Great post, Don.

Can I make this "permanent" on the Wiki FAQ?

Shawn

: As was pointed out above, a filter unit doesnt do anything to keep the dust
: out of the air you breathe. To do that, you must either capture it at the
: source, wear a mask, or both.

: If you purchase a dust collector, and hook it up to the tools, you will soon
: find it to be one of the most used tools in the shop, and you will wonder
: how you ever got by without it.

: All that said, I'm assuming you have a box fan? Which is a propeller fan, not
: a certrifugal like is in a furnace. This will work, but not as well as a
: furnace fan. A prop fan will have significant changes in airflow with
: slight changes in the static pressure - filter pressure drop in this case.
: A furnace fan is better, and free or almost free from your friendly HVAC
: shop if youre willing to pull it from thier boneyard.

: But it will still work. Filters are rated by pressure drop and efficiency at
: 500 FPM face velocity. As the air velocity drops, pressure drop goes down
: and filtration efficiency goes up - both desired effects. So add more
: filter area, the more the better. I have a rectangular box configuration,
: with a furnace fan blowing out one end. All the other three sides are
: solid filter area, almost 20 square feet in all. Doing this lets you use
: the cheap filters available at your local hardware store.

: You'll want two sets of filters - one pad type, the lower efficiency. And
: directly behind it, a pleated type. Hardware stores have these in 1"
: pleats, 2" is better but either will do. This way the prefilter keeps
: the more expensive pleated filter clean longer. You can reuse them several
: times, by vacuuming them off. Also BUY THE FILTERS FIRST! Find a local
: supply, and a standard stock size for them. 20x20, or 16 x 20 probably. 24
: x 24 is a great size but (as I found out) it's a commercial size, not
: residential and local hardware stores dont stock them.

: Once you have the thing built, try to position it to keep the air in the shop
: stirring. This keeps the fine particles in suspension while the filters
: clean it. It will take several air chjanges in the room to clean it well,
: you want to size the volume (CFM) of the fan for about a 10-minute air
: change. For example, if the volume of your shop is 10000 cubic feet, you'd
: want a 1000 CFM fan. Dont bother to run the thing while you are working
: and producing dust - it's function is to clean the air AFTER the
: dust-makers are turned off. It may help a little while youre working, if
: youre standing in the clean air path. But generally it just stirs up the
: dust and brings more of it into the breathing space.

: And finally, dont assume that the air is safe just because you cant see any
: particles: The most damaging particles are 50 microns and down, and you
: cannot see them anyway. You still need a mask, no matter what, if you are
: suffering from allergies.