Design Summary
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Design Summary

1.      Summary Overview

In summary, we need to carefully control airflow to:

  1. Make sure the fine dust is not blown away and scattered all over the shop before it can be captured by having well designed or carefully modified tools and hoods;
  2. Provide enough air volume (CFM) at each tool to collect the fine wood dust at the source before it escapes;
  3. Make an efficient system with large enough ducting and cleanly designed duct runs to efficiently move the volumes of air we need at each tool.
  4. Keep the air speed (FPM) fast enough to move the dusty air so we do not get plugging or dangerous dust piles in our ducting.
  5. Use filters large enough to support the volumes of air we move with filter material independently certified to provide sufficient fine dust filtering.

2.      Here Is The Goal

The goal is to capture the fine dust at the source and get rid of it. To do so, you need to:

  1. Learn and use the right tools to make a minimum of dust. Although the vendors would like for us to only use power tools, there are many hand tools that do the job well if not faster that don’t make huge amounts of dust. For example, proper use of a sharp plane or a well-tuned scraper can save a lot of time over using a power sander. Both leave a better finish and neither creates any fine dust problem.
  2. Buy well made tools with built in dust collection that controls the fine particles without spraying them all over. Most tools have fast moving blades, cutters, belts, cooling fans, etc. that will blow unprotected fine dust all over. It is important that each tool protect, control and direct all dust made during use to its dust hood and not blow the dust all over. When we cannot control that dust, we should take that tool and woodworking outside while wearing a good dust mask.
  3. Buy or make good quality dust hoods and ports for every tool. Sadly, most hobbyist dust hoods are poorly engineered permitting the fine dust to escape from all over. Likewise, most machines come with too small of an inlet port to support the needed volume of air for good dust collection. Both the hoods and ports often need rebuilt or replaced to be more efficient. You can look at the AAF dust hood examples (click here) for more information. Even some of these examples use too small of ducting, so only use them as guidelines for building dust hoods and ports that will pick up the fine dust at the source. Also, Wood Magazine, Wood Central, the Oak, Saw Mill Creek, and other woodworking forums have many excellent homemade dust collection hoods in their archives. Be careful of the advice you get on these forums, much of what you will hear is from people who are still on their first round of dust collectors and so enamored that they will defend their systems and ducting nearly to the death. There have been some very ugly wars on the forums, as woodworkers get more concerned about addressing the fine dust.
  4. Collect that dust and store it in metal cans to prevent fire danger. Yes, lots of people collect into cardboard and plastic drums, but we are going to be smarter than that!
  5. Efficiency is everything! This rule is based on a two simple facts.
    1. Air at typical dust small shop dust collection pressures will hardly compress at all. As a result a poor design, undersized pipes, rough ducting or flex hose, sharp bends, etc. all act just like a water valve and kill airflow. You can make this up, and large commercial shops do just this, but what they live with is a need for a much larger blower. In practical terms adding 1/2 horsepower (HP) and a bigger impeller typical 1.5 HP blower only adds 10% more air volume! Adding horsepower and a bigger impeller is not an efficient way to gain capacity.
    2. A poor design or air leaks will kill system efficiency. You must use straight or nearly straight duct runs using efficient piping. Every joint, curve, turn, or Y connection will hurt your efficiency. Every restriction will hurt your efficiency. Either you make a really efficient system, or you will have to live with terrible dust collection or buy a very big blower that will be expensive to purchase and run.
  6. Build a system with enough blower and well-designed ducts to meet the CFM requirements for all your machines. You can do lots of homework, or make it easy on yourself and just look up the answer by using a CFM requirements table designed to capture the fine dust. The AAF table I shared above shows that 800 CFM is ample for all larger hobbyist sized woodworking tools.
  7. Without big enough pipes, fittings, duct, and hose even the best system will be strangled and not move enough air! Your design must use large enough ducts to support the needed air volumes without being too large and killing the air speed needed to prevent clogs. From lots of experimenting and engineering tables we know we need 800 cubic feet per minute (CFM) air volume at our larger tools for proper dust collection. We also know that anything less than 3000 feet per minute (FPM) airspeed in horizontal runs and 3700 FPM in vertical runs will create clogs. Air engineers design to make their ducts run at 4000 FPM. Sadly, even professional small shop dust collection system designers do a lot of reductions and strange things that reduce the volume so much that the mains end up plugging because without the volume they also don’t see enough airspeed.
  8. Now decide upon what is a big enough blower to overcome the resistance of your system. Picking a big enough blower can be a fairly exact science where you calculate all the resistances in your system then pick a blower that is big enough to overcome those resistances and still give that 800 CFM air volume at your larger machines. On my web page are the detailed steps along with a resistance calculator to walk you through deciding your own blower requirements. At the same time, this is not rocket science and hundreds if not thousands have already been through this exercise. The bottom line comes out the same for almost all who have normal hobbyist machines. If you have larger professional units, then you need to do the work.
    1. For those who move a dust collector from machine to machine they can get buy with a good quality 1.5 hp dust collector that turns at least an 11″ impeller.
    2. For those with small roughly one-car garage sized shops who have ducting but no cyclone, they can barely get by with a good quality 1.5 hp dust collector that turns at least an 11″ impeller, but really should use a 2 hp dust collector with at least a 12″ impeller.
    3. For those with small roughly one-car garage sized shops who have a cyclone, that cyclone will add enough resistance that they need at least a 1.5 hp dust collector with no less than a 12″ impeller.
    4. For those with medium roughly two-car garage sized shops who have a cyclone, they need at least a 2 hp motor turning at least a 13″ impeller or 12″ airfoil impeller. There are a lot of concerns with the airfoils that need considered before going that direction. Most with this sized shop find themselves far happier with 3hp motors turning 14″ impellers.
    5. For those with large roughly three-car garage sized shops who have a cyclone, they need at least a 3 hp motor turning at least a 14″ impeller or even more depending upon amount of ducting and needs of their tools.
  9. Now buy good quality filters. As I said before, I don’t recommend messing with filters at all. If at all possible just blow the dusty air away outside. If you cannot do that, then I recommend buying commercial independent laboratory certified 0.5 micron or better cartridge filters to protect your health. The amount of filter area you need depends upon the type of filter. Fine spun bond polyester filters let us use the least area, but tend to be expensive compared to blended filters. Most can get by with one 300 square foot blended filter, but will have far longer filter life, less cleaning, and much better performance by buying a pair of filters.
  10. Now buy or build a good quality cyclone. Many try to use a garbage can separator, but quickly learn these units that worked so well with their smaller blowers, get almost instantly emptied of all but larger pieces of wood at airflow rates much over 400 CFM. Those with tiny shops and minimal ducting can get by with 1.5 hp motors and efficient cyclones, but most need a 1.5 or larger dust collector that gets put outside. If you cannot put your dust collector outside where the fine dust just blows away, then you will probably need fine filters with a cyclone separator to protect that filter from clogging and wearing out too quickly. There are many cartridge dust collectors available, but you need to ensure the provided filter provides the level of protection you want as most of these are made with very open cartridges to keep the filters from plugging so quickly and keep the filter pleats from getting all jammed up with wood chips.

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