Molding and Casting Kit Parts for the Y-Wing Project

DaveG said:

The first thing to say about vacuum chambers is to NEVER under estimate the power of a vacuum! You do not want to be around a chamber when it implodes, I speak from experience here. My first DIY chamber imploded because I didn't know what I was doing. I was standing only two feet away from it and was lucky to have not sustained any injuries. A real "brown stain moment" if you know what I mean!:eek

Some people have made pretty good vacuum chambers from heavy duty professional kitchen stock pots, the kind that are made from 1/4" thick aluminum, and a Lexan (polycarbonate) cover. I recommend a 3/4" or 1" thick polycarbonate cover over acrylic. Less likely to break or shatter. www.bestvaluevacs.com sells these kind of chambers. I've not had any direct experience with their products but that look pretty good and are reasonably priced.

For a vacuum pump you must get one that can pull a vacuum of 29 inches of mercury, or else you're wasting your money. Many cheap pumps that you'll find on EBay won't pull that high.

Good luck!

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All excellent information in this thread and I really appreciate the effort put in here DaveG.

I to am looking to get a vacuum chamber, any recommendation on sizes for both the chamber (1,2 or 5 gallon?) and the pump (1 stage or 2 and 3,4 5 CFM)? There are lots of choices and having a hard time deciding as I only want to buy this once.

Asking what size tank and pump you should buy is a little like asking what car should you get. There are lots of variables to consider. Budget, of course, is one. But I will say that I'm a big proponent of buying the absolute best tools you can afford, and only buying them once. I'm still using the same vacuum pump I bought more than 20 years ago.

The size of the vacuum pot depends on the size of molds you plan to make and the amounts of silicone you think you'll be mixing. Remember that you'll be mixing the silicone in a disposable bucket and then putting that into the chamber, so the volume of the chamber is not the actual capacity. If you're going to be making molds for models you'll probably be mixing up relatively small batches. But even so, I would get a chamber at least big enough to hold a 5 quart paper or plastic bucket. Call the seller and get the actual dimensions, not just the volume, of the pot if it's not listed on the site. Remember silicone expands and foams up 3 to 4 times as you degas it, so a 5 quart bucket will only be good for about a quart and a half of material. I'd stay away from too big a pot as it takes longer to get to full vacuum. If you need to mix larger amounts you can always do it in batches. Most silicones have a 60 to 90 minute pot life which is plenty of time to mix, degas and pour several batches for one larger mold.

As far as a pump goes, the higher the CFM the faster it will pull a vacuum. My pump is relatively slow, about 1 CFM. It takes about 5 minutes to pull a high enough vacuum on my 7 gallon tank, after that the silicones takes about 6 to 7 minutes to degas sufficiently. The silicones I use have a 60 minute pot life and a 24 hour cure time so that's fast enough. If you're planning to use a silicone with a shorter pot life and faster cure time you will need a faster pump. But I'm not a big fan of faster setting silicones, they have a higher shrink rate and don't last as long. Besides, who needs to be in such a big hurry anyway?

And as I mentioned before, make sure the pump you get can pull at least 29 inches of mercury. Anything less than that and you're wasting your money (again, I speak from experience here!).

Thanks Dave, once again I appreciate the input. I have done some large molds before, but nothing more than 1/2 a gallon at a time and that may be pushing it. I'm also not pushing the pot life on anything I use so there should be plenty of time to degass even with a smaller pump. Thanks again as this has helped me with my decision.

I use a lid like this:

http://www.ebay.com/itm/Vacuum-Cham...081009?hash=item3d231c95f1:g:NzkAAOSwMmBVic0i

on my 5 gallon HF paint tank (they no longer sell this size tank, unfortunately). I also use a HF vacuum pump and it does the job just fine.

So here's an obscure casting tip... whenever I mix up resin in a paper cup I always stir quickly in a counter-clockwise direction. There is a specific, direct benefit to this and it has nothing to do with my being right-handed, mildly OCD or living in the northern hemisphere. Any guesses why? If you study the attached photo closely enough you should be able to figure out the reason.

The seam line, it's a bubble maker?

Yes, it has to do with the cup seam, no it has nothing to do with bubbles. Here's another hint, stirring counter-clockwise has no effect on the quality of the casting, but is still none the less beneficial.

Dave, I see you using a paper cup and wooden stir...in your experience, has the potential moisture they could absorb ever affected your resin batches? I used to use wooden stirs and never had a problem, but switched to metal after reading about moisture contamination. Overreacting?

Hardly wooden particles coming off when hitting the seam is it , or is not all the hardening getting mixed correctly as it's getting trapped in the seam?

Vacformedhero said:

Hardly wooden particles coming off when hitting the seam is it , or is not all the hardening getting mixed correctly as it's getting trapped in the seam?

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Nope.

Don - I've never had any issues with moisture contamination from paper cups and wooden stir sticks.

So you don't open the seam up

DaveG said:

So here's an obscure casting tip... whenever I mix up resin in a paper cup I always stir quickly in a counter-clockwise direction. There is a specific, direct benefit to this and it has nothing to do with my being right-handed, mildly OCD or living in the northern hemisphere. Any guesses why? If you study the attached photo closely enough you should be able to figure out the reason.

http://i1053.photobucket.com/albums/s480/GoldbergArts/Mixing Cup_zpsamvtugqh.jpg

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Does the seam, unmolested by the stick, become a natural "pour channel" once you're ready to start pouring it out? Does it create a thin "fine line" pour funnel by the physics of the seam?

Nope. Nothing to do with the pour

Dave your driving is nuts, I think I have it,
after a long session of casting the inside of the cup and seam are sealed with resin,
which you can now use as a vodka glass without fear of leaks
after a couple of these all your casting fears go away

So the cup doesn't peel open at the seam as it soaks in?

Main reason why I use paper cups is for when I have any leftover resin. Eventually any leftover dregs that I've accumulated into the paper cup will reach the top of the cup and I can peel all the paper away and us it as a resin plug to spin on the lathe and turn stuff down.

Okay, the word "quickly" was also a clue. If I stir quickly in a clockwise direction the stir stick catches on the overlap seam and can cause a little splash of resin out of the cup. I told you it was an obscure tip!

I never stir clockwise...ever, even when I cook!

Great post Dave - very informative!
Question - could you tell me what kit the circled part comes from?
I have been trying to find it for weeks, but I obviously just don't have the right kit.
Thanks!

That is from the Tamiya 1/700 Scharnhorst

Boba Flint said:

That is from the Tamiya 1/700 Scharnhorst

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OMG - You Rock! I must have looked at that kit 20 times and just didn't see it - thanks so much!