Tablesaw dust collection with shop vac
Many woodworkers have dust collection systems, which use suction and large pipes and hoses to collect sawdust and other particles from power tools. For the hobbyist, these systems can be affordable, below $1000 for a decent system. Naturally, I therefore wondered what I could accomplish with my old shop vacuum, some junk from the garbage can, and about 20 bucks.
The Tablesawweld on extra corner tabs, creating flanges to sit on the rim of the saw opening.
For the dust-collection tubing, I took the cheap route. I used 3-inch water drainage tubing and 1.5-inch sump pump tubing, both from the local home improvement warehouse store.
What's That Noise?!
I put two dust collection points into the tablesaw collector: the large main 3-inch hose in the collector hood, and a second 1.5-inch hose to pick up stray sawdust from the top of the table. I attached them together with a Y-connection made from a plastic peanut butter jar. The 1.5-inch hose came out of the side of the jar, but I heated and warped the jar to make a Y connector for better airflow through the smaller hose.
The first time I turned on the shop vacuum with this setup, I got a big surprise. In addition to the usual loud shop vac whine, I got an additional loud piercing whistle noise from the 1.5-inch hose. Some Internet research told me this was a "standing wave" harmonic vibration, caused by the uniform ridges in the hose. The factory did an accurate job of creating all of the ridges in the hose the same. When air passes through the hose, the ridges cause the air to vibrate at the same frequency all along the hose, causing a single tone to come out. It's one big whistle.
Ironically, my web search efforts revealed much about how to produce such a noise, but not how to surpress it. However, some thought and experimentation led to a simple answer: If the uniform ridges make the whistling noise, making them non-uniform should eliminate it. I heated the hose with the heat gun, and stretched it by different amounts at different points along the hose. It didn't take much stretching to disrupt the harmonic effect, eliminating the shriek and producing quieter air flow.
I use the tablesaw to cut both wood and plastic at different times. I want to keep the two separated so the wood sawdust can be used for composting, without being contaminated by plastic pieces.
I made a pre-separator to collect the wood sawdust using a 5-gallon paint bucket. The separator bucket sits between the tablesaw and the shop vac. Scraps and larger sawdust particles settle to the bottom of the bucket, while the air and fine dust pass through to the vacuum. It is patterened after professional cyclone separators, where the incoming airflow is directed towards the side of the cylinder and the air exit is in the center. As the particles are blown towards the sides, they lose velocity and swirl down to the bottom.
There are just a few parts to the separator. The vacuum port (air exit) has a tube going down the center of the cylinder, which I made from a clear plastic applesauce jar with a mouth sized to the 2.5-inch vacuum hose, screwed into the bucket lid . The intake port goes to a deflector which sends the air towards the inside wall of the bucket. The intake port is a snap-on connector for the drain tubing, and the deflector is a scrap of plastic. Since the tube connector, deflector, and bucket lid are all HDPE plastic, I welded them together with the heat gun. I also cut a window into the side of the bucket, to indicate how full it is.
Now when I cut wood, I plug the vacuum in to the separator, and my wood cuttings are collected in the bucket. If I want to cut plastic, I bypass the separator and suck the plastic scraps right into the shop vac.
Airborne dust filter