Downdraft Sanding and Routing Table by Ed Sheriff
I have two compelling reasons to control the fine dust that results from sanding and routing with handheld power tools: My shop is in my house, next to my home office and on the same floor as two bedrooms; and I've developed an allergy to wood dust.
Commercially available downdraft sanding tables control that kind of dust well, but they're too big for my small shop, not to mention expensive. My solution was to build my own downdraft table. It's basically a piece of casework with a furnace blower mounted inside that sucks dust and chips down through the grille that forms the top of the table. Three layers of furnace filters trap the dust and chips, letting clean air exit through the blower's outlet.
I put casters on the table to make it portable. It stands the same height as my bench, so that I can use the bench to help support long workpieces. (See photo, right).
The length and width of the table are based on the size of the filters. The 20-in. by 25-in. filters (nominal size) in my table are about twice the width of the blower. This lets air flow freely into both sides of the blower, without taxing the motor or hurting the filter efficiency.
The power plant for my sanding table is a used, 1/3-HP furnace blower, which provides just the right amount of power for a table this size. Heating contractors are good sources for used blowers; or you can buy a new one (average cost: $200) from a heating, ventilation and air-conditioning (HVAC) supplier.
If you need a larger working surface on top than mine offers, you'll have to start with a larger furnace filter—they come in a wide range of sizes—and calculate your case dimensions from there. Then you may need to use a '/2-HP blower (which can cost up to $300 new). If in doubt, ask your HVAC dealer for guidance in matching up an appropriate blower with whatever filter size you choose.
The kind of switch you need and the wiring scheme depend on the type of motor in your blower. You can get advice on switches and wiring from the same HVAC dealer or from an electrical-supply house.
As shown in Fig. 1, the base for my table is just a case made from 3/4-in. plywood. I joined the sides and bottom with rabbet joints.
I positioned the blower outlet in the interior of the cabinet so that the air can expand, and therefore decrease velocity, before it exits. The outlet wall and its "shelf fit into stopped dadoes cut in the sides. The size of the outlet wall depends on the dimensions and mounting details required for your blower.
The baffle redirects the airstream coming from the blower, to avoid stirring up dust on the floor of your shop.
Lining the case interior with acoustical tile helps to deaden the noise of the blower. And a layer of felt, glued to the top edge of the case, fights any tendency the top might have to rattle when you're using the table.
My system for mounting the filters is simple. A ledger is screwed to the case interior to support a stack of three filters and the two spacer frames that separate them. Each spacer frame consists of four pieces of 3/4-in. by 2-in. hardwood, joined with miters at the corners. I glued a layer of ^/8-in. polyurethane foam (available at fabric stores and upholstery shops) around the case interior above the ledger to create a seal around the edges of the filters. The foam compresses just slightly when I lay the filters in place.
To change or clean the filters, you simply lift off the top and then lift the filters and spacers out.
With its l-in.-square openings, the grille takes time to make, but it's worth the effort. The ample air spaces allow much greater air flow than pegboard.
I made the grille out of '/8-in.-thick oak strips. But if I were to do it again, I'd use maple or poplar, which are less
Deluxe grille. Chips and sawdust get sucked through the hardwood grid that forms the top. Shop-made plugs help hold the workpiece.
(left) collects most of the dust; and the other two catch the rest.
likely to crush when you hammer the parts together.
The shorter grille strips are in. wide; the longer strips are 1 in. wide. I simply ganged the longer strips together and cut '/S-in.-wide, V8-in.-deep slots on the
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