Emails this morning scolded me for not posting this as a new thread, plus leaving a few things off. Here is an updated version of what I shared at the end of the last cyclone thread. bill
Making a dust collection decision requires you to first decide on what it is you want to do. If you just want a shop with no chips, then just about any hobbyist 1.5 hp or larger dust collector or cyclone will work well for you because you only need about 450 CFM airflow for chip collection. If you seriously want to get the airborne fine dust in your shop under control then you have a whole different set of concerns. You can go to my web pages and study for yourself the dangers of fine dust and what it takes to control, collect and get rid of it.
Many local safety standards require putting commercial cyclones and dust collectors outside. That works well because these outside units let the fine dust blow away outdoors. For hobbyists, exhausting outside is illegal in many areas. It can be hard on the pocketbook to send our heated and cooled air outside and our air conditioning equipment will mostly not keep up. The noise and debris can upset neighbors. Some types of chips and dust kill plants. Blowing our shop air outside can also suck deadly carbon monoxide backward through the vents on our heaters, stoves, water heaters, and other fired appliances into our shop air. Putting these units outside also often requires making them a special enclosure. Many hobbyists choose to just bring these outdoor units inside.
When hobbyist started bringing these downscaled commercial dust collectors, cyclones, and small shop vacuums inside it created a serious hidden problem. These smaller units make great “chip collectors” that will leave our shops spotlessly clean except for a coating of the unhealthiest finest dust on everything. That coating comes from moving too little air to gather the fine dust as it is made and too open filters that blow the finest unhealthiest dust right through. Unlike commercial firms that blow this fine dust away outside, hobbyists trap the dust inside. This fine dust builds and lingers for months getting even more dangerous as molds, mildew, and fungus break it down. Our tools and even dust collection systems become “dust pumps” that recycle previously made dust. Government testing of hobbyist shops that turn professional shows most end up with fine airborne dust levels over ten thousand times greater than permitted in commercial facilities. We as hobbyists often receive more fine dust exposure in a few hours of dusty woodworking than a commercial woodworker will get in a year.
With almost no hobbyist tools, dust collectors, cyclones or ducting setup for anything but "chip collection" getting good fine dust collection takes a lot of work. We have to remake most of our tool hoods and tool ports. We need a good downdraft table and portable dust collection hood. We need a much bigger blower that moves a real 800 to 1000 CFM at each major tool. We need larger lower resistance ducting than most hobbyists vendors sell and cannot use commercial ducting designs because the smaller down drops kill the airflow in our mains building up dust piles. These piles pose a fire hazard and will eventually ruin our impellers, motor bearings, and filters from breaking loose and slamming around. We also need to either exhaust the dusty air outside or run it through fine filters.
We can't just run the dusty air through a filter. Meeting government commercial air quality standards that many now think are not tight enough requires filtering all particles down to 0.5-microns in size. My doctor and many other health professionals recommend filtering down to 0.2-microns. We also must have enough surface area so the filters do not plug too quickly and kill the airflow needed for good fine dust collection. Most can only provide enough filter surface area by using large cartridge filters. Fast moving wood chips quickly plug and punch holes in cartridge filters as too many are now finding with their cartridge dust collectors. Cleaning rapidly also wears holes in these expensive cartridges.
Protecting these filters can be done with a drop box, meaning a huge pipe with so much area that the airflow drops below what will keep the chips entrained (kept airborne), or using a cyclone separator. Trashcan lid separators are a type of drop box that many hobbyists find work well for “chip collection”. Unfortunately, the higher 800 to 1000 CFM airflows needed for good fine dust collection scour the cans clean unless the trashcan separators become huge. Most find a 5’2” diameter seven foot tall or larger trashcan separator too big, so instead turn to cyclones for separation.
The huge cyclones we see outside most large commercial woodworking facilities are agricultural cyclone designs that work well. They provide almost exactly the same 85% separation efficiency by weight that our far less expensive trashcan separator lids provide for “chip collection”. These cyclones were designed to separate dirt and sand from cotton. They use very high internal turbulence to smash the dirt and sand loose from the cotton fiber. After breaking the heavier stuff loose it gets slung by spinning air off to the cyclone sides and gravity pulls it into a collection bin. Close to 100% of the fine cotton fiber blows right out the top of the cyclone. When used for woodworking, high internal turbulence smashes the fine dust from the heavier chips. Close to 100% of the heavier chips and sawdust drop into a bin and near 100% of the fine airborne dust away into the outside air.
Sadly hobbyist vendors discovered that if they feed their cyclones only large heavy chips, say from planers, they can advertise close to 100% separation efficiency for cyclones that provide 85% separation efficiency. Feeding these same cyclones all fine dust, say from MDF, puts close to 100% of the dust into the filters.
It is no secret that almost all hobbyist cyclones are downscaled copies of agricultural cyclone designs sold by Delta to small commercial shops for decades. These units require a 7.5 to 15 hp motor for the same sized cyclones that hobbyists try to power with 1.5 to 3 hp motors today. With lots of help we worked through countless design changes to improve these hobbyist agricultural cyclone separation efficiencies. We learned most hobbyist vendors did not know the cone on the bottom of the cyclone requires just the right shape and proportions to keep that heavier material from causing plugs or getting sucked back into the exiting air stream. We learned inlet size, shape, length, and angle is critical. We also learned that the incredibly high turbulence was not needed if we wanted to separate off all the dust. With clever modifications we got these cyclones from 85% efficient by weight to the low nineties.
That was just not good enough. In spite of adopting many of our recommended changes, hobbyist vendors continue to sell cyclones that require more time to fix than building a cyclone from scratch, plus cutting up a brand new unit just hurts too much. Hobbyist cyclones still constantly plug their undersized filters, pass much of the finest unhealthiest dust right through their too open filters, fail to move enough air for good fine dust collection, and fail to move enough air for good separation with anything less than 3 hp or larger motors.
Larry Adcock with his WoodSucker II design, my design plans available off my web pages for free, and cyclones based on my design sold by Clear Vue Cyclones made major steps forward. Larry used a more efficient caged impeller and I used an airfoil impeller. Both move 3 hp air volumes with a 2 hp motor. We also both got our separation efficiency up into the middle ninety percentile before filtering. My continued testing moved me away from the caged and airfoil impellers. They generate so little air pressure they only have enough power to collect from small shops plus they need regular cleaning. I refocused my design enhancements into building an overall more efficient cyclone and blower. Everyone who uses the result can attest to their air movement and separation efficiency.
Meanwhile, if you won’t use large enough ducting, upgrade your machine hoods, move enough air and use fine enough filters, just buy a good 1.5 to 2 hp dust collector and be happy, because your cyclone is not going to give what is needed for good fine dust collection.
bill
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... but I got lucky and stopped before I filled the filters! 
