Unusual & cheap (but valid?) approach to air filtration?

(Jonathan Shockley) #1

So given room size and cash limitations, I wasn’t going to install a standard air filtration system for the Nomad. So my roughly $150 approach was as follows:

1- Seal possible escape routes for the dust with top quality (audimute) weather stripping (except the fan and other necessary apertures). Since I was also using some soundproofing materials like audimute’s peacemaker rubber sheeting with duct tape this not only had the benefit of noise reduction, but also dust containment. Here’s a video showing what this looks like

2- Buy a shop vac, seal all air crevices with Gorilla tape, and add a special HEPA filter in the back for the air to go through https://www.amazon.com/gp/product/B0100FJ7E4/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1 Just as with the Nomad, I also added 3.2mm peacemaker to make it quieter, which worked quite nicely.

3- Get a Holmes True HEPA Air Cleaner for medium rooms https://www.amazon.com/gp/product/B000H0Y5XQ/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

4 - A Comfo Classic mask with cartridges (which I already had)

(Jerry Gray) #2

You cant be too careful.
I almost died from an unknown lung infection 2 months ago, and I’m suspicious it’s from routing old, moldy, wood, oh yeah, and smoking cigs.
I had fluid behind my lung and had to have surgery to remove it.
Split me 8" wide, and spread my ribs to manually remove the stuff.
I quit smoking, and I take the wood dust way more serious now.
I don’t use old, moldy wood anymore, either!
Wood’s cheap compared to weird, awful, pneumonia.

(Tony) #3

Unless you are cutting a material that you are allergic to or that is a special case, using a shop vac with a bag liner and the best filter will be plenty even with no additional sealing to the enclosure. It takes very little air flow to keep the fine dust from escaping. I’ve tested the output of my rigid shop vac with a bag and filter using a laser particle counter and the air coming out is cleaner than the ambient room air.

I use a cyclone before the shop vac so I never have to change the bag or filter.

(Tony) #4

Running a shop vac for more than a few minutes becomes maddening if you use your machine much.

I’ll propose a nearly free and easy option that is nearly silent and would have plenty of air flow and great filtration …

Cut a dryer hose size hole in the enclosure and run a dryer hose to a box with a high end furnace filter inside. The “box” could literally be a cardboard box sealed with duct tape but needs to be sealed well enough to maintain a vacuum at the Nomad end of the system. You don’t have to worry about small leaks because everything is at a slight vacuum so leaks will only allow ambient air into the system but it won’t allow the dirty air out as long as the filter blower is running. The outlet (low pressure side) of that filter box would be plumbed and sealed to the intake of your HEPA air filter system. The furnace filter would not affect the flow rate much and it would catch 80% of any fine dust. Your HEPA air cleaner would catch practically all of the rest. You could still run the filter even when you aren’t machining to keep the room air clean. Using magnets to couple the hose to the air cleaner inlet would allow you to use your air cleaner in other rooms without much hassle.

(Jerry Gray) #5

I have a recycled dryer blower I plan to hook up, when I get an enclosure built :slight_smile:

(Tito) #6

Tony, any recommendations on really quiet blowers? I spent an afternoon a while ago trying to figure out what might be a quiet high cuft/min blower for a setup much like you describe but there isn’t much objective data (that I saw at any rate), and what’s quiet to some is loud to others. Hence my question. Thanks.

(Dan Nelson) #7

I’m not Tony, but I’ve tried a couple different shop vacs with varying degrees of quietness. First I just used my well used/abused Rigid vac that I’ve had for years and it was definitely louder than my SO3. Next I looked at and purchased another larger Rigid vac based on the db ratings and it was quite a bit quieter, but still louder than the SO3. On the larger one also after a long cycle, like 4 hours it started screaming a little, shop vacs just aren’t made to run for hours at a time. Just as I was musing building an enclosure for the shop vac, and debating on if it would just be a short while before buying another one, I just took the plunge and bought a Fein tools Turbo I. Much quieter and since I used a dust deputy in between it should be ok on filters. Haven’t done any long runs with it, but it appears as though I made the best choice. Time will tell, but so far I’m pleased.


(Tito) #8

Thanks @DanoInTx. I have a Workshop 14 gallon that’s pretty quiet as shop vacs go (don’t feel the need to wear hearing protection), and a tiny little ShopVac from years ago which shrieks. I’m still realky curious about blowers and exhaust fans (there is, for instance, quite an industry around indoor growing fans and associated odor filters–but little objective data).

Edit: Forgot–I also have the small Festool that is decidedly quiet. I got it when I thought I might use my Nomad in the house, but I’m more comfortable using the Nomad in the garage, where I have the Workshop vac (going through a cyclone). So the Festool stays inside these days.

(Tony) #9

The easiest option would be to plug your shop vac into a $15 router speed control (Amazon.com) and turn it down until the flow rate is just high enough to create some flow through your enclosure. I have run any tests but my guess is that 20 CFM would be enough to keep any fine dust from escaping a Nomad enclosure. At 20 CFM even a shop vac will be quiet.

I’m running about 100 CFM through my Shapeoko enclosure which.is probably 10x the volume of the Nomad enclosure and the air quality inside the enclosure never gets bad.

(Tony) #10

To give you a feel for power, CFM and vacuum pressure for various air pumps I’ll offer this overview. …

The power output of a blower equals the vacuum it draws in inches of water column x the CFM output divided by 8.5. For reference, 1 psi = 27.7 inches of water column pressure.

Shop vacs are noisy because they are designed to produce 2 - 4 psi of vacuum which requires around 30,000 rpm at the impeller which is around 4" in diameter. They need to offer higher pressure so the flow rate doesnt drop too much when the filter starts getting dirty. More rpm usually means more noise. The big ones draw around 1500 watts and provide around 130 to 180 cfm with a clean filter and no restrictions other than the hose. If you block the hose most will produce around 2 psi of vacuum.

A 1.5 hp dust collector also uses about 1500 watts but it will have a large 11" impeller turning at around 3400 rpm. Dust collectors produce a max of 0.5 psi or less when the inlet is blocked and around 800 cfm free flow (for a 1.5 hp one). Since the impeller is turning 1/10 th the rpm a dust collector is much quieter. They use huge bag or cartridge filters so they don’t need much pressure to move a lot of air through the filter.

There are all kinds of fan designs in between those two. A furnace blower operates at around 1200 cfm and 0.2 inches of water vacuum (0.2/27.7 psi) with just around 500 watts. They don’t flow much at all through a restriction though.

That should give you a basic feel. Feel free to ask if you have more questions.

(Jude Marleau) #11

The cheapest solution is probably a real good face mask respirator, it’s a pain to wear all the time but it will protect you while you figure, calculate, consider, contemplate, calibrate and convince your budget that it is worth the expense. Just my thoughts and what I do now.

(Dan Nelson) #12

This is a good/inexpensive solution for sure. I have a close friend that makes custom gun stocks and pistol grips for a living and he started with a dust mask, worked up to full blown respirator and has now for the last several years used a forced air respirator with his air supply pump outside of his shop. He works year round in an unheated/uncooled metal building in North Texas weather, but never works without his respirator after a few good hospital visits due to lung issues. Granted his exposure is higher than most of us and he cuts some crazy exotic woods and colorful laminates that are potentially worse than most, but even our little exposure risks can be life threatening. Be safe!