shop air filter

[Edward Fornoff]

Does anybody have a plan for filtering dust out of workshopor know of magazine that might have a article on one with a squirl cage.

Thanks guys

[Jim Becker]

WOOD Magazine had one awhile back.

Just be sure you understand that the air filtration system is good for helping keep some of the find dust off your shelving, floor and bench, but it's not going to help you relative to your health...you must collect the dust at the source for that. Once it's in the air, you are breathing it in...and it's the dust you cannot see that is the worst for you.

[Todd Hyman]

Woodsmith #95 has a good article on it.

[John Grossi]

Jim, you said to contain the unseen dust you must get it at its source. How does a hobbiest do this without spending a lot of money? In an earlier thread, I asked about the box air filter type that hangs from the ceiling. You replied it was good but I would still be breathing in dust. A good quality dust mask which is cumbersome, a chip collector and an air filter is all I can think of. Any thoughts? Paul

[Charles McKinley]

Hi Paul,

I believe that Bill Pentz said that the Jet 1200 with the canister was acceptable. if you could find tha Harbor Freight DC and retro fitted it with a cartridge may be an acceptable budget solution. I use a 3M airstream helmet but it is expensive. Several people like the Triton that is considerably less.

Depending on your tolerance and how much work you do you can roll the dice and use nothing. People did it for years. Read Bill Pentz 's websit and at least make an informed decision.

[Greg Stanford]

My shop is a two car garage & whenever I'm out there the double door is open -- basicly one wall open. I have a couple of box fans w/ ac filters taped to them that I run & I wear the "Dust Be Gone" mask when sanding but that's about it. Most of the sanding that I do is done on sawhorses in the driveway (this is south mississippi, we don't get cold). Most of the work I do is done on the table saw (contractors, no dust port) or the lathe. Is dust collection really something I need to be concerned with? Noise & $$ have kept me reluctant.

thanks,

g

[Charles McKinley]

Gregg brings up a good point. According to Pentz some of the cheaper bag units actually can make the problem worse buy pumping more of the ultra fine dust into the air. A case where something is worse than nothing.

[Wilbur Pan]

Just be sure you understand that the air filtration system is good for helping keep some of the find dust off your shelving, floor and bench, but it's not going to help you relative to your health...you must collect the dust at the source for that. Once it's in the air, you are breathing it in...and it's the dust you cannot see that is the worst for you.

I've been thinking about this for a little while, and I think that an air cleaner may be underappreciated as far as dust control goes. Of course it's best to trap the dust at the source, but if the fine dust is going to escape, which has been shown to be more or less unavoidable, then trying to trap it is better than not trapping it at all.

I did some modeling of an air filter system to see what might happen. My shop is small, 20' x 10' with low ceilings. But let's assume I have normal 8' ceilings (I wish!). That gives me 1600 cubic feet of air.

So if an air cleaner operates at, say, 750 CFM, that means that it will cycle the air in the room every 1600/750 = 2.1 minutes. During that cycle it will trap some percentage of the dust due to filter inefficiencies, not actually circulating all the air evenly, leaks in the air cleaner, etc. Most manufacturers specify dust collection efficiency well into the 90% range. Let's say that the air cleaner really only traps 75% of the dust in one cleaning cycle. 2.1 minutes later, 75% of the remaining dust gets captured. Another 75% of the remaining dust gets captured at the 4.2 minute mark, and so on.

The important thing I found was that because of this, the effect is exponential. At just under 11 minutes, 99.9% of the dust will be trapped by the air cleaner, with these parameters.

After fiddling with the numbers, I've found that the main factors in play are the ratio of the CFM of the air cleaner to the room, and the estimated efficiency of the dust trapping. This probably explains why air cleaners are not often thought of as that important. It seems that most woodworkers have much larger shops than I have, yet most air cleaners that are purchased seem to be on the small capacity size. It's like expecting a cheap 1 HP dust collector to collect all the dust from a 20" planer.

As far as the efficiency goes, one of the frequent criticisms of air cleaners is that they clean "the same air over and over". Certainly the "racetrack" phenomenon has been shown to be true. But one of the easiest ways at improving air circulation and mixing would be to put the air cleaner at one end of the shop blowing air towards a wall, and to place a fan at the opposite end of the shop aimed in the direction of the air cleaner. Make it an oscillating fan, and air mixing would become much more efficient, resulting in more dust being processed by the air cleaner with each cycle.

Even better, it may be that two or more smaller size air cleaners are more efficient than one large air cleaner of equivalent CFM capacity, due to the air mixing issue. Spending $600 on two JDS 750-ER (1500 CFM total) units and potentially getting better results than a single $750 JDS 10-16 unit (1600 CFM) certainly appeals to me.

My conclusion is that air cleaners can be very effective if they are matched to the size of the workshop they are installed in, and if efforts to ensure good air circulation are taken. Again, playing around with numbers, aiming for a total CFM that is 50% of the volume of the room seems to give very good results.

None of this is meant to supplant the importance of collecting dust at the source. But this seems to be a nearly impossible task, and this makes for an effective backup system.

I'd be willing to post my spreadsheet if anyone's interested.

[John Grossi]

Wilbur, Thanks for the info. I would like to see your spreadsheet. My shop is 2300 sq. ft, so I figure a 750 cfm air cleaner moves air around every 3 minutes. Any input on a brand or type of air filter that is better then others? Also how often are the actual filters swapped out? Paul

[Todd Hyman]

Why not make your own. That is what I am going to do. All you need is a squirrel-cage fan and some furnace filters. You can get a used fan from any hvac contractor and then build a box around it and install 2-3 filters on the intake side and one on the exhaust. Woodsmith #95 has a very good article on this.

[John Grossi]

Todd, Know where I can get a copy of this article? Just checked Woodsmith's web site. Not going back as far as issue 95. Paul

[Greg Stanford]

I'd be interested in that article as well, also wonder if anyone knows how much good these little box (window, 20') fans w/ the filter do? I've seen others use the same setup.

g

[Wilbur Pan]

Wilbur, Thanks for the info. I would like to see your spreadsheet. My shop is 2300 sq. ft, so I figure a 750 cfm air cleaner moves air around every 3 minutes. Any input on a brand or type of air filter that is better then others? Also how often are the actual filters swapped out? Paul

Here's my spreadsheet. Sorry that I can't help you much with the other questions. I've worked out the math so far, but I'm still shopping for an air cleaner myself. I'm leaning towards the JDS air cleaners. They seem to get consistently good reviews, and their specs seem to be based on real world performance. But I do plan to incorporate an air cleaner with an extra fan to help circulate the air in my shop as part of dust control.

[Todd Hyman]

Todd, Know where I can get a copy of this article? Just checked Woodsmith's web site. Not going back as far as issue 95. Paul

I can scan it on Monday and I will send it to you. I don't know if I can attach it to a pm so send me your email address.

[John Grossi]

Wilbur, Thanks for the spreadsheet. Very informative. Paul