home made vacuum chamber 4 molding & casting..

[Donny_Harijanto]

Hi, Is there any way to build a home made vacuum chamber.
I want to buy this machine, but no one sold it in Indonesia.
please help me..

[Dalhimar]

For one, do you know this is a 3D art&sculpture forum?
second all you need to do is get a flat board, a large glass jar and a vacume pump, or a bike pumped rigged to suck air, a pump connector and some silocone sealent/caulk. Make a small hole in the board and put in a connector for the pump and caulk around the connector. Put the glass jar over the connector hole on the other side and draw a circle around it with a pen or pencil. Caulk around the pencil line, just slightly outside, this will help seal the jar to the board. Afterwards put what you want on the board and put the jar over it, while inside the ring of caulk. Attach the pump to the connector and pump away.
Mind you this will not create a full vacume most of the time, but will suck alot of the air out, the ammount depends on the quality of materials and pump, the type of wood and the seal around the edge of the jar.

[Donny_Harijanto]

I'm so sorry...,
I thought this would help everyone who want to build vacuum chamber to molding and casting their sculpture.
it's not directly 3d & sculpture topic though, sorry guys.

anyway, Thaaank You sooo much Dalhimar you are a life saver.
I think I can build that in my garage.

and last questions,
does an air compressor can suck the air instead of vacuum pump?
is there any way to do it?

[Monkeywiz]

I can't answer your air compressor question I'm afraid, but I will say be very careful attempting this with just any glass jar, as you wouldn't want to be next to an imploding one.

Also I think this is still a valid question for a 3d art forum, if anyone wants to mold and cast any items they've made it's still just an extension of the process, and there are guys here who are also part of the garage kit community and might have some handy tips as to how to go about this.

[MikeMakesModels]

An alternative to a glass jar could be an old (or new) pressure cooker - I know it's pressure in the other direction, but those things are fairly sturdy and have a good seal.

As for the pump - have you seen this?
http://www.instructables.com/id/E791HNXF23Z39P6/?ALLSTEPS (check the comments as well)

...

A completely different solution would be to make a decent vibrating table. A good motor with an off-centre whirly thing should work wonders for working the bubbles out.

[ps: I agree this is a perfectly valid post - not everyone loves super sculpey :P]

[RSchrader]

Hello Donny, I agree!!!!! This is a very valid post for this forum!

I suggest that you never vacuum cast! Always cast under pressure! I use a vacuum chamber to degas and an old paint pot as a pressure chamber. This combination gives me perfect, bubble free castings every time.

For my vacuum chamber I found a section of 8 inch, schedule 40 PVC pipe at a construction site that they let me have. I then used 1/5 (.5) inch Lexan to make the top and bottom. I sealed the bottom with silicone caulking and on the lid I used a weather strip foam seal. This only cost me about $16.00 US.

Here's the problem, I tried to take every short-cut to avoid paying the high price of a proper vacuum pump. I tried everything and nothing worked!

Watch this video from Freeman: Degassing and pressuizing (http://www.freemansupply.com/video/preparing/vacdegas.htm)

What this video tells you is that you absolutely have to have a vacuum pump that will pull a minimum of 29 inches in Hg (in-Hg) to successfully degas silicone or casting resins. Anything LESS and you may as well not even attempt a vacuum chamber.

I won't get into the technical end of vacuum pumps, but if you have any further questions I will be happy to answer them for you if I can.

Ray

[Donny_Harijanto]

wow thanks monkeywiz, Dunefish, and RSchrader.

I am not fully understand the exact function of pressure pot for casting.
a Vacuum itself can force the bubbles to come out from mold, isn't it?

in my country everybody just mold and cast manually, so the cast need a lot of sanding and filling to fix those air bubbles.

please someone help me describe these two device function.

Vacuum chamber for making bubble less silicon mold (???)
Pressure pot for casting resin (???)

I want to invest on something to help me produce perfect garage kit.

Ps: sorry for my messy english, i Hope you guys still understand what i'm talking about.

[RSchrader]

Donny

I hope I can explain this for you. Not that it can not be done, but I tried vacuum casting with very little success. The most luck I had was with single part silicone molds. Any two part silicone molds almost always failed.

Here's why...... As an experiment, If you take freshly mixed resin in a plastic cup and place it in a vacuum chamber, depending on the pot life and the type of resin, it will set SOLID before it will stop bubbling!

This same process occurs when the resin is in a silicone mold under vacuum.

Also, If you do not degas the resin before you pour it into the mold, then it will degas while it is in the mold! This means it will rise and fall, thus, spilling the resin out of the mold.

If it is a two part mold, the seams can be never sealed well enough. In a vacuum, trapped air in the resin has a tendency to flow from the center to the outer edges. This process allows resin to be removed from the mold through the seams in the form of flashing. As the resin escapes, it will lower the level in the mold thus causing a defect. To solve this you must build a large redundant reservoir in your filling sprue of the mold in order to re-supply the lost resin. You still may have bubbles in the cured casting.

I gave up on vacuum casting and started pressure casting. Pressure will compress any bubbles in the resin or silicone into microscopic bubbles that can not bee seen with the naked eye!

Although you do not have to, I always degas my resin. Then, it goes into a pressure pot at about 25 psi until it cures. Perfect casts every time!

Look at this Website (http://www.alumilite.com/index.php?page=show_info&type=HOWS&id=52).

Ray

[Donny_Harijanto]

thanks a lot Ray

i couldn't find anyone sell a vacuum pump..

can I do a pressure casting with non-degased silicone mold?
what happen if I do it?
coz I have an air compressor, and I can build a pressure pot.
and I don't have a vacuum pump.

Oh I forgot to mention,
I knew only one person sell this vacuum pump(1hp).
But it's so expensive about 15.000.000 rupiahs (1600 US dolars)

I want to ask, how much power do I need for the vacuum pump (in hp) ?

[drcrash]

Donny, what kind of compressor do you have?

Some compressors can be used as vacuum pumps, if you attach a fitting to the air intake.

Other compressors, if they're big and powerful enough, can be used to drive venturi vacuum generator, which you can get for about $15 at Harbor Freight. That generally requires a compressor that can pump at least 4 cubic feet per minute at 90 pounds per square inch. That's not an efficient way to generate vacuum, but it works if your compressor is big enough.

Doug Walsh is selling some nice surplus vacuum pumps for under $100 right now at www.build-stuff.com. (They're 120V pumps, though---what is the standard AC voltage where you live?)

The pumps at build-stuff.com are Thomas oilless rocking piston pumps. They pull about 28 inches of mercury, but I suspect that's over their specifications and they're only rated for 26 or something like that. (Piston pumps don't seal quite as well after you've used them for a while.)

I do think that will work for degassing most things. I've never done it, but people have told me that even if the specifications for your silicone (or whatever) say to degas at 28 inches of mercury or more, 26 usually does a pretty good job anyway.

Those Thomas piston pumps will work either as compressors or vacuum pumps, so you can use them for both vacuum degassing and pressure casting.

[CSharp]

Ray (RSchrader) - you rock. I've been having the same problem trying to vacuum cast and no matter what I tried, I ended up with bubbles.

After reading Ray's post, I started digging around and found that pressure casting is indeed the method of choice for bubble free castings. So, I ordered a compressor, air hose (with accessories), and a 2 1/2 gallon paint pressure tank from Harbor Freight for a total of just over $100.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95275
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91860
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93119

...and though I haven't received this equipment yet, I'm pretty confident it will work well.

Thanks for sharing!

[jlamarche]

I understand why you use the vacuum pump to degas, but what does casting under pressure do?

[Monkeywiz]

I think Ray answered that one a couple of posts up

'Pressure will compress any bubbles in the resin or silicone into microscopic bubbles that can not be seen with the naked eye'

[jlamarche]

I think Ray answered that one a couple of posts up

Doh! Sorry about that

[coyote1066]

Hi,

I love the info in this post and decided to register to add a few notes:

I see some are asking about what kind of pumps work. I use a 6 cfm 2 stage pump with an ultimate vacuum rating of 15 microns. You may be able to use a 5 cfm pump as well. As far as price you're looking at $180 to $280 depending on brand. Try eBay, look for "vacuum pump", specifically those for HVAC servicing. I have a CPS Pro-Set VP6D which can pull degassing level vac in about 15 seconds. I have basically the same vacuum chamber described above...8 1/2" PVC pipe with 1/2" lexan sheet covers, 1/2" fittings and line. 1/4" will work but will be a little slower.

Also, be aware of your altitude. The majority of folks out there are within a couple hundred feet of sea level meaning 29" Hg is what you're shooting for. I'm at 5200 ft (Colorado) so for me my max vacuum is 25" Hg which equates to 29" at sea level. Here's a formula I found to help you determine your degassing vacuum target:

"Method for Determining in.Hg. Vacuum at Elevations Above Sea Level

Present Altitude (Feet) X 0.001 = X.

Full Vacuum @ Sea Level = 29.921 in. Hg.

Full Vacuum @ Present Altitude = 29.921 – X = Y"

So my calculation is: 29.921 - 5.2 (5200*0.001) = 24.721" Hg

calculations came from this site:

Here (http://www.impco-inc.com/page210.html)


Hope all this helps.

[MrGreen]

...and though I haven't received this equipment yet, I'm pretty confident it will work well.

I'm very interested in this kind of "budget" setup myself--not really excited about dropping $1000 or more for a hobby kind of thing just yet.

Does anyone know if you can use the same chamber/pump to do vacuuming and pressurizing? Killing two birds with one stone would be great.

[RSchrader]

Hey Guys,

I just PM'd you CSharp!

As I told him I was in a car accident just over a month ago and suffered a bad shoulder injury that I have just had surgery on 4 days ago. I will try and contribute to this thread some more but if I drift off into LA LA land......it's the drugs! LOL!!

can I do a pressure casting with non-degased silicone mold? what happen if I do it?

This is a FANTASTIC QUESTION! Here's my hard learned answer. If you do not degas the silicone before you make a mold then nothing will happen UNTIL you try to pressure cast with that mold!

The determining factor is the type, quality, and gel time of the silicone you choose to use! A lower quality and fast setting silicone will give you some problems. You see, the surface of this silicone that comes into contact with whatever your molding will appear nice and silky smooth after you demold. No bubbles! What you don't see are the bubble pockets that are hangin' out just behind that smooth surface! Now when you add resin to the mold and place it under pressure two things can happen.

1. You will have small depressed bumps all over your cured resin cast. This is caused by the hidden bubble pockets, closest to the smooth surface, collapsing inward towards the casting by the pressure.

2. You will have porcupine spikes! These are caused by those same bubble pockets fracturing under the pressure and allowing resin to be forced into the now open pocket. Oh, and you will be scratching your head because you won't see the tiny fractures or the hidden pockets until you start cross sectioning the mold for closer examination! LOL!!!

Conclusion: Buy the best silicone you can afford. Vacuum degas if you can. If you can't, then only pressure cast at about 15 to 20 psi.

Does anyone know if you can use the same chamber/pump to do vacuuming and pressurizing? Killing two birds with one stone would be great.

I think you can easily make your own vacuum chamber. BUT pressure is a whole new animal! I would never try to use it as a pressure chamber!

I believe that a viable vacuum chamber must have a view port or window so you can watch the degassing process. Unless your an engineer and built the port or window strong enough for pressure as well, I would not even remotely try to use the same chamber to restrict pressure! You don't need to watch the pressure casting so any good used paint pot will work great!

OK, my finger is tired of typing! LOL!!

Gotta rest and take more drugs!

Ray

[RSchrader]

DONNY

I forgot to mention that you can also place your silicone molds in a pressure chamber during it's curing process! This will eliminate all bubbles in the silicone mold. I always degas my silicone before pouring. If the mold will fit I will then place it in the pressure pot after it's poured!

Ray

[Donny_Harijanto]

RSchrader

Thanks a lot for the info Ray.
But unfortunately, I stil got no vacuum pump...

Because of my condition, I want to ask you one more question

If I only use "pressure silicone mold" without degas it,
and then "cast" it under pressure. Does it works..? :dad:

I only got an air compressor..
Vacuum pump is hard to find here in my homeland..

[RSchrader]

Donny
I hope this will answer your question. If not.............let me know and I will try again!

There are four ways to make a silicone mold bubble free.

1. Use high quality silicone, stir gently, use the "bombs away" method of pouring and hope for the best!

2. Degas the silicone in a vacuum chamber before pouring it.

3. Pour the silicone in the mold box and then place the whole thing in a pressure chamber during the curing process.

4. Degas the silicone before pouring, and then pour the silicone in the mold box and then place the whole thing in a pressure chamber during the curing process. This is the best method!

If you place the whole, original, silicone mold into your pressure chamber while it is curing out...................this will eliminate all or most bubbles from the silicone mold. It's just like you would have degassed it!

So, the silicone mold I described above in blue.................will give you perfect resin castings as long as you cast them under pressure!

So, Donny my answer is yes! LOL!!!!

Ray

[Donny_Harijanto]

YEEEEAAAHHH!!!
Finally, the answer i seek for so bad.

now i can make a good cast, without that expensive vacuum pump.

Thanks Ray, you're a life saver.

[lantzn]

Here's the bombs away method in this video.

http://www.youtube.com/watch?v=M400dj19nUs

[AerialInk]

I'm seriously considering that 2 1/2 gal. pressure tank from the link that Csharp provided. Is there a certain amount of psi that is needed to pressure cast? The reason I ask, I have two sources to pump air into the pressure tank: My dads huge air compressor in the garage( it's almost as tall as me), and my airbrush air pump. But it's really cold this time of year, and I'd rather not have to go in the garage to pressure my molds.

[the_mick]

Hi,
Hey, Ray thanks for all the information! What kind of vacuum pump do you use (brand)? Was it expensive?
thanks!
mick

[Donny_Harijanto]

wow it's almost 2 years since the thread started..
and i get a lot info from this.

i want to thank all the guys here helping me out.
i'm now become a professional toy designer for a company in Netherland.
just because of all of your simple comments and answers.

thanks a lot guys!

now, i'm gonna share something here.
i only used pressure pot for both casting and do the silicone mold,
and the result was PERFECT.
for resins i cast it under pressure about 50-60 psi
and for silicone i press it 70-80 psi
but be carefull, some presspot can't exceed 60 psi.

that's it i never used vacuum.
simple and cheap

[the_mick]

Hi,
Cool, maybe I should also try it with preassure only.What preassure pot /compressor do you have? (brand)
thx
mick

[Donny_Harijanto]

i ask someone to make a custom build pressure pot.
i just gave him the design and how the mechanism,
and he build it from scracth.

cost me about 150$ for a 30 cm height and 30 cm diameter of pressure pot.
i only use 1 hp air compressor KRISBOW brand.

[the_mick]

Thx donny for the info! lucky you that you found someone who can build this.
@C.Sharp
Are you happy with the equipment you ordered at harbourfreight? maybe I ll order the same?!
thx mick

[GIROVACMAN]

I was reading your thread regards the degassing of resins (or any materials). You must be aware that you can degas resin of air but if yoyu leave it to long then you may start to pull of some of the necessary chemicals needed with in the resin.

A simple step by step guide see http://www.girovac.com/page.asp?id=105