Wood and Metalworking Machine Basics Editorial Product Review

by Bob DeLucas

Reprinted courtesy of John Otto JET Equipment & Tools.

Before you purchase a dust collector, you should first layout a system, determine how many and what kind of tools will be connected to the system, and where they will be in relation to the dust collector. Once you have done your layout, with a few simple calculation you can determine what size dust collector best suites your needs based on capacity in CFM (Cubic Feet per Minute of air flow) and Static Pressure Loss. Step 1 How to Layout Your Shop The example above illustrates a simple 3 machine layout. In laying out your shop, try to follow these basic guidelines: Place machines requiring the highest CFM closest to the dust collector (see chart below). Try to keep runs as short as possible. Try to keep all duct work at the same height level as the dust ports on the machines. Try to keep directional charge fittings (T's and Y's and Elbows to a minimum. Machine CFM Required Machine CFM Required 12" Planer 350 13" + Planer 400 Shaper 400 Bandsaw 400 Radial Arm Saw 350 Tablesaw 350 Disc Sander 300 Belt Sander 300 Floor Sweep 350 Jointer 350 Drill Press 300 Scroll Saw 300 Note We recommend installing a blast gate for every tool to help direct all of the air flow to the tool being used.   Step 2 Determining the Dust Diameter Needed Find the tool(s) you will be using that require the most CFM from the chart above. If you will be running more than one tool at a time, add the CFM numbers of those tools together. Using the chart below, determine the duct diameter that will be required for your system. JET does not recommend using duct smaller than 4" in diameter. 250 - 400 CFM 4" Duct 400 - 650 CFM 5" Duct 650 - 800 CFM 6" Duct If you determine that your system will require greater than 800 CFM, you can calculate the appropriate duct diameter using the equation below. Duct Dia. = (CFM x 183) / 350 Step 3 Determining Static Pressure Loss Determine the length of straight duct work in your layout from the dust collector to each tool. Count the number of each type of directional change fitting s to each tool, (Y-fitting, T-fittings, Elbow fittings). Each type of fitting is equivalent to a specific length of straight duct in the amount of Static Pressure Loss it causes (refer to the following chart). Duct Dia 90" Elbow   30" Y    4" 6 feet  3 feet  5" 9 feet  4 feet  6" 12 feet  5 feet  7" 13 feet  6 feet Duct Dia  90" T  4"   7 feet  5"  10 feet  6"  13 feet  7"  14 feet Determine and add up the equivalent number of duct feet for of the directional change fittings for each tool. Add this number to the total length of straight line duct from the dust collector to each tool. Once you have determined your total length of duct to each tool, (straight line duct plus fittings), you can then calculate the Static Pressure Loss for each tool based on the chart below. (Static Pressure Loss is measured in inches.)  Duct Dia. Static Pressure Loss per ft. of Duct 4" Duct .055 in./ft. 5" Duct .042 in./ft. 6" Duct .035 in./ft. 7" Duct .026 in./ft. 8" Duct .022 in./ft. Example In our sample layout, the system consists of 3 tools, a jointer a planer, and a tablesaw. The calculation for this system look like this:   Jointer Planer Tablesaw 4" dia. duct 15 ft 11.5 ft 22 ft 90 elbow 1 = 6 ft 0 1 = 6 ft 30 Y-fitting 0 1 = 3 ft 0 90 T-fitting 1 = 7 ft 1 = 7 ft 1 = 7 ft Total Feet 28 ft 21.5 ft 35 ft To determine the Static Pressure Loss for each tool, multiply your total feet by .055" (4" dia. duct).   Jointer Planer Tablesaw Static Pressure Loss 1.54 1.182 1.925 (We recommend adding 1" of Static Pressure Loss to compensate for a dirty filter bag.) The highest Static Pressure Loss for this system would be 1.925" for the tablesaw plus 1" for a dirty filter bag resulting in a total Static Pressure Loss of 2.925". Step 4 Determining which Dust Collector is Needed Use the tool with the greatest Static Pressure Loss and the tool requiring the greatest CFM to determine the size of dust collector needed for your system. (If you will be running more than one tool at a time, you must add the CFM's and Static Pressure Loss of these tools). In our example, the tool with the greatest Static Pressure Loss is the tablesaw with 2.925". The tool requiring the greatest CFM is the planer a 400 CFM. Therefore, we must purchase a dust collector with a Static Pressure Loss rating of 2.21" or greater and a CFM rating of 400 or greater, (using only one tool at a time). The JET DC-650 with a Static Pressure Loss rating of 8.5" and a CFM of 650 would do the job. It would be wise in this circumstance to consider a larger Dust Collector such as the JET DC-1200. This would allow you to add more tools to the system at a later date. Step 5 Preventing Static Electricity Build-up There is always the danger of static electricity building up in the duct system and causing a flash explosion or fire. To prevent this, run ground wire through both the inside and around the outside of all the piping. Use standard aluminum or copper, or solid copper wire for the inside and aluminum antenna guy wire for the outside. (The JET Dust Collector Grounding Kit JW-1053 contains all the necessary components to safely ground your system.) At directional change fittings, you can solder the wires on the inside of the fittings, (wires in Y-joint fittings must be soldered facing away from the air flow), or you can drill a small hole in each branch of the fitting - bring the wires out of the fitting and connect them with a wire nut. You must do this for all Blast Gates so you can completely close the gate. Seal the holes with caulk after the system is put together to prevent air leaks. Wrap a wire around the outside of the hose and fittings to remove any static electricity that might build up on the outside of the ducts. Ground both the inside and outside wires to a metal part on each woodworking machine - including the Duct Collector. You may need to use a screw or bolt with a lock washer to ensure a complete ground connection.

Information courtesy of John Otto JET Equipment & Tools.

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