ARTICLES & REVIEWS
Overarm Dust Collector/Saw Guard
by Will Reyer
I spent 18 years breathing sawdust in junior high school wood shops before I started doing mechanical design. When I retired I bought a 2HP dust collector that blew all the fine sawdust back into the shop. Enough was enough. I found Bill Pentz’ site (billpentz.com) and bought some 6" PVC pipe and ran it from my jointer and table saw and made a couple other blast gates so I can hook up my other tools. My shop is on a small farm, so I kept the impeller and motor from the dust collector and blow the sawdust outdoors.
I had a wye that went from one 6" to two 4" diameters. I ran one of the 4" legs to the base cabinet of my Powermatic 66, but what I really wanted to eliminate was getting a face and shirt full of sawdust off the blade. I looked on-line at commercial overarm dust collectors, then at home-made ones. I made sketches of ideas and mechanisms I found that looked useful. Then one day in the Dollar Store with my wife, I saw a semi-transparent plastic shoe box that looked big enough to clear the 10" blade on my table saw, bought it, and what follows is the result.
The dimensions to fit my saw may not come close to working with yours—but perhaps you could use my text and photos as a point of departure. Do the math. Make a layout (CAD or full-scale pencil). Be adaptable, and open to what’s available. I make no warranties that this is a good, safe, or useful design. If you need dimensions and blueprints, you’re probably better off purchasing a manufactured product.
I made a run to the city to the surplus steel place—new stuff indoors, rusty stuff outdoors. I knew I wanted some 2" square tube, because my Powermatic has an angle iron on the back that aligns the tables and extensions—easy to attach to. They had some rusty 2" square tube in both 18 gauge (.0478") and some thick-wall stuff. It didn’t look like it required heavy equipment so I bought 10 ft of the 18 ga. I also wanted some small, light 16 gauge angle or some 1⁄8" flat aluminum for the horizontal parts of the parallel bar assembly. They didn’t have any. I wanted some tubing to telescope into the 2x2—they didn’t have any. They did have one 20 ft length of ¾"x¾" square tube, so I bought that and the 2x2 for $9.65.
The leg of the overarm that fastens to the back of my saw with two 5⁄16" bolts is 24" long. The vertical member is also 24", butted on the lower member. The top horizontal is 51" long, sitting on the vertical member. Miters could work instead.
I used some like-thickness scrap sheet metal and boxed in the end of the lower arm that’s nearest to the saw blade with my MIG welder. It’s barely visible behind the rip fence in the rear view of the saw. Leaving the tubing open-ended there would have meant that the hold-down bolt would have collapsed the tubing.
I also cut two 4" pieces of sheet metal and boxed in the open ends of the two horizontal tubes that face away from the saw blade. Without making extensive and massive welding fixtures, plating in the two open ends will move the top horizontal arm up past horizontal when the welds cool. I just took my Sawzall and kerfed the three sides of the vertical tube nearest the saw blade, and re-welded the cut. This pulled the top horizontal down below vertical slightly, so I padded the back side of the vertical column a couple times until the shrinkage drew the top horizontal back near level. I needed to drill some diameter ¾" holes in the side of the lower horizontal to clear the bolt heads that align the table extensions on the saw.
I wanted to be able to move the plastic shoebox dust collector left and right from the blade so I could get the rip fence as close to the blade as was practical for narrow rips. For this reason the top (horizontal) arm of the overarm stops short of the saw blade to the right, as you face the saw. If you’re going to rip narrow strips, you’ll need an auxiliary rip fence from ¾" stock as a spacer lying flat between the blade and the saw’s rip fence in order to cover the blade with the dust collector.
I had wanted to telescope some square tubing into the open top end of the overarm, but didn’t have any. I settled for some scrap red oak from a pallet. I laminated up a piece about 19" long. I chamfered the two bottom corners to clear the small inside radii on the 2"x2" tube—typical machine-design procedure. I let the top of the oak be short of the top of the overarm, and used a sheetrock screw on the inboard end of the oak, vertically, left proud, to provide a stop from tipping. I faced the sides of the horizontal oak arm with scrap Formica for bearing surfaces. Get a close fit to the sides of the tubing, as any sideways movement will be magnified as fore & aft motion down at the plastic dust collector box near the saw blade.
A piece of the same red oak made the two vertical pieces of the parallel arm assembly, gusseted with scrap pine at the top of the upper piece and the bottom of the lower.
The lower vertical arm sits on a piece of ½" plywood, fastened with glue and a sheetrock screw. The plastic shoebox dust collector is fastened to the plywood with four short sheet metal screws and flat washers.
The horizontal arms of the parallel arm linkage are from the ¾" steel tubing, with plates welding up the open ends, just for appearance. All holes are drilled at nominal size, .250" diameter. The stance of the bolts for the parallel arms in my case is 8½" vertically and 15" horizontally (diagonally). There are four ¼-20 x 3" hex bolts assembling the parallel arm mechanism with 16 ¼" flat washers spaced between parts. The front two bolts use nuts with nylon locks. The back two use T-handles ($1.48 ea, p/n KLK-25, from Reid Supply, www.reidsupply.com).
I made a quick and dirty wood assemblage of the geometry of the parallel arms to verify my layout using some scrap 3⁄8" dowel as pivot points before I made the real thing. I wanted to be sure that the back edge of the shoebox missed the saw blade by a good margin when the blade was all the way up. Keep in mind that as the dust collector rises above the table it swings an arc.
The upper parallel arms are 32" long, made long for several possible purposes:
I was out of scrap steel thick enough to make a splitter for the saw blade—an important safety feature. I found a scrap of 14 gauge (.0747") behind the shear at the local welding fabricator’s, and paid him $3 for it—expensive, but cheaper than another 60 mile round trip to the city. I used the original Powermatic blade guard geometry for the interface to the saw.
The front of the lower vertical arm, above the plastic dust collector shoebox, is fastened to the 4" PVC pipe (ASTM D-2729—the thin-wall stuff) with a 5-Minute epoxy kit from the Dollar Store. I had the 4" ribbed plastic flex pipe on hand. I ran a length of this up to an elbow and more PVC ASTM D-2729 S&D pipe to the vacuum line which was constructed of 10' sections of 4" diameter D-2729 ($6.40 each at one of the local big boxes). Elbows are $3-4 each (also at the big box). For smoother air flow, two 1⁄8 bends (45° elbows) make more of a sweep curve than one 90° elbow.
To adapt the flex pipe to the PVC, I cut a 4" length of the PVC, ripped it lengthwise on one side, overlapped the cut, inserted it into an uncut piece of PVC, and marked the overlap. I cut outside this overlap line and planed the mating edges of the PVC with a low angle block plane until it was the correct diameter to just fit into the pipe. I cleaned and glued the edges of my reduced diameter pipe. When set up, I glued 2" of the 4" length into the end of the PVC that rises from the plastic shoe box dust collector. The plastic flex hose is a snug fit over this 2" length of reduced diameter PVC—so much so, that the radiator (Breeze) clamp in the photo is redundant.
The plastic ribbed flex pipe rises to a 4" PVC that is fastened to the 9’ ceiling in my shop. It's a simple expedient so I didn’t have to fabricate brackets to keep it stable in the air lower down or fasten it to the overarm. I’m sure I give up some efficiency this way, as it’s a longer route for the suction.
The 2HP motor and 12" impeller pull vacuum through 11 feet of 6" PVC and then it wyes into two 4" diameters which run to the saw cabinet (8') and the overarm dust collector (19'). The vacuum at the saw table is pretty strong. I usually adjust the clearance of the pickup to about an inch above the top of what I’m going to rip, so it doesn’t suck the basket down onto the work.
This was an all metal project involving welding, and we are, after all, woodworkers. However, if you don’t have metal-working skills (or tools), I’m convinced you could still build a similar concept mostly out of wood, except for the pivots, the plastic pipe, and shoebox (none of which are, strictly speaking, metal working anyway). One could laminate components for strength and stability from warping, for example—perhaps make the overarm an I-beam cross-section.
. . . Will Reyer
© 2007 by Will Reyer. All rights reserved.
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