• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Small spray booth

#21
One thing I really worry about with the small spray booth is highly turbulent air currents. I suppose the filters help to diffuse that a bit, and it looks like Hambone's is designed specifically to prevent that.

Getting a more laminar air flow inside the booth is one advantage I can see to pulling the air in through a large opening rather than forcing it in through a small one.
 
#22
pilotjones said:
Hmmm, interesting idea. Sort of like a venturi, sort of not. Have you ever seen something like this working? The possible hitch is that unlike a venturi, a) you don't have a tapered exit funnel, which reduces drag; rather you have an exit cavity, blocked by a filter; b) the side port is huge compared to the "main" flow pipe. If it doesn't work it will be because the chamber is simply pressurized by the airflow, rather than being "vacuumized."
Click to expand...

Almost - the bottom exit doesn't have a filter allowing complete air flow down through the shop floor. If the "booth" is kept small like 4' x 4', there should be enough draft to keep the operator totally out of the vapor stream.

Nope, never seen anything like this but I've been around lots of styles of paint booth and I've taken ideas from all of them.
 
#24
PaleMelanesian said:
With a negative-pressure (fan pulling) setup, air will find its way in thru any tiny holes and cracks you missed. With this air comes dust. With a positive-pressure (fan pushing) setup, air will be going out these holes. There will be just the one path for air coming in, and you have control over the dust in that path. That's the way Intel does their silicon chip manufacturing - positive pressure filtration. Their demands are MUCH higher than ours - a single speck of dust could cost them 10s of thousands of dollars.
Click to expand...


I`m not saying there is any right or wrong here. Both types of systems have advantages, and disadvantages.

Take it from a guy who set up and ran Hamer`s finishing area for a decade. I also set up the Washburn Custom Shop finishing area so I feel I can speak with confidence here as I had to deal with OHSA.

The key to setting up a spray booth is to not have any unfiltered holes.
If there are any holes in a positive pressure spray booth, it pushes the fumes out these holes and introduces a fire hazzard, which defeats the whole purpose.

Also, small cubic Ft. positive pressure spray booths don`t lend themselves well to shooting sunbursts. The volume of air needed to push the dust and fumes out the exit side creates too much turbulance for my liking. Another factor to consider is turbulant air pushing on the exhaust filter where the solids (overspray) are collected which can create a dust situation.

95% of most major manufacturers use negative pressure spray booths and I have been spraying in them for 30 years, so I`ll stick with proven designs which works for me and the safety of my shop. It`s also more difficult to get OSHA`s approval for positive pressure systems where flamables are used.
 
#26
I agree with Mike. I painted cars for a lot of years. You want a clean environment to minimize dust, which is what the booth is for, but you want to suck the overspray out of your way as quickly as possible.

Greenman, you could always turn your vac around to suck mode, couldn't you?
 
#28
msherman said:
Take it from a guy who set up and ran Hamer`s finishing area for a decade. I also set up the Washburn Custom Shop finishing area so I feel I can speak with confidence here as I had to deal with OHSA.
Click to expand...

Mike, you are certainly qualified to speak to this - anyone that's been in charge of OSHA compliance just gets that way. I, too, have had the pleasure of required OSHA reading and compliance with this subject only my industry is sign painting - sometimes BIG sign painting. I am only mentioning this because I want to make something perfectly clear about my design idea and the diagram that illustrates it. This is an unproved design, that was created around a particular set of parameters to limit it's cost and complexity. My goal was to achieve the same operator exposure levels as each of my company's 4000 cu.ft. negative flow booths. We have had exposure tests performed by Georgia Tech (in response to an OSHA complaint - you can guess the scrutiny) and I used those results to gauge how much draw I needed for this type of booth. This booth is NOT designed to do anything more than evacuate a small spray area safely and without the use of non-explosive fans. It was designed for a simple framed shop that sits above the ground. It MIGHT be adaptable but I don't know. There is no guarantee that it would work without major tuning. All I know is that the science is sound and it would accomplish my own personal needs.

Everyones mileage will vary.
 
#29
Hamebone, I was more referring to palemelasian`s post of forcing air into a spraybooth in general.

I see where your headed with your system. You are forcing air after the booth into a manifold/diffuser to create negative pressure.
I can see that you will need to move alot of air with those blowers.
I imagine once you get the manifold tuned, with an expansion chamber (diverging cone) it will deliver a constant vacuum.
Your going to need some hefty blowers for a booth large enough to shoot a neck-though.

Your developing the first spraybooth with an expansion chamber:hyper:

keep us informed on how she progresses:)
 
#31
there is a range in which paint fumes are explosive. (LEL = lower explosive limit, and HEL = high explosive limit).

The trick when using a vacuum fan is to guarantee air flow sufficient to dilute the fumes to well below the LEL. Not a simple task, requires lots of math. Why? because electric fan motors, if not explosion proof, can ignite the mixture.

The alternative is to blow the air in...fan motor not exposed to explosive mixture...

the trick of course is to ensure that booth is slightly pressurized (can easily be tested using a homemade J-tube manometer) and that the overspray (ie exhaust) is directed downward (let gravity help you)

do an online search for J-tube manometer, these can be made by fixing a clear bit of flexible hose to a piece of plywood and adding water. An inclined manometer (J-at a slant) is even more accurate.
 
#32
Mike, you have a good point about leaking flammable fumes. I hadn't thought of that. I was thinking entirely about cleanliness inside the booth, and not about safety outside. That's definitely a priority.

I think I'll sit back and learn, now. You, Hambone, and Bud are definitely qualified to teach me something.
 
#34
The ideal conditions to have in a booth are to have as close as you can get 0 pressure on the inlet side graduating to negative pressure towards the exhaust side. This will create the least amount of turbulance at the part (point of spraying). This requires larger inlet filter banks than the exaust side.
I like to have a slightly larger than required inlet filter bank as I can tune the inlet tract as needed by blocking off a filter or two to adjust for when I shoot one guitar and open them up for a large batch. The more guitars in the booth, the cfm requirements change.

As a general rule of thumb, cross flow booths should be as close as you can get to 100cfm or higher. Downdraft booths should be close to 50cfm or higher. These require less cfm due to gravity like Pilbarabass mentioned.

If you are setting up a booth that will require duct work on the exhaust end, you need to calculate the Static Pressure (the resistance of air flowing through a tube, diameter, length, elbows...) as well as cubic ft. of the booth when choosing a exhaust fan with the right cfm needed.

Setting up a booth can be a daunting task, but if you do the math correctly, it will reward you with a safe environment and a quality finish.

And if your booth is metal, or plastic, make sure you ground everything to avoid static build up.
 
#35
Not having any experience with spraying beyond seeing it done on low quality structural (non-decorative) items, my first thought was that this thread could make things easier, and maybe possible. Then I saw all the complications that can happen if either the booth or the spraying are not done correctly, and I thought, wait, it's probably easier to work something out with an automotive painter. Then there was the post about poor results obtained until an auto painter learned by trial and error how to do guitars. Now I'm thinking, TruOil or something else that's not sprayed are looking better and better. :eyebrow:
 
#36
it's certainly more difficult to obtain good results by spraying than with wipe-on finishes. This thread has not even started to discuss viscousity, tip size, pressure levels, HVLP vs conventional ....yikes!

I spray with a mini-hvlp in the same room I do all my woodworking. I just make sure I don't do anything else while I'm spraying. I will not say I get the best finish possible, but it's pretty darn good. I don't have any filtering, exhaust or anything else. I use waterbourne, mind you.

I'm not saying that all this stuff is redundant, but good results are obtainable without them. Especially if you're not doing any kind of production work (I finish a bass every 3-4 months).
 
#39
Sorry, I didn't mean to put a damper on the conversations! Please don't drop the detail discussion. I never expected to see this type of experienced opinions here (in the paint area)--it's great.

What I have gained here is a greater appreciation of the complexities of professional finishing, and a more informed concept of what might and might not be doable in a small volume / home shop.
 

Latest posts

Top Bottom
Back