Before I say anything else, let me say that I'm not an expert in the field of dust collection. I've had an extensive background in maintenance and machining and have even designed an industrial dust collection system, but I'm not an expert.  It has been suggested that this site needed a simple beginners corner if you will that would explain some of the rudimentary principles of dust collection. I will begin with a link to Bill Pentz's site for those of you who want more (Click here) for Bill's site. He has everything you ever wanted to know about dust collection but were afraid to ask. I'm going to try to keep this page as short a possible but still cover the things I think will help give the beginner a better understanding of hobbyist dust collection.

The picture to the left shows a 100 micron human hair. To give you another idea of the size, 100 microns is about the thickness of a piece of paper.

The following paragraph was written by Bill Pentz.

It is similar to the information on his site and I appreciate his help. 

Fine wood dust is defined as airborne dust that takes a while to settle. Most airborne wood dust particles are 30-microns in diameter and smaller, roughly one-third the thickness of a human hair which is about 100-microns in diameter as shown in the scaled diagram on the right. Unless highlighted by a beam of sun light or by a laser pointer, we normally can only see particles 10-microns and larger. Fine wood dust rapidly spreads evenly through our shop air, any connected areas such as our homes, and offices, then lingers for months. During this period it grows molds and fungi that break the dust down into finer particles which get tracked to expose everyone around us and even our pets. Almost any shop activity will stir previously made dust right back into the air.
Fine wood dust is linked to many health issues. The largest immediate danger is from toxic reactions. Medical studies show that almost all are sensitive to wood dust and this sensitivity increases with exposure and time to become potentially life threatening. What may start as a plugged nose, sore throat, or persistent cough will with continued exposure often grow from irritations to mild rashes to far more serious conditions including asthma, emphysema, cancer, plus even respiratory failure and death. In addition to these immediate reactions, wood dust also causes some serious long term health problems. Although our bodies do a good job with particles 10-microns and larger, we have problems with finer particles. Medical research shows the most dangerous particles are near invisible 2.5-microns and smaller because these tiny particles go right by our natural defenses then lodge deep in our tissues where we have a difficult time getting rid of them. Particles sized 1-micron and smaller go from our lungs right into our blood where they can end up anywhere in us. By far the most health damage comes from the 2.5-micron and smaller particles, dust so fine we cannot even see it.
Careful medical testing shows fine wood dust exposure over time causes almost all woodworkers to eventually develop wood dust related health problems. Each of us is affected at a different rate, but the insurance data shows that commercial woodworkers who work in large facilities that comply with OSHA air quality standards have about one in fourteen forced into an early medical retirement. Six out of seven professional woodworkers and all hobbyists do not work in facilities subject to OSHA monitoring. Insurance data shows commercial woodworkers who work in facilities that do not meet OSHA requirements but do blow most of the fine dust away outside end up with one in eight forced into an early medical retirement.
Most hobbyist woodworkers think they do so little woodworking that we have minimal risk. It turns out that hobbyists have by far the highest risk! Unlike commercial shops forced by NFPA fire regulations to keep most of their dust collection equipment outside where the fine dust just blows away outdoors, most hobbyists keep this dust trapped inside where it lingers for six months or longer. Regardless of vendor claims, most hobbyist fine filter bags, cartridge filters, and air cleaner filters freely pass these 2.5-micron sized particles until so caked with dust they have trouble passing air. Note on the diagram how small these particles are compared to a human hair. Most standard dust collector bags freely pass 30-micron particles. Our tools, dust collection, and air compressors launch this previous made dust airborne over and over building to concentrations growing to dangerously unhealthy levels. and hobbyist dust collection equipment uses such open filters that these units turn into "dust pumps" cycling previous made dust over and over. This explains why government testing agencies that inspect hobbyist shops changing to commercial consistently see hobbyist shops testing with over 10,000 times the airborne dust levels permitted in commercial shops. At these dust levels hobbyists frequently get more exposure to fine dust in a few hours of woodworking than a full time large facility commercial woodworker will get in a year. Many medical respiratory professionals agree because hobbyist woodworkers and their families often have the worst fine dust related health problems. Any hobbyist woodworker who does not make fine dust collection a top priority is making a dangerous mistake. 

Fine dust collection is expensive but that is relative. If you have been in an emergency room of a hospital or stayed overnight, dust collection is cheap insurance by comparison. 
Now, I'm going to try to save you some money ... a lot of money. The cheapest dust collector you can get on the market today is a good fine dust cyclone unit in the price range of $900.00 to $3000.00 not including ducting. The most expensive dust collector you can get is a shop vac for $99.00. I say this because if you go that route, you will then end up with a bigger shop vac ($349.00 on sale), then a 1 hp dust collector with 4" pipe ($500.00), then a 2hp dust collector, an air cleaner and some 6" pipe ($850.00). After and maybe several trips to your doctor for your "allergies" (75.00 ea x 2/yr x 3 years = $450.00), and lets throw in one trip to the ER ($2,000.00 - $10,000) then finally after you have gone through all that and it still does not work you have to buy a good cyclone dust collector. I know you really want to make chips ..... you have woodworking to do and spending money on a dust collector is the last thing you want to think about. It takes away available resources that you could be spending on more woodworking machines to make even MORE dust....<smile>. Believe me or not, the best time to get your dust under control is before you start making it.

If you are new to this whole subject, I have one major piece of advice: Don't get a bag or cartridge filtered type dust collector! They are a waste of money and a source of aggravation. I speak from 10 years of experience here! They don't separate dust and therefore all the dust goes into the bags filters and the bags filters get clogged almost immediately. Standard bag filters only filter 30-micron and larger particles. Most "fine" bag filters only filter 20-micron particles and larger. The cartridge dust collection filters only filter 2-micron sized particles and larger until they get hit by enough chips to get full of holes and not even filter 30-micron sized particles. All of the bag and cartridge filtered dust collectors give a false sense of security, but are mostly useless - they just blow the fine, most dangerous dust, all over your shop. 
I spent several hours on some woodworking forums the other day reading posts about dust collection. Over and over again several people (who should have known better) were talking about a dust collector taking less horsepower than a cyclone because of the cyclones' built in static pressure drop. That is true if the bag filters on the dust collector are clean. What they failed to mention is that if you are using that dust collector the "clean bag filter condition" is only going to last for a few minutes. (10 minutes of using a belt sander, cutting MDF board on a saw or router will almost completely clog the bag filters on a dust collector.) I am talking from experience. I had a 2 hp dust collector and used it for over 10 years. I was constantly cleaning the bags so it would pull some air. Cleaning or shaking the bags produced more dust than my machines. The only excuse I have is at the time I didn't know of a better solution. Thanks Bill Pentz for the information on your site.

Hobbyist Dust Collection.

There are basically two ways to go about designing a dust collection system. In an industrial situation where many machines are being used at the same time, a system is designed to handle collection from all of the machines at the same time. Airflow needs are added up from each machine to get a total. The blower and ducting are sized to handle that total plus the resistance of the ducting, separator, and filters for the entire system. These systems are BIG and EXPENSIVE to buy and run, plus most home power needs extensive rewiring to handle motors this big.
This site and our cyclone dust collector system is a hobbyist system. What that means is it is sized to run one or two machines at a time. The size of the system is determined by the CFM requirements of your largest machine. In a hobbyist system we only run one machine at a time, so the size of our blower is set by our overhead using our longest run and the airflow required for our largest machine. Almost all tools and hand operations that produce fine dust need 800 CFM (minimum) of air to capture the fine dust. Now, if you ever plan on owning a table saw, a planer, a radial arm saw, a 3hp table router, a shaper or a 6" jointer, you are going to need the 800 CFM at those machines. Our system is a fine dust cyclone separator designed to handle that load with some extra. The extra means that you can run one 6" machine and open a 4" port somewhere else and still have good suction. It has the airflow to meet not just government minimum air quality standards but the tougher standards recommended by respiratory doctors and researchers. It also means that you can run a pipe 45 feet down the back wall of your shop to a CNC router (like Matt did) and still have good suction at the router. If you need to run 3 or 4 large machines at one time you need to look elsewhere. Our system won't do it. 

Some definitions:

Cyclone:   A cyclone is simply a separator. Cyclones have been around for a long time and have a wide range of industrial applications. For our purposes the goal is to separate as much wood dust from the air as possible before the air gets to the filters. This keeps the filters clean and operational longer than in a bag type dust collector that has no separator. 

CFM Cubic Feet per Minute.  This is usually what we use to compare dust collectors. The more CFM the better..................BUT......and there is a BIG BUT! But, everyone seems to want to measure CFM differently (and to their own advertising advantage). Air at typical hobbyist blower pressures will barely compress at all, so we are building our fine dust cyclone system that is sized for 6" pipe. That is the correct size to support the 800 to 1000 CFM needed for good fine dust collection. Any smaller pipe kills the airflow needed for good fine dust collection. Likewise, larger pipe lets the air slow down so much the mains build up piles that can catch on fire and ruin bearings and filters when they break loose. a practical size to work with in a hobby workshop. Why would we measure CFM through a 10" pipe?....Or advertise a 2 hp blower that produces 1900 CFM ( free air ). Free Air??? What does that mean? Is that the opposite of air you have to pay for? Well no, what it means is they didn't have anything hooked up to blower when they measured CFM. It also means the motor was drawing more than it's full load amps and would have burned up or over heated very quickly. 

Static Pressure:  The pressure exerted by a still liquid or gas, especially water or air.(that's right out of the dictionary.) The simplest way to look at static pressure is to just think of pressure ..... period. We measure this positive or negative pressure relative to atmospheric pressure and we usually refer to the result in inches of water. To put that in perspective, a perfect vacuum will support a column of water about 32 feet high at atmospheric pressure (14.7 pounds per square inch). Most dust collection systems (pneumatic conveying systems) work with a maximum of about 12" (1 foot) of static pressure....or less than 1/2 pound per square inch. That is a very small pressure difference. This is important because we move a lot of air through a 6" pipe with a very small change in pressure. When looking at different blower curves, resistance in pipes, cyclones, and other dust collection components, small differences in pressure or resistance produce large differences in terms of air flow. It is important to note that when we refer to positive and negative pressure we are comparing it to atmospheric pressure (14.7 lbs./sq. in.) not to a perfect vacuum.

Blowers:   At this point it is appropriate to talk a little about blowers. In terms of Static Pressure and CFM, each blower or fan has it's own characteristics. A 20" floor fan will move a lot of air, but will produce almost no pressure. A vacuum cleaner will produce a very high vacuum (maybe in the range of 100" of SP or vacuum) but very small CFM. What we are looking for in a dust collection system is a blower that will move enough air through a 4" to 6" pipe to capture the fine dust at the machine and to convey that wood dust and chips from one point to another without having that dust or wood settle out in your pipes. The type of blower fan used for conveying systems is called a Material Handling Impeller. It is a flat round plate with blades attached to it. (pictures on our order page). Almost all conveying systems use this type of impeller in a blower housing. It has the right characteristics for our purpose.

HP Horse Power.  Size of the blower and horse power required. I have been asked so many questions about this. Do I really need a 5 hp blower? My answer is this: I used a 2 hp blower with a 12" Impeller for many years. I had all my machines ducted with 4" pipe and my shop was dusty. Now it stands to reason that if my shop had a layer of dust all over everything that I was breathing that same dust. I retired as of April 1, 2005 and my first project was to redo my entire DC system I installed 6" pipe, our blower housing, impeller and 5hp Leeson motor and treated myself to a new cyclone. The difference this has made in the cleanliness of my shop is amazing. By the way, my shop is 24 x 24. With one 6" gate open close to the cyclone the 5hp Leeson motor is drawing about 16 amps. It is rated for 20.8 amp full load. That means that we have a safety cushion and that is a good thing. When I go out in my shop to work, I want to do woodworking! I don't want to worry about whether my DC motor is going to overload and burn up, plus I really don't want to spend 4 hours "cleaning up".

Blast Gate: A blast gate is a device that shuts off air flow to a machine. In small systems we only produce enough air flow to run one or two machines at a time. If there are 6 or 8 machines in your shop you have to keep the airflow to ones that you aren't using closed.

After Filters:  A cyclone separator (I'm talking about Bill's design here) will separate very fine dust from the air....but there is a small amount of it that will get past the cyclone. We use two cartridge filters in a stack to catch 99.9% of all the particles down to 0.5 microns.