Shrinking a mold or a cast by 30%

macfrank · Post by **macfrank** » Sun Jun 19, 2005 3:15 pm

I want to duplicate an existing part, but make it about 30% smaller. I know that with teh right combination of mold material and resin i can get 5% or so, but don't have any good ideas on how to get 30%.

The closest I've come is to make a mold ogf the original, then pour alginate into the mold. When the alginate cast dries, it should shrink... but I don't know if it even gets close to 30%, if it's controllable or if the shrinkage is consistent (I don't want one dimension to shrink 30% and the other 10%).

Any other ideas? I don't really want to mix up some alginate.

Frank

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Sun Jun 19, 2005 4:19 pm

It seems like cobywan was mixing alcohol or something into his RTV and getting a large shrinkage in his molds from pour to final cure. Not quite 50 percent, but quite a large value.

Shinnentai · Post by **Shinnentai** » Sun Jun 19, 2005 4:40 pm

macfrank wrote:The closest I've come is to make a mold ogf the original, then pour alginate into the mold. When the alginate cast dries, it should shrink... but I don't know if it even gets close to 30%, if it's controllable or if the shrinkage is consistent (I don't want one dimension to shrink 30% and the other 10%).

Nah, alginate distorts and develops weird surface textures when it shrinks. Cobywan's trick w/ the RTV (I think it was naphthalene) seemed to work pretty smoothly, though I wonder if it prematurely weakens the rubber.

karim · Post by **karim** » Sun Jun 19, 2005 6:40 pm

The Complete Sculptor has a couple of products that do just this... they had a demo of one such product line at their Wonderfest table that could go in either direction (scale up or down).

I can't remember what it was called, but if you call them up, they can help you out. The examples they had at their table were really incredibly impressive.

macfrank · Post by **macfrank** » Sun Jun 19, 2005 8:43 pm

karim wrote:The Complete Sculptor has a couple of products that do just this... they had a demo of one such product line at their Wonderfest table that could go in either direction (scale up or down).

They have Reducit which sounds a lot like Alginate.

Adding something to the RTV to make it shrink would work, but what happens to the master? Won't it just tear through the mold?

Shinnentai · Post by **Shinnentai** » Sun Jun 19, 2005 11:34 pm

IIRC the shrinkadge would happen over the course of a few hours after the rubber had set up (as the dillutant evaporated out), so one would demold, then set the rubber aside for it to do it's voodoo all by itself.

TimeScape · Post by **TimeScape** » Mon Jun 20, 2005 7:45 am

Shinnentai wrote: though I wonder if it prematurely weakens the rubber.

If this is an issue (ie production run) then I would use the first casting as the master for a new mold.

Gerry-Lynn · Post by **Gerry-Lynn** » Mon Jul 04, 2005 4:16 pm

The complete sculpter has a product called "Hydrospan 400" You use one part resin - to three parts water. It will slowly shrink down to about 41 to 42 percent - The toy and action figure companies love this stuff. It does work very well, and does not disort. I like this stuff.

Gerry-Lynn 8)

They have a great section and question and anwers.

macfrank · Post by **macfrank** » Mon Jul 04, 2005 7:22 pm

Gerry-Lynn wrote:The complete sculpter has a product called "Hydrospan 400" You use one part resin - to three parts water. It will slowly shrink down to about 41 to 42 percent - The toy and action figure companies love this stuff. It does work very well, and does not disort. I like this stuff.

Gerry-Lynn 8)

They have a great section and question and anwers.

The hydrospan looks like it will expand an object by 60%. I need to make it shrink. It looks like Reducit is the only material that they have available.

Johnnycrash · Post by **Johnnycrash** » Mon Jul 04, 2005 9:16 pm

There are two types of the Hydrospan. 100 and 400 I think. One shrinks, and the other expands. Hydrospan 100 will expand when soaked in water, while the water in H400 will evaporate and the part will shrink.

I really wish they has sampler packs of this stuff.

Migmaker · Post by **Migmaker** » Sat Jul 09, 2005 4:53 pm

ok, as this product interests me i contacted the company and asked about both productsm hydrospan does just as it says expand the casting using water to get uniform expansion..pretty cool!
hydroshrink obviously does as it says too it is a urethane polymer not alginate it has strength to take a silicone mold

.gonna try this stuff could be a fun product for me anyway!
shrink some of my scratchbuilds

William

karim · Post by **karim** » Sat Jul 09, 2005 5:00 pm

That's the stuff I mentioned... couldn't think of the name.

They had it on display at WF, and it is truly amazing stuff... VERY clean results.

macfrank · Post by **macfrank** » Sat Jul 09, 2005 6:55 pm

Migmaker wrote:ok, as this product interests me i contacted the company and asked about both productsm hydrospan does just as it says expand the casting using water to get uniform expansion..pretty cool!
hydroshrink obviously does as it says too it is a urethane polymer not alginate it has strength to take a silicone mold :).gonna try this stuff could be a fun product for me anyway!
shrink some of my scratchbuilds :)
William

Do you have a contact or web page or distributor? Compleat Sculptor only carries the 100 (the expander),

davehal9000 · Post by **davehal9000** » Tue Jul 12, 2005 11:54 pm

Any updates on this stuff? I need a subject in an oddball scale no one makes, and it sounds like this might do the trick. How complicated is this kind of thing to work with? Do I need an atomic scale to measure it out, or is it forgiving?

davehal9000 · Post by **davehal9000** » Wed Jul 13, 2005 4:31 pm

Would the shrinking be uniform if you cast a model in pieces? If you cast an aircraft and wings separatly, would the final parts still be the same scale?

karim · Post by **karim** » Wed Jul 13, 2005 4:45 pm

macfrank wrote: Do you have a contact or web page or distributor? Compleat Sculptor only carries the 100 (the expander),

Try calling them. They had both at their table at WF.

macfrank · Post by **macfrank** » Thu Jul 14, 2005 7:31 pm

Thanks Karim, I called it, and finally found it!

First, they changed the name from Hydrospan to Hydroshrink. But it won't appear in any search on www.sculpt.com.

I emailed them, and they gave me a link on their other web page. They currently only have the gallon in stock for $65, code # 3196404. They also have a quart for $20, code # 3196403 but they're out of stock and won't get more for two weeks. I placed my order anyway. The Hydroshrink shrinks to 51% of the original size, which is ideal for what I want.

Items placed in the cart on compleatsculptor.com appear in the cart on sculpt.com , so you can continue shopping.

Frank

Frank

Migmaker · Post by **Migmaker** » Sat Aug 27, 2005 12:23 am

anyone try this stuff yet?
William

macfrank · Post by **macfrank** » Sat Aug 27, 2005 11:40 am

Migmaker wrote:anyone try this stuff yet?
William

I finally got my quart, but haven't had time to use it.

Migmaker · Post by **Migmaker** » Sat Aug 27, 2005 9:05 pm

did you get the hydroshrink or the hydrospan? i ordered some hydroshrink

DasPhule · Post by **DasPhule** » Mon Aug 29, 2005 5:43 pm

I ordered some of the Hydrospan to play with. Wish I'da known they had it at WF, would have bought a gallon kit of it and already been playing with it.

Erin
<*>

macfrank · Post by **macfrank** » Mon Aug 29, 2005 6:45 pm

Migmaker wrote:did you get the hydroshrink or the hydrospan? i ordered some hydroshrink

I ordered the hydroshrink.

Migmaker · Post by **Migmaker** » Mon Aug 29, 2005 11:29 pm

my hydroshrink is on da truck.... comin. Erin, did you try the Hydrospan yet? i says it has a 35 shore A hardness to it for remolding once fully expanded...... thoughts?

DasPhule · Post by **DasPhule** » Tue Aug 30, 2005 12:04 am

I ordered it today and talked to the dude about it a little. He hadn't personally used it but said that everyone who he had talked to who has used it said it's pretty easy to work with. Not sure how long it'll take to get here, but I will definetly be trying it the day after it shows up. I've got several gundam bits molded, ready to go for it, all I gotta do is pour it in and wait.

35 is hard enough for molding, SmoothCast is what? 45 once set up? My main concern is how thick is it when pouring it into molds, and how long do I REALLY have to get it into the mold. I'll be pressure casting it of course, but if it's thick stuff that doesn't always mean good castings. From what I've read online in various forums, the shrinking stuff is a total pain to work with, the main complaint is that it's really fast setting before you can pour it. FYI, use ice cold water and you'll have more time. I didn't see anyone complaining about the Hydrospan 100, so i'm hoping it'll be easier. We'll see I guess!

Still, I'm excited about it. I have tons of things I wanna do with it, mainly for my own enjoyment. The main use I see for it is to scale up all these gundam kits me and Sal want that come in 1/144 scale but not 1/100. I'd also like to get some of my favorite figure's heads blown up to life size to play around with. This stuff is definetly gonna be fun....and end up costing me loads of money!

Erin
<*>

Migmaker · Post by **Migmaker** » Tue Aug 30, 2005 12:20 am

yeah i talked to a lady rep that explained about the ice water to retard gelling time for the hydroshrink. sounds feasible just can't pressure cast the piece though with 32 sec to pour why would you want to lol on a good note i understand the hydroshrink is like water to pour considering it's mixed with it lol same with the hydrspan...we'll see

DasPhule · Post by **DasPhule** » Tue Sep 06, 2005 8:52 pm

Got my hydrospan yesterday. No instructions, no MSDS sheet, cans are stamped October 2004. They did send me instructions for Aquaresin and Winterstone, two totaly unrelated and completely different casting mediums though.

So, lemmie get this stuff mixed up and let's see how well it works....

Erin
<*>

Migmaker · Post by **Migmaker** » Tue Oct 18, 2005 9:43 pm

any progrees report on this stuff
William

davehal9000 · Post by **davehal9000** » Wed Oct 19, 2005 9:27 pm

Yeah, i'd like to hear how it's working as well. I've got some plans for the stuff if it's good stuff.

DasPhule · Post by **DasPhule** » Thu Oct 20, 2005 7:47 pm

I'm still trying to decide what I wanna blow up with it. I'm gonna use it soon, though. The stuff is EXTREMELY sensitive to humidity according to the reps, so I wanna make sure I have a lot of molds ready before I open it.

I'll let yall know how it goes, though.

Erin
<*>

macfrank · Post by **macfrank** » Fri Dec 30, 2005 7:58 pm

It's been a while, but I finally got around to trying the Hydroshrink.

Rather than doing something easy, like shrinking a PL TOS sensor dish, I decided to try and make 1/700 and 1/1000 figures from 1/350 and 1/500 resin and plastic figures. I figured I'd get something useful out of the first few tries without wasting too much of the hydroshrink.

I made suitable molds, made quick resin test copies, and all looks good.

First try - I mixed a small amount of hydroshrink with tap water (in the correct ratio and at the recommended temp - around 72F) , and stirred it (it forms a milky white watery liquid) for about 30 seconds.

I put it down for maybe 45 seconds to prepare the molds.

I went to pour, only to discover that I had a soft, bouncy white blob in my mixing cup - It had already set. Arrg.

Second try Same setup, only I used cold water from my refrigerator. It took a little longer to set, but I was able to pour it into the molds. I let it set and took the molds apart. This stuff does not form any sort of hard or even firm plastic; it's soft and floppy, like the plastic used in some fishing lures. It would be difficult to cast anything from this stuff in this condition - the weight of the silicone would deform the part!
I put the results in my dehydrator. Maybe they'll get firmer as they shrink.

Next, I thought that instead of trying to shrink a part with the hydroshrink, I could shrink the molds. I made a lego dam, put the parts in, poured in just enough to cover the lower half, waited for it to set, painted on some mold release, poured in the upper half and tried to demold.
I couldn't; the mold release didn't work and the two parts of the mold were stuck together! Luckily, I was able to remove the masters without damaging them or the mold, and it looks like I'll be able to pour resin in as well.

I stuck the mold in the dehydrator as well, while I figure out some sort of mold release.

That's where I am so far. I'll let the hydroshrink bake for a day or so and see if anything is usable.

Frank

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Shrinking a mold or a cast by 30%

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