Air Purifiers-Do they really help control the dust? Trying to prevent fine Dust

Using a box fan like that for intermittent air flow works just fine. Folks should be careful, however, about running these long-term/constantly in a dusty environment. There are a lot of folks in the equestrian world who have done that for summer stall cooling because of cost and suffered tragedy when their barns burned down with loss of equine life. Our woodworking shops are easily as dusty as a barn can be, if not more sometimes, even with good DC. Consumer grade box fan motors are not particularly well suited to the conditions. For a little more investment, one can buy a very nice fan that's rated for the environment and they are even available designed for ceiling and wall mount.

I haven't done this yet, but have been thinking about it, wonder what people think.

I'm planning to build a downdraft table into an outfeed/assembly/multipurpose table that will likely live at the outfeed end of table saw most of the time. This will be connected to my 5hp 16" CV cyclone with 6" ducting. The sanders etc will be attached to my CT26. Thinking that double collection will work well for the handheld sanding operations...

Eventually looking to spend the coin for the iVac system for the major equipment. One feature of that system is the automated blast gates and timed overrun for the dust collector, plus one blast gate will always be open even if no equipment is running. I was thinking I'd set up the downdraft as the open gate when all others are closed, and extend the time the dust collector stays on a while, so that this downdraft table would be pulling air from near the middle of the shop (where a TS typically lives), at machine height where most of the dust is created. It would also keep the DC running for a little while between machine operations to avoid too much short cycling of the DC, all while cleaning the air a bit better (cyclone and HEPA filters). Not sure I'd want to leave my cyclone on for 2 hours after leaving the shop or anything like that, but might do a pretty good job of capturing the majority of airborne dust right after its created, and with much higher airflow/filtration than the typical ambient air filtration systems.

Might still do an ambient of some sort like the Pentz design, with a timer for air cleaning after leaving the shop, etc. But any thoughts on the downdraft/air cleaner concept?

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Originally Posted by Jim Becker

Using a box fan like that for intermittent air flow works just fine. Folks should be careful, however, about running these long-term/constantly in a dusty environment. There are a lot of folks in the equestrian world who have done that for summer stall cooling because of cost and suffered tragedy when their barns burned down with loss of equine life. Our woodworking shops are easily as dusty as a barn can be, if not more sometimes, even with good DC. Consumer grade box fan motors are not particularly well suited to the conditions. For a little more investment, one can buy a very nice fan that's rated for the environment and they are even available designed for ceiling and wall mount.

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Jim and others,

could the same concern exist for an attic gable fan, put there mainly for cooling but inevitably in a dusty environment? Or maybe those have TEFC motors?

jon

"Theoretically" the same concern could exist, Jon. A TEFC motor certainly would be desirable. Presumably, fans designed for attic/gable cooling are likely designed for continuous duty, too, unlike a common, cheap, consumer box fan. That said, I would hope that the dust concentration up that high wouldn't be anything like in the shop if one was collecting well at the source, etc.

One possible solution that I don't think has been mentioned yet is a powerful window fan in exhaust mode. I always use mine when the weather is suitable. It is an Air King model 9166F and it moves about 3500 cfm on high. That is far better than you can get with any filter system and you never have to clean it.

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Originally Posted by Thomas Crawford

Finally found some actual data on the woodworking specific machines:

https://www.finewoodworking.com/fwnp.../011213054.pdf

Is anyone concerned that these aren't HEPA rated? Seems like its just blowing the small stuff around.

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Thanks for posting the article link. The particles they're measuring in the test are 0.1 to 10 microns. A HEPA rating is based on the ability to extract particles 0.3 microns and up, with something like 99.9% efficiency. And keep in mind that filtration isn't instantaneous - it's still going to take some time for the particles to get sucked into the filter.

So I thought that the fact that these systems returned the shop to the starting level of particulates in 13 minutes or less, after they stopped cutting wood, was pretty impressive. Even while the sawdust was being made, all but the Delta kept the concentration at less than half the level of the control conditions. Combined with collection at the source, it seems like these will help maintain a pretty clean shop.

I have never been convinced about down draft tables because inevitably some of the available air flow get blocked by placing the object being sanded on the table and light fine micron dust floats and never gets pulled down by the draft. The least I would do is put a three sided enclosure around the table to trap some of the floaters. Getting really pedantic about the whole thing a clear three sided enclosure and a strip curtain front like you see in some door ways would contain most if not all of the sanding dust. Over kill? possibly but it would fix the problem for sanding small stuff. We built a dedicated sanding room for a chair manufacturer which was ventilated by a CV Max and it worked brilliantly but not everyone has the space or need to go to that extent. The incoming air was dragged from the floor up and there was very little that escaped the air flow.

Chris, I think that the size of the downdraft table matters because a larger surface that's perforated will have enough air flow to capture dust that comes off the workpiece, despite said workpiece blocking part of the surface. Of course, that sets up the conundrum of having enough shop space to accommodate a larger down-draft table, but being creative can help...and auxiliary work surface could be placed on top for things like incidental assembly and "portable" tool usage when sanding isn't being done.

My take on DD tables is if you can't feel a strong draft past your face onto the table then fine micron dust is floating away from the table and even then I would doubt that a DD table gets more than a large percentage of the fine dust. Call me a sceptic.

I read several years ago it was not good to run these air filters when in the shop. They stir up the fine dust and that becomes the problem. On the way to the filter, the dust passes by the woodworker. The recommendation is to run the filter after leaving the shop. I use 2 box fans that I place on the window sills and vent the air directly to the outside after leaving the shop. I have a cyclone but I also use a dust mask.

David (OP)
If you install it to pull air from the saw room and blow it into the other t=room it will keep the other room pressurized relative to the saw room.

BTW cheap furnace filters are not very helpful, good ones are better, HEPA are best.

A box fan is a poor choice as they are designed to move air with very little resistance, the kind of resistance you get by putting a filter in front of it. A cheap furnace filter will only catch large particles, so you need one with a high MERV rating, and those have a lot of resistance. I know. For several years I used a box fan with a Merv 8 or 9 filter with a cheap pre-filter in front. Even on high, the air flow was cut to almost nothing, especially after the filter started clogging. If you DIY, use a furnace blower which uses a squirrel cage fan which is designed to flow air with a filter in front of it. I ended up with a DustRite filter from Rocker (they no longer make it). Even with the filters far from clean, I still get a lot of airflow.

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Originally Posted by Chris Parks

My take on DD tables is if you can't feel a strong draft past your face onto the table then fine micron dust is floating away from the table and even then I would doubt that a DD table gets more than a large percentage of the fine dust. Call me a sceptic.

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You haven't used a proper downdraft table if it doesn't do that.

Ours is 4x6 and moves 3900 cfm. Not much escapes it.

Having a small shop with little space, I simply run the cyclone for an extra 10 or 15 minutes.......Much more cost effective for me than buying a separate ambient air cleaner.......regards, Rod.