I will be trying to build one this week.
For the lid, Chinese vac chambers seem to be 12mm acrylic, like this but much smaller.
VEVOR 1.5 Gallon Vacuum Chamber, Vacuum Degassing Chamber Glass Lid Stainless Steel Degassing Chamber Silicones for Gas Extraction and Protect Food : Amazon.co.uk: Business, Industry & ScienceBuy VEVOR 1.5 Gallon Vacuum Chamber, Vacuum Degassing Chamber Glass Lid Stainless Steel Degassing Chamber Silicones for Gas Extraction and Protect Food at Amazon UK. Free delivery on eligible orders.www.amazon.co.uk
Theres a plastic shop near me that has small offcuts of 12-20mm thick acrylic and polycarbonate sheet. I'll try to get some tomorrow, but which would be better?
Acrylic can be brittle?
Polycarbonate is greatly weakened by any solvents, unsure if acrylic is degraded as much?
I may use it for epoxy/silicone resins, plaster etc.. if that makes a difference.
For the chamber, my plan is to over build it with 5mm wall/base so that its not springy. I have not tried to weld anything like this. Its a relatively low volume at a maximum of -1bar, it should be safe enough?
Pete if you have two 1" thick rounds of Delrin perhaps sink a recessed hole in the top one and insert the thick Perspex disc on an "O" ring in a shallow groove in the Delrin the top , mastic seal the top ring via a small groove to the top of the cylinder. Putting cling film over the mastic bead to stop it gluing it to the cylinder . That way it's easily taken apart & is reuseable .Mine will have a delrin base secured with mastic, perpsex top with probably an o-ring seal.
A decent vacuum ( Henry ? ) cleaner might also be OK to de-gas the investment slurry in the vacuum chamber quite quickly , especially if the table it sits on has a vibrator device attached to it . Once the enlarged bubbles are in motion they will rise to the top , you don't need to boil the water off under vacuum . You just need to get the gas bubbles moving away from the object being cast over .Slow(ish) but reliable is one of the Edward's Vacuum pumps. I have used mine for degassing wine, mostly. They will create a high vacuum.
To some, 14psi seems not a lot - but remember, that is the pressure and it’s the force that is important if it implodes.
Laboratory desiccators were always covered with a cloth, when evacuated.
Never seen the evacuated-can experiment on a pressure can? Or inverting a beer can, filled with steam at close to boiling point, into a sink/basin of water? If you haven’t, you clearly missed out on your science lessons.
The earliest steam engines operated at 14psi maximum. They were powerful enough to drive some large pumps.