How To Build A Perfect Woodworking Dust Collection Systems
A dust collection system has one aim: to capture most of the wood dust created at each of your woodworking machines and prevent it from ending up on the shop floor, or, worse yet, in the air. There are a series of variables in every system that must be coordinated to ensure a strong enough flow of air: the power of the collector;the location and requirements of the machines in the shop; and the type, size, and layout of the duct work.
The design of a central system begins with a simple bird’s-eye view sketch of your shop,arranging the machines and collector in their preferred locations. Then, draw in a main line running from the collector through the shop. Sketch in branch lines as needed to accommodate each machine and any obstructions-joists, beams, or fixtures–that may require special routing. For the best air flow, keep the main line and branch lines as short and straight as possible, and position the machines that produce the most dust closest to the collector. You may choose to run ducting along the ceiling of the shop, or, to increase the efficiency of the system, at machinetable height along the walls.
Since in most home shops only one woodworking machine will be producing dust at a time, 4- or 5-inch-diameter duct is sufficient for both the main and branch lines. There are several suitable types of duct available for dust collection systems. The best choice is metal duct designed specifically for dust collection. However, many woodworkers opt for plastic pipe, typically PVC or ABS. It is easier to seal and assemble (and disassemble for cleaning), Iess expensive, and more readily available.
Because plastic is an insulator, however, static build-up inside the pipe can reach dangerous levels during use-possibly high enough to ignite the dust passing through it. To prevent this, ground all plastic ducts by running a bare copper ground wire from each tool, inside the duct, to an electrical ground. As a safety precaution, have the system checked by an electrician. Smooth-wall rubber hose and flexible plastic hose, frequently used as branch ducts to connect machines to the main line, are other duct options for the home shop. Most of these products also require electrical grounding.
A central dust collection system requires a selection of fittings to route and join lengths of duct and dust hoods. If you run the main line along the ceiling, you can secure it in place with wire straps nailed to furring strips mounted between the joists.
Fittings directly affect the efficiency of the system, so choose them carefully. As a rule, gentle curves are better than sharp turns, so use Y fittings instead of Ts for branch connections, wherever possible. A blast gate should be located at each branch outlet to seal ducts when they are not being used, thereby increasing air flow to the machine in use. Hoods, whether commercially made or shop-built, should be positioned as close as possible to the source of the dust.
You have a choice of methods for connecting ductwork. Many ducts and fittings can be friction fit and secured with adjustable hose clamps. Duct tape can also effectively join plastic pipe, but
it is unsightly and will decay over time. A high-quality silicone sealant is probably a better choice for a permanent system. To ensure smooth air flow metal ducts should be joined with rivets, rather
than screws or bolts.
Once you have completed the layout of your system and selected the type of duct you will use, it is time to calculate your dust collection needs and select a collector. This involves determining the requirements of the heaviest dust collection task vour system must handle. This usually will be the sum of system losses and the air volume demanded by the machine most distant from the collector. Purchase a collector with slightly more capacity. System losses are caused by such inefficiencies as bends in the line, corrugated ducting, leaks, and hoods without flanges.