Dust haze.Even if you have a dust collection system
you’ve probably found yourself in the
middle of it. This fine dust settles onto all the surfaces
of your shop where it is a fire hazard (as well
as a nuisance) and can lead to respiratory problems.
A strategically placed air scrubber can trap much of
this dust, keeping your shop cleaner and safer.
Here are three shop-built air scrubber designs:
a between-the-joists design for small shops with
limited headroom; a hanging model for larger
shops; and a benchtop model to catch dust near its
source. Each scrubber is based on a kit available
from Penn State Industries (see Sources, below).
Once you’ve gathered your materials, you can
build any one of these scrubbers in a day. The
benchtop and between-the-joists models can be
built for $150, the larger model for $220. If you are
resourceful enough to find a used furnace blower
and use shop scrap,any model can be built for $60.
Although these designs are similar to scrubbers
available commercially, our scrubbers either cost
less or have better features.To make it easy for you
to find components, we’ve used kits and filters
available through catalogs (see Sources, page below).
Remember that no air scrubber is a substitute for a dust collector attached to your machines. It is always best to
catch dust at its source, before it becomes airborne. However, an air scrubber can trap much of
the fine dust that eludes your primary dust-collection system.
Which Design is Best for Your Shop?
These scrubbers are variations of the same machine, differing
in size and where they are placed in your shop.Choose the
one that’ll work best for you.
The benchtop model is small enough to be used where it’s
needed,whether it be on your bench when hand sanding, or
placed on a stool near your lathe. The between-the-joists
model is ideal for a small (500 sq. ft.) basement shop with low
ceilings.The larger model has two blower fans enabling it to
clean air in a shop twice as large (up to 1,000 sq. ft.) as the
other two models.
The capacity of your scrubber is another important consideration.
For occasional woodworking you need a scrubber
that can recirculate all the air in your shop six times every
hour or once every 10 minutes.A scrubber’s performance is
measured by the number of cubic feet per minute (cfm) of air
it can handle.
You can determine exactly how many cfm are required to
change the air in your shop six times every hour by measuring
the cubic feet of air space in your shop (LxWxH) and
dividing that number by 10 (professional woodworkers
should divide by 6). For example, if your shop floor space is
25 ft.by 20 feet and your ceilings are 8-ft.high, then your cfm
requirements are: 20 x 25 x 8 = 4,000 cubic ft./10 minutes
which is 400 cfm.Each of the motors in the Penn State kits are
rated at 465 cfm, which is adequate to handle a 500-sq.-ft.
shop with 8- to 9-ft. ceilings.For a 1,000-sq.- ft. shop, use two
of the single-blower units or build the larger double-blower
unit.When in doubt, over do it.This is one case where more
is definitely better.
There are usually two filters used in an air scrubber: a pre-filter
and a pocket filter. The pre-filter prolongs the life of the
pocket filter by capturing most of the larger particles first. The
pocket filter has a much greater surface area for trapping the
To make a scrubber small enough to fit on a bench we substituted
a 4-in.pleated filter for the pocket filter. Pleated filters
can provide as much or more filter area as pocket filters and
are available from Grainger in different levels of efficiency (see
Sources, below).For our air scrubber we chose a 75-percent
efficient filter ($28) which is more efficient than the pocket filters
found in most air scrubbers on the market.A 90- to 95-
percent efficient filter is available for $84. If you’re willing to
fork over the money, it’ll last longer and catch finer dust.
The Finishing Touches
Mount the between-the-joists
scrubber with corner brackets
(Photo 3). The larger model
should be hung using eye bolts,
ceiling hooks and chain. Add
handles and rubber feet to the
benchtop model so it can be
used vertically or horizontally.
It’s best to place a scrubber
where you make the most dust,
and as low as is feasible.None of
the three models are heavy, but
mounting the overhead models
safely is a two-person job.
Add ribbons to the exhaust louvers
so you know when it’s time
to replace or clean your filters
(Photo 2). A timer switch
enables you to leave the scrubber
on when you’re not in the shop.
The exhaust port of the air
scrubber can be ducted outside,
like a bathroom fan, to vent lowconcentration
brushing or rag-applying finish
(Photo 3). The cost for parts is
less than $30. To make, simply
cut a piece of plywood slightly smaller than the back of the scrubber to use as a mounting
flange for the stack boot. Cut an opening in the flange to allow the
boot to fit through. Attach the boot to the inside of the cutout with
silicone caulk and screws.To hook up the stack boot for outside
venting, simply screw on the flange over the exhaust port with a
pair of screws. Be sure to remove your pocket filter to help
increase airflow when operating your scrubber as a vent. When
you’re done venting, simply unscrew the mounting flange, replace
your pocket filter and you’re back to scrubbing the air in your
shop.Now you can breathe easier.