A Shop Built Air Cleaner

 

A common topic that pops up on the newsgroup rec.woodworking is how to make your own air cleaner.  Some have never heard of them, others confuse them with dust collectors (DC's).  First, a DC is made to collect wood shavings, chips, and sawdust direct from the source via hoses and pipes which lead back to a dust collector.  I do have a dust collector (a Grizzley G1029) like the one on the right.  While DC's do a good job getting dust through the hoses, some always seems to escape, and sanding, handling stock, and just moving things around always seems to kick more into the air. If you've ever cut MDF, you know how much dust can get into the air...nasty stuff to work with (IMHO).  
So, people make (or buy) air cleaners.  The simplest version is a plain box fan with a couple of filters attached to it.  While this works, it doesn't trap small dust since the filters used are fairly coarse (think big holes) and they don't have the suction needed to use finer filters.  Commercial units are easy to come by and shop sized units cost about US$250.  One example is this unit from JDS (rated for 750 CFM).  All work well, and use a blower similar to that found in a forces air furnace to move air through a successive array of fine filters.  This removes a considerable amount of the dust left hanging in the air and gets it away from your lungs as soon as possible.

 

Since I didn't have a lot of cash to buy an air cleaner, I thought I'd make my own.  The general suggestion for people looking to make their own is to check around with the local HVAC contractors (heating-ventilation-and-cooling) to get a used blower from a furnace someone replaced.  I always planned to do that, but never got around to it.  Then one day I ran across an old furnace that someone had just tossed out for the trash.  Since I have an old beater pickup, I tossed the whole thing into the back.  My quarry?  The old blower.  It was just what I was seeking for the air cleaner I wanted to build.  The blower was rated at over 1200CFM and has three speeds.

I used this to build my own air cleaner.  The size is 36"L x 24"W x 16"H.  The size isn't very important as you will see in the steps I outline below.   It really depends upon a couple factors.  First, how big is the blower you are going to use!  Don't forget you need a little extra room for air flow (more below).  Second, how big are your filters?  You can buy pocket filters from a number of places and they come in a variety of sizes.  Likewise, you will probably want a couple disposable filters as well to get most of the dust before it hits your pocket filter to extend its life.

I decided to try my hand at using MDF in building this.  Never again for this kind of project.  Too heavy, FAR too dusty (I needed the air cleaner building the air cleaner :-)  I also ended up controlling this with an X10 module and remote control.  I did the same thing earlier with my DC and both work great.  I've got small remotes scattered around and can turn on either without walking across the room.  It really helps to make me USE the cleaners!  I've got more on the X10 stuff here.

 

Here you see the old blower ready to mount onto the bottom piece of the assembly.  It is mounted to a piece of MDF (and the blower outlet rough cut with a jigsaw then cleaned up with a flush trim router bit).  The blocks are to make up the difference in height, support the blower, and give it a little more inlet area to improve the flow.
The blower in place.  If you look at the full size pictures (click on any  picture for a huge one) you can see I used spline joinery (splines from strips of thin plywood).  I don't have a biscuit cutter yet so that was the best I could do.  It turns out that it is NOT the best for MDF.  The outer lip of MDF that results when making the dado looks good, but tends to shear off when doing the final glue up.  Several of my dado/splines turned into rabbit joints :-(  If I were to recommend this to someone else, use some good 1/2" plywood.  It will probably cost the same, weigh less,  and be easier.
The inlet side of the unit after glue up and assembly.  You can see the switch box on the right.  Note: This is an all glue project.  The only mechanical fastners are the bolts holding the blower (seen below), the eye-bolts at the top to attach chains to, and the screws holding the two end covers on (to allow for filter cleaning).
Ready to install the filters.  They included a cheap $0.80 "big stuff" filter, a $6 3M pleated filter, and a JDS replacement 5-pocket filter from Amazon (which took forever to arrive).  Current price of this is $32.
The assembled inlet side.  The switch was a three position 6A rotary switch from the local hardware store.  Leviton # 806.  I used a blank cover plate and drilled a hole in it.  This switch is still available from Leviton, although it is not in the on-line catalog.  If you can't find it in your hardware store, try an electrical supply house. Here is a PDF of the specifications sheets
Leviton Switch Information.pdf (247k)
View from the outlet side.
Another view of the outlet.  You can see the small bolts I used to hold the blower in place, and the outlet for the power cord. Note the threaded inserts in the corners for the cover screws.
I used a single cheap filter on the outlet as a diffuser, and to give it a slightly cleaner look.  I was going to paint the whole thing white, but have never gotten around to it
Here it is hanging in my basement shop, inlet side.  It turns out to be so strong, I use it on "low" most of the time.  It seems to help keep fine dust out of the air pretty well.
Middle view
and outlet side.  If you look closely at where it plugs in, you can see the X10 RCA appliance module I use to turn it on and off from remote.  

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