Vacuum chamber and plastic for lid?

[Kram]

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.

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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?

 

[Tom O]

I’d go for the thicker just to put it out of mind

 

[gaz1]

i like quick easy access and get on with it so

but you can use a circle seal better note it uses thick steel better to use a circle framed just like the bubble tanks used when divers get the bends

if both are mixed together you will have quick access and easy to close and seal unit for both projects or more

just in case you dont know

 

[daedalusminos]

my plan is to over build it with 5mm

Jeez, are you sending it to the bottom of the ocean? As you state, only has to withstand 14PSI, I have a commercial 12l (I think) and it's not much more than a large saucepan.

The lid is toughened glass and quite thick with a soft silicone seal

 

[8ob]

If you were to cut the plastic base/ lid oversize you could cut a deep groove in them the diameter of the tube on the lathe, four bits of studding up the outside with wing nuts and use one end to access the chamber. Rubber o ring in the groove each end and no glue or solvents would be needed. Basically using the lid and base to clamp on the tube .Just thoughts

Bob

 

[julianf]

Could you laminate them together if you want to increase strength?

Of course a lamination may, somehow, weaken the job (things don't always work out how you expect!) but it's a consideration?

 

[DAPPH]

Put inch angle iron or 1/2 " square bars as a cross supports flat side to the Perspex underneath it in a hinged lid ?

 

[Pete.]

I have a couple of pieces of half inch thick perspex. Rectangles about 170x200mm. Personally if I was making a tube with 2 ends for a vacuum chamber I'd use delrin for the base and perspex for the lid. Delrin will withstand attack from most chemicals if you happen to have a spillage.

 

[gaz1]

Put inch angle iron or 1/2 " square bars as a cross supports flat side to the Perspex underneath it in a hinged lid ?

i was looking at this last night showing the door as reference

not forgetting these are pressure chambers

 

[DAPPH]

Myself doing KISS principle .

I'm hoping to use long light weight carpentry " F " clamps to hold both square cut ends plates , one or both of thick perspex / thick plexiglass on a tube , that has a cured run of silicone on the rims / edges ( Let it cure for 24 hrs .unmolested ) .
Put the kit inside , lightly clamp up & the vacuum will do the rest of the clamping at -14.7 PSI or greater . Have a gas ball valve to shut it off / release pressure if needed , making sure you have the flow the right way round so the vacuum pulls the ball onto the " O" ring inside the valve .
I'm be using a 10 mm Allen key in a drill chuck ... zip tied to the vascuum cylinder or steel woirk bench to give it a decent hands free vibration fot bringing out air bubbles whilst the vacuum is being attained . If it fails to work well in the time available I'll have a bigger cylinder ( old steamed put gas cylinder ) for a large vacuum reservoir to call on for a heavier quicker evacuation of the air in the chamber .
I might even use solvent welded joints on clean round waste for the flat fsce to put the silicon seals on . or round ribbed 400 or more mm rain drain pipe / gas or potable water piper to get a bigger diameter ... depends which arrives in my car boot first .

For those that don't know & have the ambition to experiment & accept damage or losses if things go pear shaped .
To get a cheap vacuum tap off .....the vacuum in a non turbo charge air inlet manifold is about 17 to 21 inches of mercury when the car engine is running in good condition at just over mid range RPM . A lot of manifolds have a removable screw plug on the manifold for checking the vacuum when tuning or fitting of a vacuum gauge .

 

[gaz1]

whilst the video uses 3mm steel he does use strengtheners

id make it bigger so that i could have a flat plate at the bottem for pulling down heated perpex

but its depth is handy for bigger pieces

id still prefer a front door for fast quick access to load and unload it and lock seal it quickly

 

[daedalusminos]

Don't make it too large or you'll be forever looking for fillers to reduce capacity in order to keep vac times down.

Here's my setup, I use it for degassing (mainly) polyurethane which has a pot life of approx 4 mins (need to fit mixing, degassing and mold fill in that time) then use the vac chamber for pressure fill.



For hard resins the general consensus is to pressure cure in order to shrink the bubbles, rubbers tend to be degassed and ambient cured (any pressure differential could lead to any remaining bubbles expanding/contracting when returned to ambient)

 

[Parm]

whilst the video uses 3mm steel he does use strengtheners

id make it bigger so that i could have a flat plate at the bottem for pulling down heated perpex

but its depth is handy for bigger pieces

id still prefer a front door for fast quick access to load and unload it and lock seal it quickly

You must be struggling tonite with you tube

Second time in the same thread you’ve posted the same video

 

[gaz1]

You must be struggling tonite with you tube

Second time in the same thread you’ve posted the same video

i couldnt eddit as was posted late at night compared to the day post

to really state was built out of 3mm instead of the 5mm the op wants to use
the inner strengthening is also 3mm as its built within the circle the structure stops it collapsing in on itself while in a vacuum

adding extra info by welding a flat plate gives other usages

 

[Kram]

Jeez, are you sending it to the bottom of the ocean? As you state, only has to withstand 14PSI, I have a commercial 12l (I think) and it's not much more than a large saucepan.

The lid is toughened glass and quite thick with a soft silicone seal

More for practical reasons.. cant easily chuck 1mm wall tube in the lathe and doesnt have much sealing surface area on the end, easier to weld if I do it that way.

Once the vacuum starts it should be self holding without any clips or hardware, and due to degassing/pouring timescales it needs to be quick for access.

Lamination, I was thinking about that, plus acrylic can be solvent glued. From what Ive seen I'd need to leave it a month to fully dry, atleast with ABS, solvent gluing is slow to harden with MEK. Any solvent left will weaken and cause cracking.

I have a couple of pieces of half inch thick perspex. Rectangles about 170x200mm. Personally if I was making a tube with 2 ends for a vacuum chamber I'd use delrin for the base and perspex for the lid. Delrin will withstand attack from most chemicals if you happen to have a spillage.

I have been thinking about that as I have a lump of 160mm delrin. I could use it both ends with the top having a shoulder for a small acrylic window, so smaller peice needed.

still prefer a front door for fast quick access to load and unload it and lock seal it quickly

A lid will have a bigger opening and quicker, suit the work better. I dont have space for a massive 5 gallon vac chamber which may suit that design better.

 

[DAPPH]

If the tube is vertical simply put a weight on the lid , on it's side perhaps a quick attach bungee arrangement ?

 

[Onoff]

I have a couple of pieces of half inch thick perspex. Rectangles about 170x200mm. Personally if I was making a tube with 2 ends for a vacuum chamber I'd use delrin for the base and perspex for the lid. Delrin will withstand attack from most chemicals if you happen to have a spillage.

@Kram was talking to me about maybe putting a shoulder on the bottom "plate" so no welding required, just a seal. Would it need epoxy or some other sealant? I've this piece of 197.3mm OD to give him when I next go down to see him. Could the bottom plate be done like that in Perspex? The CHS seam would need too be machined off inside...

 

[Pete.]

I'd just glue it on with RTV. Pull a vacuum in it to gas it out

 

[DAPPH]

@Kram was talking to me about maybe putting a shoulder on the bottom "plate" so no welding required, just a seal. Would it need epoxy or some other sealant? I've this piece of 197.3mm OD to give him when I next go down to see him. Could the bottom plate be done like that in Perspex? The CHS seam would need too be machined off inside...

View attachment 347924

View attachment 347925

OOOOh I'm jealous ! That's what I'm looking for too .

 

[DAPPH]

I'd just glue it on with RTV. Pull a vacuum in it to gas it out

I'd also run a radiused bead of white curing silicone round the top once I've inverted it on the viewing end , cover my viewing / top plate in sticky back plastic leaving pull off tags on the edges then put a weight on top thus making an effective top seal at the same time.