It took me a while to get it ready for flight (over a year *cough*) but I’ve since completed it and maidened it.  It’s still in one piece.  I have a number of comments I’d like to share about my experiences with the plane and I’ll be putting together a more lengthy post soon. (I hope)

My original plan was to use rigid ducting and I firmly believe that is the only viable solution to have a FULLY ventilating booth that can handle aerosol.  If your just  looking to ventilate for oil based brush painting etc, then your probably fine.

So, without a way to vent directly to the outside via rigid ducting I’m official mothballing this project.  The booth has been sent to the scrap heap and the squirrel blower has been packed away.   

I’ve actually already completed the booth and have it setup but I haven’t finalized the installation so there is still a few more posts on this epic journey to spare myself from asphyxiation.

So, it was off to Home Depot to get some more MDF and build a booth from scrach.

The biggest challenge is cutting the wood without a table saw.  Circular saws are horribly inaccurate for cutting wood.  They are fine on a deck, or framing as you can be off 1/8″ or more without any major issues.  Trying to build a box that lines up perfectly is just not possible with a circular saw.

The only way to improve the quality of a cut using a circular saw is to use some sort of guide for the saw.  This is doable with some sawhorses, a straight piece of wood for the guide and some C clamps.  I happen to have all of those things available but this technique results in significant delays so it’s not something I’d recommend if you have a lot of cutting to do.

Fortunately Home Depot will cut wood for you as long as the cut is 90 degrees.  This will take care of 95% of my cuts so I had them do all of the 90 degree cuts for me.  I highly recommend sketching out how you want the board cut, with measurements, before you get them to cut it though.  The fellow I asked at first was going to the 5 pieces one piece per board, when I had sketched out all the pieces on two boards!  I politely showed him how the cuts should be done and he graciously blushed and used my sheet from then on.  Apparently Rona will do angle cuts too; so it might be possible to have all of the cutting done for you.

After assembling the box, I still had the job of mounting the plenum and blower from before.  I was worried that the combined plenum and blower would weigh too much and tilt the booth backwards.  My fears were confirmed and I ended up mounting the plenum and blower flush with the bottom of the booth so the plenum and blower rested on the table; thus holding its own weight and not tilting the booth.

I should mention at this point that I having the plenum mounted on the back as a separate piece is not the best way to do this.  I did it this way as I had already built the plenum and I didn’t want to waste all of that work.  The easiest way is to simply include another back panel in the booth that would create a plenum chamber a as part of the booth.   This would also simplify the blower mounting as it too would be integrated into the booth.  You will also be saving a fair amount of MDF.  Probably 30%.   You’ll be saving 50% aggro though.

Anyways, I used standard 1/4″ rubber weather stripping to create a seal between the blower and the plenum and the plenum and the booth.   This provided a great seal.

I did encounter a major issue with the design.  If you recall earlier photo’s I had made provisions for the filter to trap the overspray to be inserted into the side of the plenum.

Due to some aerodynamics I don’t completely understand this feature was a total failure.

What seems to be happening is the plenum is being pressurized by the blower, and you get very good flow out of the vent, but some of the air in the plenum is leaking out the slot I made for the filter.  It’s enough that the booth was basically useless as there was plenty of fumes coming out of the slot.

The only solution was to seal the slot and put the filter inside the booth in front of the grill.  Easy fix but what a waste of all that work on the plenum.

The other consession I was forced to assume because of having to use the window is the flexible ducting.  Man that stuff really impedes airflow.  I can hear the blower change speeds if I collapse the flexible ducting or stretch it out.  I’m going to see what I can do about making most of the ducting rigid and only have flexible ducting to allow removal from the window.

Plenum with Blower Cut Outs

Plenum with Caulking

Plenum Marked Up for Cutting Intake

Note the white grill in the background.  That’s a cheapo plastic cold air return from Home Depot.  It had very little blockage of airflow and I don’t really care if it gets covered in paint.

I should probably explain the design.  As you can see in the photos above there is a plenum which the blower will pull air from and exhaust air out the rectangular cutout at the top left.  The top of the plenum is wider than the actual inside of the plenum as the blower is actually hanging from the top outside of the plenum.  Another feature that is noticeable in the photo’s is that the right side wall of the plenum is not as tall as the left side.  This difference in height is to allow an opening for the cheapo air filter to fit in.  Basically, there will be a slot where the filter will go in once the front of the plenum is installed.

Plenum Test Fit

The above photo shows the plenum test fit onto the bench.  The plenum has L brackets on the top, right side, and bottom to secure it against the pegboard.  Weatherstripping is going to be used to create a seal between the plenum and the pegboard.  The L brackets don’t actually carry the weight of the plenum and blower.  That’s what the 2×2 is for.  I measured the 2×2 to 4′ and drilled holes into either end that aligned with existing bolts on the bench.  I replaced the existing bench bolts with longer ones and then secured the 2×2 horizontally. Once that was done I rested the plenum and blower on top and test fit everything to see how it hung together.  As you can see in the photo it looks pretty good even without it being secure tightly.

Plenum Illuminated From Inside

With the plenum test fit I used a table lap to illuminate the plenum which then shone through the pegboard; clearly showing where to cut the pegboard.  Luckily I didn’t actually cut the pegboard.  At this point I moved on to the exhaust as I like to get parts of a project to the point they are close to their final form and then test fit everything.  This is a custom solution after all so there are bound to be fitment problems etc.

Grill on Bench

The above photo shows the size of the grill to the bench.  Pretty good.  The plan included movable side panels to accommodate different shapes or adjust for over spray etc.

The blower exhaust is 5 1/4″ and the ducting is 4″ so I used a 6″ to 4″ duct reducer mounted on some scrap MDF left over from building the plenum.   I marked out the holes for the blower exhaust plate.  The exhaust, blower, and plenum are all going to be bolted together.  Weatherstripping will be used to seal the exhaust plate to the blower.  I traced the shape of the duct reducer onto the MDF  and then traced those tabs you see inside the circle.  These are what the duct is going to rest on.  I wanted to minimize the amount of interference to the air flow that is going to occur here.  The blower exhaust is a slight rectangle and will be blowing into a circle.  By cutting the MDF to the exact size of the duct and using the tabs I’ve reduced the air flow interference to a minimum in comparison to cutting the hole to be smaller just to support the duct.  Even so, there the circle is covering the corners of the rectangular exhaust.  I’d guess that ~5% of the rectangular exhaust is impeded by the MDF.  Best I could do anyways.

Exhaust Duct Reducer

To mount the duct I used two home made L brackets from some duct hangers that Home Depot was giving away.  I used some tin snips to cut out a rectangle then used some heavy pliers to bend them into shape.  Crude but effective; they are definitely strong enough.  I had to drill pilot hole for the screws.  After mounting the reduced to the MDF I used some proper duct tape (i.e. the foil kind) to seal the MDF to the reducer.  Below it is partially complete.  Spare no foil on this seal.  This is the seal that is most likely to leak.  The rest of the ducting is designed to fit together and provide a good seal.  This is a hack of the highest order.  No point in building a booth to vent fumes if it leaks now is there?

Exhaust Duct Reducer Partially Foil Taped

Once the exhaust was complete I decided to move on to creating the hole I needed for the dryer vent to be installed.  This is where it all went horribly wrong.  While I’m not an expert in construction I can use Google and talked to some friends about what I should run into.  The consensus is that there should be no issue cutting through the end plate to the outside.  Besides, my high efficiency furnace is already going through to the outside on the same wall.  So I proceeded to cut the hole.  Imagine my surprise when I hit concrete.

I won’t go into all of the details but the following photos are useful as towards an explanation.

Joists

Outside

Furnace Intake and Exhaust

The first photo is the back left corner of my house looking along the joist.  The 2×10 showing it’s flat surface towards us is the end plate I expected to cut through and then see day light.  The second photo is of outside where the furnace intake and exhaust are.  Notice how they are just over the concrete.  The third photo shows the same pipes and gives a clue by their placement as to why I hit concrete.

As best I can tell the joists here are sitting on a ledge.  If you look at the first photo again you’ll see that the foundation concrete on the left is the same height as the joists.  Basically, my joists are not sitting on top of the highest foundation and therefore I’d have to cut through concrete to get the duct out.   This sucks but the real issue is that the vent would then be below the siding.  If you look at the second photo that means it pretty close to the ground.  That’ s no good.

I’m pretty sure that the furnace guys must have butchered their way through the sill plate on the outer foundation (I can see the cut from the outside) and probably part of the framing that makes up the plate that the first floor framing is sitting on.  Probably the same for the A/C pipes but they are smaller.  There just isn’t 3″ of clearance to cleanly cut to the outside.  I don’t know what the idea was behind building the foundation this way was.   It puts the subfloor of the first floor even with the top of the foundation and there is no way to get to the outside from the basement.  The only reason I could think to do this is if there was a grade from the back to the front but there isn’t.  Even then raise the house by 6″ for God’s sake.

Anyways, that’s the end of venting to the outside using a dryer duct.  The main problem here is that the blower is sized for a 4″ duct.  If I go smaller I’m not going to get the correct CFM.  In fact the chart from http://www.briansmodelcars.com/tutorials/tutorial/23 show that the max CFM for 3″ is 200 CFM.  Remember that I needed 300 CFM or better.

I considered connecting to the existing dryer vent on the main floor but it’s 30′ of ducting away with tons of bends.  Again I won’t get the CFM I’m looking for, and I don’t think lacquer smelling clothes are popular.  With no way to cut a 4″ hole to vent to the outside, and nothing I can tap into, my only other option is to use a window.

Of course there are no windows positioned that I could run ducting to them.  Not to mention it would be a total hack job to leave the vent in the window all the time.

This doesn’t leave me with any other option than to go to the window.   Which means not using the bench as it’s just too big for the window I’m going to use, which is in the future exercise room.  YEEEHAA!   This gets better all the time.  At this point I’m ready to hunt down the builders from 20 years ago and get them to build me a new foundation.

Fresh Blower

Very nice.  It’s pretty hefty at 13.3  lbs too.

My next task was to wire it up.  Just in case anyone needs any proof that those Chinese factories are pumping stuff out as fast as they make it; the screws on the conduit box were stuck to because the paint was still wet when the screws were added to close the conduit box.  This required some serious screwing.  Something I’m out of practice with.

Anyways, after getting the conduit box open I discovered a screw for the ground, a white wire, and a black wire.  Time to splice!

The blower doesn’t come with any wire so you need to supply your own.  In my case I used a normal grounded extension cord.  This particular cord had three plugs available so I figured it was able to handle the current requirements (2.05 amps for the 1TDT2).  Turns out it conveniently had a tag specifying the specs of the extension cord.

Extension Cord Specs

13 amps is plenty.  When looking for your ‘donor’ see if you can get one with a tag.  Nothing reassures like a nice spec.

The next step was to cut off the plug end of the cord and strip back the insulation of the individual wires about 3/4″.   For my extension cord only the ground was identified.  The neutral (white) and hot (black) wires were not clearly identified.   This is where it pays to have friends.

I called up one of my friends who I figured would know which prong of the wall plug was the hot (black).  Turns out it’s the left prong when looking at the plug.  See below.

Extension Cord Plug - Left Prong Is Hot

Now that I know what prong is the hot (black) the next step is to find out which of the wires is the black.  To do this you need a multimeter.  The multimeter will allow you to test for resistance from a prong to the cut wire by placing one probe on a prong and the other probe on the cut wire.   If you don’t get a reading, it’s not the same wire.  Try the other and you should get some kind of resistance reading.  That means that the prong and the wire are a match.

Using the above technique I determined which wires were black and which was white.  After that it was simply a matter of using marrette’s to connect the wires to each other.  Marrette’s are the orange cap like things in the photo below.  This is the only way to connect wires safely.  Don’t even think of using anything else.  2.05 amps is enough to kill you if the wiring isn’t secured properly.  Do not cheap out or rush the wiring.

Blower Wiring

Voila!  A blower with wiring is born!  Let the blowing of air begin!  Before buttoning the conduit box back up I figured a test blowing was in order.

With some trepidation I placed a firm hand on the blower and plugged it in.  WOOSH!  Within a second the blower was up to speed and scattering stuff off of the kitchen table.  Very nice.  Its worth noting that I made an effort to make sure the blower was secure.  Anything with a motor attached that goes to full throttle as soon as you plug it in is going to torque.  In the case of the blower there was just a light nudge and that was it.  Probably because the chassis and motor weigh a lot more than the fan.  Anyways, don’t just let it rest on a table and plug it in.  Make sure it’s secure some how; and don’t actually touch the blower when plugging it in for the first time unless you wear an insulated glove like I did.  Keep in mind that electricity of the kind we are talking about will kill if not done properly.  In fact if you have any reservations about wiring the blower than don’t! Find someone that knows what they are doing and ask them to do it.

And on a lighter note here is the wired blower.

Wired Blower

The next stage will be to determine the routing of the ducting, shape and style of the booth and come up with a plan to implement them.

Dayton 1tdr7

The long story is I started off looking for a blower that could do 300CFM @ 0.4in based on the information from here: http://www.briansmodelcars.com/tutorials/tutorial/23.  His requirements were pretty close to mine so I just used his numbers to ballpark a blower.

Not very scientific I know! . I was being lazy…

I felt comfortable just ballparking it as a blowers CFM over increasing pressure is pretty linear which  meant that I had a margin of error.  To be honest I don’t know exactly what the configuration is going to be for the size of the booth and duct length.  I know what is too big and what is too small, and I know how much I want to spend ($<200) so it was always going to be a bit of juggling game. Basically I have to build to a price.

Now that I have a blower in mind that meets the price criteria and looks like it is flexible enough that it can support any miscalculations on my part I did run the calculations with what I thought should be close to the actual implementation.

So:

A booth  of 2.5 ft x 1.5 ft x 85 = 318 CFM.  The 85 is the FPM face velocity.  100 is best but 85 is all I can do with this configuration.  Building to a price again.

My ducting is going to be no more than 14′ calculated.  It should be all straight with one 90 degree bend.

SP over 100′ for 325 CFM in a 4″ duct is 4.87.

1/100 of duct length is 0.14.  0.14 x 4.87 = 0.68 in.

So in reality I’m looking at .7 more than .4.    Ideally I’d get a blower that can do 318 CFM at .7.  The 1TDR7 does 275 CFM @ .7.  Pretty close.  If I can reduce the ducting to 12′ (which might be possible as I can raise the position of the box) the new number is 318 CFM @ .6.  The 1TDR7 does 325 CFM @ .6 and that’s pretty much bang on.  The other option is to increase the duct size to 5″.  For 14′, 5′ diameter ducting the requirements are 318 CFM @ .2 and the 1TDR7 does 448 CFM @.2.  I have no idea where to get 5″ ducting though so I’m just going to keep that as a plan B.

The other option is to upsize the blower to the GGS1TDT2 model.  It’s on the same chart as the the 1TDR7.  https://www.acklandsgrainger.com/images/catalog/1106.pdf It does 390 CFM @ .7 and 435 CFM @ .6.  Going to the 1TDT2 would allow the ‘face’ value to increase to the 100 CFM that is recommended.  Also, I imagine it’s fairly easy to add some kind of bleed into the ducting if the blower is too strong and the CFM needs reduced.

Anyways, I think I’m going to go with the 1TDR7 and see what I can do about the ducting; if required.  It’s pretty much bang on what I’m looking for at 12′, 4″ ducting.  I like the idea of the 1TDT2 but I still need to buy ducting, some wood for a plenum, a vent for outside, etc.  I’d like to keep the cost to a minimum.

As for the hazardous stuff,  a TEFC (Totally Enclosed Fan Cooled) would be great but they are too much money.

The thing with the hazardous issue is that there are people out there using bathroom fans for DIY booths.  That puts the motor in the air flow and so far nobody seems to have heard of anyone blowing up.  The reasoning seems to be that the bathroom fans are inductive so no contact on the motor and therefore no sparks.  I figure the blowers motor is out of the airstream completely, and the general air won’t be saturated (or I’m dead) so the motor should never come into contact with fumes anyways.  I’m not sure if the blower motor is inductive.

I’m still not 100% convinced about the 1TDR7 though.  I might still go with the 1TDT2 in the end as I can always just reduce the airflow.

My research into what kind of CFM I’m going to need put me in the same area as the link  http://www.briansmodelcars.com/tutorials/tutorial/23 indicated for the author of that article.  Namely, about 250-300 CFM with ducting (static pressure).   Actually, his needs and proposed setup were very similar to my own.  I suspect that most people building a spray booth would have similar requirements.

I was going to write out the whole calculation but you really need to read the article and the author does a walk through on how he calculated his CFM.  A short summary of the whole process is below values are from http://www.briansmodelcars.com/tutorials/tutorial/23:

1) Calculate CFM required.  For example a cross draft spray booth measuring 1.5′ x 2′ multiplied by the recommended face velocity of 100 FPM gives you 1.5′ x 2′ x 100 FPM = 300 CFM

2) Calculate the length of your ducting using the below chart.  For example 4′ + 6′ + 3′ + 3′ = 16′

Ducting Chart

3) Calculate Static Pressure in ducting.  Quoted from http://www.briansmodelcars.com/tutorials/tutorial/23:

“To calculate the static pressure of your ductwork, multiply 1/100 of your duct length by the static pressure value.

For example, to meet industry standards, I need to calculate the SP for 300 CFM airflow through 16′ of 4″ duct. Multiply 1/100 of the duct length (for my booth – 16′ x 1/100 = 0.16) by the SP value for the duct diameter:
4″ Duct x 300 CFM = 4.19″ SP (static pressure value from table)
0.16 x 4.19 = 0.67″ SP (static pressure in the ductwork)

To meet industry standards, I need a fan capable of delivering 300 CFM @ 0.67″ SP.”

4) Find a fan that meets 300 CFM @ 0.67″ SP.

Since the spray area of my booth will be about the say size as the article I’m going to be looking for a fan that can do 300 CFM @ 0.67″ SP.

Our calculations of 300CFM with ducting is well above what a standard bathroom fan wil be able to achieve.  In fact a typical bathroom fan achieves about 100CFM with no ducting (no static pressure).  Which means the effective CFM  is a good bit lower.

I’m not sure how well those bathroom fan DIY booths actually work.  They’re obviously better than nothing, and will vent a space given time,  but I have my doubts about whether or not they are actually going to successfully attain a zero vapour, and therefore no respirator required workspace.

Just for fun I went into all of my bathrooms at home and with a bottle of baby powder tested out the effective CFM.  Well, I learned two things.  One is that baby powder is close but probably a little lighter than primer overspray and two, that baby powder doesn’t taste good and makes a mess.

I didn’t try to saturate the air but I did pump out enough that you could clearly see the wind currents in the bathroom.  The fans definitely weren’t able to pull the baby powder up and away.

It might just be my current older (20 years) home but I don’t remember my previous brand new home being better.  I tried the trusted toilet paper test on the new houses fans and I remember  unimpressive results.

In my opinion bathroom fans are designed to help move hot humid air that is already rising.  I don’t think they are designed to truly ventilate in a meaningful way.

On the other hand my kitchen stove fan worked noticeably better but still wasn’t strong enough.  Overspray towards the edge of the hood still came down to the counter.  It was definitely better though.  You could see the baby powder being pulled up towards the fan. Again, keep in mind that the baby powder is probably lighter though.

My conclusion is that bathroom fans, at around 100CFM will not be good enough to protect you from the harmful effects of an aerosol can or from airbrushing in general.  If your health is important to you then don’t use a bathroom fan.

A possible alternative is a stove hood, but even that isn’t 100%.

In the interest of fairness all of these tests were done with no ‘airbox’.  Meaning the fans were operating is a way that there was no cabinet surrounding them which would probably improve the ability of the fans to create an airflow that would remove overspray or fumes.  A spray booth would obviously have walls and is essentially a box with one side removed.  The smaller the box the better the fan would work I’d imagine.  However I still don’t think that a bathroom fan at 100CFM will cut it.  Especially in a cross draft situation.  A spray booth with a down draft configuration requires less CFM than a cross draft so maybe a bathroom fan would be fine in that configuration.

In the end I feel that I should get a fan/blower that can move 250-300+ CFM with ducting.  The cost of a centrifugal blower that can achieve that performance is around $150-200.  Not cheap but I’d rather have my health.

Also, there are a number of different industries that use centrifugal fans so it may not be that hard to come by one.  For example, a gas furnace uses one, hydroponics, and general commerce uses them.

I’ve asked a friend of mine that works for an industrial company to see if he has any at work that are due for replacement.  Normally they are just swapped out after x number of hours and still have life left in them.

Bottom line is good ventilation is worth it.  Put a bit of work into finding a good fan and understanding what your requirements are.