I had a need for a particular project (mold for a 3d printed logo ) and several projects in the future where I needed to degass silicone as well as remove air from investment for casting in metal.

I currently have very little real estate in my garage so I needed a custom solution, also it didn't hurt that this project saved me a couple bucks along the way from purchasing a commercial unit.

Let's build a Vacuum Chamber!!

Step 1: Supplies for the Chamber of Secrets

To get started with this build you will need the following items

Cooking Pot:

I purchased the cooking pot from Bed Bath and Beyond. I was looking for a tall pot with a diameter that wasn't larger than 8" inches. The pot was made for steaming asparagus so it was tall and had the diameter I needed.

Asparagus pot

Polycarbonate Or Acrylic Sheet:

I stopped by my local plastic supplier and picked up a piece of 9" x 9" x 1/2" polycarbonate sheet. I decided to spend the extra dinero on polycarbonate as it's less prone to cracking and is much stronger than acrylic.

Silicone RTV Gasket Maker:

To create a seal for the lid I picked up some silicone gasket maker from the automotive store. The silicone RTV comes in different colors and I decided to go with the blue for personal preference.

Permatex Multipurpose RTV Silicone Gasket Maker


All the fittings such as the vacuum gauge and bulk head were purchased online. You can find equivalent parts at your local hardware store but I took the easy route after driving all day finding the above ;-)

1X 2-1/2" Oil Filled Vacuum Gauge -OEM - 1/4" NPT - Lower Mount - -30 Hg to 0

2X Female Ball Valve 1/4" NPT

1/4" NPT Female Ball Valve

2X Bulkhead 1/4" NPT

1/4" NPT Bulkhead

1X Branch Tee 1/4"NPT Female

Tee Fitting

Step 2: Layout for Your Day Out


I traced the outside of the pot as a reference as the pot was not completely cylindrical.

I then use a center finder and mark a line on two opposite sides of each other to find the center of my material. In my case this was extremely easy to achieve as my polycarbonate was completely square.

I then locate my compass at the point in which the two lines intersect and draw a circle for the inter diameter to give me an accurate circle to locate my borders for my endmill. I mark a line for the outer diameter as well and try to space the circle about a 1/4" from my reference outline of the pot (You may need to increase this number if your pot is really oval), This ends up giving me a border of about 1/2" around the reference outline of the pot.

Step 3: Subtractive Manufacturing of Goodness

I head to my mill to start the drilling and cutting operations.

I use a scrap piece of wood and set my piece of polycarbonate on top

I drill a hole in the center with a drill bit about .30 thousandth of an inch smaller than the wood screw I intend to use.

I then screw the wood screw in and tighten everything in place

I drill a pilot hole in the center of my outline I drew earlier and follow with the same diameter as my endmill which is 5/8".

Please note that most end mills do not have the capability to center cut and do not like to be plunged straight down. This is why we drill the relief hole.

I insert the end mill into my mill and take a depth of cut of about 30 to 50 thousandth of an inch per pass. This is about the thickness of about 3 to 4 business cards.

Once the slot is complete I move the end mill half an inch from the slot to round the sides of the top (I used an endmill with center cutting which allowed me to plunge if you watch the video.

This part is strictly for esthetics and not necessary if you prefer a square top.

I then drill a pilot hole with an 1/8" drill bit for all my fittings,these can be located anywhere you prefer.

I switch the drill bit to a .266 (H) drill bit and drill the remaining holes to the clearance diameter of my fittings.

And were done with the milling and drilling.

Step 4: Seal the Deal With Some Silicone

I laser cut a squeegee out of acrylic to apply the silicone to the proper height to prevent the pot from being pushed down to far (you could easily make a squeegee without a laser)

I apply the silicon RTV and make sure that I apply a liberal amount. Once applied I then use the laser cut piece to set the height of the 1st layer of silicone.

I apply my second layer once the silicone has completely cured and smooth the top with a razor blade.

I apply some vaseline as a release agent as this is adhesive based silicone and put the top of the pot on the silicone we just applied.

Once cured I then pull the top off and remove the protective masking on the front and the back of the polycarbonate.

And were ready for the next step!

Step 5: A Fitting Day to Make Everything Stay

Since our top is complete it's now time to add the all the fittings to complete the chamber.

I added two ¼” npt bulk heads with neoprene washers to extend the fittings further down as my lid was a 1/2" of an inch thick.

Please note I add teflon tape to any connection with a thread and tighten firmly.

I grab the vacuum gauge and attach it to the furthest bulk head from the center.

I then use a tee fitting to attach two ¼” npt ball valves

I attach both ¼” npt ball valves to the tee fitting and tighten till I firmly align them with the knob facing the top.

I then use a quick connect fitting to easily attach and detach my vacuum pump

And were done with the Vacuum Chamber!

Side note: I decided to add a custom vinyl cut sticker as I felt the pot needed a little more style.

Step 6: Mold My Heart and Cast Me Away

Now it’s time to test the Vacuum Chamber!

Pouring the silicone mold:

I grab my part A and part B platinum silicone and mix vigorously. Once completely mixed I put the container in the chamber and pull my vacuum.

I’m using a 7 CFM vacuum pump for my chamber but you can go with a much lower cfm unit.

Once the vacuum pump is on I sit back and watch the silicone grow. :)

Please note silicone expands two to three times it’s volume so it’s ok to release some vacuum to prevent the silicone from spilling over the cup and into the container.

Once the vacuum has completely degassed the silicone I pour the silicone into a mold box with a 3D printed logo I made for my friend Nick Ferry who has a youtube channel here.

Once the silicone is completely cured I use 91% isopropyl alcohol to release the hot glue surrounding my mold box.I then pull the 3d print out of the mold and the mold is complete

Casting the resin piece:

I grab some talcum powder and apply it to my mold. This causes the resin to absorb finer details and reduces bubbles in the resin especially on corners.

I pour some urethane resin into the mold and move the resin around.

Once cured I pull the resin part out slowly from the mold, the remaining flashing can be removed with a finger nail or exacto knife,

That’s it finished bubble free resin copy!

<p>I love this video. What kind of drill bit was being used to do the milling? What was that laser thing he was cutting with? How do you measure absolute zero for determining absolute vacuum?</p>
<p>Can we use the thickness of polycarbonate sheet other than that what you mentioned?If yes,then to what extent of thickness we can use???</p>
<p>Excellent. One of the best videos I have seen , good use of time lapse(speeded up) so we dont have to wait through the boring stuff. Great job.</p>
<p>Top for those who want to make with fewer tools:<br><br>Start with a pressure-cooker, as they have flanges and gaskets typical for vacuum. It will be harder or impossible to incorporate a viewing port, though. </p>
<p>actually i use a large vacuum desiccator, that i bought on ebay for this. the viewing port is at all angles, since it is made of thick, borosilicate glass. and the valve, is already included in the unit. but as far as this goes, i guess i could also use my large bell jar.</p>
<p>Thanks for the instructable! I've been wondering if you could use a pressure cooker to make both a vacuum and pressure chamber at the same time - just switching if you have a vacuum pump that can also pressurize.</p><p>I want to make stabilized wood and afaik both pressure and degassing is important for that.</p>
<p>well it depends on how much pressure, you are talking about. pressure cookers, are limited to under 30 psi max. and many makes, could be even be much less. using a pressure cooker as a high pressure chamber, could result in a dangerous explosive rupture condition if the pressure relief valve is defeated. high barometric pressure chambers, are a very special design. and even then, usually have some sort of over pressure relief limit valve or rupture disk.</p><p>but a good pressure cooker, would most definitely handle a 10 to the -3 vacuum of an good vacuum pump. but not every vacuum pump, can handle being a compressor also. 10 to the -3, is about the lowest limit of vacuum for a really good mechanical pump.</p><p>and to make a view port, for both a vacuum and pressure chamber would be a very special requirement. would not recommend a view port for a high pressure chamber at or above 20psi. requiring a very special and expensive, quarts and polycarbonate thick multi-layer composite.</p>
<p>instead of view ports, i used to put a cheap wide angle webcam inside the container i was to affraid to stand close to :)</p><p>seal the cable hole, add another 5m usb extension and watch from another room</p>
<p>well if i were only using a vacuum, i would use all thick 1/4&quot; wall polycarbonate tube or plates to make an octagon if i wanted viewability. even considered at one time, using a propane tank. but my welding abilities, are not that advanced.</p>
<p>Thanks! I see it's gonna be a hot mess when it explodes lol. Yeah by now I've seen an instructable using a pressure paint tank as well. For pressure you don't need a window either I guess. I've seen another video using a piece of thick wall PVC pipe but I guess that is really dangerous. </p>
<p>as a safety precaution, check the pressure certification on paint tanks. so that you do not exceed, it's maximum pressure. the airless paint tanks, use a mechanical screw rather than pressure.</p><p>most high pressure tanks, are x-rayed for internal cracks weaknesses. pvc pipe is not normally, x-rayed for these kind of defects. i believe it is the blue pvc, that can handle over 100psi. but then it, can't handle excessive heat. since it is usually compressing cold water around 55*F. heat is removed in flow, below the frost line heat sink. so that it comes out much colder than 55*F.</p><p>i, have used clear thick walled polycarbonate for high vacuum. but it cannot take the stress, of too much internal pressure. and a vacuum outgassing, will eventually weaken it to unusable. going from 15psi to 0, is a lot different than going from 15psi to even 45psi pressure.</p><p>what is your target pressure, you are aiming for. so that i, may be of more help in this regards. any thing that can handle over 45psi, will most likely handle down to to 0 vacuum. the weakest link in accessible high pressure enclosures, are the bolt down flanges and gaskets.</p><p>may my close to death failures and injuries, keep you safe.</p>
<p>Thanks, but I've looked into stabilizing wood some more and you don't really need a pressure pot for this - you simply suck out all the air and water out of the wood in the vacuum pot while the wood is submerged in resin and then let normal air pressure do the job of pushing the resin into the wood. So while some do use a pressure pot it's not really needed. Here is a good pdf about this for anyone interested: http://azwoodturners.org/pages/tips/Vacuum_Stabilizing.pdf</p><p>So TLDR; I can &quot;safely&quot; abandon this idea of combining both ;)</p>
<p>the more extreme the condition, the greater is the danger.</p><p>vacuum implodes, pressure explodes, so they are opposites and danger increases with size. so you, want to avoid materials that can shatter.</p><p>and for safety sake it is best, to not exceed a length two times the diameter or exceed 80% of it's rating.</p><p>i am familiar with the vacuum technique, which sounds similar to varnishing transformers to prevent them from singing.</p><p>and it would be easier to convert a pressure tank, as a vacuum tank also.</p>
<p>Not sure about PVC pipe it would depend upon the Class, but PE 100 pipe (used for water/sewage pumping) could be safe to use depending on the rating. e.g. SDR11 PE 100 is rated to 16barg (232 PSI) and to water vapour conditions. This should certainly handle a normal vacuum pump. Small off cuts could probably be picked up for very little from contractors.</p>
<p>Thanks. I guess it's a rather stupid idea to combine the two. It makes more sense to have both separate.</p>
<p>oh and i want to add, any tank that can contain 250 to 500 psi being able to handle 0 psi, is not stupid. but to design a tank to contain 0psi to 250 and over psi is the opposite way to look at it. the highest vacuum pulled by men, is 10 to the -15 but not absolute zero. and outer space, is only a variable average of about 10 to the -12 to -14. it is, easier to build a vacuum chamber safely than it is to build a high pressure chamber.</p>
<p>i just wanted to, reveal the dangers involved. i am not saying it, can't be done properly. a compressor tank, could be modified to accomplish both. and a little bit more involved, than using a pressure cooker. a compressor tank, needs to be above your targeted highest pressure safely. and would most definitely handle less than 10 to the -3 vacuum. safety is your biggest concern, at these extreme opposing conditions. i have a small compressor tank, 24&quot; x 12&quot; where i can do both from 500psi, to 10 to the -3rd. though the inside is not accessible. i, have seen one pressure cooker explode. thankfully i, was not near it when it did cause it was not pretty. at double atmospheric pressure 30psi, at ambient room temp the internal temp will be initially near 300*F without any significant time for heat dissipation. so you must compensate, for the increase in heat load. </p>
I recommend considering a seperate device for vacuums as for pressure. It may well be possible, but you should probably choose a vessel rated to 20+psi higher pressure than you would normally. The extra range of going from high pressure to vaccum will increase the range of the stress cycling.<br>Moreover, the types of fittings and gaskets youll add may well change the strength of the vessel.<br><br>There are many ways it can be done, but in terms of reusing cheap mass market things, its harder. <br><br>You also will have to always remember to turn on your over pressure fittings when going from vacuum to pressure, where the vacuum would probably require the overpressure closed. Designing a pressure saftey requirement to be flawlessly operated by a human is bad design
<p>Thanks, I read some more about this and it turns out you don't really need pressure for wood stabilizing anyways: Here is a good pdf about this for anyone interested: <a href="http://azwoodturners.org/pages/tips/Vacuum_Stabilizing.pdf" rel="nofollow"> http://azwoodturners.org/pages/tips/Vacuum_Stabil...</a></p><p>I wonder if you could do the same for casting as well - put the pour into a vacuum chamber to pull out any trapped bubbles and then crush the remaining ones with letting air pressure back in.</p>
<p>Hi DejayRezme, </p><p>Thank you! </p><p>I HIGHLY recommend steering clear from building your own pressure pot. I've heard many horror stories with cheaper commercial units let a lone building your own. I would save your money on that one and buy a good quality unit.</p>
<p>Thanks :) </p>
<p>You can-sortof. It's what I use, but the gaskets will all leak, especially the little &quot;won't open when pressurized&quot; cylinder near the handle. I just took the rocker off and hooked an air-powered-vacuum-pump (mine was harbor freight, but similar to this one <a href="http://amzn.to/1OcijhR">http://amzn.to/1OcijhR</a>) to the rocker nipple. I think I'll make a lexan top for it though... </p>
<p>Great suggestion!</p><p>Just as you stated though you wouldn't be able to see inside which is important to see if the silicone has completed degassed. You can easily make this with just a piece of plastic with rubber cut out in a donut shape, the vacuum will keep the seal by adjusting the differences in height of the lip via the rubber. </p><p>I have a tendency to focus on aesthetics as well and wanted my chamber to look like a commercial unit :) </p>
My donut shape, do you mean a ring with outer and inner radius? A donut shape makes me think of a torus and then I am confused what you mean. <br><br>Your chamber absolutely looks wonderful. Eventually I will probably update my pressure cooker pot to have a viewing chamber. It worked well enough without seeing the silicone, but would be much better to see it. However I spent 10 ish hours getting parts and troubleshooting (mostly getting parts) for my pressure cooker pot so I have to wait till I have more uses for it before justifying modd'ing it :). ....Or do I? Sometimes fun to just make tools :D. <br><br>thanks again.
<p>You're correct a ring with an inner and outer radius. I feel you on that! When a project is complete and works great it's hard to go back and make changes.</p><p>No problem thank you!</p>
<p>Thanks for the useful instructable; however, the links (at it were) aren't usable because they're truncated and no URLs are coded - making this body of work an unnecessary exercise in Googling for the desired components. Is there any way you could remedy that for us? I for one would be most grateful.</p>
<p>Sorry about that! instructables most of stripped the links since I didn't use hyperlinks. All should be corrected now and thanks for the feedback! :)</p>
<p>Foam Air Retrieval Tunnel.... or FART for short... </p>
Well done, professional job, and I picked up useful tips. Thanks, Miguel Geneva Switzerland
<p>Good job!</p><p>I plan to make a cover for my vacuum chamber too. I plan to use it for high vacuum. So a question is how to choose a right silicone for a gasket to be used for high vacuum?</p><p>A gasket thickness matters too I think?</p><p>And how to calculate a correct thickness of a glass?</p><p>A chamber I have is taken from ELARA 11 Class B Autoclave.</p>
<p>1. Polycarbonate is much stronger than acrylic, so I strongly recommend using it least a high vacuum implode the lid! (PS: PC deteriorates over time and under UV.)</p><p>2. In this case, the color of RTV sealant doesn't matter. Blue is usable under water (after curing), and makes thicker, more compressible gaskets. Red is high temperature (hottest parts on an automobile engine), and black is extra resistant to hydrocarbons and some solvents.</p>
<p>Could one simply use a thicker piece of poly carb? or laminate two pieces?</p><p>sweet build if you need one!</p>
<p>I did use polycarbonate! lol I also don't plan on using this under the sun but thank you for the feedback!</p><p>You're correct on the colors but side note they also do offer different colors with the same specifications such as clear, gray and black.</p>
<p>i can honestly say this Instructable sucks big time!</p>
<p>That's my joke!! lol </p>
<p>@Machine Right: I apologise, I found it in the street and thought no one wanted it. I'll post it back to you. It's still in good nick, I've only used it the once.</p>
<p>Real good stuff! Congrat'</p>
<p>thank you! well done ?</p>
<p>Great, easy and work </p>
<p>Thank you pol514!</p>
<p>Pretty cool. Very precisely done.</p>
<p>Thank you John!!</p>
<p>Well Done! Well thought-through... Audio good....Photography very good...Easy to follow with a little shop experience....and truly creative.</p>
<p>Thank you Abe I really appreciate the feedback!! :) </p>
<p>You might want to approximate the hoop stress in your chamber (sigma=P*d/2t), where P is pressure difference, d is mean diameter of the cylinder and t is the wall thickness. Compare this with the ultimate tensile strength of the material (looks like SS?). I'd aim for a FOS&gt;=2.</p><p>Keep us updated if your chamber implodes.</p>
<p>Two months going on three and still going strong. This is stainless steel the wall thickness is plenty for this application and I can pull about 29.7 at my current elevation. I've left the pot accidentally at 29.7 for over 4 days a couple of times and no leaks, no implosions and works great!</p>
<p>To get rid of that static charge wipe everything with a used dryer sheet. Works wonders on glasses and face shields also. New dryer sheets have too much fabric softener on them and cause streaking. Don't ask me how I know......</p>
<p>Thanks for the great tip Mark!</p>
<p>I didn't even think you could make these at home. Perhaps a 2nd 'ibble using tools the more average guy would have? Circle cutting with a router instead? (not sure if it'd work on polycarb though). Pro job though.</p>

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