Achieving a high-quality spray finish requires a proper booth. I've been designing and building this downdraft spray booth for over three years now and it's finally fully functional. My last update was more than a year ago so I'm happy to say that the booth is now fully operational, and several projects have been successfully sprayed!
This booth has evolved from the 2020 open air version to the current closed booth. During use, the door is shut, and air enters the booth through the orange sticky filters to significantly reduce dust. The filter material arrives in a big roll which is cut to fit and then tie-wrapped to the filter holders.
ELECTRICAL - All electrical connections and switching are done outside of booth to prevent accidental VOC ignition. This is accomplished within a dedicated column of space sealed off from the spray area.
Outside of the spray area main shop power enters the booth through the conduit with the green arrow. From there it divides to go up to the booth lights and down to the outlet and switch box. The booth lights, fan, drying booth, and electrostatic ion generator transformer (at the bottom) are controlled through the switch box. There are still plenty of open outlets for either direct or switched operation.
Accessibility from the inside is needed to make fixes and updates. The transformer for the ion generator transformer (bottom arrow) was later moved outside where it should be.
LIGHTING - Two modified LED strips provide plenty of light and deliver the numerous, sharply defined reflections in wet paint needed to show proper surfacing and finish application.
AIRFLOW PATH - This is a downdraft system like many automotive spray booths. Ambient air is pulled into the booth through the openings with green arrows (to be fitted with orange filters). It moves through the plenum chamber (not shown) and enters the fan at the red arrow and moves down, around, and up following the orange arrows. Finally, it is exhausted out through the open vent in the window.
The explosion-proof fan has enough oomph to easily overcome the bends in the airflow which reduce air velocity.
An air baffle/moderator was constructed from 16 3D printed squares held together with 3D printed clips on the back. That's the set of gray squares leaning against the side of the booth.
Exhaust air (orange arrow) exits through this rotating gate. First the blocking slide is moved to the right (horizontal green arrow) and then the circular plate is rotated 90 degrees (angled green arrow) to clear the path out. Exhaust can move through the vent or be blocked to seal against the weather.
A block of insulation fits into the recess when not in use to give additional winter weather protection.
This vent was one of the trickier packaging bits to fit all the parts and motions within the confines of a 1940's basement window. It gets cold here, so the whole thing had to be heavily insulated to provide a sufficient barrier when closed. Now I can now spray in any weather.
PLENUM CHAMBER - The plenum chamber is the horizontal box that provides a volume of air that helps control the flow within the system. The white curved styrene sheet resting on the green filters above the plenum chamber helps direct air flow into the fan at the point with the highest velocity.
The gray baffle/moderator under the green filters slows down and spreads out the air so the plenum can do its job. The red arrow indicates air flow direction.
The system has proven to be quite effective as there is almost no overspray on the curved styrene which is directly in the spray path. Paint is pulled down and onto the piece being sprayed. The green filters then catch most of the dried overspray and keep the fan clean.
A removable tray hangs on the front edge of the plenum box to provide a paint mixing and spray gun cleaning area within the tiny booth. Moving it out of the way gives enough room to reach the back of the booth for operating the vent flap.
The flammable paint rags disposal can is barely visible on the floor below the tray to the right.
I used an anemometer to measure air flow throughout the spraying area to zero in on highest velocity areas. Temporary filters were used to test the effectiveness of various configurations.
The gray baffle grid is used to slow down and spread the incoming air stream. It was 3D printed in 16 sections and is held together with 3D printed clips. Each section's slots are sized to allow enough air flow while also providing support for the filters.
Replaceable green filters do the main job of capturing paint solids before they enter the fan. The plenum chamber is about 8" deep and holds a sufficient volume to allow better air flow control.
To keep the plenum chamber open to air movement, a piece of vinyl coated fencing was cut and bent to support the baffling grid and filters. The orange blocking cap over the fan shown in previous iterations has been removed as it proved to be unnecessary.
The bolted blocks are removable panel connectors. Like the rest of the booth, the entire box and overspray walls can be taken apart with a couple of wrenches and a screwdriver. This was done to allow the flexibility to make changes, if needed, as the booth was completed.
DRYING BOOTH - To the left of the spray area is a drying booth that is heated and has fan-driven air movement which is especially important to remove the moisture from waterborne paints.
There is storage below, but the most frequently used items end up as clutter on top of the drying booth. I need to do a better job of keeping the area clean since the incoming air flows directly over it.
It has been a long process to design and build a proper spray booth, but it will provide benefits for years to come. Now that it is functional I can spend more time on projects!
To view the design and construction from the beginning click on the links: