I bought the alumilite mini casting kit the other day. Today was the acid test. I really enjoyed the experience, but...ahhh the ever present but....

I decided to do something simple, as this was my first test at casting...anything. I picked up the tamiya modern vehicle acc. kit the same time I got the alum. I figured I can always use lots of ammo cans and rucksacks. The RTV was super easy to use, (the kit is pre measured to mix everything...so I made a big mold of lots of little parts) I chose the ammo cans and the like specifically because I figured they would make good open end molds. The Alumilite quickset RTV picked up every detail. I was impressed. What I wasn't impressed with was the freakin bubbles. Of course they couldn't be in easy to fill locations. Top corners of the cans.

So, why on earth is the "super plastic" bubbling at the BOTTOM of the mold? The bubbles are trapped at what would be the bottom of the mold. (wait, did I just say that?) Is the resin...or whatever super duper plastic setting too fast for the bubbles to escape?

Now, the real reason I wanted the casting stuff was for one part. The back 1/4 of a TOW missile from the old verlinden M901 conversion. I have one (where the other one went to I have no idea. But, I want to cast a bunch of them, as they are the only accurate rear end caps of TOWs out there. problem is, the thin end cap portion (saucer lookin thingy) isn't coming out at all. Is this the same scenario as above? sets too fast for the resin to get into that tiny space?

PLEASE HELP! (I am going to lose sleep over this) #:-)

OK, take a deep breathe and calm down.

I've used Alumilite before and it's pretty good stuff -- you just need a few tips.

First -- chill your Alumilite. If it is cold, it slows down the setting time.

Second -- Stir it thoroughly, but not so briskly to make bubbles. I use a toothpick, then tap the mixing container on the table top to loosen the bubbles. You probably won't get rid of them all, but you can try to minimize them.

Third -- Use the toothpick you mixed with to put a bit of the resin in the mold and rub it around the sides. Those disposable micro-brushes also work good for this. Work a little resin into the nooks and crannies -- like those undercuts in the mold for your TOW endcaps. If you coat the mold well, any bubbles in the casting will be inside it, not stuck to the sides of the mold and leaving open holes.

Finally -- carefully pour in the resin from one side, letting the air escape on the other side. It's like pouring a draft beer and trying to keep a small head of foam on it. . When the mold is about 3/4 full, look to see if there are any bubbles, then poke at them with your toothpick. top it off and go a little over (bubbles will rise and you can trim/sand them off).

These tips won't completely eliminate bubbles, but they will help reduce them.

AHAH!

Hollowpoint, you da man! I consider myself a relatively intelligent monkey, and I should have thought of that. (relative to fish it seems sometimes) Do you just keep the A+B parts in the fridge? and if that is the case, why does the instruction sheet tell me to put the mold in the oven? Do you coat the mold, let the first coat set, then pour?

The mad scientist in me is coming back out.

PZKFWW11,
Chill your resin like explained before, You can also chill the mold too. This slows down the cook off time of the resin once mixed. You only have about 2 mins to work w/ the resin before it starts to set, so time and preparedness are essential.
Precoat the mold right before you pour in the rest of the resin. This allows the mold to be covered in a light film of resin before you put in one big glob. This cuts down on the bubbles that are trapped in against the mold walls.
I dont use Alumalite because it sets so fast and you dont have much time to work the resin in the mold., But try these tips and see how it goes. GOOD LUCK Todd

You can, but I never did. Coat and go.

One last tip -- I made a couple molds of 55-gallon drums and use them as my "overage" bins. That last bit of resin in the cup goes into a 55-gallon drum mold -- the layers of resin seem to stick to each other OK (plus I always seem to get that Dairy Queen swirl on top that helps lock them together. Sometimes I squeeze the mold to create dented or crushed drums.

I never kept my Alumilite in the fridge, but I did put it in there a couple hours before I intended to cast. In the winter, I just set it out on the window ledge of my model room and brought it in when I needed a pour.

Chill, Brush on a little resin into the nooks and crannies, and also squeeze the mold a little, as you pour the resin, slowly release the pressure on the mold, you with then cause a small vacume to suck the resin further into the mold. And remember it's practice, practice practice, and not all are going to turn out winners. The more you do it, the easier it becomes and better the casting get. I just started doing my own photo etch, most are thrown out, but everytime I do it they get better. Was the same way when I did my first casting. I have to laugh, alot of them still get tosed. Alumilite is a great product, but cures very fast. Might want to look around for a slower curing resin.

Hi,
I got the chance to watch "Mr. Alumilite" ( a retired dude that does it for fun) do demos at two different places. He puts the molds on a warming tray to REDUCE the time it takes to get a finished mold. He keeps the Alumilite on ice to increase the working time before the mixture sets up. Ahah!
Another tip for bottom bubbles is to give the air a place to go by gluing on some extension to your piece, then trimming the extnsion (with the bubbles) off the finished piece.

Sealhead (Kansas Sunflower)

If you are making a lot of one item, try making a bottom feed mould. this requires about twice as much RTV, but the results are alot better. You have to create a reservoiur to one side of the part you are creating, and a channel from the reservoir into the cavity left by the part master. You pour into the reservoir and let the resin flow into the part cavity from the bottom forcing the air out the top. Guarranteed no bubbles. By the way i produced a dozen TOW tubes that way.

Well never used it, but have an idee they juse on cement pouring for buildings. They shake the cement so you have to shake it somehow... Maybe you could shake the molds with your hands but there must be another simple way.
There is some site on the web that has a way to do this .... can't remember it.
They use a rope to hang the mold on and twist it around... just like you can do with a bucket of water, you twist it around hard enough and the force will press the water to the bottom so it won't come out. By doing this with your mold the air bubbles will be forced out by the resin that is beeing forced into the mold.
hope this helps

if anybody knows this site please post the link

I'm working on a Homemade "Pressure Chamber" for casting..... I'll keep everyone Updated as I have time to Procede

Its called Centrifical casting and the article in question was posted on Track link .com

HEY MATT; BEEN there done that.

Hey Hey Hey!

Be real careful about making your own vacuum chamber. Implosions of vacuum due to force times area have the same power as explosions. Also, remember, your molds may have to have room to allow a temporary rise of up to three times the original volumn.
Yes, you can "jolt" the molds after the Alumilite is poured to encorage the bubbles to rise.
Again, a "cheap" way to get bubbles off the bottom is to add a small conical shaped piece of styrene or even wood to the top of the master. Then the mold has a chamber for the lowest part of the pour to go with the bubbles.
Mr. Demo also squeezed the mold a little to encourage bubbles to rise.

Sealhead (Kansas Sunflower)

It's not going to be a vacuum chamber. I've been chatting online with a fellow who uses A Pressure Chamber (10-30 psi) to remove his air bubbles.

Please remember a pressure chamber is even more dangerous than a vacuum chamber, because "BOOM" travels outward and "MOOB" travels inward.

Spinning the mold is similar to centrifigul casting. It will cause bubbles to move, but generally outward, not upward.

Best bet, chill the Alumilite and tthe mold to increase set-up time. "Paint" on a little around the surface of the mold. Pour down a small dowel to avoid splashing and to get it into corners. Bounce the mold a few times to help the bubbles reach the top and go away.

Let us know what happens.

Sealhead (Kansas Sunflower)