Measurements

Nothing special

The dimensions were determined by material at hand. I had a piece of 3/4" plywood that was 29" wide by 15" high. The 29" dimension worked well so that piece became the back - a good sturdy piece to mount the fan and provide a connecting surface for the bottom, top and sides. 

I had a piece of Masonite left over from making backdrops that was 8 feet long by 23" wide. The overall size was determined by how much I could get from that sheet. The front to back measurements are 23".  The overall width is 29" to match the plywood. The height at the front is 19" ((96 - 29 - 29) / 2). There is a 1/4" fudge factor so the top and bottom would overlap the sides.  

The Masonite pieces were glued and screwed to 3/4" square molding strips for strength and also glued and screwed to the plywood back. It's nice and sturdy since it will be moved around a lot between uses.

I made a plenum behind the furnace filter to help air flow and make it easy to change the filter. A 1x2 frame was constructed to support the filter and 1/2" closed cell foam was stuck on the frame. Masonite strips were glued to the outside of the frame to locate the filter side to side and a short strip was edge glued to the bottom to hold the bottom of the filter. Another piece of Masonite was put on a hinge at the top of the frame to hold the top of the filter in place. 

I feel the need to paint!

Safety First!

A very nice project that is neat and well done. Their is a safety question about the exhaust system.

I would have some concerns about using a bathroom fan if you use oil base paint. The household bathroom fans are not rated for explosion proof exhaust. This may be a fire hazard. Would be OK if only water based paints with no alcohol thinner is used.

Safety first

Good catch on the fan.  Maybe bathroom fans should be explosion proof considering the methane gas that's often present?

Rick

Rick - that's only a concern

After a good pot of Red Beans and Rice . . .

Safety last

The motor is a brushless AC induction motor. Exactly what would you expect to trigger an explosion?   

Fire up that airbrush!

Metal to metal contact is taken into account when determining explosion proof. The blade striking the housing as the result of bearing failure for example.

It's a moot discussion anyway. Short of dumping a gallon of lacquer thinner into your spray booth you will never come anywhere close to the necessary vapor concentration needed to support ignition in the airflow. Besides, it's a wood enclosure for crying out loud. Keep on paintin' George!

Plastic blade

Thanks Alan.  The blade on the fan is plastic, so not much of a problem there. I'm sure something could go wrong if Murphy worked on it hard enough.  I'll try to keep large quantities of paint thinner away from the booth.  

Solvent Problems

I don't like people who criticize a fellow hobbyist's project, but in this case I believe there is a real chance of injury.

There are more than mechanical concerns with motor located in the air flow. Solvent from the paint may attack the insulation of the motor, causing a short.  Maybe not today or even next week, but one day in the future there is a good possibility of a flash back.

The solvents on many paints are very explosive when mixed with air. Often we use a solvent to clean our air guns. A flash back will not only be in the exhaust duct but also back to the nozzle of the paint gun. The gun is often near the face and eyes.

Some times we don't use a air brush in the booth, We often use a spray can. I have seen the results of spraying a solvent based paint over an open flame. The result is like a small flame thrower

The cost of a fan that is designed for this type of exhaust will no doubt be higher than a fart fan, but the cost may be cheap compared to the possible results. At the very least a fan assembly that places the motor outside the air flow would lower the risks.

I have posted a link that offers other ideas to improve the safety of a paint booth fan.

http://modelpaint.tripod.com/booth2.htm

Spoken like a

true native!!!  

red beans and rice and/or a trip to Copelands....

well if we're talking methane generation

a crawfish po-boy with shrimp gumbo at Mother's is really preferred . . . . but that's enough thread-jacking.

I keep wanting to do what George did and build my own, but motor selection has always stopped me.  I search for all sorts of motores and fans, but very rarely do I see one labeled explosion proof.  If anyone has that sort of information, it would be welcome here.

Have to ask a stupid question

O.K.  I have to ask a stupid question:  Do the commercially available paint booths come with a explosion proof motor?  The reason that I ask is because a true explosion proof motor is very expensive.  I've got a paint booth that I haven't used for awhile, so I guess I'll have to dig it out and look at the plate on the motor.

Rick

Rick, I keep asking the same question

I seriously doubt any but the high-end Paasche's would have such a motor.  My guess is the designers hope they can keep the volume of solvents below the flash point with whatever motor they installed.

I suppose one could use

a 12V bilge-blower fan from a marine outlet.  After all, they're intended to extract gasoline vapour and _must_ be ignition-protected (as must the control switch).  Dunno about the relative sensitivity of the plastic components to paint solvents vs gasoline, though....

David

Spray Booth Fan

For what it's worth, a quote from Paasche regarding their most expensive booth (similar for the least expensive):

"Hobby-Shop Spray Booth---Rugged, compact in size and easy to assemble. This portable booth features galvanized metal panels for easy cleaning and durability. Working dimensions are 30 Inch wide by 16 Inch high, perfect for all you hobby and craft spraying. Equipped with two 115 Volt fans. Not intended for use with hazardous materials, flammable or explosive paints or materials. If necessary, wear goggles and/or protective paint and vapor mask. 4" dryer duct adapter included."

Dante

A worthy follow up

This is from a previous thread on this subject that Bob shared in a post sometime ago......

For those of you who are still interested, I just got off the phone with a Paasche rep asking about their Model HSSB-22-16 spray booth. He confirmed what Steve had said in his earlier post that the fan motor on the Model 22-16 is neither sealed nor explosion proof. The Paasche rep uses their larger HSSB-30-16 booth and has never had a problem with it. He said that Paasche sells a large number of the Model 22-16 booths and has never heard of any fire or explosion problem with it. He said the air flow rate is approximately 230 cfm in the Model 22-16. He also said that if you were venting the booth to the outside you probably did not need to use the charcoal filter. The fiberglass filter, Paasche part #AG-8, will stop the particulate overspray and needs to be replaced when it gets full. He also warned against placing a light source on top of or inside the booth since this would potentially introduce an ignition source for any solvent that might be present when spraying with solvent-based paints, e.g., Floquil.

https://forum.mrhmag.com/post/spray-booths-and-charcol-filters-12185835

At about 0.5 CFM coming from the airbrush and say over a 100 CFM from the smallest hobby style spray booth you would hard pressed to get the the Lower Explosive Limits of hobby solvent spray booths, even with a broad range of 3% - 11% explosive limit (reference the MSDS for the exact info for your brand of paint).  With the bath and kitchen fans getting down to the 45 CFM range I would be more concerned about pushing the numbers a little  but that would be a from a health stand point not a fire stand point in a chronic situation.

Just my thoughts -  your mileage and personal preferences may vary......

Steve

I tend to agree...

I agree.

I think that as long as the fan is moving enough air to keep the concentration of fumes low enough that the user is not getting "dizzy" just sitting outside the booth, it should be fine.  Otherwise, I think the user would likely drop the brush/rattle can and fall over, long before the paint booth exploded. [wink]

I would avoid any sort of open frame motor of course.  The plastic fan blade is better than metal on metal too.  An externally motored belt-driven squirrel cage fan with a plastic blade would seem like the optimal choice to me, if available and at a reasonable price.

I've made rattle can flame throwers myself.  When I was 13 or so I discovered a product called Bon Ami, IIRC.  It would throw a five foot inferno if you sprayed it over an open flame.  Very effective, DON'T TRY THIS AT HOME!  My mom used to spray it on cloth and then run a hot iron over it.  Luckily it wasn't as inflammable then!

I have also seen lit cigarettes effectively extinguished in a FULL can of gasoline. DON'T TRY THIS AT HOME!

I'll never forget being at a country landfill where they were burning the wood pile while I was dumping a load of scrap lumber and sawdust from Dad's shop.  I dumped a can of sawdust and the wind took the dust just as something nearby went from smoldering to burning.  The result was a large mid-air INFERNO that darn near singed my eyebrows off!

It's all about the fuel to air mixture.

Now the caveat.  To be truly safe, you should use an explosion proof motor.

Ohhhhhh, fire

Kevin, your Bon Ami comment made me grin. It reminded me of my younger, more inquisitive, more mischievous days. I had to repaint the garage door of our house when I discovered that very fine particles of many things will ignite if suspended in air.

Using a bucket, blowing through a length of tubing, and a propane torch as an igniter I just had to find out what created the biggest fireball. Turns out plain ole flour makes one heck of a big fireball. Enough so that it scorched the paint on the open garage door above my test apparatus. Dad wasn't too thrilled about my curiosity of all things ignitable as he handed me a brush and bucket of paint to repair the damage I had done.

Inquiring minds need to know! 

PS the gasoline cigarette example is a function of temperature. Gasoline has a relatively low vapor pressure. The very reason it was originally selected as motor fuel of choice - safety. Keep the temperature below gasoline's decomposition temperature and you can use it as an ashtray. Don't try the experiment on a hot summer day!

Fire

I know Alan, I can't believe I never set anything important on fire!  Crazy stuff now that I look back.  Kids playing with fire, tsk tsk.

I remember Myth Busters testing flours explosive flammable qualities.  The only thing I've seen to compare it to is Napalm!

This JABSCO  12-24 VDC blower fan has a dielectric plastic housing and closed motor.  It is approved for exhausting fuel vapors from marine engine rooms before starting the engine.

Truly safe

To be truly, truly safe, stay in bed and do not do anything.  And don't put a pillow over your face.  And don't let the cats suck the air out of you.  

Adults

I hope you didn't miss my smiley, JRG1951.  I couldn't resist that tongue in cheek remark.

Your concern does not dissuade me from further postings. If I was sensitive to criticism or notes on safety issues, I would have stopped posting a long time ago.   

Since my layout infrastructure is now complete, I will probably have no more postings that would involve electricity or codes or any of the other things I have run afoul of in this forum. I hope that people will have equally useful comments about my modeling projects. 

A guy named Booth

Truly safe - truly funny!

George,

You gave me my morning laugh - thanks!  And please keep posting as I really enjoy you input!

Rick

Finally...

... someone noticed the posting title (or actually made a comment about it).  Thanks Scarpia.  

"Eponymous paint booth".  I amuse myself sometimes.