Dust Extractor

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As a result of our recent interest in doing some woodwork as increased recently (Inspired by acquiring some Triton saw benches and a freebie router), it became apparent that with all the new saw dust flying around the shed and the garage this wasn’t going to work well with our cars or our lungs! Using our vacuum cleaner works ok, but the dust will soon damage the motor so a better solution was needed.
I decided to have a look at some dust extractors.. There are basically two designs, both of which use a cyclonic effect to spin the dust around inside a chamber where gravity allows it to fall away into the lower part of the container. Inspired by the ingenious work of  Matthias Wandel I decided to make our own…

1 → First you need an air tight bucket of some decent size. I got this one from a bakery for $6 – I’m not sure of the volume but its about 25L I would guess.PSX_20150629_002219
2 → Next you need to cut a timber baffle to provide the cyclonic effect. I used J. P. Thien’s design and used a jig saw to cut 12mm plywood into a circle that would fit inside the bucket about 100mm below the lid. Then re-cut the inner circle at roughly 20mm less in radius for about 240 degrees (2/3rds of the circumference). I sized the outer circle to suit the inside size of the the bucket at the widest inside diameter less about 6-8mm to allow for the taper of the bucket wall. You could do some better trigonometric calculations to achieve a better fit, but this did the job well enough.
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3 → Using 1/4″ dia threaded rod I drilled three holes to fix the baffle to the plastic lid of the bucket. This proved a bit flimsy in the end so I cut another circle to fix to the top of the lid (after I cut the holes for the pipe connections).

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4 → Using a suitable hole saw I cut holes to match the 25mm (ID) pipe that I found laying around in Bert’s pipe collection. The Pipe OD was about 30-32mm so the hole saw by coincidence made a hole that was a tight fit to the raw pipe passing through. Depending on the pipe you choose of course this will vary. Using smaller pipes increases the flow rate of the air which in turn increases the speed of the cyclonic action when spinning the dust. I think this particular design is a bit too powerful causing some inefficiencies in trapping all of the dust in the bucket.

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5 → Threaded rods now fitted, the pipe holes are cut, and plywood circles top & bottom which “sandwich” the plastic lid of the bucket as such. Initial testing showed that the vacuum hose attachment (and the dust hose from the router table) were heavy enough to cause the pipes to bend & skew due to the side load of their hanging weight. So I decided to stiffen up the connection points by adding a timber brace that would hold the hose connections firmly upright.

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6 → I found a spare piece of 70 x 45mm pine framing timber and used the Bladerunner jigsaw table to cut the ends round (roughly) to suit the outer diameter of the lid area.

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7 → Then using the disc sander I finished off the rounded ends.

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8 → The most difficult part of this whole construction was drilling the large holes to fit the pipes through the brace and plywood lid and aligning all three holes. I used a larger connector in the middle (outlet) pipe to that used for the edge (inlet) pipe so a larger hole saw was used to create a clearance hole. I used pan head screws with some sealant to screw the plastic lid to the plywood and the pine brace from underneath. One of the threaded rods aligned with the brace which worked well as a reinforcing point as well.

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9 → The final connections used a combination of sleeves and 90 deg elbows to achieve the right joins to the vacuum nozzle and the dust hose respectively.

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10 → The 90 deg elbow underneath the plastic lid sits on top of the Thien baffle. It is positioned (by my best guess based on reading the J. P. Thien’s article) just on the inside of one edge of the outer baffle circle pointing slightly toward the inside wall of the bucket and facing the other edge of the outer baffle. Best described by the photo below.

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11 → During testing I found that the twisting on & off that is needed to fix the hoses on top causes the 90 deg elbow to turn away from its set position. So I added a U bolt to hold it in place.

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12 → Having constructed it its best to explain what should happen. The idea is that air is sucked out of the centre pipe (which is set about 30-50mm below the inside top of the lid), this results in air being sucked inward from the dust pipe connection on the edge of the baffle. Due to the position and direction of the 90 deg elbow, saw dust and flakes are sucked in at high speed and are thrown around the inside wall of the bucket. The weight of the dust particles are heavier than air , so they (should) fall down the walls of the bucket in a spiral cyclonic shaped wave. This means that the air that is sucked out of the central pipe should be relatively free of saw dust thereby protecting your vacuum cleaner motor and allowing you to collect the saw dust easily at the bottom of the bucket.

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13 → It works! But I’m not sure how efficiently as yet… but I think the speed of the cyclone wave inside is a bit too fast as there is a buildup of a fine layer of dust on the rear edge of the 90 deg elbow. Also, the system is so air-tight that if you cover the inlet pipe (accidentally or otherwise) the thin walls of the bucket collapse quite quickly. Test video to be uploaded shortly.