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Specially manufactured metal duct, on the other hand, is quite expensive. Metal duct is also generally more difficult to cut and assemble. FLEXIBLE HOSE Flexible rubber hose, polyethylene, plastic flex- hose and other flexible ribbed hose is generally used for short runs, small shops and at rigid ductto- tool connections. There are many different types of flex hose on the market today. These are manufactured from materials such as polyethylene, PVC, cloth hose dipped in rubber and even metal, including steel and aluminum. There are also many kinds of pure plastic flexible hose, such as non-perforated drainage type hose and dryer vent hose. Drainage type hose, while being economical, does not quite have the flexibility required for dust collection. The inside of the duct is also deeply corrugated and can increase the static pressure loss by as much as 50% over smooth wall duct. Dryer vent hose, while being completely flexible, is non-resistant to abrasion and has a tendency to collapse in a negative pressure system. If using flex-hose, you should choose one of the many types that are designed specifically for the movement of solid particles, i.e. dust, grains and plastics. However, the cost of specifically designed flexible duct can vary greatly. Grizzly offers polyethylene hose which is well suited for G9958 4 H.P. Dust Collector -13 the removal of particulate matter, especially sawdust, since it is durable and completely flexible. Polyethylene is also very economical and available in a wide variety of diameters and lengths for most applications. PLASTIC DUCT The popularity of plastic duct is due to the fact that it is an economical and readily available product. It is also simple to assemble and easily sealed against air loss. The primary disadvantage of plastic duct for dust collection, whether black ABS or white PVC and even rubber or polyethylene flex-hose, is the inherent danger of static electrical build-up. System Grounding Since plastic hose is abundant, relatively inexpensive, easily assembled and air tight, it is a very popular material for conveying dust from woodworking machines to the dust collector. We recommend using flexible hose (flex-hose) to connect the woodworking machine to the dust collector. However, plastic flex-hose and plastic duct are an insulator, and dust particles moving against the walls of the plastic duct create a static electrical charge build up. This charge will build until it discharges to a ground. If a grounding medium is not available to prevent static electrical charge build up, the electrical charge will arc to the nearest grounded source. This electrical discharge may cause an explosion and subsequent fire inside the system. To protect against static electrical charge build up inside a non-conducting duct, a bare copper wire should be placed inside the duct along its length Guard against static electric build up. Ground all dust collection hose and pipe. and grounded to the dust collector. You must also confirm that the dust collector is continuously grounded through the electrical circuit to the electric service panel. If you connect the dust collector to more than one machine by way of a non-conducting branching duct system and blast gates, the system must still be grounded as mentioned above. We recommend inserting a continuous bare copper ground wire inside the entire duct system and attaching the wire to each grounded woodworking machine and dust collector. Be sure that you extend the bare copper wire down all branches of the system. Do not forget to connect the wires to each other when two branches meet at a Y or T connection. Use wire nuts. Ensure that the entire system is grounded. If using plastic blast gates to direct air flow, the grounding wire must be jumped (Figure 12) around the blast gate without interruption to the grounding system. Plastic Blast Gate Metal DuctCopper Ground Wire Figure 12. Ground jumper wire when using plastic blast gates and metal duct. We also recommend wrapping the outside of all plastic ducts with bare copper wire to ground the outside of the system against static electrical charge build up. Wire connections at Y’s and T’s should be made with wire nuts. -14-G9958 4 H.P. Dust Collector Attach the bare ground wire to each stationary woodworking machine and attach the dust collector frame with a ground screw as shown in Figure 13. Ensure that each machine is continuously grounded to the grounding terminal in your electric service panel. Ground Screw Flex-Hose Internal Ground Wire External Ground Wire Figure 13. Flex-hose grounded to machine. Design Suggestions When designing a successful dust collection system, planning is the most important step. Before you set out to run the first section of duct, consider these general guidelines for an efficient system: 1. Machines that produce the most saw dust should be placed nearest to the dust collector. These machines include thickness planers, shapers, sanders and bandsaws. 2. Ideally ...