How to Make a Vacuum Chamber

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

Fittings:

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 To Male Ball Valve 1/4" NPT

1/4" NPT Female To Male 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

Layout:

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!

Comments

[KellyCraig]

P.S. Thanks for the ible, and for reminding us we can get out of the box to solve a problem, build a VERY handy tool and save money doing it.

[KellyCraig]

I don't have an end mill, but do have an over-arm-pin-router. Like an end mill, it carves from the top, but has no problem with plunge cutting.

If the item being cut were on a lazy Susan and the router were supported over the project, like a pin router, a groove could be carved into the poly using a router and just spinning the acrylic.

Alternately, a center pin hole would allow one to spin the poly so a table mounted router accomplished the same thing.

Finally, and the easiest for most would be to just make a new router base that extended, say, twelve inches. Once the router was mounted, you would only need to measure from where the bit lands to the other end for the center pivot, then using that center pilot hole, you could spin the router to cut a circular groove.

[KellyCraig]

I used to make coffee tables that required oval, rectangular and other shapes of 3/8" tempered glass. I would have the glass company cut the shapes for me based off templates I made for them. It's not as expensive as one might think.

An obvious plus with using glass is, it will not be prone to cracking or crazing in reaction to the off gas of things like Cactus Juice used for stabilizing wood.

A peek at many stabilizing systems reveals some companies punch holes near the top of the can to install gauges and air ports, but the glass company may be able to drill holes in your glass to give you an alternative.

[The-Hoogzy]

Nice work mate.

Quick question and sorry if it has been answered... How deep did you cut your slot?

Cheers

[iamashwin99]

Can I use "rtv silicone sealant" instead of "silicone gasket maker" or something called acquarium sealent

[NakashV]

Hi,
Very nice and helpful video...u made.
I want to know...something more.
As i trying to make.this.
1.What type of steel basket and firbre thickness we should use.?
2.And blue...paste you use..whats that??

[georgew93]

Can you use the chamber to degas plaster of paris?

[YvonneK18]

Very nice Instructable, thanks for sharing! How much would you say you spent on your vacuum chamber?

[UNSEPARABLE TECHSCIENTIFICS]

EXCELLENT WORK MY FRIEND!!!!

VERY COOL!!!!!

: D

[1911S]

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?

[DiamondD6]

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???

[AntonyK6]

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.

[Kinnishian]

Top for those who want to make with fewer tools:

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.

[jimmie.c.boswell]

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.

[DejayRezme]

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.

I want to make stabilized wood and afaik both pressure and degassing is important for that.

[jimmie.c.boswell]

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.

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.

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.

[dud_hr]

instead of view ports, i used to put a cheap wide angle webcam inside the container i was to affraid to stand close to :)

seal the cable hole, add another 5m usb extension and watch from another room

[jimmie.c.boswell]

well if i were only using a vacuum, i would use all thick 1/4" 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.

[DejayRezme]

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.

[jimmie.c.boswell]

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.

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.

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.

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.

may my close to death failures and injuries, keep you safe.