Vacuum Chamber WIP

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Established Member
14 Feb 2016
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Nr Cross Hands, South Wales
So as the title suggests I'm making myself a vacuum chamber to go with the new vacuum pump I bought a couple of weeks ago when ebay had a 10% off everything deal.

There are many options to buy ready made vacuum chambers on the internet but they 'aint cheap', and for one with a larger capacity they are way too expensive for me! Don't get me wrong, making this myself is not exactly cheap, but its atleast half the price of buying one. (It would be a lot cheaper to make a smaller one though!)

I like to future-proof myself where possible, so I wanted to maximize the capacity of my chamber. When researching how to make one it appears that I shouldn't go for any old cheap pan as the walls are so thin that it would collapse in on itself under a vacuum (especially for a larger one), so I needed to find myself a pressure cooker pot as they are a lot more sturdy with much thicker walls. The pot I went with was a 20L capacity one I found on Amazon at the below link... ... UTF8&psc=1

And dont be fooled by the price, it seems that they are sold out since I bought it, I paid £38 for it (i had a £20 amazon voucher which needed using so that's why i went with Amazon).

The next step is the lid. I wanted to get a clear lid to enable me to inspect inside while its working under a vacuum, so I decided to go with Perpex. Again, if you go for material that's too thin then it may collapse in on itself or even shatter/explode. I was originally looking for 20mm thick perspex in order to go get something much thicker that I would need, but 20mm thick perspex was too expensive with not many suppliers about, so I decided to go for 15mm thick which should still (hopefully) be more thickness/strength than I’ll need. I waited until I received this pressure cooker pot before ordering the perspex to ensure that I had something big enough. I went with the below perspex from ebay... ... 2749.l2649

It worked out cheaper to get a 600x400mm section than it was to get something that was 350x350mm which I need! So it was £31 for the perspex. (Total so far approx. £69)

By the way, this is the vacuum pump I bought... ... 2749.l2649


The lid... so the first thing to do was to cut the sheet of Perspex I got into a rough circle on the bandsaw. I chose to make the clean circle using a very quick/easy jig on the router table. First of all I cut a 6mm hole in the centre, which is a lot less that I’ll need when attaching the plumbing fitting. I had a scrap piece of MDF with a couple of scrap blocks of ply a little thicker than the 15mm thick Perspex. I stuck a 6mm dowell into the scrap wood and clamped this in place over the blocks to either side of the router table. I could then gradually turn the Perspex by hand while the router is spinning pretty fast (I used a cheap 1/2” four flute spiral bit mean for milling machines, but seems to work well in the router table).


The finish to the cut edge of perspex turned out surprisingly well with no chip etc. I’ve worked with thinner Perspex before for some of the early picture frames I’ve made, and that chips a lot and is quite brittle, but this is my first time working with thicker Perspex. I’m guessing the faster speed of the router bit helped.

Next step was to cut a circular groove into the lid around where the rim of the pressure cooker pot meets the lid. This is to provide a channel for silicone sealant to help create as airtight a seal as possible. So u used the same simple jig on the router table, but measured carefully to get the location correct. I did this by locating the jig in the correct position from the router bit (without the Perspex in place, as the protective film is still there which stops being able to see through it), then marking the scraps of ply on the router table with a pencil and then get the Perspex in place and just hope that my pencil marks/measurements are correct!

Note that I purposely clamped the Perspex down clear of the height adjustment feature on my Trend router table. This is to enable me to raise the router bit in shallow passes. Note that the manufacturer does not recommend doing this while the bit is spinning (but I was very careful!). I did this using the same spiral bit to relieve as much of the material as possible before using a wider 3/4” straight bit for the finished width. Finished depth was 5mm.




The next step is the silicone. I’ve seen someone recommend putting a thinner layer of silicone to the bottom half of the groove and leaving that dry before putting more in and placing the pot on top (ensuring that the pot is in contact with silicone rather than in contact with the perspex to the base of the groove). But I wanted to try and dye the silicone, because why not, so I didn’t trust myself to be able to mix exactly the same colour/consistency twice, so I decided to do it all in one hit. So I bought some clear silicone and just mixed in some really cheap dry I bought from China for resin (which I’ve not tried out until now). Surprisingly the dye mixes with the silicone quite easily, but it’s a messy job so rubber gloves on! I have seen somewhere that you can mix this with cornflour to make it more opaque and less messy to use (try googling proto-putty), but I think it looses its adhesive qualities somewhat when doing this and I need it to stick to the groove in the lid to try to ensure a good seal. But the colour turned out alright.

Before the silicone came anywhere near the Perspex I used Vaseline to lube up the rim (haha) of the pot. (The girl in B&M bargains did look at me funny only buying silicone and Vaseline).


I then placed the silicone into the groove as best as I could and used a vazzed-up lollipop stick to try to level off the silicone clean to the surface. To ensure that the rim of the pot doesn’t contact the Perspex I used some scraps the correct thickness to support the handles of the pot and suspend it above the rim just enough, but this wasn’t perfect as I should have made use that the scraps of wood were at the perfect thickness! It will hopefully still be ok, but time will tell once I test it for the first time once it’s finished, but it does feel like a pretty good seal though so fingers crossed!






And that’s where I’m at currently. I have ordered all of the plumbing bits’n’bobs, so fingers crossed they are all what I need. I could probably get the stuff cheaper from China, but I’m impatient and wanted them sooner so ordered from the uk. Is surprisingly all adds up though, so the order list of plumbing bits came to £52!!! So the hopefully finished total spend so far is approx. £121 - but it’s well over £200 to buy one with a comparable capacity.




Also I know 20L will be overkill for what I use it for to begin with, and I also know it will take longer to reach a decent vacuum, but I will now have the capacity to stabilise bigger pieces of wood. I do also have a spare 250x400mm piece of the perspex, so maybe in future if I ever feel the need for a smaller chamber then i can use that. As I said, if you make a smaller chamber in the first place then the cost of parts should work out a lot cheaper (except for the plumbing bits).
It looks an ambitious and well made project... But excuse my ignorance - what is it for please?
If you put some non-porous items in the chamber, i.e blocks of metal, you will effectively reduce the chamber volume.
AndyT":14ezjjk6 said:
It looks an ambitious and well made project... But excuse my ignorance - what is it for please?
Hi Andy, it’s for stabilising bits of wood with a low viscosity heat activated resin. So any wood that’s weak/rotten or too light, or you just want to add density, you go through the stabilising process and hey presto. You ensure that the wood is fully dried of all moisture (I.e. in a toaster oven on a low heat), and there’s a 2 part resin (look up cactus juice resin) which you submerge your wood blank into which then goes into the chamber. Then when under a vacuum your pump pulls all of the air present within the wood which then gets replaced with the resin. This type of resin stays liquid until you oven it, so once you’re happy that’s the wood has absorbed as much as it can (I.e. no more bubbles of air) you then wrap your wood in foil and set in the oven at a specific temperature and the resin hardens. This can sometimes more than double the density of the wood in cases like when severely spalted, and it also stabilises it.
Sawdust=manglitter said:
Before the silicone came anywhere near the Perspex I used Vaseline to lube up the rim (haha) of the pot. (The girl in B&M bargains did look at me funny only buying silicone and Vaseline).

You have to go back and make a follow up purchase - same cashier. Maybe some large cucumbers and a first aid kit!
So I’ve finally receive all of the parts I needed, so I’ve finally been able to finish putting it all together.

The vacuum pump didn’t come with a hose connector at the pump, and turns out that the thread type was some obscure SAE something or other, so I needed to order the fitting directly from the manufacturer of the pump, which meant it had to come from China. Anyway, I won’t count that fitting as part of the overall cost as some other manufacturers of vacuum pumps will probably come with the fitting.

Having received the originally ordered plumbing bits it turned out that I could have done with a few other plumbing fittings, so I ordered the below. The 90 degree elbow probably isn’t necessary, but it sounds like once you finish vacuuming your resin and blanks if you open the valve to let in air too quicky the burst of air directly downwards can cause the resin to blow all over the place marking a mess, so with the elbow it directs the air to the sides first.


I waited until I received the first hose fitting before ordering the actual hose to make 100% sure that I got the right size. So I decided to buy a clear unreinforced pvc hose which had an internal diameter of 6mm and external diameter of 12mm. The very thick walls is probably excessive, but wanted to make sure that it wouldn’t collapse in on itself under vacuum, which some people say happen with the standard hose that comes with some cheap pumps. ... k9crQ_1C7w

Anyway, I drilled the required 11.8mm diameter holes into the perspex ready for tapping, but unfortunately I did get a bit of a blowout to the top face where I drilled the original 6mm hole at the centre! It only chipped out around 3mm in two locations, so there was still plenty of thickness left so I just filled that back up with epoxy and it’s been fine after tapping. Just be aware of this risk if you ever drill thick Perspex. Once both holes were drilled (and one repaired) I then tapped both holes.

I’ve finally just fitted it all together. With plenty of the gas ptfe tape, but not too much, I got everything together. Although probably not necessary I also added a couple of o-rings to the bulkhead fitting into the Perspex for luck.



Just tried it for the first time and it seems to work great :D. Have left a vacuum in the chamber overnight to see how well it holds up, so we shall see in the morning. So total investment, including some bits which are probably not necessary, is around £128. It’s a good chunk cheaper than some you can buy of a comparable size, and I’d like to think it’s better quality or at least heavier duty than the ones you can buy, so all in all it was worth doing (he says while touching wood).

I had to wait until payday before I could order the cactus juice resin, so that will hopefully get delivered on Tuesday. Got that resin from Metal Clay Ltd, which seems to be the only UK source of that stabilising resin that I can find. Will keep you posted with my successful or failed experiments :D
So I’ve done some playing with the stabilising, and it’s been working great!

So after a couple of experiments the OH wanted me to make her a new gear stick knob for her car, only she wanted it to be purple. So I bought some Alumilite dyes which work with cactus juice, so I mixed the violet dye with some blue and red to try to get it as purple as I can (I am colourblind by the way!). Anyway, I used some punky oak burr and this blank was the result (once the sides were cleaned up)...



So if you hadn’t guessed it the most dyed areas were the punky soft rotten areas of the oak burr, but once out of the oven it was rock solid! The blank almost doubled in weight after being stabilised too [GRINNING FACE WITH SMILING EYES]. The area without as much dye was the densest area of wood, which I think is why it didn’t take up any colour, but I also think it may be that the oven was a bit too hot when curing the resin which caused some ‘bleed out’, but will experiment with the temperature in future. But I think the contrast between the wood colours and the dyed areas looks quite nice.

So I’ve now also turned the gear stick knob and the stabilised blank turned well, but was dustier than normal wood, but I think finishes quite well...





Anyways, the wood stabilising opens up doors for the future.

Having now used the vacuum chamber a couple of times I have also now determined that 15mm thick Perspex is not strong enough. Under vacuum the lid deflects by around 6mm at the centre and there is what appears to be sporadic stress cracking to the inside face of the lid, so before doing any more I’m going to wait until i have the cash to buy some 25mm thick Perspex. So far the cheapest I’ve found is around £50 for a 400x400mm square of Perspex, so if anyone knows of a cheap source of 25mm thick Perspex then I’d really appreciate it.
I have read online that polycarbonate is preferred over perspex for vacuum chambers.
I would look at using a steel lid - maybe the one from the pressure cooker? And fitting a small sight glass to that.
Something like this
With a torch you should still be able to see whats going on in there. We have an old airless spray canister at work I've been eyeing up for something similar! Great results with the gearknob, thats really impressive.
without knowing the costs involved... if you really want a clear lid use two layers of 15 mm sandwiched around a layer of clear silicone. Same way car windscreens and glass side panels on stairs are made.
2 x 10 mm would be cheaper but still a lot stronger than 1 x 15mm.

Very complicated project, and I did wonder "why", untill I saw the finished product. Thats a spectacular way of using otherwise scrap wood. =D> =D>
or... another thought on the lid. Silicone an upright rib across your existing, same way steel is reinforced
Nice result from the vacuum chamber and the gear knob looks fantastic, well done. =D> =D>
On the new lid if you replace the T fitting you have now with a cross or 4 way fitting, the pressure gauge can be put on it and then you only have 1 hole in the lid.


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