Shrinking a mold or a cast by 30%

Migmaker · Post by **Migmaker** » Fri Dec 30, 2005 8:11 pm

frank,
my understanding from the techs is that you have to use ice water to do the pour. The mixture is kept as cold as possible before pouring and only then do you have about 32 secs according to them to do the actual pour, no time to pressure cast well not really anyway....but they claim it's not necessary. demold in about 30 minutes and let stand in open air for 15 days to get maximum proportional shrinkage or so they claim......looking foward to final results with this
William

macfrank · Post by **macfrank** » Sat Dec 31, 2005 5:51 pm

Migmaker wrote:frank,
my understanding from the techs is that you have to use ice water to do the pour. The mixture is kept as cold as possible before pouring and only then do you have about 32 secs according to them to do the actual pour, no time to pressure cast well not really anyway....but they claim it's not necessary. demold in about 30 minutes and let stand in open air for 15 days to get maximum proportional shrinkage or so they claim......looking foward to final results with this
William

The 32 secs is close to what I got with the chilled water. The mixture is water thin until it gels, so if you can get it into your mold in that time or less, you'll be OK.

Demolding can be done almost as soon as it gels; I didn't notice much of a change in material strength 30 minutes later.

The dehydrator is the only positive result so far. After about 16 hours in a dehydrator, my test objects shrank 60%.

Here's a mold (not a cast) next to a Lego brick. It's firmer now, but still very, very soft.

It also formed bubbles like crazy, as this detail shows. Maybe I have to use chilled doubly ionized water?

I'll let this cook for another day or so, but so far the hydroshrink has been disappointing.

stringvault · Post by **stringvault** » Thu Jan 12, 2006 2:42 pm

I've been following this thread with interest. Is there anything new to show? Has it cured fully now?

Cheers

macfrank · Post by **macfrank** » Thu Jan 12, 2006 4:17 pm

stringvault wrote:I've been following this thread with interest. Is there anything new to show? Has it cured fully now?

Cheers

Yeah, it cured quickly in the dehydrator, and indeed the parts shrunk by 51%.

That said:

- The material is (and will probably always be) very soft and rubbery. What I duplicated was fairly flat, but a large structure may well deform slightly under its own weight.

- It needs a mold release applied to it, even if you're duplicating it in RTV.

- The material forms bubbles. I guess you can use de-ionized water, pure water or somehow degass the water before chilling it, but I think most of the bubbles formed during the mixing, which must be quick and vigorous.

- Using it as a mold material probably isn't a good idea, in part because the Hydroshrink will deform under its own weight (limiting you to very small molds) and in part because the material will tear badly when removing the cast resin part from it. I put some mold release in the mold before making a test pour, and still managed to cause a tear.

I'll try it again, maybe with almost freezing water and report back. I think that at best this material is good for small, flat objects. Shrinking something as "big" as a PL 1/1000 TOS Enterprise would probably fail, miserably. Shrinking something the size of the sensor dome, or the bridge might work.

I guess Hydroshrink is also known as "Reducit II". I think the older version, which produces a harder cast, might be better (although it doesn't reproduce details as well).

Frank

Post by **TER-OR** » Thu Jan 12, 2006 7:01 pm

I do have a figure I want to reduce in size about 80% of its original size. Then I need to resculpt it a bit, and then build a diorama.

karim · Post by **karim** » Thu Jan 12, 2006 7:07 pm

I believ ethis stuff is intended as an intermediate material. You are meant to reduce the part, then immediately cast the reduction in a harder, more stable material.

macfrank · Post by **macfrank** » Thu Jan 12, 2006 7:18 pm

karim wrote:I believ ethis stuff is intended as an intermediate material. You are meant to reduce the part, then immediately cast the reduction in a harder, more stable material.

Yes, but I'm saying is that it's barely suitable for that if you're reducing a small part.
The cured material has very little rigidity and it's very soft and rubbery - I wouldn't be surprised if the weight of the RTV is enough to deform it.

The material does firm up if you make a larger part, but I've noticed that some of the larger parts I made retained the warps introduced as they dried.

Since the material sets so quickly, making larger parts would be very difficult - The material gels in 30 - 40 seconds or less.

That's why I think the original Reducit, or even Alginate may be a better solution.

Frank

macfrank · Post by **macfrank** » Thu Jan 26, 2006 11:21 pm

Some more experiments.
I haven't been pleased with the Hydroshrink (for many reasons) the two main ones are the softness of the fully cured material and the unpredictable warping of thin parts and edges.

I noticed that a couple of drops of unmixed Hydroshrink in my sink had set up after coming in contact with some water, so I decided to try an experiment to test the effects of various mixing ratios of Hydroshrink and water.

The ratios I picked were 1:1 (equal amounts of both) 1:2 (1 part Hydroshrink to 2 parts water) 1:4 (1 part Hydroshrink to 4 parts water - the recommended ratio) and 1:5 (1 part Hydroshrink to 5 parts water). Just to make the samples distinct, I used 5 ml of Hydroshrink for each test, and varied the amount of water. My "test piece" was simply the plastic mixing container for each sample.

I used cold water and mixed each sample. The radios didn't affect the gel times appreciably and after a few tens of seconds, I had four samples - 10ml (1:1) 15ml (1:2) 25ml (1:4) and 30ml (1:5).

The samples had set nicely, and the only difference was in their consistency. The 1:1 and 1:2 samples were firm while the 1:4 and 1:5 were very soft and Jello-like.

I placed the samples in my dehydrator for a couple of days, then let them fully air cure for about 5 days.

Here are the results

I haven't measured the exact shrinking ratios, but they're all roughly the same size, and roughly 50% smaller. The most noticable difference is that the 1:1 and 1:2 mix ratios did not deform - unlike the 1:4 and 1:5 mixes.

The 1:4 mix (which is the recommended ratio!) is badly deformed, and the 1:5 mix ratio is even worse. All four samples are rubbery but the 1:1 and 1:2 ratios are much stronger and firmer and would probably maintain their shape as RTV is poured over them. The 1:4 and 1:5 would probably deform under the weight of the RTV.

I think that the 1:1 and 1:2 mixing ratios produce the best results, with the 1:1 being the best. So much for following instructions!

Frank

macfrank · Post by **macfrank** » Thu Feb 09, 2006 10:46 pm

Yet more experiments.

After talking on the phone with Migmaker, I thought it would be an interesting project to shrink something more useful than the inside of my mixing cup. I decided to shrink the Leif Ericson conning tower.

I made two versions, using a 1:1 mix of Hydroshrink - hollow cast like the original part and a solid cast. I ended up making two versions of the solid cast.
I also played with the mixing ratios again, making a 2:1 test sample (2 parts Hydroshrink to 1 part water) to see if that made the cured material any stiffer.

After a few days of drying, here are the results:
A First family portrait of the parts. I put the first solid cast on its side in the dehydrator, and it warped. The other two were placed facing up.

I cut the 2:1 test sample in half. I tried an x-acto knife, but the material is too rubbery - I ended up cutting it with scissors.
I painted one of the cut faces with radome tan acrylic... and boy can you see bubbles! It's like a loaf of bread.
I also painted the two conning towers. The solid cast is above - many bubbles popped through the surface. There were fewer bubbles on the hollow cast, but I think that's because there was less Hydroshrink.

The hollow cast looks almost usable, but it's too flimsy to retain its shape.
If I were to cast this, I'd fill it in with clay, get it into shape (making sure I don't distort the part too much) cast the outer surface, remove the clay and cast the interior.

Increasing the Hydroshrink to water ratio had little effect; a 1:1 ratio works well. I've also been experimenting with ways of extending the pot life. A little bit of Acetone helped, probably because its evaporation helped keep the mixture cool.

The biggest problem, by far, is the formation of bubbles. I'm going to build a small vacuum chamber and see if I can degass the water and Hydroshrink before mixing, although I think a lot of bubbles are introduced during the mixing and are set in place by the very fast gel times.

Another big problem I haven't solved yet is sticking. The Hydroshrink will gladly stick to Oomoo and Siloxane RTVs... even with a mold release. I'll try talc and see if that works. I don't care if the Hydroshrink master is destroyed - I just don't want to leave small pieces stuck in the mold!

Frank

davehal9000 · Post by **davehal9000** » Thu Feb 09, 2006 11:43 pm

Man, that's discouraging. Keep us informed though, as I've got big plans for the stuff if it works out for you.

macfrank · Post by **macfrank** » Sat Feb 18, 2006 2:32 pm

I was looking at some of the LE test parts I shrank -with the 1:1 mix it's been a while and I'm certain that all the shrinking is done - and they looked... bigger than I thought they'd be.

So I measured the parts and compared them to the original. It's hard to get a good caliper measurement on soft parts, but I measured and compared several points on all three copies and compared them to the original:

The 1:1 mix only shrinks 30%... which isn't bad, just not the original 50%.

If getting a 51% shrinkage requires a 1:4 mix of Hydroshrink to water then it's really discouraging. At this ratio the cured Hydroshrink is just too soft to cast, especially if the part is small or if it's a hollow cast.

Putting the water (or the mixture) in a vacuum may help (it has to be done anyway, because it's just useless with all the bubbles) but I think I'm going to try Alginate next. It doesn't shrink 50%, but the resulting cast is pretty hard when dry.

Frank

davehal9000 · Post by **davehal9000** » Sun Feb 19, 2006 12:24 am

Sounds like it's more trouble than it's worth. Let us know how the Algenate works.

I may end up just carving what I need instead of shrinking...

Migmaker · Post by **Migmaker** » Thu Feb 23, 2006 4:30 am

Frank,
one thing i recently learned, if your water is not distilled(purified) , and can lead to lots of bumps(bubbles)....did you use perified water for these tests?
Best,
William

macfrank · Post by **macfrank** » Thu Feb 23, 2006 11:37 am

Migmaker wrote:Frank,
one thing i recently learned, if your water is not distilled(purified) , and can lead to lots of bumps(bubbles)....did you use perified water for these tests?
Best,
William

No... I can get distilled water easily, too! I'll try it again. Reducing the bubbles would solve one major problem, leaving the rubbery, floppy castings as the otyher main problem.

Thanks, I'll try it!

Frank

davehal9000 · Post by **davehal9000** » Thu Feb 23, 2006 4:57 pm

There's a difference between distilled and purified. Which is needed?

macfrank · Post by **macfrank** » Thu Feb 23, 2006 5:42 pm

davehal9000 wrote:There's a difference between distilled and purified. Which is needed?

I'll bet it's distilled; there are probably fewer dissolved gases in distilled water.

I used purified water - cold water from my Brita filter/pitcher.

Migmaker · Post by **Migmaker** » Thu Feb 23, 2006 5:51 pm

now yoda dont go getting all technical on me....
the cleanest water ya got! purified!

Migmaker · Post by **Migmaker** » Thu Feb 23, 2006 5:52 pm

ok distilled!

macfrank · Post by **macfrank** » Mon Mar 13, 2006 2:11 am

I tried using chilled distilled water, and it indeed reduces or eliminates bubbles. I'm not 100% certain, but I think I also got a slightly longer working time.

I made a hollow cast of the LE conning tower, and it came out with a perfectly smooth finish. I also added microballoons, thinking that it might make the material stiffer, but alas, it didn't.

So the problem of bubbles forming in the Hydroshrink is solved by using chilled distilled water (99 cents a gallon at the supermarket). The lack of stiffness in teh material is still a major problem, though. Even fully shrunk, the hollow conning tower is just too floppy to retain its shape.

Frank

davehal9000 · Post by **davehal9000** » Mon Feb 19, 2007 10:25 pm

Any updates on this stuff?

macfrank · Post by **macfrank** » Mon Feb 19, 2007 11:56 pm

davehal9000 wrote:Any updates on this stuff?

The Hydroshrink was a good idea on paper, but the material has far too many negatives to make it worth pursuing:

1 - very short working time, even when cooled.
2 - The cured material is too soft and floppy to allow a good, dimensionally accurate duplicate to be made.
3- It's expensive
4- Hydrospan has a short shelf life once the can is opened. I backfilled the can with dry CO2 and the material still managed to start gelling on its own after a few months.

I haven't played with the alginate, but from previous experience I don't think it'll be much better than the Hydrospan.

Frank

Clony80 · Post by **Clony80** » Mon Sep 24, 2007 10:37 am

Hi, I just found this thread. I also did some tests with hydroshrink. I´ve got some pictures somewhere. Maybe I´ll post them today.

Clony

Clony80 · Post by **Clony80** » Mon Sep 24, 2007 10:53 am

Here we go, one picture:

http://img65.imageshack.us/my.php?image=img0001tq1.jpg

macfrank · Post by **macfrank** » Mon Sep 24, 2007 11:07 am

Clony80 wrote:Here we go, one picture:

Hi,
Inline images aren't allowed here. This should work

http://img65.imageshack.us/img65/928/img0001tq1.th.jpg

They look great, and far better results than anything I got. How big is the original and how small are the copies?

Frank

Clony80 · Post by **Clony80** » Mon Sep 24, 2007 11:14 am

Hi, I´ve changed my posting.
The original figure is 3 3/4 inches and the others I don´t know exactly, but about 40 % smaller. I also had my problems with this stuff, you haven´t got much time to pour...
Here another pic:

http://img59.imageshack.us/my.php?image=img0003mt4.jpg

You can see, that the mold wasn´t good, I casted the whole figure but doesn´t poured the whole figure

Migmaker · Post by **Migmaker** » Mon Sep 24, 2007 12:02 pm

so give us the scoop on how you obtained these results please
Will

macfrank · Post by **macfrank** » Mon Sep 24, 2007 12:46 pm

Clony80 wrote: The original figure is 3 3/4 inches and the others I don´t know exactly, but about 40 % smaller. I also had my problems with this stuff, you haven´t got much time to pour...

Considering how hard this stuff is to work with, you've gotten outstanding results.

Can you please (please please please!) describe the steps you took? Cold water, etc., but any other tricks?

Frank

Migmaker · Post by **Migmaker** » Mon Sep 24, 2007 2:11 pm

I second that, please tell us about your experience and is your casting as hard as resin>? keep minds out of gutter please!
Will

davehal9000 · Post by **davehal9000** » Mon Sep 24, 2007 3:48 pm

I've had a project shelved for a year trying to get the courage up to carve a part I'd rather shrink. Any updates on this stuff would be GREATLY appreciated.

Clony80 · Post by **Clony80** » Tue Sep 25, 2007 12:33 pm

Hi,
I did it the same way you did. I tried different mix ratios. 1:4. 1:5, 1:1,5....
I used icecold water. First I mixed it with a electric whisk, because I mixed about 250ml but I had to much air bubbles. Later I used a spatula and mixed about 50ml. After de-molding the pieces I put it on some paper and protected it from dust. And than I had to wait....
You´ve put it in a dehydrator, maybe that wasn´t good.
The casting is not hard as resin, it´s like, hmm as a hard jelly

Here some pictures of the parts on the paper:
http://img104.imageshack.us/img104/8493/img0003re2.jpg
Few days later
http://img410.imageshack.us/img410/1494/img0015gr5.jpg
and later
http://img410.imageshack.us/img410/52/img0016vn7.jpg

Clony