How to mold and cast small parts

scratchshipnut · Post by **scratchshipnut** » Wed Oct 18, 2006 11:10 pm

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scratchshipnut · Post by **scratchshipnut** » Wed Oct 18, 2006 11:12 pm

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scratchshipnut · Post by **scratchshipnut** » Wed Oct 18, 2006 11:13 pm

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scratchshipnut · Post by **scratchshipnut** » Wed Oct 18, 2006 11:14 pm

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scratchshipnut · Post by **scratchshipnut** » Wed Oct 18, 2006 11:16 pm

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scratchshipnut · Post by **scratchshipnut** » Wed Oct 18, 2006 11:17 pm

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scratchshipnut · Post by **scratchshipnut** » Wed Oct 18, 2006 11:18 pm

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scratchshipnut · Post by **scratchshipnut** » Wed Oct 18, 2006 11:32 pm

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Sean Hert · Post by **Sean Hert** » Thu Oct 19, 2006 12:37 am

Well, there goes most of an article I've been working on for a year now....

I do a number of things differently, but that's just variation.

BTW- you must use sulfur-free clay, as Gary says, because sulfur will inhibit the cure of the silicone.

Vagabond is also avaiable in some hobby shops.... like mine....

I use Vagabond and HSIII in my casting class @ the shop- good products. HSIII is a little softer and stretchier than HSII (lower Durometer for you technical guys). Both are great hobby-level products.

I've never had much use for squash molds personally, but Gary sure makes them work!

Art · Post by **Art** » Thu Oct 19, 2006 5:34 am

[quote="garyj36"]
I have a vacuum chamber to suck the bubbles out of the silicone after I mix it. You won't be able to use this wonderful device unless you invest a few hundred bucks. 'Til you do, all you have to do is pour real slow and puncture the bubbles out of the silicone as it covers the master/s. It's slow and tedious but you will be doing small items and taking your time anyway. Many, many modelers do it this way and get great parts.

Hi Gary,

I have been doing a variation of the technique for yonks. There is a procedure posted on the net somewhere, can't remember off-hand.

The point of this post is in answer to your statement about vucuum chambers and the few hundred bucks cost .

For nix you can build your own pump that will remove a cubic metre of air in 2 seconds flat ( or less ). I use a recycled domestic fridge/freezer pump, an old oxy bottle from a welding set as a vacuum storage unit and the piping and regulator from an old welding set that gives me the required 28 inches of mercury level.

True, the fridge pump will take forever to create a total vacuum in the oxy bottle, but once you have it, the top up time after each use is negligible.

The largest use to date has been a 7 foot DD hull that was vacuformed in one hit. Perfect results. ( the plastic bag was from some left-over (( n microns )) shade house sheeting. Too thick anyway. I have to get thinner sheet to enable it to conform better to undercuts.

Great fun and the items for moulding are limitless. I refined my technique after the details from Weta Workshop and LOTR production became available.

scratchshipnut · Post by **scratchshipnut** » Thu Oct 19, 2006 7:30 am

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diezmon · Post by **diezmon** » Mon Oct 23, 2006 9:16 am

garyj36 wrote:I have a vacuum chamber to suck the bubbles out of the silicone after I mix it. You won't be able to use this wonderful device unless you invest a few hundred bucks. 'Til you do, all you have to do is pour real slow and puncture the bubbles out of the silicone as it covers the master/s.

Another option is to use pressure. I found myself a paint/pressure pot on craigslist for $20. When I pour my RTV, I put it in the pot and pressurize to about 40psi.

Then, when pouring your resin, pressurize at the same psi.. absolutely NO bubbles

You can find cheap compressors at places like Walmart these days, so the pressure method is pretty affordable.

Tim

scratchshipnut · Post by **scratchshipnut** » Mon Oct 23, 2006 9:28 am

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diezmon · Post by **diezmon** » Mon Oct 23, 2006 9:36 am

garyj36 wrote:What kind of container? An open container would blow out everywhere

That's why you don't use and open container

A paint pressure pot is one of these:

scratchshipnut · Post by **scratchshipnut** » Mon Oct 23, 2006 9:40 am

No, I mean containing the rtv 'in' the paint pot. Ive forgot to put the lid on a few molds and had most all the resin blow out

diezmon · Post by **diezmon** » Mon Oct 23, 2006 9:43 am

garyj36 wrote:No, I mean containing the rtv 'in' the paint pot. Ive forgot to put the lid on a few molds and had most all the resin blow out

OH

did you mean in the vacuum? In a pressure container this wouldn't/shouldn't ever happen.

scratchshipnut · Post by **scratchshipnut** » Mon Oct 23, 2006 9:48 am

Maybe its because my tank sits upright. Thus the air inlet is right above the molds

diezmon · Post by **diezmon** » Mon Oct 23, 2006 9:53 am

garyj36 wrote:Maybe its because my tank sits upright. Thus the air inlet is right above the molds

OH, ok I get it.

What I did was epoxy and kind of blocker in front of the air-in hole so the air doesn't shoot straight down at the bottom