Downdraft Table
This describes my version of a combined
downdraft and table saw outfeed table. This outfeed table also serves as a
whole shop air filter when it is run periodically during the day where
significant airborne dust has accumulated in the
shop. I also decided to build it as an integral part of the table saw
including dual miter gauge slots and an opening for
a blade guard, incorporating a 6 in. extension onto the downdraft table to
enable this. The extension is attached to
the downdraft table with 4 in. angle brackets spaced evenly along its' length
with sufficient clearance for the blade
guard pivoting shaft.
downdraft table keeps it solidly in
place utilizing the outboard adjustable levelling feet all around. The heavy-duty
handle at the front enables me to grip the
table to move it forward or sideways for any require maintenance.
When the
levelling feet are raised at the table saw
end, there are 3 attached casters which enable me to roll the
downdraft
table away from the table saw.
The top is a grid of 1 in. holes spaced 2 in. center to center. Drilling these
holes can take upwards of 2-3 hours
or so. You can make a small jig or template with the preferred hole spacing with
a 1 in. dowel attached, this
keeps the holes straight and accurate. The tabletop itself is a particulate
board with melamine surfaces on either
side. Holes were drilled using a 1 in. forstner bit. The diameter of the holes
and spacing were selected with
respect to both the size of the top and the need to maintain sufficient airflow
into the blower and filter system.
For example, if sanding a large piece which blocks an area of holes, the
remaining exposed holes can easily
compensate for the missing airflow. The underside of the drilled top has 3/4 X 1.5 inch hardwood
lengths of
board on edge
screwed to the top, reinforcing the top and making it much more rigid. I
currently have three
of these lengths
of reinforcing boards
running in different directions, perpendicular to each other.
The downdraft table is composed of a frame of 1 X 2 members and plywood skins
all around. The interior is
composed of 2 sections; the blower section and a similar empty cavity on
the table saw side. Both these
sections have sloping plywood tops which direct any dust into the dust pit at
the middle of the unit.
Heavier particulate falls to the bottom of the dust pit whereas finer dust is
directed to the pleated filter assembly.
The section with the blower has an additional frame to hold two separate pairs
of pleated filters. The pleated filter
pairs are easily removable for cleaning, and the bottom of the dust pit can
easily be vacuumed out with the top
removed. My criteria for this downdraft table and combined outfeed table were
that the unit be at my table saw
height and of sufficient width and length to adequately perform as an outfeed
table without taking too much
space up. I also used typical outfeed table dimensions to determine the length
and width of this unit.
The approximate dimensions for this downdraft table are as follows:
36 inches deep
6 inch extension
42 inches deep (combined)
34 inches high ( adjustable +/- .5 inch)
The blower and motor assembly is surplus and purchased for approx. $50.00 CDN. The motor can be purchased
either as an integral part of the blower, or separately. I decided to purchase the motor independently of the blower,
and construct my own wooden swivelling adjustable motor mount for it. The motor itself is 1/3 HP and very adequate
for the this application. The motor is not a TEFC type, since it is unlikely this sealed part of the downdraft table will
accumulate any dust. A TEFC motor is an option, or if available, easily adapted..
This portion of the downdraft table is also sealed with silicon caulk and I also
went over any seams with a flashlight
to ensure there is no air entering aside from through the 4 filters in the dust
pit area. For annual maintenance and
checkup, I remove one of the top manifold plates by breaking the caulk seal and
lubricate the motor bearings,
check the tension on the drive belt, and verify pulley screws, and belt tension.
Below, a side view of the combined outfeed and downdraft table. Notice the
extension between the downdraft
table and the back of the table saw. This serves both to permit clearance for
the factory blade guard and to
extend the depth of the outfeed table for the miter jig bars. If, in the future,
the outfeed table is no longer
necessary, this extension can be unscrewed and the downdraft table can be used
on its own in another
part of the shop. A molding has also been applied to the upper edges of the
downdraft table to protect the
plywood edges of the table.
The filters are arranged vertically in pairs. The filters are all pleated
filters. I have had success with this type of
filter in a ceiling mounted air cleaner I built a few years ago, and their price
is reasonable at approx. $5.00CDN
per filter. There is a short wood cleat and rubber band assembly which keeps
tension on the filters and serves
to keep them tightly against the blower housing portion of the downdraft table.
It is very simple to clean the filters
and dust pit with a vacuum. The top is removed, the inside is vacuumed, and the
filters are then removed and
vacuumed individually.
In the testing I have performed, it is sufficient to vacuum the inside of the
downdraft table with the filters in place
every few days or so. A thorough vacuuming of the dust pit with filter removal
is probably due on a weekly basis,
depending on the amount of sanding you perform, and the amount of airborne dust
in your shop.
The electrical system for the downdraft table is composed of a 60-minute timer
and a 120v dual receptacle on the
other side of the downdraft table. The timer is wired to the motor and the
dual receptacle is wired directly to a 120v
feed into the unit. The 60-minute timer allows me to run the downdraft table for
a period of time after I exit the shop
or for a few minutes after a dusty operation in the shop. This is the whole shop
air filter component of the unit.
The dual 120V receptacle allows me to plug in a small hand-held sander
for sanding work at the downdraft table itself.
Additional views of the downdraft table below:
Above, photo of the 60 minute mechanical timer. This timer allows me to
leave the downdraft table running
for a few minutes unattended to remove any airborne dust from the shop.
Above, photo of the dual receptacle for hand-held sanding tools along with a
close-up of the extension for the
table saw blade guard.
Above, photo of dust pit and pleated filter assemblies with filter frames.
Above, another view of the sloping components and the dust pit. The filter
frames are designed to have the
filters very easily removable for cleaning or replacement. Additional peripheral
support for the top can also be
seen. The underside of
the drilled top has 3/4 X 1.5 inch hardwood lengths of board on edge screwed to
the
top, reinforcing the top and making it much more rigid. I currently have three
of these lengths running in
different directions, perpendicular to each other.
Above, the filter frame assemblies. The filters are self- sealing to the
edges of the frame opening when blower
suction is applied.
Above, the adjustable outboard feet which lock the table at a fixed position.
These feet are easily backed off
to move the downdraft table for maintenance or to another part of the shop. The
other support are casters.
I no longer use the factory blade guard on my table saw, but rather use a
overhead blade guard unit and detachable
splitter. I can, at this time, remove the 6 in. extension and butt the downdraft
table directly to the table saw, but I
appreciate the additional 6 inches of length the extension provides.
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