Vacuum degassing chamber

[Canobi]

Hi all

I got into making custom and replica props as a hobby which in no small part, involves moulding and casting.

In most cases, resins and silicones come in two parts that need mixing together. This is more than slightly problematic as it introduces a heap of air bubbles into the mix which needs to be removed before using or they can cause all kinds of deformities and weaknesses in the moulds and castings. To do that job, I was going to need a vacuum degassing chamber, preferably of adequate size in case I ever decided take on a large project.

One thing I learned quickly though is that many materials may be affordable, but the equipment needed to use some of them properly often aren't. In this case, a purpos made chamber matching the size I had in mind can cost around £600 minus pump, so I set about making my own. I also set myself the challange of making it for as little cash as was feasibly possible.

I looked at a plethora of items that could be used or converted, including very large pipe couples, butane bottles and pretty much anything around the 12" x 12" size I was after but in the end I chose a helium bottle as it was free, already empty and met my size requirements. They're also rated to over 200 bar (3000psi) and absolute vacuume is a meagre -1 bar so knew the bottle could easily handle it.



---------
"The build"
---------

Not being overly equipped with tools, I needed to find a way to cut the top off the bottle, after a bit of hard thinking and fiddling about, I came up with this cutting jig for my dremal:






2 metal cutting discs and 5 standard ones later.... job done:




One of the chest of drawers in my kids bedroom was in need of replacing and that provided the perfect opportunity to make a work unit for the chamber and pump.


All striped down



I then drew around the chamber lip and drilled a pilot hole for the jigsaw





Hole cut, then the plug secured to a couple of cross bars added to set the hight of the chamber (and add a little extra structural integrity)







I then added a shelf for the pump underneath the worktop







A quick test fit:




And as a neat touch, a bit of acoustic foam I had lying about from my old recording studio that fit the gap perfectly, no cutting needed.





I then set about acquiring a vacuum gauge and other fittings:




After assembing the parts I used a bit of JB Weld as a thread locker. It was then supported till it was stiff enough to move to a warmer place to cure:




I then drilled a hole near the top of the bottle for the inlet/outlet and test fitted the assembly:




Once the flange was welded on and valve assembly fitted properly, the chamber and pump were installed into the work unit to finish the build:




<edit> found a pic of the gasket I made with clear caulking. I used a spare piece of acrylic with soapy water to flatten it. The soapy water acts as a release agent that prevents the caulking from sticking to most surfaces (inc fingers)



And this one with the guage showing the chamber at near full vacuum:




Well, that it for this one. Thanks for looking

[Christophe Mineau]

Fine !
what kind of pump did you use ?

[DIYer]

Thanks Canobi! We've added your Tank Cutting Jig to our Miscellaneous category,
as well as to your builder page: Canobi's Homemade Tools. Your receipt:

Tank Cutting Jig by Canobi

tags: jig, rotary tool, cutting

[DIYer]

Thanks Canobi! We've added your Vacuum Degassing Chamber to our Miscellaneous category,
as well as to your builder page: Canobi's Homemade Tools. Your receipt:

Vacuum Degassing Chamber by Canobi

tags: gauge, pump, vacuum, tank

[Canobi]

Fine !
what kind of pump did you use ?

Hi Christophe


I used a 3CFM vacuum pump (the sort used for air cool systems). I did find it to be slightly under powered as pullung a completed vacuum can take up to 3 mins. It's not a problem for most silicone rubbers as the catalytic procress doesn't start till about 20mins after mixing. Resins are a different ball game with some only taking minutes before they start turning, or "gelling".

The pump itself is a good unit and can't really justify getting a replacement as they get more expensive the more CFM they can pull.

One workaround I'm looking into is a secondary chamber to use as an air dump for the main chamber. I could then just use the pump to reach the required negative pressures in a much shorter time.

As a bonus, most gas bottles can be used as the secondary since it only takes the right fittings to connect the two chambers and as such, no potentially dangerous modifications to the bottle are required.

[Ed ke6bnl]

so you put the product in the can and set the clear acrylic on top and pull a vacuum that helps to seal the plastic to the silicone

[Canobi]

so you put the product in the can and set the clear acrylic on top and pull a vacuum that helps to seal the plastic to the silicone

That is indeed correct good sir.

[DIYSwede]

Excellent illustrated writeup and clever use of limited resourses,
I just might borrow this entire concept for our (private) vacuum needs at work,
in particular for re-casting potted transformers when rebuilding vintage audio gear.

Thanks, and keep up the good work!
Cheers

[Canobi]

Thank you for the compliment

The only thing I'd change if I did it again would be to install the valve essembly into the lid and not the tank.

Good luck with your build, do share some pics too