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Yes, I understand there are calculators for CFNM.

What I'd like to know is people's experience with DIY Spray boxes. My greatest concern isn't "doing it right" or "air resistance". Have you actually made one? What kind of fan did you use? Most importantly, did this kill most of the spray smell?


ender502

At the most basic, all you really need is a box fan that will fit within your open window, a cardboard box that can fit around that box fan, and a table for both to sit on in front of that window. I did that once, years ago. It's a janky setup, but it does work with a good fan. You can certainly get creative if you have access to cardboard, tape, ducting, fans, etc.
I still spent the $100 bucks for a portable spraybooth from Amazon that has the hose that can run the air out through a much smaller opening in the window.

Also, in this context, what does CFNM mean? I know what it means in an entirely different context.

I've made a few of them. And my requirements were probably much different than yours. As an example I sprayed a *lot* of Lacquers and even to this day I still clean all my airbrushes with Lacquer thinner. So my requirement was to safely extract the paint over spray *and* fumes. Most people will of course laugh at this and "But I only spray acylics" is bandied about. Even so .....

The big problem with fans is that darn few of them are actually meant to work into any form of backpressure (think of it as a natural resistance to airflow. The fans that do not suffer from this are commonly referred to as squirrel cage fans. A common use for this is to pressurize a portion of an electrical device ( RF Power Amplifiers. This pressurized air flows through the ceramic socket for the power tube(s) and said air flows up around the tube by using a Pyrex chimney. Additionally these fan motors are not exposed to any possible combustible fumes potentially being used.

Muffin Fans are NOT the answer. Period. Full Stop.

I always made the boxes bigger than I thought I would need. And always included a fluorescent light fixture in them as well as additional switched outlet(s) for the compressor etc.

I generally use plywood and the front opening is is roughly 25 inches square. I use furnace filters cut in half. But I even used cardboard once to prove the idea would work.

Here you go

 Tannhauser42 wrote:
At the most basic, all you really need is a box fan that will fit within your open window, a cardboard box that can fit around that box fan, and a table for both to sit on in front of that window. I did that once, years ago. It's a janky setup, but it does work with a good fan. You can certainly get creative if you have access to cardboard, tape, ducting, fans, etc.
I still spent the $100 bucks for a portable spraybooth from Amazon that has the hose that can run the air out through a much smaller opening in the window.

Also, in this context, what does CFNM mean? I know what it means in an entirely different context.

just a measurement of how much air it moves.


Automatically Appended Next Post:

 Grimoir wrote:
I've made a few of them. And my requirements were probably much different than yours. As an example I sprayed a *lot* of Lacquers and even to this day I still clean all my airbrushes with Lacquer thinner. So my requirement was to safely extract the paint over spray *and* fumes. Most people will of course laugh at this and "But I only spray acylics" is bandied about. Even so .....

The big problem with fans is that darn few of them are actually meant to work into any form of backpressure (think of it as a natural resistance to airflow. The fans that do not suffer from this are commonly referred to as squirrel cage fans. A common use for this is to pressurize a portion of an electrical device ( RF Power Amplifiers. This pressurized air flows through the ceramic socket for the power tube(s) and said air flows up around the tube by using a Pyrex chimney. Additionally these fan motors are not exposed to any possible combustible fumes potentially being used.

Muffin Fans are NOT the answer. Period. Full Stop.

I always made the boxes bigger than I thought I would need. And always included a fluorescent light fixture in them as well as additional switched outlet(s) for the compressor etc.

I generally use plywood and the front opening is is roughly 25 inches square. I use furnace filters cut in half. But I even used cardboard once to prove the idea would work.

The amount of work is relatively minimal I think. I'm more concerned with fumes because my wife will kill me if I stink the house up. Lol.

I've seen the furnace filter and that does seem to work.

What are muffin fans?

 ender502 wrote:
Yes, I understand there are calculators for CFNM.

What I'd like to know is people's experience with DIY Spray boxes. My greatest concern isn't "doing it right" or "air resistance". Have you actually made one? What kind of fan did you use? Most importantly, did this kill most of the spray smell?


ender502

Yeah I've made one. I didn't try and use it to filter air though, I just used it to dump air directly out a window. It was a box + a tube + a fan and then straight out the window.

The fan I used was a 35W desk fan, I found this was powerful enough to dump air fast enough that I could use spray cans (not just an airbrush, actual spray cans). I could use the fan on a setting of 1 or 2 when airbrushing, but cranked it up to its maximum (3) when spraying rattle cans.

My cheap little Chinese hobby spray booth does not dump air anywhere near fast enough to use a spray can, and barely dumps the air fast enough for an airbrush. I certainly wouldn't use it with lacquers or enamels. At one point I did take my same 35W desk and adapt it to the hosing of the cheap Chinese hobby spray booth, and that allowed the Chinese hobby spray booth to exhaust fast enough that I was again happy using lacquers and enamels, but still not fast enough to use a spray can.

A word of warning is that fan motors sometimes create sparks, and often the fumes are flammable, so you can theoretically make things go boom, I've never had that problem and being aware of the issue I was fully ready to throw my fan out the window at a moments notice You can buy fans where the motor isn't inline with the fan, but they're more expensive and specialised, I literally just used a desk fan from a hardware store, lol.

One other thing to note about fumes. Even if the booth can vent out all the fumes from the airbrushing process, you'll still have fumes coming off of the models as they dry/cure, depending on what you sprayed them with.

 Tannhauser42 wrote:
One other thing to note about fumes. Even if the booth can vent out all the fumes from the airbrushing process, you'll still have fumes coming off of the models as they dry/cure, depending on what you sprayed them with.

That's one of the best thing about lacquers, and one of the worst thing about enamels. Both have terrible fumes, but lacquers cook off very quickly so the painted models don't continue to stink. Enamels can keep fuming for ages though.

But yeah, if I'm using my spray booth for rattle cans I leave it running for a couple of minutes with the model in the booth after finishing spraying for that reason, or I go and stick the painted model in the spare room with the door closed while it de-fumes.


Automatically Appended Next Post:

 ender502 wrote:

 Tannhauser42 wrote:
At the most basic, all you really need is a box fan that will fit within your open window, a cardboard box that can fit around that box fan, and a table for both to sit on in front of that window. I did that once, years ago. It's a janky setup, but it does work with a good fan. You can certainly get creative if you have access to cardboard, tape, ducting, fans, etc.
I still spent the $100 bucks for a portable spraybooth from Amazon that has the hose that can run the air out through a much smaller opening in the window.

Also, in this context, what does CFNM mean? I know what it means in an entirely different context.

just a measurement of how much air it moves.

What's the "N" stand for? The measures I'm familiar with are CFM (cubic feet per minute) or the SI unit of cubic metres per second (sometimes abbreviated "cumec").

AllSeeingSkink wrote:

 ender502 wrote:
Yes, I understand there are calculators for CFNM.

What I'd like to know is people's experience with DIY Spray boxes. My greatest concern isn't "doing it right" or "air resistance". Have you actually made one? What kind of fan did you use? Most importantly, did this kill most of the spray smell?


ender502

Yeah I've made one. I didn't try and use it to filter air though, I just used it to dump air directly out a window. It was a box + a tube + a fan and then straight out the window.

The fan I used was a 35W desk fan, I found this was powerful enough to dump air fast enough that I could use spray cans (not just an airbrush, actual spray cans). I could use the fan on a setting of 1 or 2 when airbrushing, but cranked it up to its maximum (3) when spraying rattle cans.

My cheap little Chinese hobby spray booth does not dump air anywhere near fast enough to use a spray can, and barely dumps the air fast enough for an airbrush. I certainly wouldn't use it with lacquers or enamels. At one point I did take my same 35W desk and adapt it to the hosing of the cheap Chinese hobby spray booth, and that allowed the Chinese hobby spray booth to exhaust fast enough that I was again happy using lacquers and enamels, but still not fast enough to use a spray can.

A word of warning is that fan motors sometimes create sparks, and often the fumes are flammable, so you can theoretically make things go boom, I've never had that problem and being aware of the issue I was fully ready to throw my fan out the window at a moments notice You can buy fans where the motor isn't inline with the fan, but they're more expensive and specialised, I literally just used a desk fan from a hardware store, lol.

I really should have specified that I am looking to exhaust fumes rather than filter. I would be setting up the box withing...3 feet? of a window.

ender502


Automatically Appended Next Post:

AllSeeingSkink wrote:

 Tannhauser42 wrote:


What's the "N" stand for? The measures I'm familiar with are CFM (cubic feet per minute) or the SI unit of cubic metres per second (sometimes abbreviated "cumec").

"N" stands for my bad typing. LOL

ender502


Automatically Appended Next Post:
I have seen some pretty pedantic posts on hobby forums about what kinds of fans to use for the exhaust portion of a paint booth. I see some pretty reasonable fans around 150-195 CFM fans. Do you think that would work to exhaust funmes a distance of about 3-4 feet ?

 ender502 wrote:
I have seen some pretty pedantic posts on hobby forums about what kinds of fans to use for the exhaust portion of a paint booth. I see some pretty reasonable fans around 150-195 CFM fans. Do you think that would work to exhaust funmes a distance of about 3-4 feet ?

I'm not sure what you mean be "a distance of about 3-4 feet", what's your final arrangement going to be?

I'd be hesitant to say yes or no on your 150-195 CFM fans, I don't have a CFM rating for my fan to compare it with. As my fan was just a hardware store fan, 240V AC and 35 watts. I believe it was a 30cm diameter fan.

Just talking logically, 150CFM would mean 2.5 cubic feet per second, if your booth is 2 feet wide, 1.5 feet tall and 1 foot deep, that'd be 3 cubic feet, so you'd be dumping the contents of your booth every 1.2 seconds, which sounds okay to me for airbrushing, maybe borderline but probably okay for rattle cans.

However, depending on how the fan is rated it may not be running anywhere near its rated CFM. Some fans will list CFM at the fan's design point, others will list an unobstructed CFM which is unobtainable in reality. If I'm designing something for work (industrial aerodynamics) I'll generally ask the manufacturer for fan curves (pressure rise vs flow rate) so I can calculate for myself how it'll run given an estimated pressure loss coefficient, if they can't provide curves I go to a different manufacturer. Even if you have the fan curves, you need some knowledge of the final system to estimate the pressure loss coefficients.

But for my own setup at home I basically went to the hardware store, turned on a fan, felt the air coming through and thought to myself "that'll do pig, that'll do". I didn't try and do any calculations like I would do if I were building a system for my job, I just bought something that felt like complete overkill and adapted it into my booth.

I built myself a spray booth (but I used an industrial blower on it. 3ph, capable of 65,000 cfm air movement (I don't know what that is in metric, it was only labelled in "not metric" - whether that was British Imperial or American "standard" I don't know).

That thing can suck up metal dust). It's at my inlaws, because their house is wired for 3ph and mine isn't.

All I built, though, was the enclosure and the scoop to make the airflow more efficient. This is where family with metal bending gear came in very handy.

 chromedog wrote:
I built myself a spray booth (but I used an industrial blower on it. 3ph, capable of 65,000 cfm air movement (I don't know what that is in metric, it was only labelled in "not metric" - whether that was British Imperial or American "standard" I don't know).

That thing can suck up metal dust). It's at my inlaws, because their house is wired for 3ph and mine isn't.

All I built, though, was the enclosure and the scoop to make the airflow more efficient. This is where family with metal bending gear came in very handy.

I'm assuming your inlaws already have insanely high electricity bills and thus don't notice you running it? Or do the lights dim ever time you crack out the airbrush to spray a Spehss Mehreen? They're probably paying more for the electricity than you paid for the models.

I recently bought a blower for work, it doesn't have a CFM rating and instead has a fan curve, but it peaks at about 70000 CFM when driven by an 18.5kW motor, though we run it against enough resistance to drop it down to less than half that flow rate (but much higher pressure rise) and have it hooked up to a 22kW motor.

Using that as an airbrushing spray booth would be like using a 20 ton mining truck to go get the bread and milk each morning

You can get some crazy stuff from industrial 2nd hand yards though.