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Auberon

My Spray-booth Building Journey

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Note that I am in no way an expert.  I just did a little reading and combined it with things I've heard. Also I didn't really proofread.  There may be typos.

 

So I bought an airbrush long long ago.  I don't have it yet, but this has given me plenty of time to come up with a work area for when it finally arrives.  Basically I have two options - buy a booth or build one.  After looking at which I could purchase off of Amazon and a few other sites, I decided it would be more fun to build one.  Looking at the materials, it also appeared to be cost effective as well.  But then again, it depends on how big you go and how much power you want.

 

Step one - the dust trap. 


 

Spoiler

 

Because I have limited options for venting my overspray outside, I need some type of trap for the atomized paint dust that I will be creating.  For this I went with a bucket dust trap using the basic plans you can find online, modified slightly for what was available locally.  Buckets by their nature lack holes, so I used a 1 1/4 inch hole saw to make a series of 12 holes around the upper rim.  As you can see, I went for a 4" pipe.  It's the standard size for dryers, which seems to be what the commercial booths I saw for sale use for their flexible tubing.

 

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I made a series of cuts around the base of the pipe and then bent half of them up in an alternating fashion.  Thus the air enters at the bottom and exits through the holes I drilled at the top after passing through the filter.

 

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Speaking of which, the filtration.  To keep costs down I used the cheap blue filters as filler and then covered the holes with a higher quality carbon filter.  In fact I think that filter doubled the cost of my dust trap.

 

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And last the lid, with a hole cut in it for the pipe.  After this I put a ring of clear caulk around the pipe to force all of the air to exit through the holes.  It may not be strictly necessary as any dust that manages to escape would still have to pass through a foot of cheap filter, but I paid for the expensive filter so its going to have to put some effort in.

 

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Step two - the spray booth. 

 

Spoiler

 

If I had just gone with a commercial one I wouldn't by typing this, so you can guess what's coming.  The booth itself is a 64qt clear container.  I believe that is pretty close in area to what the portable booths fold out to, but I'd need to double check that.  I cut a hole in the back and inserted a collar that I can attach to my air moving system of choice.  Clear allows light in so it is what I would recommend, though I suppose you could use an opaque container with the proper lighting.

 

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For an unplanned bonus, I had a leftover section of carbon filter left over from making my dust trap.  It was the perfect size to cover the bottom of my container so in it went.

 

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What I had originally planned to use was a regular furnace filter.  There was nothing in the store that was sized for a 64qt container (I can't imagine why), so I purchased a larger one and made it fit.

 

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Why larger you ask? Well it turns out you don't want your filter to directly cover the exhaust pipe (bonus filter above notwithstanding) because it will force all of the air to go through that part of the filter and leave the rest unused.  Instead there should be an airspace to allow the air to circulate behind it and pull across the entire filter.  I accomplished this by snipping the cardboard frame and bending it over.  This creates a 1" gap for airflow.  In a properly built booth the gap is there by design and you would simply insert your properly sized filter.  Since this is not properly sized it should also have a strip of tape run around the edge, which will hold the filter in place and make sure air doesn't make its way around the filter rather than through it.

 

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So we have a hole, we have a filter, so next we need light.  While I suppose the choice back in the day would have been a fluorescent tube, in this day and age we have LED strips.  I purchased a six-pack of the daylight variety and used some scotch tape to see how they would work.  They shine right through the clear plastic and should give a nice even light for whatever I'm working with. And yeah, since I'm into doubling the costs the light strips cost more than the container/collar/filter put together. But they can be repurposed if needed so they are a better long term investment than a container with a hole in the bottom.

 

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A mini for scale.

 

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Step three - more power

 

Spoiler

 

Dust trap check. Booth check. Now I just need some way to move the air.  The designs I saw tended to use bathroom fans.  I suppose the cheap ones are cheap, but they also don't move much air.  The expensive ones have a better cfm rating, but they also cost as much as a portable booth, so at that point you may as well just buy the commercial booth.  Next I looked at booster fans.  They actually appear to be a better choice than bathroom fans as they are cheaper and move more air.  They just can't attach directly to the back of your homemade booth, so you have to use a collar like I did above.  I almost stopped there, but after looking at the more expensive booths I realized there had to be another level beyond the booster fans.  This led me into hydroponics and inline fans/blowers.  They were a step up from the boosters in price and performance, but safety first.

 

Now when it comes to inline fans there are a couple of things to consider.  One is size.  I learned long ago with 80mm vs 120mm case fans that larger fans can move just as much air at a lower, quieter speed than the smaller fans.  At the same time I don't want to move too much air so I can't go super size.  The best thing to do would be to try it before buying, but since that's not going to happen the next best option is a variable speed controller.  Ideally whatever I purchase can run at the quieter 50% speed, but if necessary I can crank it up to get airflow at the expense of noise.  Another is axial vs. centrifugal.  Axial fans we are all familiar with.  In general they have high flow at low pressure.  They are great for moving air around where there are little to no obstructions. Like your room. Centrifugal are the opposite.  They are lower flow but higher pressure so they are good where there are a lot of obstructions, like your building's duct work.  Since I want a lot of air movement to keep the paint going out the back of my spray booth an axial fan would seem ideal, but I'm routing everything into a bucket instead of out the window.  That much filtration is going to create a lot of pressure so I was worried that an axial fan wouldn't be able to handle it.  In the end I chose an 8" centrifugal fan with a variable speed controller. It is rated for 677cfm, which is much higher than the Masters portable booth (4 cubic meters = 141 cubic feet by my calculations). As a bonus I almost forgot to mention, centrifugal fans also tend to be slightly quieter than axial.

 

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At this point I realized that I had created a pretty stationary system.  I need to be able to take this down and move it for storage.  My imperfect, but totally functional, solution?  Bungees!  They hold the booth onto the blower, but it can quickly be disassembled.  I also still have the lid for my container, so when not a booth it can double as a storage container for the bungee cords and other light weight airbrush items.

 

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Last, and most important, is how well does it work?  To test it I borrowed a cheap vaneometer from work and tried out the various filtration options.  The best flow will obviously be with just the carbon filter; the worst hooked up to the bucket.  The real question is just how much of a drop am I going to get with it all put together?  Did I overbuild or is it still not enough?

 

I suppose at this point I should throw in a bit of context.  For my day job I work in a lab where we are constantly working with chemicals you don't want to breath.  Our minimum target for the face velocity of our hoods is 80fpm (feet per minute), though we would prefer 100fpm.  At this flow rate you can boil acid in the hood and everyone can happily walk around without a respirator.  I figure if I have that kind of flow on my booth all of the paint should be sucked away as well.  This also brings me to the ever popular tissue test that I hear about people doing.  It turns out that you can achieve a high enough flow for your tissue to flutter in the breeze below 80fpm, i.e. less than the escape velocity of whatever you are working with.  You can get one of these cheap vaneometers off of Amazon for $35.  If you have a concern about your booth you can at least check it for a reasonable price.

 

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And without further ado, the results.

 

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So with just the filters in my booth there is sufficient airflow to run at the quieter 50% power setting and still pull everything through the filter.  Attaching the dust bucket though causes a large drop in flow.  50fpm is enough to pull a tissue into the booth, but it is too low to guarantee that no paint will escape.  There is just enough flow at 100% power, but it is noticeably louder as well.  Considering an inline fan rated for 677cfm can barely sustain flow into a dust bucket, I don't see how any of the bathroom fan contraptions people put together can manage it.  For that matter, the commercial ones likely can't either given what they are rated for.  Best to find yourself a work area where your exhaust can reach a window.

 

Obviously there is a second issue that I haven't tested yet - how much will the high airflow disturb my painting.  I'm not really worried for priming, or even basecoats, but it may be that I need to dial it down for detail work.  That however is an experiment for another time.

 

 

 

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Nice write up, especially the airflow testing. I'm in a similar boat but I'll have access to vent outside but this is very useful to me.

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Thanks for the write up! Roughly what was the cost to make this set up?

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4 hours ago, Cyradis said:

Thanks for the write up! Roughly what was the cost to make this set up?

 

Hey Cyradis.  Because of my build restrictions I incurred quite a bit of additional costs.  Most people reading this will be able to save a bit of money and I'll try to point out where I think they can. I don't have the receipts in front of me so this is approximate:

 

Bucket dust trap (optional)

 

5 gallon bucket w/lid $5

2'x4" pipe $6

3 cheap filters @94¢ each

1 you cut to size carbon filter $15

 

So we'll call that $30 for the bucket, though you could cut the price in half by using all cheap filters. If you have a window the price drops to $0!

 

Spray booth

 

64qt clear container $10

8" collar $7

Left over carbon filter $0 (free!)

HEPA furnace filter $10

LED light strips x6 w/cord & switch $35

 

So about $60 for the booth itself, most of which is for lighting.  My basement doesn't have the greatest lighting so I would have needed something regardless.  This way I got the color I wanted as well.  The reviews I read of the portable booths like Masters indicated they shipped with LEDs that cast a blueish hue and only illuminated from the top.  With better room lighting you could probably get away with a set of 3 LED strips for about half what I paid.

 

In-line blower

 

8" centrifugal - $70

 

Here's where most of you will be able to save some money.  I went big because I was expecting the dust trap to cause a large restriction in airflow.  With a window you could easily drop down to a 6" blower and save some money.  4" might even work, but the cheaper ones I saw don't have a much higher flow than the portable booth (141cfm vs. 200cfm) . OTOH I am hoping my fan holds up.  It was from the cheap tier of options.

 

Ducting

 

8' semiflexible duct $10

Reducers $15

 

You won't need reducers if you go right out the window.  I just needed to connect an 8" fan to a 4" pipe.

 

Miscellaneous costs for things you may not have

1" Hole saw <$5 (only if you make a bucket)

Caulk tube <$5

Caulk gun <$10

2 48" bungee cords <$5

Roll duct tape or worm clamps $1 to $2 each

 

So the cheap version of my build - no bucket, no LEDS, will be about $25 for the booth, $15 for some ducting + clamps/tape, and then whatever you choose to pay for a blower.  Looking at the raw cfm, a 4" blower should slightly outperform a portable spraybooth.  Spending a bit more for a 6" variable speed blower will allow your booth to work significantly better than a portable booth.  In fact you have as much or more raw power than a $300 spray booth at significantly less cost.  And really, that's what I am comparing my build to - the power of a stationary booth for the cost of a portable. 

 

Actually let us go ahead and compare:

Masters portable: 141cfm for $80 ($120 w/LEDs and such)

Passche HSSB 22-16: 270cfm for about $300

Paasche HSSB 30-16: 540cfm for about $470 (larger work area, uses dual fans)

Me: 677cfm for... well more than I wanted to pay but still, even the $300 HSSB 22-16 is going to struggle with my bucket. 

 

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Thanks for the breakdown! Shopping for airbrush boxes is rough, and it is hard to know what is a reasonable expectation. I do have a window, sortof. It isn't configured in a way that I can use it well, and I may be moving eventually - we aren't big fans of this apartment in general. 

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A good source for cheap blowers (not spark safe) are old hepa air purifiers once they stop selling the right size filters for them they sit in closets and thrift stores unused forever and the blowers in them are made for moving air through filters without a problem.

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