24-11-2012, 05:28 PM
Airfoil Blower
Airfoil Blower.docx (Size: 896.68 KB / Downloads: 25)
Caution
The purpose of this site is to share what I have learned with other woodworkers about the hazards of wood dust and what I did to help protect myself and my family. This particular page steps you through the process I used to build a blower. A blower is a powerful high-speed device that if you build wrong could cause serious injury or damage. Please read the following disclaimer.
Foreword
Although I very much like the idea of an almost twice as efficient impeller, most cannot use an airfoil impeller safely and they are not readily available. There are two major problems with airfoil impellers. Unlike a self cleaning material handling impeller, airfoil impellers have tops making them caged impellers. This means they can build up wood shavings and stringy material. When they do this they can become badly out of balance. Worse, typical airfoil impellers have bad stalling and buffeting problems when the pressure gets over about 6”. A one car garage sized shop will have a maximum pressure of about 7” even with very carefully chosen large ducting. I worked with Paul Payton of Sheldon’s engineering and came up with a center vane in the airfoil that keeps this impeller from stalling up to about 8”. With an average two car garage sized shop running about 10” of static pressure, we cannot use an airfoil impeller in shops larger than a one car garage. When the airfoil impeller gets out of balance or begins buffeting it can quickly ruin motor bearings and even cause these impellers to explosively fly apart. Even if you meet these needs, unfortunately Sheldon’s Engineering, the firm I had making the custom extra heavy duty airfoil impellers was sold and the new owners have discontinued selling these units.
Introduction
I did considerable homework on cyclones and dust collection that convinced me the key factors to effective dust collection were good tool hoods, efficient ducting, a blower that moved ample air able to overcome the resistance of our system static pressure, venting outside when the weather permits and otherwise venting inside into certified fine filters, and using a good cyclone. I strongly recommend that you either build my cyclone design or buy a kit from us because only the 5 hp small cyclone move ample air and none of the small shop cyclone provide ample separation to work with good fine filters. Most actually come with 10-micron filters which the vendors misrepresent as 1-micron filters. It is the 10-micron and finer dust which not only quickly clogs and ruins our filters, this same dust is well studied and the peer reviewed medical studies are clear that this same sized dust is responsible for causing the most long term damage to our respiratory systems. If this does not make good sense, then please read my Dust Collection Basics pages. My Dust Collection Basics page covers much of what a hobbyist woodworker should know about collecting the dust in their workshop. That Basics page explains much of how airflow works and gives blower capabilities and tables for air requirements thanks to some generous support by Chris O'Connor, APC Sales Manager for AAF, a professional air engineering firm that designs industrial dust collection systems.
Requirements
You are welcome to go to my other pages for detailed explanations, but the bottom line is we need a blower that will not just move 1000 CFM, but will move that 1000 CFM against the overhead resistance of our shops. We can get by with just 450 CFM to our larger tools if we just want to do “chip collection” meaning keep our floor clear of the sawdust and chips we would otherwise sweep up with a broom. If we move 800 CFM to our larger tools and we upgrade tool ports and hoods we will be able to meet the OSHA air quality standards. Unfortunately, even our own government says those OSHA standards are dated and the EPA says we should at least meet the five times tougher ACGIH standards. The medical community has long pushed for a standard that is fifty times tougher than the current OSHA standard and this much tougher standard is already the standard in Europe. I think it is foolish to build a blower that moves less air than is needed to meet the higher standard.
Blower Top & Bottom
Now route the grooves in the top and bottom for the sheet metal.
a. Start by centering the template on the top and bottom with all oriented just as they will be when assembled. If you look real close you will see that under the router I extended the template right to the edge of my board. Remember to double check that the template outlet is pointed in the right direction for your impeller. Backward inclined (BI) and airfoil (AF) impellers don't work so well unless turning in the right direction. I drilled a hole through the center and one at 6" inches away using a 1/4" bit through the template and both the top and bottom. Those holes ensure the template sits in the right place on both pieces to make perfect mirror images and will hold things stable for the carriage bolts that whole the whole thing together later. I slipped a couple of threaded knobs through these holes and drew them tight to hold the template firmly in place for routing.
Frequently Asked Questions
I'm a hobbyist with an insane job. I enjoy making things in wood as a form of stress relief. I just want a system that I can turn on when I need it, empty the collection barrel when it gets full and enjoy using the system while knowing I am protecting my family's and my lungs. Is this the right blower for me? Although I like the airfoil because it moves far more air with minimum power making it ideal in my shop, these are no longer available, so I would recommend you use a little larger motor like the Leeson I recommend and buying a material handling impeller.
When I first built my cyclone I was out of circuit capacity. I either had to use an airfoil or go with an impeller and motor too small to move the air we know is needed for good fine dust collection. It was not practical for me to make a huge investment in upgrading the power to my home.