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experiments with household goods casting

 Post subject: experiments with household goods casting
PostPosted: Wed Jun 22, 2011 12:02 pm 
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just tried a couple of experiments with white glue
aka PVA glue or wood glue depending on where you're from.

this was all very ad-hoc as I'd intended to experiment with normal silicon sealent, except my father in law seems to have borrowed it. Since I'd already decided to try something, I grabbed the white glue.
all inital experiments used a mix of pure PVA glue and shredded toilet paper. no added water.

experiment 1- Admech skull icon for 40k chimera

1 squashed plasticine into small container.
2 heated up container by microwaving over a small bowl of water - plastacine melts to pure liquid, bubbles removed.
3 allow plastacine to cool back to normal texture
4 squish desired shape into it: in this case was skull, piece of cable tie for grid panel on half of skull, small piece of pipe for bionic eye and small screw for cable down side of jaw.
5 place in freezer for 15min or so - plastacine now totally rigid
6. squeezed mix of toilet paper and PVA glue into mold. placed under slight pressure and set aside to dry.

Experiment 2 - random ork head as a test piece

1 - superglued ork head to bottom of container
2 - squashed large amount of toliet-paper and glue mix down into container
3 - embedded handle to thorectically allow mould to be removed from container later

Experiment 3 - shotgun weapon for my 40k squats

1 placed layer of the papier mache mix in jam jar lid
2 placed weapon
3 placed second layer of papier mache
4 since didn't look very robust squuezed some glue over the top


RESULTS:

after 24 hrs drying (in tropical heat)

experiment 3 - failure. mold was spongy and springy. toilet paper fibers made it surprisingly difficult to cut open using scalpel. still wet on inside.

experiment 2 - failure. pulled on handle. mold ripped in two. still wet at core. also really stupid idea to superglue head in. took some effort to remove. next time fill container with mould liquid and press part in.

experiment 1 - initial failure. when removed the weight on top of the mould 80% of pva mix came up, mould still wet inside. similar issue with sponginess. total loss of detail.
cleaned gently and poured pure PVA glue in for repeat. still not dry at 24hrs. experiment ongoing.


CONCLUSIONS.

not to be tried if you're in a hurry.
for mould making, will try household silicon sealant next, as soon as I find where it's got to.

did not add water to try and minimize shrinkage. this might have resulted in air trapped in the tissue fibres and thus the sponginess. a watery mix of PVA drys very flexible. pure PVA normally dries rigid. the tissue fibre was to try and increase the strength of it. Possibly not a suitable technique for these small scales.

will eventually report on results from 2nd attempt.

Plasticine is good for 1 or low use moulds. especially good for tricks like my skull, as it saves you having to sculpt a coherent master. Obviously useless for any metal as the mould will just melt. Being able to model with it, freeze it for rigidity or easily melt it down for reuse is a bonus.

If anyone can suggest a good casting material that doesn't get hot and better still can tolerate freezing let me know.
On the list for trials are epoxy glue, clay, cement and cemititous clay.

The only bloody resin I've found so far for sale here is ultra high strength stuff for structural repairs to concrete. It's a tad pricey. There must be other stuff for car body work ect but not found it yet. Assume the budget is minimal.


Last edited by madd0ct0r on Thu Jul 07, 2011 11:20 am, edited 1 time in total.

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 Post subject: Re: experiments with white glue casting
PostPosted: Wed Jun 22, 2011 7:08 pm 
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Car body fiberglass resin will do fine if thats all that availible ;)


Regards epic,, never mind casting anyway get that shrine painted ;D


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 Post subject: Re: experiments with white glue casting
PostPosted: Thu Jun 23, 2011 6:46 am 
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glue still not dry. removed pressure weight to allow more air to get to the glue.

this is what the mold looked like originally: Image

have also just tried microwaving pva glue. it boils the water out of it, creating bubbles and a fast set on thin films. not suitable for casting.


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 Post subject: Re: experiments with white glue casting
PostPosted: Fri Jun 24, 2011 12:24 pm 
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and 2 days later, the glue has dried (i'd estimate it takes about 24 hours, as long as the mold is exposed to the air.)
Some minor shrinkage, made the item easy to remove, except on the cheek cable, where it ripped off bits of the plasticine.

Image

even the cog pattern around the head came out. Even using pure glue the item is still quite rubbery - clean up of the cog will be very difficult, high risk of tearing.

I'll try and get some plaster of paris (gypsum) tomorrow.

the natural side of the face came out fine, the bionics look a bit messy, but on inspection I think it was my poor molding. I'll be able to fix it in the paint stage anyway. (bone growth)

all in all, remarkably little effort and and cost. certainly good enough for the 5-6 skulls I'll need.


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 Post subject: Re: experiments with white glue casting
PostPosted: Fri Jul 01, 2011 2:29 am 
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Still not found resin of any form, but managed to get some gypsum plaster (plaster of paris).

First attempt using pure plaster and water was too fragile for use - managed to break the bionic eye off when lightly sanding the back. Detail replica poor - worse then the white glue.

Second attempt used white glue, water and plaster. Also added a blolb of white glue to mold on bionic eye - this was a mistake as it trapped a huge airbubble. Material shrank considerably when drying (in part due to the airbubble). Resultant cast is stronger, but looks like it has an enormous scar running across it's face. Accidental, but I like.
Material is stronger, but still fragile in 2mm thick sheets (the cog around the skull)

Third attempt: this time cast a small loop of wire and pipe into the back of it, to allow me to pull the cast out of the mold. I pulled, and the pipe ripped straight out. bugger.
Take knife, run it around the edge of the mold and 'pop' the cast out. The back plate separates, leaving a the skull behind - it's not hardened and remains damp and powdery. Examination suggests all of the white glue had separated under vibration and floated to the top of the mould (the back plate). Possibly 12 hours was insufficient for the plaster of paris to harden, possibly there was insufficient water present.
Next step - mould release. stupid sticky plasticine.


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 Post subject: Re: experiments with white glue casting
PostPosted: Fri Jul 01, 2011 2:32 pm 
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I recommend UltraCal 30 instead of Plaster of Paris. You can often get it from the same craft stores and it hardened beautifully (literally requiring a tool to break apart). Otherwise it behaves the same as Plaster of Paris.

I am sure that Resin and real moulds are better for the pros, but UltraCal 30 worked nicely for the limited amount of casting that I have done (e.g. http://wargamingworkshop.wordpress.com/ ... heim-city/ )

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 Post subject: Re: experiments with white glue casting
PostPosted: Fri Jul 01, 2011 3:22 pm 
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These experiments make a good degree more sense to me when I look at MadDoctor's current location.


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 Post subject: Re: experiments with white glue casting
PostPosted: Sat Jul 02, 2011 2:38 am 
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Helge wrote:
You can often get it from the same craft stores


Ha Ha Ha. what is this craft store you speak of?

Part of my problem is that even if there is a craft/modelling store in Da Nang (it's small city, and hobbies aren't big in Vietnam) I don't know where it is. There's no such thing as the Yellow Pages here. I'd probably do better hitting the medical quarter next and see if I can find some dental equipment shops.

the other issue is proceeding through the veil of ignorance. eg Plaster of Paris becomes Gypsum which becomes Bột Thạch Cao. Which is actually plaster for walls. hence why it's so soft.

On the other hand, a kilo of it was about 25cents so I can afford to mess around. Plus I get to learn more about molds and results without losing too much money.


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 Post subject: Re: experiments with white glue casting
PostPosted: Sat Jul 02, 2011 5:12 am 
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ah, not the best hobby location I guess.

Ultracal is used by special effects people (masks, etc.), the automotive industry and even in some lumber shops. Also, you can make it yourself by mixing Plaster of Paris (Gypsum) with Portland Cement (or any fine grain cement that you can "recover" from a construction site).

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 Post subject: Re: experiments with white glue casting
PostPosted: Sat Jul 02, 2011 11:14 am 
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The dental supplies idea is a decent one, though I'd expect whatever is used for moulding dentures is expensive in large quantities. Maybe not in Vietnam though... As for resin, plenty of plastic things must be made in Vietnam, maybe the key is finding someone to put you in contact with a factory? Or maybe approach from the other way round, contact a manufacturer/distributor (via alibaba?) and ask them if there are any suppliers in your area.

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 Post subject: Re: experiments with white glue casting
PostPosted: Sun Jul 03, 2011 5:08 pm 
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Dentures aren't molded. Well, not exactly, anyway. It's odd and kinda complicated.

There are at least two ways of making molds in dentistry. Dentures are made through impressions - you mix up an impression material and make an imprint in it. That is used to make a cast, which are generally made out of something pretty close to rock. However, it's not as tough as rock (I have fond childhood memories of breaking old ones with a hammer), and so it might not be up to your needs. (this should give you an idea of the process involved). I'm also not sure how good it is at fine details - teeth are pretty smooth, after all.

In making dentures, casts are then used as reference points for the construction of the denture - usually a wax model is made, the teeth are implanted, then the wax model is sent off to a lab to be finished (which involves a stone lost-wax mold - you can do it in-house, but dental labs can afford to use pressure to remove bubbles, which ensures a better fit).

There's also a neat way involving vacuum forming an acrylic sheet. It makes mouthguards and other things. A dental vacuum former goes for $600+, and it obviously can't do anything that's too three-dimensional (since it works from a flat sheet and you'd have to break the mold to get the result out), but it would be good for detail panels. Or you could make halves and then glue the halves together.

(EDIT: Or make two halves and then make a proper mold from them *facepalm*)

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 Post subject: Re: experiments with white glue casting
PostPosted: Sun Jul 03, 2011 6:57 pm 
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How about "hot glue"?

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 Post subject: Re: experiments with white glue casting
PostPosted: Mon Jul 04, 2011 2:49 am 
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replies in approximate order:

@helga - portland cement! of course. Now if I was still working on site that wouldn't be an issue. I might see if I can cadge some off the neighbors (they're rebuilding their house)

@Kyrt: plastic powder for injection, or sheet for vacumn forming are not the same as resin. The last resin I found was ultra high strength stuff used for structual repairs to concrete. A tad pricy. There's a garage up my way, but they seem to prefer patch welding panels to fibreglass and resin. I'll try asking though.

@SK - well, I've learned something new today! I might steer clear of buying a dental former just yet, but I might be able to buy time on one. I've done vacuum forming before - you simply can't do undercuts (unless it was as a 3 part mold...). Could work well for 28mm scale weaponry, and possibly 6mm scale vehicles with smooth tops.
If the vacumn formed mold is stiff enough, might even be able to try injection moulding, but that's a long way into the future. Dental Rock sounds like a casting material to pursue.

@Lrswolf - I've experimented with hot glue before. Obviously can't use it with a melty plasticine mold, and it's so viscous that you'd need a huge amount of pressure to squeeze it into fine details. If you have it available it might be worth trying.

---

fourth attempt results exactly like the 3rd attempt. Same mix was used, only difference being a mold release agent was tested.
(the top slab came out very easily. the skull remained powdery and had to be scraped out with a knife.)

So: let's look at the chemistry:
Dry Gypsum reacts with water to form the new hard(ish) solid. It's a hydration reaction that dosen't need air, just sufficient water.
PVAc is an emulsion based glue - basically as the water evaporates the plastic part thickens up, linking to itself. Just requires the water component of the glue to be removed. so far, so compatible.

But what I didn’t know is that PVAc is sensitive to alkali conditions. It decomposes into Polyvinyl alcohol and acetic acid. Polyvinyl alcohol itself can be used as a similar type of glue to PVAc. It's a very good sealant - they use layers of it in PET drinks bottles to keep the fizz in. A weak solution of acetic acid you all know as vinegar.

Just like Portland cement, it appears the ‘set’ form of gypsum is slightly alkali, while the ‘before’ stuff is strongly so. The high proportion of PVAc I added to the mix decomposed and created a perfect plastic seal across the top of the mold, sealing in the acid. The trapped acid then reacted with the gypsum, breaking it down into the white powder I kept getting in the lower half. In the top half, the acid probably evaporated with the water, or the polyvinyl alcohol glued everything together anyway.

So. The two are fundamentally incompatible. Bugger.

Further experiments planned.


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 Post subject: Re: experiments with white glue casting
PostPosted: Mon Jul 04, 2011 4:25 am 
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Considering how small a dental vacuum former is, buying time on it would hopefully be as simple as "I'll pay for the plastic and make you a cake".

The vacuum formed mold can be pretty durable - we need pretty heavy duty scissors to cut it (they're approaching tin-snips). It does have some flex to it, though, so this is one of those things I think you'll have to experiment with. :)

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 Post subject: Re: experiments with white glue casting
PostPosted: Mon Jul 04, 2011 5:17 pm 
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madd0ct0r wrote:
replies in approximate order:
@Lrswolf - I've experimented with hot glue before. Obviously can't use it with a melty plasticine mold, and it's so viscous that you'd need a huge amount of pressure to squeeze it into fine details. If you have it available it might be worth trying.


I was thinking what about hot glue replacing the plasticine...

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