A little casting trick I pick up.

[cobywan]

I found this neat trick online. Add naptha to your silicone before pouring it. Then after it sets up it will shrink in a fairly even fashion. (Supposedly you can soak a finnished mold in it too to make it swell up to a larger size.) Think of the possibilities...

http://home.comcast.net/~cobywan/Images/Shrink.jpg

[Mechleader]

Thats cool. What is that your making?

[Gerwalker]

Naphta + silicon...seems like a new Napalm receipt!!!

Thanks!!

I've always look for this kind of trick. Could you please give us more info? (ratios, shrinkage, etc,)???

[Grayson72]

Oh man, that's a great tip! I actually need to increase the size of stuff. What the heck is naptha?

Did it say how long to soak the molds?

Edited September 9, 2004 by Grayson72

[cobywan]

AJMADISON wrote "Just doing some quick and dirtry calculations suggest that the reduction in volume is pretty much linear with the % naptha.

If I assume I'm reducing a cube but using your imperical results I get:

1X * 1X * 1X = X^3 (or 1 cubic X) with 0% naptha

.95X * .95X * .95X = .85X^3 at 20% naptha

(approximately 15% reduction in volume)

.80X * .80X * .80X = .512 X^3 at 50% naptha

(approximately 49% reduction in volume)

So there's some minor ugliness in having to calculate volumes when determining a linear reduction, but considering the tolerances involved, one could just play some calculator math until you get the approximately the linear reduction of interest. but the initial attempt would come out pretty close. If I had to guess, looks like there's a slight fudge factor because not all of the naptha evaporates during the cure, so I'd add a bit extra naptha to counter the mechanical/chemical inefficiency of the technique."

Naptha is a mild thinner solvent that doesn't hurt styrene. I actually used Zippo lighter fluid. It is 100% naptha.

As far as swelling a mold I am guessing a few hours. But be warned...the mold with naptha in it is delicate and the detail gets soft. But it should give you a great head start on a project.

[Myersjessee]

Cool...any idea how long you have before you have to pull the piece from the mold (the original. ...does it shrink over time or as it cures? )

BTW...is that a Cylon part?

[Grayson72]

As far as swelling a mold I am guessing a few hours.  But be warned...the mold with naptha in it is delicate and the detail gets soft.  But it should give you a great head start on a project.

EXACTLY! That's all I need, a rough shape to get started with.

Next to last question, if I soaked the mold to make it bigger do you think it would stay permanently larger or would it shrink back down when the naptha evaps? Just wondering how long I would have to cast a part in the enlarged mold.

Last question, where do you get naptha? Would a hardware store have it?

I'm definately going to try this technique, I've got several 1/100 models that I need in 1/72, muhawhawhawhaw!

Edited September 9, 2004 by Grayson72

[cobywan]

Cool...any idea how long you have before you have to pull the piece from the mold (the original. ...does it shrink over time or as it cures? )

BTW...is that a Cylon part?

I usually pour molds into a sealed box. Or at least I cover the top with a plate to make the top of the mold flat. So in this situation you just let it set up like normal. The rubber then shrinks over time as the fumes leech out of it. For me I can take the parts out in 8 hours or so. But you could let the full 24 pass if your container is really tight.

The part was probably used on the raider. But it is also used on this baby;

http://home.comcast.net/~cobywan/Templates/Galactica1978.htm

[gnollman]

What the heck is naptha?

A combustible chemical. Lighter fluid is primarily naptha....

[whytwolf]

I usually pour molds into a sealed box.  Or at least I cover the top with a plate to make the top of the mold flat.  So in this situation you just let it set up like normal.  The rubber then shrinks over time as the fumes leech out of it.  For me I can take the parts out in 8 hours or so.  But you could let the full 24 pass if your container is really tight.

The part was probably used on the raider.  But it is also used on this baby;

http://home.comcast.net/~cobywan/Templates/Galactica1978.htm

Just to double check before I try this myself....

Ths trick should work with any silicon RTV product right? I'm using Smooth-On OOMOO 30, and want to try shinking the mold...

So what I would so is mix the silicon and add a certain % voilume of Naptha (Zippo fluid sounds good), pour my mold and let it cure, then pull the master and wait for it to shrink? How long will the shrinking process take? Or does the master stay inside the mold while it shrinks? (that doesn't make much sense, but I have to ask...)

Will this work with two part molds?

Thanks.

Sean

[cobywan]

Any silicone should work. Let the rubber set then remove the pattern and let dry. You will not be able to pour two halves seperately. You can pour the whole mold at once and cut open the mold after it sets. That is my usual mold-making procedure anyway.

[whytwolf]

Any silicone should work.  Let the rubber set then remove the pattern and let dry.  You will not be able to pour two halves seperately.  You can pour the whole mold at once and cut open the mold after it sets.  That is my usual mold-making procedure anyway.

So you don't use two part molds at all? interesting. How do you determin where to cut? What about pour and vent holes and registration marks? I'd love to learn more about how you do this, as I'm pretty inexperience with casting but am trying to learn as fast as I can

Thanks

Sean

[Myersjessee]

The part was probably used on the raider. But it is also used on this baby;

http://home.comcast.net/~cobywan/Templates/Galactica1978.htm

SWEET!!! Please keep us updated on your progress! How big is she?

[cobywan]

Any silicone should work.  Let the rubber set then remove the pattern and let dry.  You will not be able to pour two halves seperately.  You can pour the whole mold at once and cut open the mold after it sets.  That is my usual mold-making procedure anyway.

So you don't use two part molds at all? interesting. How do you determin where to cut? What about pour and vent holes and registration marks? I'd love to learn more about how you do this, as I'm pretty inexperience with casting but am trying to learn as fast as I can

Thanks

Sean

This is a practical mold that addresses every concern you posed;

http://home.comcast.net/~cobywan/Templates/Lncrmld.htm

[cobywan]

The part was probably used on the raider.  But it is also used on this baby;

http://home.comcast.net/~cobywan/Templates/Galactica1978.htm

SWEET!!! Please keep us updated on your progress! How big is she?

29.125" long

[Neova]

Any silicone should work.  Let the rubber set then remove the pattern and let dry.  You will not be able to pour two halves seperately.  You can pour the whole mold at once and cut open the mold after it sets.  That is my usual mold-making procedure anyway.

So you don't use two part molds at all? interesting. How do you determin where to cut? What about pour and vent holes and registration marks? I'd love to learn more about how you do this, as I'm pretty inexperience with casting but am trying to learn as fast as I can

Thanks

Sean

This is a practical mold that addresses every concern you posed;

http://home.comcast.net/~cobywan/Templates/Lncrmld.htm

Wait a minute here, so you can make the mold, soak it and blow it up proportionally? I have some ideas here but since I can't find resin casting supplies here, can someone try?

I was gonna do the Mcguyver way with a tube of silicone to make the mold and will find a suitabilit "resin" - probably some kind of epoxy as explained by another member.

Can someone try this : Blow up a 1/72 piece to 1/48? Think of the possiblities!

[cobywan]

Any silicone should work.  Let the rubber set then remove the pattern and let dry.  You will not be able to pour two halves seperately.  You can pour the whole mold at once and cut open the mold after it sets.  That is my usual mold-making procedure anyway.

So you don't use two part molds at all? interesting. How do you determin where to cut? What about pour and vent holes and registration marks? I'd love to learn more about how you do this, as I'm pretty inexperience with casting but am trying to learn as fast as I can

Thanks

Sean

This is a practical mold that addresses every concern you posed;

http://home.comcast.net/~cobywan/Templates/Lncrmld.htm

Wait a minute here, so you can make the mold, soak it and blow it up proportionally? I have some ideas here but since I can't find resin casting supplies here, can someone try?

I was gonna do the Mcguyver way with a tube of silicone to make the mold and will find a suitabilit "resin" - probably some kind of epoxy as explained by another member.

Can someone try this : Blow up a 1/72 piece to 1/48? Think of the possiblities!

That's the theory. I started a test. It didn't really work so I need to try another approach. I'll let you know what works.

[Grayson72]

Yes yes, please let us know your results. If it's possible I've got a lot of 1/100 stuff to blow up to 1/72

[GreatMoose]

It does work (i've used this technique myself), but the detail gets a little soft, and you must be very careful (seeing as it is LIGHTER fluid). The maximum expansion is about 2x or 200%. You'll need to make a permanent mold quickly as the cast tends to shrink. Also, if you use this method, you really need to soak the CAST and not the mold, as the mold will probably not expand proportionally, or you could lose detail. I do NOT recommend using this method for multiple expansions of the same object (say expanding a 1/144 to 1/48 or 1/32), as you'll wind wind up with very little detail on the finished piece.

[whytwolf]

It does work (i've used this technique myself), but the detail gets a little soft, and you must be very careful (seeing as it is LIGHTER fluid). The maximum expansion is about 2x or 200%. You'll need to make a permanent mold quickly as the cast tends to shrink. Also, if you use this method, you really need to soak the CAST and not the mold, as the mold will probably not expand proportionally, or you could lose detail. I do NOT recommend using this method for multiple expansions of the same object (say expanding a 1/144 to 1/48 or 1/32), as you'll wind wind up with very little detail on the finished piece.

When you say soak the cast, you mean the resin piece you just pulled?

Are there any health hazards (other than lighting youself on fire, and I've done that before--I was in the army) to using naptha with your casting/molding materials?

Thanks

Sean

[GreatMoose]

There is, however, a WONDERFUL little product called Hydrospan 100. It's slow, and it's not cheap, but man, does it work. It is an expanding urethane polymer that after you've casted an object, you then soak in water, for around 14 days. It will then grow to 1.6 times its original size. Seems slow for relatively little result, but here's the kicker: you can do it as many times as needed, and you won't lose detail (at least not enough to worry about). There's a competing product called Expandit, but it's not as refined and exact. It does however grow faster (4 or 5 days) and larger (1.9x) per sitting.

Edited September 14, 2004 by GreatMoose

[GreatMoose]

When you say soak the cast, you mean the resin piece you just pulled?

Are there any health hazards (other than lighting youself on fire, and I've done that before--I was in the army) to using naptha with your casting/molding materials?

Right, you'll soak the silicon/resin piece in the naptha. That's the "cast." The "mold" is 'negative' of the original part, what you pour your resin into.

No health hazards other than fumes, but you don't want to store your naptha-soaked piece for very long just because of the risk of fire. The naptha-impregnated parts will ooze kerosene long after they've dried.

Edited September 14, 2004 by GreatMoose

[whytwolf]

When you say soak the cast, you mean the resin piece you just pulled?

Are there any health hazards (other than lighting youself on fire, and I've done that before--I was in the army) to using naptha with your casting/molding materials?

Right, you'll soak the silicon/resin piece in the naptha. That's the "cast." The "mold" is 'negative' of the original part, what you pour your resin into.

No health hazards other than fumes, but you don't want to store your naptha-soaked piece for very long just because of the risk of fire. The naptha-impregnated parts will ooze kerosene long after they've dried.

Right, but I guess my question was more along the lines of after soaking the resin piece, will that piece expand, or do you mean pour another mold based on that naptha impregnated resin piece and it's THAT mold that will expand? And if you are talking about having the resin expand, do you simply soak the cured resin piece, or mix the naptha with the resin A+B?

Have heard of the Hydrospan and have always wanted to try it, but have no idea where to find it in Canada.

Sean

[Grayson72]

Wait, now you guys are getting confused, the Naptha is for expanding/shrinking the silicon molds, the Hydrospan is for expanding the actual smaller resin cast piece. I actually like the Hydrospan method better.

[GreatMoose]

Actually, the naptha works 'better' for expanding a cast rather than expanding a mold. And yes whytwolf, the piece you casted will expand. I like hydrospan better, too.

Edited September 14, 2004 by GreatMoose

[Grayson72]

Aha, didn't know that, thanks for the tip Mr. Moose

Here's the link!

http://www.industrialpolymers.com/water_ab..._urethanes.html

Edited September 14, 2004 by Grayson72

[GreatMoose]

You can also buy it directly from www.sculpt.com. It's awfully cool.

[Grayson72]

Ordered the 3 quart!

Thanks man!

If this works I'm gonna be creating a whole slew of never before released items in 1/72.

[cobywan]

I'm in for a 1/72nd scale Jagd Mirage with Twin Tower.

[Grayson72]

I'm in for a 1/72nd scale Jagd Mirage with Twin Tower.

What the heck is that?

[Gundamhead]

I'm in for a 1/72nd scale Jagd Mirage with Twin Tower.

What the heck is that?

Really large.

[cobywan]

I'm in for a 1/72nd scale Jagd Mirage with Twin Tower.

What the heck is that?

It's this;

http://www.mechadream.com/VjagdC.htm

I have one of the Volks kits. The canons are six feet tall.

[captain america]

a 1/72 Jagd would be insanely large; just the mold-making process would be hellish.

I'm also concerned about how Hydrospan would affect the dimensions of the kit. On the website, they used it on a Scooby Doo head, which is a very organic part with just a simple, flat bottom. They say that it expands uniformly, but for complex mechanical, interconnecting components I'm quite sure that there would be distortion of parts. This combined with the shrinkage of the mold material and then the resin would most probably lead to parts that fit so poorly as to not be worthwhile to enlarge.

It's still an interesting product, but it has its limitations.

[cobywan]

a 1/72 Jagd would be insanely large; just the mold-making process would be hellish.

I was joking. (And bragging.)

[Neova]

...

I'm also concerned about how Hydrospan would affect the dimensions of the kit. On the website, they used it on a Scooby Doo head, which is a very organic part with just a simple, flat bottom. They say that it expands uniformly, but for complex mechanical, interconnecting components I'm quite sure that there would be distortion of parts. This combined with the shrinkage of the mold material and then the resin would most probably lead to parts that fit so poorly as to not be worthwhile to enlarge.

It's still an interesting product, but it has its limitations.

Captain,

How about if you test this on the Valk booster you sculpted and see how it goes? Really! I would love to see that thing in 1/48 scale!

I see the product works by expanding to 1.6 so it would be a tad bigger than 1/48 though. 1/48 = 1.5 X 1/72 scale if everything is correct.

Now where I can find this stuff in HK?