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Mig Eater

Vacuum chamber question?

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I want to start casting my own parts & I'm looking into getting a vacuum chamber to help with degassing the rubber for the moulds &/or the resin. However I'm unsure about when would be best time to use the vacuum chamber, should I degas the rubber/resin in the mixing cup & then pour it into the part/mould, or is it better to degas the whole part/mould etc? The size of the vacuum chamber that I need will depend on which method I use & could mean spending £200 or £800.

An extra side question; Nearly all 2 part resins that I can find for sale are clear, to get the typical beige/white colour is it just a mater of adding a dye to the resin?

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I degass the silicone after mixing and again after pouring it over the pattern to ensure that there is no air trapped in the crevices of the pattern.

 

For the resin, I use pressure instead of vacuum after I pour it into the mould.

 

Vedran

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I dont have the budget to get both a vacuum & pressure chamber, especially if they need to be big enough to put the whole mould into both of them. That would cost thousands of pounds for all the necessary equipment 😕 

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What sort of size and complexity are the parts you hope to mould?  I have been making resin castings for many years without a vacuum to degass or pressure to keep bubbles down, mainly relying on a gravity pour which is led down underneath the main mould area and then displaces the air out via vents as the resin rises through the mould.

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I'm planning to scratch build/3D print several 1/35 tanks & I want to cast copies of them, which would include everything from individual tracks to large hull plates. The hull of the largest tank will be around 28cm long so I'd need chambers 35cm+ in height/width to hold the mould, which can be very expensive. I was hoping I could just vacuum the resin in the mixing cup which wouldn't need as large a chamber.

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For the resins ( see the range offered by Sylmasta ) I use,  the main cause of bubbles in the final mouldings is because air has been trapped in parts of the mould as it is filled.  So degassing before pouring wouldn't help I suspect.

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On 1/21/2019 at 6:09 PM, Mig Eater said:

 That would cost thousands of pounds for all the necessary equipment 😕 

Buy a pressure cooker. Have someome drill a hole and braze an air valve on it.

 

Vedran

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I looked into modifying a pressure cooker but I couldn't find one big enough, the largest one I could find was 17 litre but I'd need something about 40-50l though.

 

Anyway to my main question, it's best to put the whole mould in the vacuum chamber then?

Edited by Mig Eater

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I haven't used a vacuum chamber yet. It seems a necessity for finer parts. I have a paint pressure pot that painters use to pressurize paint for spraying in houses. It's about the size of a 5 gal pail, bit shorter. It just needs a bit of valving, air line quick connects and a pressure guage. I'm not exactly sure on the parts. I have a picture of one set up. It's cast aluminum with locks on the lid. For vacuum I was going to try a refridgerator pump, but never did more than find the pump. I also just got some semi clear Smooth-on mold rubber called "sorta clear" I saw a video on it and you can see through it which will be very helpful. I also used Alumiltie slow set resin. I found it has a much better shelf life than Smooth-on which has a short life once opened even with the air displacing spray. The lids I guess don't seal to good no matter what. I do a little casting, just small stuff. Don't have anyone to instruct me on doing bigger stuff and I'm limited to space for a proper set up, have to keep it movable.

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