Why Use Metal Ductwork?
Metal pipe is smoother inside than corrugated metal or flexible hose. It is much more efficient at the wye, elbow, and branch fittings. Smooth transitions result in less air turbulence, friction, and static pressure loss. Metal pipe is less expensive than PVC in diameters over 4" and has a much larger variety of adapters available. Metal ductwork is robust and rigid–it will withstand any level of stress and high vacuum. Choose either premium ductwork or the economy ductwork.

Planning Your Dust Collection System
Planning your duct layout on paper is the first step. First, draw the locations of your woodworking machines, doors, windows, cabinets and other fixtures that may obstruct your ductwork. Certain machines should be located closer to your dust collectors. Figures 1 and 2 show two alternatives for laying out ductwork in a typical shop. Any one of these runs may best suit your shop depending on the placement of your collector, machines and obstructions.

figure1

figure2

The Diagonal Run, locates your dust collector in the corner of your shop, away from high activity, usually in dead space. This generally results in the use of less ductwork.

The Central Run, locates the collector centrally on a wall with a short run of main pipe running down the center of the shop. The advantage is that your dust collector will generally be located closer to all of your machines and may require less overall length of pipe. It allows you to run your pipe along your joists.

The Perimeter Run (not shown), requires a long main run around the walls of the shop. The advantage of this plan is that it is the best design for avoiding obstructions at the ceiling level that would eliminate one of the other plans. Drops from your main to machines will tend to be out of the way. With this design the pipe can be run at ceiling, wall or even floor level. The drawback of this plan is that it requires more main ductwork and fittings as well as it creates more static pressure resistance.

Dust collector location:
Variables that play a role in where to place the dust collector include: Noise level of the collector, footprint and height, the overall length of your duct, obstructions at the ceiling and wall levels, level (e.g. heating and plumbing obstructions), direction of joists (for running pipe), electrical service, locations of doors and windows.
Keep the length of runs to a minimum: Your system will perform best with shorter runs. It will be less expensive to equip, and easier to build and maintain.

Placement of woodworking machines:
Certain machines require more CFM and should be placed closest to your dust collector providing better airflow and chip collection (Chart 1). Place your least demanding machines at the end of a run. A floor sweep [#N-FSW] should be used near machines where dust collection is inefficient or impractical.

Design Elements of Your Dust Collection System:

figure3

Start your main run off the dust collector (Figure 3) a 90† elbow (the same diameter as the opening)
connects to the intake port of your dust collector (Chart 2). Use a draw band connector (#N-DBC) for most flexibility. You’ll need to determine the distance from the end of the elbow to the ceiling. Use another elbow to connect the vertical pipe to the main on the ceiling.

The diameter of your main duct normally will be determined by the diameter of the intake port of your dust collection system (Chart 2). (Remove any wye adapters before measuring this opening, cyclone units typically will not have this adapter). Avoid runs of ducting (and machine ports) smaller than 4" diameter. Spiral ductwork requires couplers to connect pipe sections and fittings together.

Placement of 45† laterals and wyes [#LAT] or [#WYE]
Branches off your main run may be a smaller diameter (4" is typical for a small shop). Use laterals and wyes as transitions from main to branches and to reduce to the smaller diameter of the branch. To determine the placement of a wye on the main duct branch, draw a line from the machine to the main duct meeting it at 45†. The intersection will determine the placement of the wye (Figure 1). In the case of an obstruction, use a combination of 45† elbows [#45E]. A length of flexible metal pipe [#N-FH] can be used to circumvent the obstruction.

Drops to your machines are shown in Figure 3. If your machine has a 4" port, a length of 4" flex hose (#N-CVD or #N-J13) will run from the port to a blast gate. In Figure 3, the gate connects to the main via a lateral, 45† elbow and a length of 4" pipe. At the drop at the end of a run, a 90† elbow off the branch is used. Connect your pipe to the ceiling or wall: Use ceiling brackets (#N- HB), for a ceiling and wall suspension use brackets every six feet of main pipe. Brackets and hangers should be at least four inches from any pipe couplers or other joints. Once your drawing is complete, indicate what components are needed and make a list of components (bill of materials).

Installation Tips
For safety, always use work gloves and goggles when assembling your system. The main duct may be assembled on the ground in sections. If you work on top of scrap plywood you can layout the position of angled branches, to determine the length of straight pipes that extend between them. If you have to cut a piece of pipe, use a saber saw and a metal cutting blade. Wrap tape around the pipe at the position of the cut, drill a pilot hole and cut using the edge of the tape as a guide. Apply caulk at the connections and force fit the components together. Secure with pop rivets.
Note: Sheet metal screws may snag wood chips and cause obstructions.