Most small shop owners would like their shops to be as dust free as possible, but the calculations and information required to develop an efficient dust collection system sometimes seem daunting. However, there are a number of resources and simple guidelines that make designing the best dust collection system for your shop much easier.
Analyze your shop
Most of the dust control experts we talked to agree that the first place to start designing an effective dust control system is by taking a good look at your shop and your needs.
"The main question most people ask us first is how large of a system they need," says Jeffrey Hill, engineer and sales manager for Oneida Air Systems Inc. , a company that specializes in dust collection systems for small- to medium-size woodworking shops. Hill says the answer to that question depends on the answers to a number of other questions: What kind of shop is it? What machines will be used? How many people will be working at one time?
"You need to figure how many machines and ports will be open at one time," says Hill. In designing a system, he recommends that it be based on the worst case air demand to ensure maximum efficiency.
Start with a floor plan, recommends a new brochure developed by Air Handling Systems, which manufacturers and sells piping and dust collection accessories. "The guide gives people an A-to-Z look at what's involved," says Jamison Scot, manager of marketing at Air Handling Systems. Titled "Designing Your Air Handling System," the guide takes you through a step-by-step approach with simple charts and calculations to help you develop an efficient system for your shop. Typical of the practical, headache-saving advice in the brochure is the caution to consider floor-to-joist measurements and any possible obstructions that may affect your piping layout.
Sandor Nagyszalanczy, who wrote the book "Woodshop Dust Control," says even the layout of your machines can have a bearing on how efficient your dust control system will be. "If you bring tools like shapers and planers that produce heavy chips closer to the collector, or shorten branch lines to the central collector, you can improve efficiency," says Nagyszalanczy. "You can pick up a lot of performance that way."
Calculating your needs
Before you order a new dust collector and ducting, you should first calculate what you need in the way of air volume and air velocity. Air volume is measured in cubic feet per minute, while air velocity is measured in feet per minute. Most woodworking dust collection systems should have 4,000 fpm velocity in the branches and 3,500 fpm in the main, according to recommendations from Air Handling Systems.
To determine the size of ducting and air requirements for each machine, check with manufacturer recommendations. General specifications can be found in the chart on page 32.
Ducts for primary machines (machines that will be operating at the same time in a worst case scenario) feed through branches into a main. The sizes of branches and mains must be calculated to handle the correct air volume and velocity. For example, two 4-inch branches for machines requiring 350 cfm each might feed into a 6-inch main to handle the total 700 cfm at a woodworking dust air velocity of 3,500 fpm.
Charts in the Air Handling brochure or a special slide rule calculator, also available from Air Handling, can be used to calculate all the combinations for most shops. Air Handling also offers an online calculator program on its website at www.airhand.com .
The length of piping also affects dust collection performance and con tributes to system resistance or total static pressure. The number of elbows and how sharp the turns are in the pipe also contribute to this calculation. Again, charts or the Air Handling calculator can help make specific calculations for most systems.
For many shops that are unsure of the calculations or want additional help, companies like Oneida Air and Air Handling Systems offer consultation services to help design the system that's right for your shop.
Choosing a collector
Once system needs are determined, you have a much better chance of matching the right collector to your operation based on the air volume, air velocity and static pressure numbers you've developed. But don't forget to also add in a factor for planned growth, considering any new machines or operations you might add in the near future.
As to choosing the type of collector, for a serious central shop system, virtually all the experts recommend a two-stage system with cyclone collector. Single-stage bag-type chip collectors may remove larger debris from a single machine, but they don't effectively filter out fine dust, says Nagyszalanczy. He points out that the smallest dust particles, material that is 1 micron or smaller, is the most damaging to health. "The stuff that kills you is the stuff you can't even see," he says.
Getting more out of an old system
Shops that already have some kind of dust collection in place don't have to start from scratch to improve their system, says Nagyszalanczy.
He says a common problem is that shops don't have enough square footage of filtration media for their system. He suggests thinking about it like a car's exhaust system. If you cover the exhaust pipe, even the most powerful engine will die. Similarly, a dust collection system with too little filter area or clogged filters acts like a clogged exhaust pipe.
"You can probably improve performance just by adding filtration," says Nagyszalanczy.
The rule of thumb, he says, is to have a 10-to-1 ratio of cfm to filtration square-footage. For example, a 1,200-cfm system requires 120 square feet of filtration. Adding a small bag house to an existing collector system will often do the trick, he says.
Even more basic, Nagyszalanczy recommends regular shaking of collector bags to clear excess dust build-up. Some of the more sophisticated small shop collectors, such as one offered by Torit, actually have an automatic shaking feature built into their shutdown cycle. When you turn off the machine, it shakes off excess dust from filter media.
Another way to improve an existing system, Nagyszalanczy says, is to move dust pickups to the most efficient locations to collect the most material from each machine.
For example, he says, radial-arm saws are notorious for having inefficient dust pickups.
"Build a decent hood behind the tool," he says.
One of the most basic ways of improving system efficiency is to make sure that blast gates are always closed on machines that aren't in use. Automatic blast gate systems, like EcoGate, make this easier, he says. However, he cautions that some overzealous attempts to seal all air leaks on machines may actually be counterproductive to dust collection. "You've got to move enough air to pull in the dust."
Common dust collection mistakes
There are a variety of common mistakes that small shops make when it comes to dust collection. Sandor Nagyszalanczy, who wrote the book Woodshop Dust Control , says shops would do well to avoid these pitfalls.
- Scrimping on the collector. "The first thing people do wrong is buy the cheapest chip collector they can find," says Nagyszalanczy. He recommends avoiding inexpensive single-stage bag collectors in favor of two-stage systems.
- Using cheap filter material. Replacing stock filter bags with industrial bags and using quality filter materials will improve even single-stage bag systems, Nagyszalanczy says.
- Relying only on ceiling filtration. Ceiling-mounted air filtration devices will help clear the air, Nagyszalanczy says, but they must work in tandem with an efficient primary collection system to really work.
- Ignoring other dust sources. "People will spend big bucks on a professionally installed central dust collection system, but they'll ignore all the other sources of dust in the shop," Nagyszalanczy says. Hand sanding, portable power tools and other operations all contribute dust. Downdraft dust collection tables and dedicated portable power tool dust extraction systems are just a couple of ways to avoid this problem, he suggests.
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