Heritage of Hawk Ridge Wood Working Club
prepared by Barry Bingham
May 21, 2008
A dust collection system needs to be high on the list of tools and equipment to be purchased when we build a shop. Wood working produces a lot of dust and we want to avoid dust going into the rest of the house.
A “shop vac” from Lowes or Home Depot is a great item to have in the shop. These units roll on the floor. Various attachments permit cleaning the floor or getting into small crevices. Hoses allow you to position the in-take nozzle near the source of dust and wood chips such as a drill press. Noise suppressor are sold at Sear and Home Depot for less than $10. They fit on the output (if it is a circular opening) and help reduce the noise.
You can shop on-line and make comparisons before visiting the Lowes or Home Depot. Go to www.lowes.com and www.homedepot.com, and type “shop vac” into their search icon.
Home Depot offers a Rigid 16 gallon capacity 16 peak horsepower shop vac with attachments for $99. This is comparable to the unit I have in my shop.
All shop vacs use a filter that clogs easily. You can use a ladies hose to cover the filter and then remove and replace the hose when emptying the shop vac. This is a quick solution to dealing with clogged filters.
A handy attachment to purchase is a round brush for $8 from either Lowes or Home Depot. This not only helps clean up large wood chips, but also “dusts” the surface and leaves it very clean.
Many wood workers use a large dust collection system with four-inch hoses. Typical brands available from Woodcraft (www.woodcraft.com), Rocker (www.rockler.com), or Woodworkers Supply (www.woodworker.com) are:
· Woodtek Dust Collector (see Woodworkers Supply, product # 961-325 for $315).
Connecting to the dust collectors (such as those shown above) is done with any of the following or a combination of the following:
Blast gates are used to limit the air flow to a specific tool (such as a table saw). Woodcraft sells a 4” ABS blast gate (black) for $5 (see product # 85006) or a 4” aluminum blast gate for $12 (see product #85007). Similar blast gates are available from Rockler, Woodworkers Supply, and Air Handling Systems.
American Woodworker, Volume 100, May 2003 has a great article on a dust collection systems for small shops. Here are key points from the article to consider in building your system:
1. reduce the cost of piping by sharing a flex hose from one machine to another as opposed to rigid pipe to each machine.
2. effective dust collection at the farthest machine from the collector should be about 500 cubic feet per minute (cfm). A typical 1 ½ or 2-horsepower dust collection with a five or six inch inlet and a 12-inch impeller is cable of delivering enough air for machines in your shop – even at 25 feet from the collector. For single point dust collection, consider a 1 hp, 600 to 800 cfm collector.
3. five-inch pipe should be used to the machines (note: more common is a four-inch pipe)
4. minimize the number of bends in the pipe. Each 90-degree turn creates as much resistance to airflow as nine feet of five-inch straight pipe. So “keep it straight.”
5. Use large-radius elbows and y-joints rather than 90-degree turns. Sharp turns and 90-degree intersections create a “ton of drag” in a dust-collection system.
6. Change the dust collection fittings at your machine to permit a four-inch connection.
7. You don’t need a big industrial grade dust collector. A basic shop under 1000 square feet where only one machine will be on at a time requires only a 1 ½ to 2-horsepower collector with a five-inch or six-inch inlet and a 12-inch fanwheel. The “Editor’s Choice” from the American Woodworker is the Oneida 1 ½ or 2-horsepower cyclone collector.
8. Metal pipe is recommended over PVC or plastic pipe because:
a. only metal pipe comes in five-inch diameter, the ideal size for small shops
b. metal systems are much easier to disassemble and change as your shop evolves
c. static electric build-up in PVC and plastic ductwork can be a problem. There is a concern about a dust explosion (note: see discussion below on this issue). All commercial codes require metal pipe for wood-dust collection.
d. metal ductwork is only about 20% more expensive than PVC in sizes over four inches.
9. seal all joints with silicone caulk to minimize leakage.
You can make your own blast gates using a pair of PVC water closet flanges attached to your 4-inch hoses. In between the flanges, make a U-shaped opening out of ¾ inch MDF and sandwich it between the flanges. Then cut blast gates from ¾ inch plywood: one to block the air and one to allow it to flow. Since the ¾ inch plywood is thinner than MDF, the handles slide easily in and out.
Large dust collectors need to be in the same room with all the intake points at the machines in order to maximize the air flow return. Placing the dust collector in an adjacent room decreases the air flow potential.
Placing a cyclone separator before the collector to capture larger chips and chunks of wood from hitting the impeller is frequently found in dust collection system. However, a cyclone separator reduces the suction. The local Woodcraft store does not recommend a cyclone separator.
You will often read that a dust collection system needs to be grounded to prevent an electric spark from causing a dust explosion. Woodcarft, Rockler, and Woodworkers Supply all sell copper wire that can be wound inside a PVC pipe to ground a potential charge.
An article in Fine Wood Working summarized a study by a professor at MIT who stated that the probability of a spark causing a dust explosion is remote. The real issue to focus on in a shop is metal fragments being drawn into the dust collection system, hitting the fanwheel, and becoming so hot that the metal starts a fire in the dust bag. Some people, therefore, will not put a floor sweep in their shop that is connected to their dust collection system. Floor sweeps can still be used if rare earth magnets are placed at the entrance to collect metal fragments and prevent them from entering the dust collection system.
Airborne dust in a shop can be a health hazard.
Several club members have the Jet AFS-1000BAir Filtration System (see Rockler, product # 24770 for $229). These filters can clean the air in a shop in a matter of minutes and remove 98% of all particles down to 5 microns.
A simple and cost effective air filter can be made using a box fan incased in a box that holds a pair of 20-inch by 20-inch furnace filters. You can place an inexpensive furnace filter on the in-feed side to remove large particles. On the out-feed side place a 3M micro-allergen filter to capture tiny particles (all these filter are available at Lowes or Home Depot).