Popular Woodworking 2007-08 № 163, страница 36

This gigantic dust collector services a big woodworking shop at Cer-ritos College in California. Small shops can use the same type of equipment - only a lot smaller in

horsepower (hp) motors. They can be wheeled around the shop and connected to whatever machine is running, or connected to a series of closely grouped machines that are equipped with blast gates to control the flow of air. This class of dust collector is really suited to a single machine running at a time, not a shop's worth of tools all generating chips and dust simultaneously.

There are two important benchmarks for dust collectors. One is the volume of air the machine can draw, measured in cubic feet per minute (cfm); the other is how quickly the air moves, which is described in feet per minute (fpm). According to books and magazine articles on the subject, to keep up with a 12" thickness planer (a big chip producer) the dust collector should move at least 600 cfm of air at between 3,500 and 4,000 fpm. A larger planer will require a minimum of about 800 cfm. Some of these machines are capable of that.

Another important factor in dust-collector efficiency is the size of the ducts. Portable, single-stage machines generally have inlet sizes of 4" to 6". Larger-diameter hoses are more efficient because they move a greater volume of air at a lower static pressure (resistance) than small diameter hoses. Performance goes downhill as the number of sharp bends and overall length of the run goes up. Shorter and straighter runs of duct will make for a happier dust collector so get the collector as close as you can to the machine it's servicing.

Finally, there's the filter itself. As is the case with shop vacuums, unless the filter can capture particles down to about 1 micron in size, a lot of harmful dust will simply be returned to the shop air and, inevitably, delivered to your lungs. Some machines come equipped with a 1-micron bag and some do not, but it is definitely a factor in choosing a machine. If the collector comes with, say, a 30-micron bag you should replace it with a felted fabric bag or a more effective cartridge-type filter. That will add $100 or more to the cost of the collector.

Larger Systems Cover An Entire Shop

For larger shops, or woodworkers with larger budgets, a central dust collector that handles all tools in the shop through a system of fixed ducts is a big step up in terms of convenience if not efficiency. This is the kind of system you'll find in a production shop, but they also can be sized to meet the needs of a smaller woodshop.

In a central system, a two-stage collector pulls chips and dust through a duct system to a collector where fine dust and larger chips are separated. Chips go into a barrel or similar collector and dust is filtered through one or more cloth bags or a cartridge-type filter. In these respects, a central system is doing just what a portable collector does. But the more powerful motors can pull chips and dust over greater distances while the more efficient collectors (particularly the cyclone collectors) are better at separating debris. And you don't have to move the collector from machine to machine.

A good cyclone collector for a small

shop - something like the 2hp model from Oneida Air Systems or Grizzly

- is several times the cost of a portable collector. But it has some real advantages, including a large cartridge filter, magnetic controls that can be operated remotely and a blower that can move air at a rate of more than 1,300 cfm.

Duct layout is an important - and complicated - part of designing a system. Everything from the type of duct (smooth metal vs. flexible plastic) to the size of branch and main lines have an effect on the efficiency of the system. Some companies that sell this equipment will also lay out the ductwork

- a helpful bonus when spending more money. If not, you'll have some homework to do in designing your own duct system.

However the ductwork is installed, it's important to ground it properly to reduce buildup of static electricity, which can decrease efficiency. Smooth metal pipes offer less resistance to air flow than flexible plastic, and they're easier to ground - good reasons why they're considered a better option.

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