I used a 2" dia. plastic dust collection system connected to a central-vac for a number of years. It was mounted in the garage and exhausted outside, so dust in the house was not a big problem. However, as I acquired larger machines such as a jointer and planer, the system was unable to keep up with the chip volume produced by these machines. I ended up installing a 1.5 HP cyclone dust collection system with a pleated cartridge filter.
The filter is an industrial grade spun-bond (rather than woven) polyester material effective at removing small particles, and the pleated design gives it a large surface area to reduce the airflow restriction. Normal dust collection systems using bag filters reportedly do not provide very good filtering until the bags have a good coating of dust on them, which of course restricts the airflow.
I installed 5" metal HVAC ducting in my workshop to each major machine. Flexible hose connects the ducting to the custom-made dust hoods on the router, belt sander, bandsaw, planer and jointer. Each machine is isolated with self-cleaning 5" metal blast gates, each of which includes a switch to turn on the dust collection system via a low-voltage circuit controlling the 220V to the dust collector motor.
Spiral pipe is often recommended by the dust collection system manufacturers, but it probably does more for their bottom line than the performance of the system. I had seen some warnings about using standard 30 gauge HVAC ducting due to the lack of strength and air leaks, so I checked out the performance. Taping the seams with metal HVAC duct tape eliminated any concerns about leakage. I used the central-vac system with a variable blast gate to check the performance of the duct. The central-vac is made to draw air through long sections of 2" tubing and often around a number of corners, so it is made with a good suction capacity. I found that mine could generate a maximum suction of 74" of water (which would be about 2.6 PSI), which is quite respectable. I checked a 3' section of 5" duct with the ends and seams sealed with tape. At a suction of 29" of water, the main seam started to collapse. I found that a dented section would start to flex at about 13" of water. That suggested that the ducting should be OK to maybe 10" of water, which would probably be fine for a dust colection system. The dust collection system has high flow capacity, but cannot generate much suction - the maximum suction would be around 9 to 10" of water for the system I had. Despite this, I opted for a sturdier tubing, and ended up using 26 Guage HVAC tubing.
The thinner 30 gauge tubing is much easier to work with then the 26 gauge. I ended up using an abrasive wheel to cut sections of the 26 gauge tubing to length. A hammer and chisel were used to crimp the ends for joining sections. The elbows are less of a concern for collapsing or flexing since they have ridges around them for interlocking the sections, which adds additional strength. I ended up using a mixture of 26 and 30 Gauge for them, using the thicker material where I needed more mechanical strength. I also used some conformable metal HVAC tubing for some of the elbows where strength was not a concern. For the best airflow, the elbows should have a radius that is 2 or 3 times the tubing diameter. Since HVAC elbows have a radius of closer to 1D, they are not the best choice unless they are modified. I simply readjusted the sections of the standard 4-section 90-degree elbow so that it bent only 45 degrees, and then used two of them. This provided an elbow with about 2D radius.
All the seams and joints were taped with metal HVAC duct tape. This reduced air leakage, which also had the effect of decreasing the noise that the system made. It also strengthened the ducting, especially the elbows.
| Type: | Cyclone, 35 gal drum |
| Power: | 1.5 hp |
| Filter: | 13 x 39", pleated, 95 sq ft, 99.9% removal of 0.2 to 2 micron particles |
| Airflow: | 500 CFM at 6" H2O static pressure |
| Done: | April, 2005 |
