Also, if you are using silicone rubber, a release agent isn't really needed for resin.

Much thanks

you really only need the release agent when making the two piece mold initially so the two sides don't fuse together. I use Smooth-on products. They're great, their website can help you decide between the different types of silicones and resins.

Polyurethane resins are generally the go for casting with.

Not as noxious as the acrylic resins but be careful to pick one with a good "pot life" if making a large item (anything larger than a heavy infantryman) - you don't want your resin to go off halfway through a pour.

chromedog wrote:Polyurethane resins are generally the go for casting with.

Not as noxious as the acrylic resins but be careful to pick one with a good "pot life" if making a large item (anything larger than a heavy infantryman) - you don't want your resin to go off halfway through a pour.

Most of the suggestions I've found browsing around here have cure times of around 20-30 min or less. I'm looking at making a very large block mold (just pouring the silicon around the entire piece) and then cutting keys into it when I remove it. I fear some of the bits on the model will be too delicate to press into molding putty to make a two piece mold that way.

This being said I need something that won't start to cure halfway down the mold haha. I also feel like a lower viscosity would be better as well to reduce air bubbles. Do you or anyone else have a good suggestion for one with a "good pot life"? Any opinions on Smooth-Cast?

tme0003 wrote:

chromedog wrote:Polyurethane resins are generally the go for casting with.

Not as noxious as the acrylic resins but be careful to pick one with a good "pot life" if making a large item (anything larger than a heavy infantryman) - you don't want your resin to go off halfway through a pour.

Most of the suggestions I've found browsing around here have cure times of around 20-30 min or less. I'm looking at making a very large block mold (just pouring the silicon around the entire piece) and then cutting keys into it when I remove it. I fear some of the bits on the model will be too delicate to press into molding putty to make a two piece mold that way.

This being said I need something that won't start to cure halfway down the mold haha. I also feel like a lower viscosity would be better as well to reduce air bubbles. Do you or anyone else have a good suggestion for one with a "good pot life"? Any opinions on Smooth-Cast?

I MEANT smooth cast, sorry. Its a great product, they have low viscosity resin with long cure times. I like their oomoo 30 silicone for molds.


Automatically Appended Next Post:
Also I would not recommend just pouring around the whole piece, its way more difficult to accurately cut it than to delicately the right way. Don't want to see you wasting good money on silicone

Suppose I just had the piece laying flat inside a box, poured in silicon to fill half the depth of the box and added in some sticks/markers/etc... to act as keys; wait for that half to dry, remove the keys and then pour in the other half? Can you make an effective two piece mold that way? Just skip smashing it into clay which would probably break the model...

The proper way is to use Legos. Use non drying polymer clay to seat the model and vents/channels, pushing clay around the piece halfway to make what will be the second side of the mold.

Then use a pencil erase to make keys in the clay, so that the 2 pieces seat properly. Apply a release agent so that your master model and the clay won't stick to the rubber. Pour rubber, starting from a corner of the mold until the master is completely covered.

Once this side has set(for Oomoo I wait 24 hours just to be safe, though 6 hours should be fine) then flip the Lego frame over, and remove all the clay, leaving the master model still in side 1 of the mold.

Once all the clay is removed, spray this side with your release agent, then once again start pouring from the corner as with side 1.

Once your second side is fully set, it will require a little work to separate the two sides, even with release agent, but shouldn't require so much force as to tear the mold.

I understand that process, however my fear is that trying to press the clay around the model will break parts of it so I'm looking/will attempt some alternatives.

Just be gentle.

Most casting silicones are actually quite flexible and can take a good deal of force before tearing.

Are your originals delicate because they are hollow? If so you could always fill them. I haven't done any casting but I am being tempted by the lure of dakka.

Sonophos wrote:Are your originals delicate because they are hollow? If so you could always fill them. I haven't done any casting but I am being tempted by the lure of dakka.

Yes, it's a scratch build out of some sheet styrene, however I've filled all the edges so I don't think filling would be an option.

I'll just try and find the softest putty I can I suppose and see how that goes, if not I can try something else. Thanks gents.

I was thinking play doh or the like to provide some internal resistance when making the mold.

I've never used Smooth On, but I've had some experience with Polytek Resin and Silicone.
Silicone:
http://www.polytek.com/cart/index.php?target=products&product_id=29782
Resin:
http://www.polytek.com/cart/index.php?target=categories&category_id=244

The Polytek silicone has the viscosity of maple syrup. It goes into all of the cracks and crevices very well. IT DOES NOT WORK WELL WITH LEGO BRICKS. You will have temporarily seal all of the cracks and crevices so there is no leakage. Also, when you spill the silicone onto the brick, OMG...

The polytek resin cures extremely fast. Maybe about a 20-25 second mixing time, and must be finished pouring in about a minute or 2. Demolding is about 15-20 min, depending on the size of the part.

Do not use polytek resin with Instant Mold/Oyumaru. After 2 casts, the mold starts to get messed up.

I would say, to try and see which types of material is available closest to you and try those.

The only way to avoid using plasticine is to create a split glove mould, which doesn't really work with the larger scale models you're planning on casting.

http://www.alumilite.com/HowTos/SplitGloveMold.cfm

do you use that easyflo 60? That seems like a lot of resin, how does it paint up? how well does it glue to plastic etc.?

I've got some easyflo60 at the moment, and I'm not too keen.

Casts ok, it's quite viscous so bubbles can be an issue, and primer doesn't stick to it, let alone a coat of paint.

Currently searching for an alternative.

http://www.theengineerguy.com/cgi/commerce.cgi?preadd=action&key=SMOOTH-CAST-300--TRI

tme0003 wrote:Suppose I just had the piece laying flat inside a box, poured in silicon to fill half the depth of the box and added in some sticks/markers/etc... to act as keys; wait for that half to dry, remove the keys and then pour in the other half? Can you make an effective two piece mold that way? Just skip smashing it into clay which would probably break the model...

Yes, this (kinda) works.

The way I do it:
1. First apply a tiny amount of silicone to the "underside" of the piece, making sure that all hollows are filled, then let it cure.
2. Stick a few needles into the "underside" and cut them to desired length using a good pair of clippers.
3. Put the piece into the box, it will be suspended on the needles, making it possible for the silicone to flow around it.
4. Pour silicone in until it covers half of the piece.
5. Let the silicone cure.
6. Cut away some silicone, making grooves.
7. Apply vaseline or similar to the silicone surface.
8. Pour another layer. Let it cure.
9. Separate the pieces, cut a pour channel and a few air escape channels.
Done.

I.e. it is possible - but way more complex than using a good clay.

Remember, you don't need to push the piece down into the clay, just put the delicate part of the piece into a "hole" in the clay and gently close the hole around the piece.
Also, it is the least delicate part that should be the "underside".
It is desirable that the piece is sticking rather hard to the silicone when removing the clay - as it will be almost impossible to ensure a good fit before pouring the second layer if the piece came loose during the removal of the clay.


... the guardsmen are originals

tme0003 wrote:

Sonophos wrote:Are your originals delicate because they are hollow? If so you could always fill them. I haven't done any casting but I am being tempted by the lure of dakka.

Yes, it's a scratch build out of some sheet styrene, however I've filled all the edges so I don't think filling would be an option.

I'll just try and find the softest putty I can I suppose and see how that goes, if not I can try something else. Thanks gents.

Sculpey makes a super soft version that's idea for supporting finer models during silicone moulding.

http://www.dickblick.com/products/sculpey-ultralight-clay/

orkork wrote:I've never used Smooth On, but I've had some experience with Polytek Resin and Silicone.
Silicone:
http://www.polytek.com/cart/index.php?target=products&product_id=29782
Resin:
http://www.polytek.com/cart/index.php?target=categories&category_id=244

The Polytek silicone has the viscosity of maple syrup. It goes into all of the cracks and crevices very well. IT DOES NOT WORK WELL WITH LEGO BRICKS. You will have temporarily seal all of the cracks and crevices so there is no leakage. Also, when you spill the silicone onto the brick, OMG...

The polytek resin cures extremely fast. Maybe about a 20-25 second mixing time, and must be finished pouring in about a minute or 2. Demolding is about 15-20 min, depending on the size of the part.

Do not use polytek resin with Instant Mold/Oyumaru. After 2 casts, the mold starts to get messed up.

I would say, to try and see which types of material is available closest to you and try those.

That seems much too quick for what I need. I appreciate the specs though, will help in my search.

AG. wrote:The only way to avoid using plasticine is to create a split glove mould, which doesn't really work with the larger scale models you're planning on casting.

http://www.alumilite.com/HowTos/SplitGloveMold.cfm

This is what I meant earlier when I said "black mold." However, like you, I doubt it would work.

AG. wrote:I've got some easyflo60 at the moment, and I'm not too keen.

Casts ok, it's quite viscous so bubbles can be an issue, and primer doesn't stick to it, let alone a coat of paint.

Currently searching for an alternative.

Again thanks for opinions on brands.

I've talked to a few companies/distributors and have gotten some opinions. Also I found out there is a gent in at the local WH40K store/club that use to work in a mold shop, so I'm hoping to catch him in the next week or so to get his opinion. Thanks again to everyone for you help.

Gavin Thorne wrote:Sculpey makes a super soft version that's idea for supporting finer models during silicone moulding.

http://www.dickblick.com/products/sculpey-ultralight-clay/

Do NOT use this clay. It chemically reacts to plastics: it melted and stuck to the sprue pieces I used for vents, ruined some plastic bits in the item being cast. and even was beginning to melt the legos being used as a frame; this after 18 hours of contact.

1. you are about 7 months late to the thread.
2. wtf rubber are you using that pieces need to be in place for 18 hours?

tme0003 wrote:Suppose I just had the piece laying flat inside a box, poured in silicon to fill half the depth of the box and added in some sticks/markers/etc... to act as keys; wait for that half to dry, remove the keys and then pour in the other half? Can you make an effective two piece mold that way? Just skip smashing it into clay which would probably break the model...

I use play-doh (it's non reactive with the silicone ) to press the original and make key marks into, then pour the silicone.
Once it has set and cured, I remove it all from the mould box (lego, as noted), remove the play-doh (washing it off if necessary), apply the release agent, mix up the other batch of rubber and pour. Mouldmaking for me is a job that takes a couple of days (I like the rubber to cure properly) for a two-part mould (the rubber may be cured in 4-6 hours, but 12 hours is better).


I've never used "smooth-on" products as we have a local mouldmaking and casting supplier here who supplies the FX industry (and the industry standard here is them) and I doubt you could get Barnes products in other countries as easily (or cheaply as other local - for you - products).

there are specific clays you need to use, to make sure they don't have certain materials in them which will react chemically with the silicon.

Also, resin is VERY expensive and as you noted, not easy to pour large pieces at one time due to curing concerns. I would break up your original pieces into seperate sections if you can.

An excellent source of all things casting can be found at;
http://www.resinaddict.com/forum/

best of luck!!

For silicone rubber mold making, you should use plasticine clay, which is non drying. It is harmless to plastic and rubber.

For 2 piece molds I use 12 hour cure silicone, for single piece molds I use 4 hour cure.

I've used a few products but Smooth-On is the only one I've really liked.