Vacuum Pressure Chamber, anyone know how to make one cheep?

[seven]

I am interested in making a vacuum pressure chamber that I could use to pull the air bubbles out of my casts before/as they harden. I have seen a few and think it seems fairly easy to do. I think I would need a pressure gage (not sure what kind), a base that is attached/sealed with the tube like chamber (one that would be big enough for the size of molds I have). A spot to vacuum out the air, and a lid. All would need to be air tight. Anyone out there who has made one or has plans for one that can be made for under $100?

 

[propsculptor]

I know that some people just buy a pressure tank from Harbor Freight tools, and they aren't too expensive either.

 

[THEWRAPOFCONS]

I fot mine from Sears. Craftsman makes a great paint pot that need just a few additions to be a great vaccume chamber. I will post pics when I get home.

 

[seven]

I have seen the vacuum paint pot at Sears before and thought it would be great to use. What kind of modifications would need to be done to make it usuable for molds. Also, what type of vacuum would I have to use? I have seen vacuum pumps that are pretty expensive, so I was hoping for a cheeper method.

 

[exoray]

That pressure tank from Harbor Freight looks like a good idea to start with.

I was just going to go with a large cooking pot, rubber gasket and a 3/4 sheet of MDF or plywood

For the vacuum pump, if you have an air compressor you can't beat the Harbor Freight venturi vacuum pump 28.3" of mercury for $15

 

[itbedave]

Someone here on the board can attest to the fact that, when you're talking about working with pressure, don't screw around with a homemade rig unless you REALLY know what you are doing. It could easily explode - sending shrapnel of whatever you built it out of everywhere.

The paint pots mentioned are all good options. Just have to be large enough inside to fit your molds. The venturi pump mentioned at Harbor Freight will work fine, depending on your elevation and your air pump. You have to provide enough CFM to get it to operate at certain levels of vacuum - so pay attention.

All you need to convert your pot for both uses is a dual vacuum/pressure gauge that you can buy from mcmaster.com, and possibly a few air hose connectors and plugs depending on the ports on your pot.

 

[THEWRAPOFCONS]

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ElmoandBloodyShow wrote:<HR></TD></TR><TR><TD CLASS=$row_color>
What kind of modifications would need to be done to make it usuable for molds. Also, what type of vacuum would I have to use? I have seen vacuum pumps that are pretty expensive, so I was hoping for a cheeper method.
</TD></TR><TR><TD><HR></TD></TR></TABLE><SPAN CLASS=$row_color>

I got a vacuume inverter from Reynolds Advanced materials, ite converts the air from my compressor and sucks the air out of the sears pot, my whole rig cost $200.00

 

[exoray]

</SPAN><TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD CLASS=$row_color>Quote:<HR></TD></TR><TR><TD CLASS=$row_color>It could easily explode</TD></TR><TR><TD><HR></TD></TR></TABLE><SPAN CLASS=$row_color>

On a vacuum chamber it would be in implosion rather then an explosion and it won't send parts flying everywhere unless the material used is prone to shattering (Glass, certain plastics). The implosion caused if any won't be that strong, remember an implosion will be pulling in not forcing the parts outward.

A cooking pot and sheet of MDF like I said above it pretty safe if the pot fails by starting to cave in it will warp the rim of the pot breaking the seal and releasing the vacuum without much force at all ending the implosion almost immediatley. If the sheet of MDF fails the vacuum will be released pretty quick as well and the MDF in the worst case will powder into small pieces being sucked into to pot.

On the other hand pressure pots are a different story, a vacuum chamber is much safer.

For any setup I would try the venturi pump as it's a very cheap solution, put a gate valve inline between the pump and chamber and once you pull down you can close the valve and then stop the pump. This will eliminate the need for a huge and constant CFM from your air compressor. And it shouldn't take much to pull down a 2 gallon or so chamber.

 

[Java]

Pressure Cookers work too. I got a giant one at a secondhand store. It was like $5.

 

[sapper36]

I've got a 5 Gallon Pressure cooker I use for both - The regular lid for pressure casting & a 3/4" plexi lid for vacuum - Just finished putting the rig together for the vacuum & it's pulling 29.25 inches of mercury. Can't wait to degas some RTV!

 

[exoray]

I have to hit up some local second hand shops, I looked around eBay and there are some great old pressure cookers that look to be built like tanks, but the shipping on them will kill the cost...

A pull of 29.25 is fantastic, most pumps only pull to about 28

 

[itbedave]

For vaccum, a pressure cooker may work fine. For a pressure chamber, you guys are taking a real chance. They recommend around 60psi to eliminate bubbles in resin - and a standard pressure cooker isn't rated anywhere near that.

 

[seven]

Thanks guys, I really appreciate all the help and ideas.

 

[rayra]

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exoray wrote:<HR></TD></TR><TR><TD CLASS=$row_color>
...Harbor Freight venturi vacuum pump...
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hmmmm

 

[steveday72]

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itbedave wrote:<HR></TD></TR><TR><TD CLASS=$row_color>
For vaccum, a pressure cooker may work fine. For a pressure chamber, you guys are taking a real chance. They recommend around 60psi to eliminate bubbles in resin - and a standard pressure cooker isn't rated anywhere near that.
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I just had a look at the Sears one on their website.

http://www.sears.com/sr/javasr/product.do?vertical=TOOL&pid=00916102000&bidsite=&BV_UseBVCookie=Yes

It has the valves and guage already fitted, it's rated up to a maximum of 80psi and costs $99. Pretty good unit for the job.

Could this be coupled with the Harbor Freight vacuum pump ( http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=3952 ) and create a dual-purpose vacuum/pressure chamber?

Steve

 

[Raygun]

I need to make a top for mine, but what I have is a 5 gallon propane tank with the top cut off and a open/close valve with an air line fitting installed near the bottom.

To cut the top off, you need to get an empty, prefferably new and never filled one. If it's used, empty it and remove the filler valve fittings so it's open to the air. You could just blow it out with an air hose to make sure it's empty or fill it with water. Then cut the top off. You'll need a big bandsaw to do it without screwing it up though. I have a piece of 1 inch thick lexan for the lid. I need to have a circular groove cit into it, so I can run a bead of silicone around it and have a tight seal. I also need to pick up the venturi pump from HF. This is for a vacuum chamber. If you want a pressure pot, I'd recommend buying one. It's probably safer that way.

EDIT: I'm not 100% sure about propane fittings, but all flamable gas cylinders have LEFT handed threads. It's so you don't screw the wrong regulator on a flammable tank. I figured you might want that info, so you don't wrench it until it snaps off

Raygun