This thread shares information about my newly constructed knock down spray booth.
I should say up front that I am really not a sprayer. Not yet, anyway. I have been very hesitant to get into spray finishing, due to concerns about safety. I don't want to breath in finish, and I don't want to blow up my house. However, after French polishing 7 guitars (my first 7), and experimenting with a brushed finish on #8, I have gotten to the point where I really want to get a better finish with less work. So, I took a fresh look at spraying. The big hurdle for me was figuring out where in my shop to spray so that it would be both safe and effective. That took work. I did a lot of research and thinking this through, and I feel I have come up with a decent solution for my shop.
Some disclaimers: The solution I came up with should NOT be used in any space with a gas furnace. My spray booth's way of getting make-up air can cause serious health/safety issues in a space with gas heat. Luckily, I have electric heat. Moreover, my spray booth does NOT fully comply with NFPA 33 or the relevant OSHA regulations. While my spray booth has superior ventilation, it does not have other safety features required by those regulations, particularly regarding fire prevention and containment. While I use an explosion proof fan, I do not go full tilt on fire prevention/containment measures, instead relying on great ventilation to minimize risk. So, be careful before you adopt any of my ideas. Finally, ALWAYS wear the correct PPE when spraying. I know I do.
After looking at a lot of information about spray booths, I came to this conclusion: The critical function of any spray booth, the thing that makes the difference between success and failure, is the ability to move lots of air at the right speed. You need to move a whole lot of air through the booth, blowing the overspray-laden air out of the booth to the open air outside, and sucking new air into the booth from somewhere that has clean air to give. That means that my spray booth needed to be located close to two holes to the outside world that are not on top of each other. After stewing on this, I decided that I needed to locate the spray booth in my main workbench area, which is close to both a window (where I can spew out the overspray-laden air) and a door to my garage (where I can open both that door and the large garage door to provide the make-up air). Of course, this meant that I needed to go with an open faced benchtop booth, and I needed to make it so that it could be set up and broken down easily and relatively quickly, and stored somewhat compactly. And, again, it needed to be safe and effective otherwise, why bother?
This is what I came up with:
Attachment: Front view.JPG
Attachment: Left side view.JPG
Attachment: Right side view.JPG
The booth itself has the following interior dimensions: 40" deep; 40" wide; and 30" tall. The box is made up of 5 lightly framed walls that I put together with my Kreg jig. I faced all of the walls with a 1/16" thick white plastic sold at Home Depot as an alternative to FRP (fiberglass reinforced panel), the stuff you see on the walls of gas station bathrooms. The walls are connected to each other with a combination of barrel nuts, T nuts, threaded inserts, and various knock-down furniture bolts. I can put the box together or tear it down in a few minutes.
Inside the booth, I have a few neat features. I stole John Hall's idea of using a rotisserie motor to slowly rotate the guitar (thanks, John) and "kicked it up a notch" by placing the rotisserie tower on top of a 24" rotating disc, facilitated by a 12" lazy Susan:
Attachment: Guitar holder.JPG
The combination of the rotisserie and the lazy Susan means I really don't have to move the spray gun around too much at all. I can maneuver the guitar body/neck however I need to.
The other neat interior feature is the removable LED tape light:
Attachment: Tape light.JPG
I cut the tape light to the right lengths and inserted corner connectors. I inlayed rare earth magnets in 1" wide strips of lauan plywood, and glued the strip lights to the plywood. The magnets stick to some of the washer-head screws that hold on the plastic wall faces. I can install or remove the lights in seconds.
The heart of the booth is the rolling cart that holds my fan:
Attachment: Fan.JPG
The fan is a Dayton 12" tube axial fan, powered by a Leeson 1/3hp TEFC, single phase motor. My research convinced me that many DIY booths do not move enough air, so I put the bulk of my budget into the fan. Because my workbench is more than a foot lower than my window, and I wanted the filter box to sit at the bottom of the booth, I needed to tilt the fan up 15 degrees to get the exhaust to flow in a straight line (a fairly big deal for air movement). This took work to plan it out, but it is extremely effective.
On the booth side of the fan, there is a filter box that connects to the back wall of the booth:
Attachment: Filter.JPG
It has interior dimensions of 20"x20" at the face, which is the most popular size for pre-cut spray booth filters. I'm using Paint Pockets for now. Many cheap HVAC filters come in that size, as well. Chicken wire keeps the filter at the face of the filter box, which helps to create a smaller version of what would be the exhaust chamber of a larger spray booth. That spreads the suction of the fan across the whole face of the 20"x20" filter.
On the window side of the fan, there is a chimney that I constructed from 5mm thick lauan plywood, with strips of pine at the inside corners to increase gluing surface:
Attachment: Chimney.JPG
The chimney goes up a 15 degree angle to the window, where there is a mating sheet of plywood to plug up the open window around the opening of the chimney.
So, how well does the spray booth work? Pretty darn well! Using a vaneometer, I clock the air speed inside the booth at an average of 150 fpm, ranging from a little above 100fpm to around 200 fpm. Must code compliant booths are supposed to shoot for a minimum of 100 fpm. For an open faced booth, a person really should try to exceed that number. In a fully enclosed spray booth, an undersized fan will eventually exchange the air; it just takes longer than it should. But in an open faced spray booth, the overspray can creep out of the booth and into the rest of the shop if the exhaust fan is not up to the task. So, bigger is better when it comes to fans for open faced spray booths. But it is critical to also plan for the provision of make-up air. You can starve the fan in a heartbeat by not providing enough make-up air. This is why having a door to an open garage nearby is essential to the operation of my spray booth.
This spray booth checks all of my boxes. It moves enough air to be safe and effective. It can be set up or torn down in a relatively short period of time. It has plenty of light. It has a great way to hold the instrument parts while spraying. And it can be stored in a relatively small footprint of space when not in use.
I can finally start the business of learning how to spray, now that I can do so safely in my shop. In case you are curious, I will spray waterborne finishes and some of the less harmful solvent finishes (shellac, Royal Lac), but I cannot ever see myself spraying nitro in my home.
I'm happy to answer any questions. Please note that this is still in the experimental stage, so some tweaks will probably be needed. If you have suggestions for improvements, I would be grateful for the input. Thanks.
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