Please note: the Bill Pentz website is a must read for everyone! Bill is living with the effects of dust damage and has undertaken to educate himself, and generously, us, with what really happens when you don't take dust control seriously. It is one of the few sites based on research and not marketing.
You must realize that in the days of hand tools, little dust was created and was not an issue. I use scrapers and hand planes and I don’t generate any dust at all. But, turn on my table saw for a moment and the workshop is filled with fine dust particles scraped off the board and flung into the air, millions of times per second. Modern machines create so much dust as to absolutely require control. It doesn't have to cost a fortune. But, you'll realize that with Bill's research, It does have to be taken seriously.
There are two parts to dust collection, the implement collector and the air cleaner.
Let's start with
the implement collector:
This is a chain of parts that moves dust-laden air from a tool to a particle removing method. This starts as a hose connected to the tool, i.e. the table saw. This hose gets connected to a fan that sucks dust laden air from the tool and blows it into a filter/collector of some sort.
1. One type of “dust collection” consists of bags on the end of a blower. The blower moves the air from the tool and pushes it into a filtering method. Commercial dust collection use cotton bags to provide the filtering. These bags are more or less effective as filters. This one is BusyBee’s.
2. Another type of “dust collection” is the cyclone. There are a variety of them available on the market and there are plenty of plans showing how these work and can be easily made. Again, a BusyBee implementation.
This one is a simple garbage can with a lid that directs moving air in a “cyclone” that removes particles from the air like a centrifuge. The suction comes from a vacuum cleaner that can be equipped with a drywall bag to serve as a fine particle filter.
Veritas® Cyclone Lids - Lee Valley Tools
Oneida Air Systems - Dust Deputy is a more sophisticated implementation of the cyclone philosophy. However, there’s the same philosophy, different adaptation from BusyBee and even Triton has(had?) a contribution.
Then, there's Phil Thein's "The Thien Cyclone Separator Lid w/ the Thien Cyclone Separator Baffle." (cgallery.com/jpthien/cy.htm) The Thien Cyclone Separator Lid w/ the Thien Cyclone Separator Baffle Phil has several versions of this and he shows you how to make it. If you dig around, I've come across various versions of the Thein lid.
Here are more links to dust collection methods:
http://www.routerforums.com/table-mounted-routing/21764-building-dust-collector.html#post185854
http://www.routerforums.com/shop-sa...st-collection-separator-small.html#post186610
http://www.routerforums.com/tools-woodworking/15742-lucky-me-new-cyclone.html#post128460
Santé's homebuilt dust collection installation and design
http://www.lescopeaux.asso.fr/Equipement_Atelier/clic.php3?url=Docs/Sante_Cyclone.pdf Even if you don't read French, this is well worth the look see. Pictures can say a thousand words. If you have any questions, just ask. Santé reads and writes English and there are other members who speak French.
The Thien Cyclone Separator Lid w/ the Thien Cyclone Separator Baffle
Oneida-air.com
The other part of dust control is the
air filter.
No dust collection system can collect all of the particles that get flung around. That leaves the need for an air cleaning method. Typically, this is a blower with some sort of fine filtering. Over time, technology started to measure airborne particles in terms of microns. All you could figure was that if your filter was rated at 10 micron that was pretty course and 1 micron was pretty fine. In 2012, that no longer is sufficient. Now we have “MERV ratings.” This chart is copied from:
HTML:
<body><table><thead>MERV rating Particle Size</thead>
<tr><td>0.3 - 1.0 Microns</td><td>1.0-3.0 Microns</td><td>3.0-10.0 Microns</td></tr>
<tr><td>1-4</td><td> -</td><td> -</td><td> Less than 20%</td></tr>
<tr><td>5</td><td>-</td><td>-</td><td>20-35%</td></tr>
<tr><td>6</td><td>-</td><td>-</td><td>35-50%</td></tr>
<tr><td>7</td><td>-</td><td>-</td><td>50-70%</td></tr>
<tr><td>8</td><td>-</td><td>-</td><td>70-85%</td></tr>
<tr><td>9</td><td>-</td><td>Less than 50%</td><td>More than 85%</td></tr>
<tr><td>10</td><td>-</td><td>50-65%</td><td>More than 85%</td></tr>
<tr><td>11</td><td>-</td><td>65-80%</td><td>More than 85%</td></tr>
<tr><td>12</td><td>-</td><td>80-90%</td><td>More than 90%</td></tr>
<tr><td>13</td><td>Less than 75%</td><td> More than 90%</td><td>More than 90%</td></tr>
<tr><td>14</td><td>75-85% </td><td>More than 90%</td><td>More than 90%</td></tr>
<tr><td>15</td><td>85-95% </td><td>More than 90%</td><td>More than 90%</td></tr>
<tr><td>16</td><td>More than 95%</td><td> More than 95%</td><td>More than 95%</td></tr>
</table>
</body>
Read the chart from left to right as follows:
A filter with a MERV rating of 14...
Will capture 75 - 85% of particles that are between 0.3 and 1 micron in size
Will capture more than 90% of particles that are between 1 and 3 microns in size
Will capture more than 90% of particles that are between 3 and 10 microns in size
No sooner do we figure we’ve got it figured out when someone else comes along and takes it to “the next step.”
The 3M Company has created the Microparticle Performance Rating (MPR). The 3M Filtrete MPR focuses on the smallest, and most troublesome particles - those between 0.3 and 1.0 Microns in size. Generally speaking, a filter with an MPR of 1000 is twice as effective at removing those tiny particles as a filter with a 500 MPR.
Micron
One micron is one millionth of a meter or approximately 1/25,000 of an inch. For comparison, a human hair is about 70 microns thick.
Typically, air filters are rated by the size of the particles they can remove. Most decent furnace filters can easily remove particles larger than 10 microns in size, but the best filters are able to remove particles smaller than 3 microns.
now if you have 20,000 sq.ft. shop you need the high end stuff but most don't.. 
