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Airfoil Blower

Created: August 16, 2001
Updated: July 22, 2020

1. 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 fire, damage, serious injury and even death. Please read the disclaimer at the end of this page.
   
   

2. 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. 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. I worked with an impeller engineer and came up with a center vane in the airfoil that keeps this impeller from stalling up to about 8". When the airfoil impeller gets out of balance or begins buffeting it can quickly ruin motor bearings, catch your motor on fire and even cause these impellers to explosively fly apart. Even if you meet these needs, unfortunately the firm I had making the custom extra heavy duty airfoil impellers was sold and the new owners have discontinued selling these units. There are other airfoil impellers available, but when asked I only recommend using them if you can put them after your filters, meaning they only move cleaned air.
   
   

3. 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.
   
   This page furthers my efforts with a very efficient blower design that you can build yourself quite inexpensively. In fact, the cost of a full cyclone system using this approach should be about the same as buying a 2-hp dust collector that will pick up the chips, but not protect your health.

4. 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.
   
   My testing shows that if you don't start by upgrading your hoods, you are not going to successfully collect the finest unhealthiest dust as it is made no matter how big the blower. The issue is our blades, bits and cutters often launch the fine dust at over 100 miles an hour and even our biggest blowers rarely provide more than about 40 miles an hour air speed, so step one is fixing the hoods. Likewise, if you don't use at least 6" or larger ducting, pipes, and flex hose going right to each of our larger machines you will not move the needed airflow. Smaller diameters will restrict the maximum cubic feet per minute (CFM) airflow that your system can support to around 450 CFM with 4" duct and about 650 CFM with 5" duct. I can't believe so many woodworkers get "tricked" as I was into buying a nice 2 or 3 hp dust collector then run it through an inefficient 4" flex hose that limits the CFM at their machines to around 450. Likewise, if you don't exhaust the air outside or use really good low back pressure filters, you are not going to get rid of that fine dust. By using a static pressure calculator that computes the overall resistance my system built with 4" ducting computed out to have over 13" of resistance and that resistance dropped to 8.5" with 6" ducting. Using my Dwyer 2010 Magnehelic gauge it tested at 7.5" for its longest run. This goes to show that the calculators only provide an estimate. Checking a material movement fan table said I could just get the 800 CFM I needed with a 2 HP 3450 RPM motor turning a 12" diameter impeller. Testing with my new Baldor 2 hp motor and 12" Cincinnati Fan's straight bladed material movement impeller left me upset because it tried to move too much air and over stressed the motor. My choices were to buy a bigger motor or choke off the air inlet further killing CFM performance to make sure I did not burn up my motor.
   
   I choked off the airflow just enough that my largest shortest run put the motor right at maximum amperage, then kept digging for other possible efficiency improvements. I slowly straightened out my ducting, replaced the rougher hoses, and got filters with more surface area, but my new cyclone with all that effort still did not work as well at just basically collecting the dust as my prior setup before all that expense and work. I then found a site that had efficiency spreadsheets on the different types of blower impellers. That site showed that the 12" material movement impeller I purchased was only going to give me an efficiency rating of about 40% versus the high-end backward inclined (BI) blowers and backward curved at closer to 60% and airfoil (AF) impellers at near 80%. With either the backward inclined, backward curved, or airfoil impeller, my 2-hp motor would do the job. Unfortunately, airfoil impellers need a constant supply of air and can stall if the pressure goes over 7" creating destructive buffeting when they run out of air.
   
   I then found better sources or impellers. Clear Vue Cyclones makes and sells impellers to my specifications. Jet Tool's Customer Service (800) 274-6848 sells replacement 11", 12", and 14" very good quality, heavy duty backward curved impellers for very reasonable prices (each under $75 plus about $15 in shipping), but these are too small unless you want to step up to all 7" diameter ducts and down drops. You can go to Jet Tools and look up the DC-1100, DC-1200, or DC-1900 for part numbers. All of these also need custom made arbors because the standard Jet bolt on motor arbors that attach the impeller to the motor shaft are setup for the Jet tapered metric motor shafts versus our standard motors with straight keyed shafts generally with 7/8" diameter shafts. Please don't mess this up for the rest of us by failing to have your information already all figured out! I bought a 12" DC-1200 impeller and it did not quite move the same as my larger and taller Cincinnati Fan 12" impeller. With my cyclone adding extra resistance that 12" impeller left me short of the 800 CFM I needed at my larger tools. I then bought a Jet DC-1600 14" impeller and that worked like a champ, but needed a real 3 hp (or so called 5 hp compressor motor to turn it). That was a real problem for me because my shop and home electrical service were already at maximum. I could either power my larger tools or my dust collection motor, but not both. We need an impeller sized to overcome the extra resistance of a cyclone, plus is made from cast aluminum so it won't spark. Unfortunately they quit selling these as separate items. Regardless of which of these ways you chose, you end up with serious bragging rights and a unit that you need to keep pets, small children and wives away from! For this cyclone article/building plan I thought I'd try to find a good airfoil then use either the Cincinnati Fan or Jet impeller as a fallback if it was not successful.
   
   Frankly, my airfoil experiment was a dismal failure. I purchased a total of five different airfoil impellers all sized just right to move the 800 to 1000 CFM I wanted through my cyclone. All moved a ton of air until I hooked them up to my cyclone and ducting. Then I had serious problems. All had severe stalling and chattering problems beginning at just over 5" of backpressure and by the time I reached the 7.5" of pressure for my longest run, I was seriously in fear my blower would self destruct from the terrible noise and vibration. I thought there should be some way to get an airfoil that did not stall quite so early.
   
   The impeller engineer for the Canadian firm I bought an airfoil from spent quite a bit of his time listening to my concerns then helping me come up with a solution. We agreed an airfoil impeller is NOT appropriate for dust collection systems that have a high static pressure, uses filters, uses ducting smaller than 6", or where at least one blast gate is not always open. He felt an airfoil impeller could be built that would work well with one. An airfoil needs a steady supply of air without too much resistance or it stalls. It also requires regular cleaning or can get out of balance. Either stalling or an out of balance condition can cause destructive buffeting. That can ruin motor bearings, cause the motor to catch on fire and cause an impeller to explode. That means this is a poor solution for larger shops and for shops where you are not willing to regularly inspect and clean the impeller to make sure it does not get out of balance.
   
   Based on the numbers of hits on my web sites, over eighty five thousand in the six months before I contacted him, that engineer felt this was a viable market for his firm and agreed to work with me. We came up with a way to modify his firm's standard airfoil impeller with extra vanes to minimize the buffeting problems. By making it a 25-pound monster with special center vanes, he thought it would be less inclined to stall and the mass from this all steel unit with thick base and huge steel arbor would minimize the buffeting. For my shop with its new larger ducting, dual minimal resistance filters, and efficient cyclone the larger of these impellers looked right for me. It promised to be an excellent solution for other small shop users as well. I agreed to buy one for testing. He said his firm would offer that specially modified impeller to those who built my cyclone design at a very attractive price. He agreed to sell at their quantity 100 price which is about half of what other airfoil impellers of the same size cost without modifications. I bought one, tested it with my 7.5" of resistance and it worked well without the stalling and buffeting problems until the resistance went over 8". It worked well enough that I paid to get these two sizes of impellers tested and certified so they could be sold and imported into the U.S. We reached an agreement to add $10 to each impeller price to pay me back for that expensive certification.
   
   My reason for wanting an airfoil impeller is of course that their performance is phenomenal. A 12" half-height airfoil driven by only a 2 hp motor is rated at 1200 CFM at 7"sp. It produces 1700 CFM at 4", 2000 CFM at 2", and 2250 CFM at 0". The full height needs a 3 hp motor but moves about 50% even more air. The DC vendors would wrongly advertise these units as 2 hp and 2250 CFM at 7" static pressure. The problem with an airfoil is when they hit their peak pressure you get minimum airflow and you cannot restrict the flow like a normal fan. This means that keeping the total system resistance as low as possible is vital. Once you exceed that static pressure maximum the airfoil begins to stall because the air begins to bounce from center to outside of the wheel causing potentially damaging buffeting. That means one blast gate must stay open at all times. This is one of the tradeoffs we have to make in order to get much better performance than other impeller types that are stable across their whole range of static pressures. Another trade off is these impellers will not tolerate large material hits, only very fine dust so they MUST be used on the clean side of a cyclone. And the final tradeoff is you have to regularly clean your impeller so it does not build up a cake of dust and get out of balance. With my cyclone only generating a few ounces of dust out of the filters for each full trashcan of sawdust and my doing limited woodworking, I put a note on my calendar to check it once a quarter. After using it for a while that proved to be a reasonable frequency.

   
   
   

   The solution to ensuring that there is always enough airflow so the airfoil will not stall is to either built a trap that will open if the static pressure gets too high or use what is known as a barometric dampener as pictured here. This store bought unit is a touch pricey at about $55 but well worth it with the airfoils. I'm using a hinged trap door that lifts and then settles onto foam weather stripping. I added weight until it also barely lifted with one gate open, but opened wide with all gates closed. Glen S. Miranker shared that he purchased his unit made by:
   
   Residential Control Systems Inc.
   11460 Sunrise Gold Circle Suite A
   Rancho Cordova, CA 95742
   (916) 635-6784
   
   
   While looking for my impeller I made up my mind to buy the inexpensive Harbor Freight motor that was on sale. To check their sales click on Harbor Freight then select the on sale link followed by motors. Their heavy duty 1.15 service factor 3450 RPM compressor motor is the best choice available from them. Personally after thinking about it I realized that my dust collection motor is the heaviest used motor in my shop, so it makes no sense to not buy a really good quality motor. You can get good quality motors from Electric Motor Warehouse. My motor choice changed when I stumbled across a huge closeout of new 2 hp Delta motors and bought one off eBay. Unlike the big material handling impellers the airfoil is nearly twice as efficient so I could use a 2 hp instead of needing at least a 3.5 hp motor to turn a 14" diameter material handling impeller. Just make sure whatever motor you get, that you accurately match the direction of rotation, shaft size, and keyway size to your impeller order. Regardless, once I had the Delta motor I ordered the impeller to fit on a 7/8" motor shaft with a 3/16" keyway. My Delta motor turns counter clockwise when looking at the end of the shaft with the motor behind and cannot be reversed as the needed leads are buried under the coils, so I had to make sure I ordered an impeller from Canada that turned in the correct direction. Both arrived in great shape and I went to work building a blower housing (shroud) to test this new impeller and new motor combination.
   
   I made this blower so the entire blower housing can slip off leaving the impeller and motor still attached and hanging from vibration dampers from my ceiling. The motor and impeller are way too heavy for me to try to lift up and down, so I want them to get mounted and stay right there. With this configuration, a wooden sheet or metal plate supports the motor and impeller weight. I will attach my supports to that plate and my ceiling beams. The plate will actually hold the cyclone as well. MDF should be plenty strong for the blower top and bottom. The MDF can also serve for the top of the cyclone, as it only has to carry the weight of the cyclone. I actually used some thick Melamine left over from another project instead of MDF.
   
   
   

5. Building Instructions
   1. Blower Template

      Start by making a blower template to route the grooves in the blower top (motor) and bottom (cyclone) for the sheet metal.

      1. Calculate the size outlet wanted. Most 1.5 to 3 hp blowers use 5" circular outlets. If the outlet was a 5" pipe the outlet area would be 2.5*2.5*pi = 19.63 sq. in. and the square root of that is 4.43" to make a square outlet with the same area. Knowing my impeller with clearances makes the blower shroud 6" tall, any outlet width bigger than 4.5" would do for me. Yours might be different. Dividing 4.5" by pi sent me off looking for a cylinder that was 1.43" in diameter. I had a new pressure regulator sitting on my workbench that measured out at 1.5". With that plus the roughly 3/8" more from using a router with collar to cut things out, I would have a plenty big enough outlet width.

      2. I laid out the impeller width on my pattern on a piece of 6mm Baltic birch plywood. It was left over from making one of my portable massage tables, but I like to use this material for templates because it is flat, strong, smooth, and does not have any voids.
         

      3. I then used double sided tape to stick down that gauge to provide a cylinder to wind around and get the changing radius needed to make a spiral. For that radius I used glass reinforced strapping tape sticky side away from the gauge. On the other end I taped a pencil that was held flat and upright by on an old tape roll. That tape roll provided a nice flat base that kept the pencil vertical, so all I had to do was keep tension on as I went around drawing the spiral. I pre-wound the tape after finding I got a much smoother circle when unwinding. With a little pressure on the gauge and pencil one time around left a nice perfect spiral.
         

      4. A little work with my scroll saw got it cut out slightly oversized except for the sharp angle that I took pains to get right on. Some sanding and I ended up with a near perfect spiral template to use for cutting my grooves!
         

   2. Blower Top & Bottom

      Now route the grooves in the top and bottom for the sheet metal.

      1. 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.
         
         

      2. With the template firmly bolted in place, carefully start routing beginning with the blower outlet edge off the side of the board. I used a 1/8" bit set to a depth of about 3/16". With a small bit you have to go real slow and let the bit do the work. Trust me, my first one let the smoke out and put me a day behind on this project waiting for a store to open to go buy a replacement. (For what it is worth, letting the smoke out is an electrical term that was used by early digital engineers. We all knew that all that fine wiring and stuff was really a ruse. Those chips worked on highly compressed smoke. When you let the smoke out they never worked again!)

      3. Before taking it all apart I marked the ends of the pieces and labeled each so they will not get turned around during the machining. I also wrote bottom and top on both faces of the template and matching top and bottom on my Melamine. Now route the other side making sure the template is correctly placed to make a perfect mirror image.

      
      
      
   3. Blower Holes

      Now make some holes for your blower impeller and your blower inlet.

      1. Now center the impeller on where it will go double checking its orientation.. I used a 1/8" clearance off the side of my impeller to the sheet metal groove, but because the impeller has a raised base the picture makes it looks more like a 1/2" spacing!
         

      2. Getting the air inlet hole exactly over the impeller posed a little challenge, even with a centering hole going through the top and bottom. The problem is the inlet into the impeller needs to sit at exactly 1/8" inside the impeller with only 1/8" clearance. With my impeller and motor mounted separately and not built onto the blower shroud. My solution was to first cut a shaft hole in the top board that would let me lower the impeller down flush. That allowed tracing around the impeller itself to make the cutout. Once the top cutout was done, bolting the top and bottom boards together let me lay the impeller down well centered then trace the inlet exactly.
         

      3. The inlet hole for an airfoil impeller needs to hold a flaring that puts the air 1/8" deep into the impeller for optimum performance. It also needs to stay within 1/8" of the sides of the impeller inlet so almost all the incoming air goes right to the airfoils. Had I not carefully drawn the blower inlet and positioning on my piece in advance, it would have been near impossible to center this just right.
         
         
         For a blower that would go on a cyclone the inlet would neck from a 9" diameter smoothly down into the impeller. For testing this blower, I wanted to limit the airflow with the same 6" diameter ducting that will be used in my system and with quite a few people waiting for some results, I made a simple inlet by flaring a piece of 6" S&D PVC pipe that I worked over with my heat gun to open it up to be 1/4" less than the diameter of my inlet. Ideally this inlet should take on a hyperbolic shape for optimum airflow with least resistance. For a normal backward inclined or backward curved dust collector impeller, 1/2" clearance is ample by itself without having to build a special inlet.
         
         Initially I recommended that this would be a piece that I would buy with the impeller, but have since found that these special inlets are very costly. I have made similar parts easily enough without too much trouble. Truthfully, making a wooden mandrel with the right shape on my lathe, then inserting about three inches of a PVC pipe segment into hot oil would soften it enough to slip that mandrel in and squeeze all down to make a perfect form. Alternatively, making that mandrel with my router would be more difficult as I would have to build it up from layers, but in my bit collection are a couple of nice curves that would work just fine. I also have access to a PVC plastic vacuum forming service that could make these up once I had a mandrel to use as a mold. The professional PVC formers use hot antifreeze to warm the larger sections of pipe, but I would use hot oil because my heat gun is just not enough unless you do a very little at a time. I was in a hurry to get those results posted so did not spend the kind of time on mine I should have. The advantage of the PVC is by cutting just the right hole in the blower it fits nicely and locked in place with a little hot melt glue.
         

      
      
      
   4. Metal Sides

      Next form the metal and put into the grooves.

      1. To size the thickness of my metal I used a micrometer on my two existing industrial blowers and found they both were made from stamped 18 gauge steel so I decided to use the same. The metal height had to be tall enough for the blower plus the depth of the grooves and enough clearance to keep the motor bolts from hitting the impeller arbor bolts. For my airfoil impeller, I used 1/2" clearance. I did have to go with multiple pieces because I did not feel like paying for a 4' x 10' sheet. I cheated and had them cut right on at my metal shop on their big plate cutter. In hindsight, having three pieces actually worked in my favor as they were far easier to work with and bend. I did roll them lightly over a large cylinder by hand to start setting their shape. To make the sharp outlet bend I skipped the one-hour round trip to the campus shop and instead used just a little applied force (read hammer).
         

      2. It took me a while to realize that I needed to carefully roll the metal over a cylinder to get it to have just the right curve. With lots of fooling and adjustment, I finally got it so that it would lay in the groove without much tension. I then flipped it over and double-checked to make sure that was also true on the other side. When both fit just right without having to force anything, I installed the pieces.
         

      
      
      
   5. Bolt Holes

      Now make holes for the carriage bolts that hold the blower halves together.
      
      I used my compass and with some messing around laid out 6 equally spaced holes around the outside of the groove. I then bolted the pieces together and drilled matching holes for the carriage bolts.
      
      
      

   6. Mount Motor

      Now mount the motor.

      1. I made the motor holes by making a "rubbing" template of the face of the motor using graph paper with a carefully cut center. The center slipped over the motor shaft and made it easy to align that paper template to the top piece. The template was taped to the top piece then holes were drilled.
         

      2. Because I am going to use this blower for some testing and will be taking it apart repeatedly until I get the hole sizes just right, I made the motor and impeller to be able to mount independent of the cyclone. Note you can see the inlet sticking up in this picture so it will fit right into the impeller.
         

      3. I needed an oversized hole in the blower housing that will let me easily slip the housing on and off. This hole is big enough to let the motor and impeller hang from their support while removing the cyclone without having to lift the blower up and down. Allowing the motor and blower to hang independently also makes it much easier to install and to take off the cyclone for repairs or cleaning.
         

      4. The motor mounting board screws tightly to the motor face so there will be no air leak. It also bolts tightly to the top of the blower. In my final configuration I'll put some insulation between it and the top of the blower to ensure no leak there as well.

   7. Completed Blower

      Here is the completed blower with motor.
      
      
      

6. Testing

   1. There were two concerns that I was testing with this setup. The first was that we had appropriately sized the impeller so it would not over stress the 2 hp Delta motors. The second was to make sure that the modifications minimized any potential of stalling at higher static pressure loads that could damage the impeller or motor.

   2. I've secured it in place and added a test pipe.
      

   3. By slowly blocking the inlet I was finally able to generate a little bit of stalling at about a 2" circular opening. As I restricted the airflow the motor current did decrease like the standard impellers do, but I limited the inlet tube to 6" to make sure my 2 hp did not try to move so much air it burned itself up. Regardless, the buffeting was minimal and did not seem appreciable even with the inlet totally blocked. I do not think it will be a problem provided those who use this unit minimize their static pressure and do not block the airflow totally. They should go with 6" ducting and none less than 4", plus open large cartridge filters and always keeping one blast gate open to avoid the buffeting.

   4. I did call for help as my cousin Phillip who is also an engineer joined us for Thanksgiving and we put him to work. My original measures on amperage were wrong because my amp meter had a tired battery and had been dropped. What we found was that wide open using all 6" diameter ducting the most we could draw with this impeller was 8.5 amps. That amp reading says that I can safely open the blower inlet as long as the cyclone stays connected to the 6" ducting without concern about burning up the motor.
      
      

   5. Hooking up the Dwyer Magnehelic gauge showed 3.2" of water which translates to 7160.34 feet per minute (FPM) air velocity. Dividing 28.313 square inches (the surface area of my 6" duct) by 144 square inches (the area in one square foot of a duct in inches) times that 7160 gave a 1407 CFM!
      

   6. The bottom line is this impeller is nothing short of incredible. It provided more airflow by quite a bit over my similar sized radial vane impeller driven by an identical motor. And it does so with less amperage!
      
      

7. Frequently Asked Questions

   1. I heard a rumor that the real reason these impellers are no longer made is sales died when you quit recommending them. What really happened? Initially I was just another customer like everyone else and I bought one of the original airfoil impellers as this was the only heavy steel airfoil I could find of the right size that was affordable. It worked well but stalled at too low of a pressure so was of no use in my dust collection system. I worked closely with their engineer and we came up with a special vane that lets the airfoil work with about one water column inch more pressure before it stalls, making it an excellent solution for a small one-car garage sized shop provided the cyclone is vented outside instead of into filters. We also came up with a bigger airfoil with a similar modification that would work in a larger shop provided all was vented directly outside without filters. Before these impellers could be used they had to go through an expensive certification and testing process. I paid for that certification and testing as I wanted these available. The plan was the manufacturer would repay me by providing a small percentage on each sale.
      
      Too many things went wrong. Many who bought these did not do the required cleaning which soon puts these impellers out of balance which quickly ruins motor bearings. Many also installed these expecting them to work well with filters and 6" diameter ducting. Unlike my 15" and 16" material handling impellers, these airfoil impellers do not generate or handle extra pressure well so really need all ducting to be 7" in diameter to handle a real 1000 CFM. When used with 6" duct many were only getting around 875 CFM airflow instead of the 1000 CFM we need at most stationary tools for good fine dust collection. The filters and 6" diameter duct also added too much resistance and that creates heavy stalling and chattering that ruins motor bearings and caused one fire. We also were having serious shipping problems as these impellers are so heavy that dropping them will cause them to bend and destroy their careful balance. Shipping them safely required careful expensive crating and lots of very dense foam padding. Although people were supposed to ask me questions, they instead asked this firm. This firm changed hands and the new owner realized he spent far more on staff time than the revenue these impellers produced. To cut costs he declined to honor their agreement to get me paid back for the testing and certification that I paid for to permit him to sell these impellers. He also reduced the packing which caused over half the impellers he sold to arrive bent and ruined. He started blaming the small shop owners and refused to make repair. Nothing I did made any difference, so I quit recommending these units. That firm continued to sell them without paying me anything, but over half ended up with ruined impellers. After too many complaints and ruined motors I finally asked the new owner to stop sales and pull my name and endorsement off their pages.

   2. 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 5 hp I recommend and buy a 15" or 16" diameter 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. If you have power problems similar to mine or just want the most efficient solution in terms of operating cost, the airfoil is the way to go. It comes with a price. You not only have to find one of these expensive impellers, but also have to make an air trap that opens so the impeller will not stall, must do regular inspections, and must do regular cleaning. If those do not suit your style of woodworking, then I seriously recommend that you instead build my budget blower and use a larger motor.

   3. I'm confused because from your picture I can see that this is a clockwise turning impeller, but the motor you chose says it is clearly a counter clockwise motor that the vendor says cannot be reversed in direction? You are correct. You cannot reverse that motor's direction easily. Unfortunately, there is plenty of room for confusion on the direction of rotation. Impeller makers determine rotation direction the same way that machinists do. They consider drill bits as right handed or clockwise turning. Conversely, some motor makers use two opposite standards for determining the direction of rotation. Some look at the shaft from the motor side and some from the end of the shaft with the motor behind. The Delta 2 hp motor turns counter clockwise when looking at the shaft with the motor behind. Because many newer motors, including that Delta, CANNOT be reversed, you need to be careful that your impeller turns the same way as your motor turns.

   4. How long to get your impeller? It took about three weeks to get the impeller made, balanced, and delivered. I do know they had quite a few of these in progress, but with the change in ownership of this firm they stopped taking orders from individuals and will only do business with businesses. They found so many small shop workers were calling that their small markup on these units was not enough to offset the staff time needed to answer questions.

   5. Any other impeller ordering concerns? You need the specially modified airfoil impellers which I have been told are no longer being made.

   6. Hey! I called about buying one of those specially shaped inlets and they charge a fortune for them! How did you make yours? I used a heat gun, some thick gloves and built mine outside with a fan blowing the dangerous vapors away. It took a lot of fussing and was a pain, but it did come out pretty well. I had no idea they were all that expensive. Sorry! If I was to go into production on these, I would turn a mandrel on my lathe just the right size and use a couple of heat guns at once to make it a lot easier.

   7. What did the motor cost, from which firm, why did you pick that motor? I wanted a good heavy duty motor that could run all day without a problem. In motor terms this meant I wanted one that had a 1.0 or better service factor (meaning can run 100% of the time at rated power). I also wanted quality without paying too much. I've had many years of good service from Delta motors made by Marathon. When I saw a vendor had purchased many new surplus 2 hp Delta motors and was selling them on EBAY with shipping prepaid, I did a little more homework, then bought one. I bought from eBay from Eric (TheGoodMember). When he sold out of these motors, I did not look for a new supplier because by then I had upgraded my electrical service and wanted a real 5 hp turning a 15" or larger material handling impeller. This is in my opinion represents the minimum to move enough air to meet the medical air quality recommendations which are now the EPA and European Union standard.

   8. How did you test this blower? When? My cousin and I finished our testing of the airfoil on Friday, November 29th, 2002. We followed the Dwyer Magnehelic® gauge recommendations to setup our test bench, mounted the pitot in the right place, and set the proper length of ducting test pipe with a threaded valve we could close to whatever opening we wanted. We double checked our gauges and work. We used a Dwyer Instruments 4015 model Magnehelic® gauge with a Dwyer 166-6 pitot tube for measuring the pressure and computing the air flows. See my measurement pages for detail.

   9. What were your test results? With an extended 6" pipe in place to limit airflow sized in length to meet the test parameters, this impeller/blower measured at 3.2" of water static pressure. After going through the Dwyer formulas and cross checking this comes out to a whopping 7160.34 feet per minute (FPM) airflow. Multiplying by the duct size in square inches divided by 144 square inches gave a real 1407 cubic feet per minute (CFM) at whatever we connect this to. Because I used a centerline single point of measure, the result needs stepped down by 10%.

   10. What amperage did the motor draw? My original amperage measurement was just over 10 amps, but my cousin found a problem with my meter from being dropped that we fixed and checked with a second meter. The actual amperage came in at 8.4 amps.

   11. Why did you check the motor amperage? Pressure blowers do the most work when moving the most air. When a blower gets too much air, you can easily over-stress the motor and cause it to overheat and die. Frankly, in helping to review some recent magazine testing I discovered that a well known cyclone vendor had their units tested with a gravely oversized cyclone and blower inlet. This will move lots more air, but caused at least three of their motors to burn up during that magazine testing. That is what we tested with the amp meter and using standard 6" test duct. We wanted to ensure the actual current it drew did not exceed the motor's designed runtime rating located on the motor plate. We also wanted a real number that others could expect to get rather than some pie in the sky advertising hype that only leads to disappointment. The results of that test showed we can run this motor all day long moving lots of air while driving this big impeller without a problem of drawing too much current or overheating. Because the impeller is so heavy and starts fully loaded, it does draw a lot of amperage on startup, but now that I've run this for almost a year, it has not been a problem.

   12. Why did you make a big deal out of the airflow you got which is not much better than the 2 horsepower inexpensive dust collector I just bought? This is not a hill to die on! Hobbyist suppliers can claim anything they want as long as they can devise a test that will "prove" their ability to perform at their claimed rate for a few microseconds. My testing found most cyclone and blower vendors sell systems that get about half their advertised maximum airflows. Even a few of the vendor sites say to figure you are going to only get about half of the claimed airflow. The advantage of this unit is it produces a real flow under real working conditions, and does so through increased efficiency.

   13. What were the limits again and why can't I use an airfoil with my existing all 4" ducting setup? Using 4" ducting limits the airflow at the pressures we get from airfoil or dust collector blowers to around 450 CFM and makes for a much higher resistance. Typically, a shop plumbed with 4" ducting needs 12" or more of static pressure to move enough air to pull in the fine dust at the source before it gets launched into your shop. All airfoil impellers have a very narrow range of static pressure that they work well within before they begin to stall. This particular airfoil impeller with its special design can handle up to about 8". Although far better than most that stall around 6" of pressure that is still way too little if your system needs 12" or more. As soon as the resistance of your ducting, cyclone, filters, etc. goes too high, the airfoil stalls and begins to chatter as the air bounces around the center. Too much of that can ruin the impeller and the motor bearings. To avoid this problem we need to only use the airfoils with shops that generated 7" or less total static pressure measured in water column inches.

   14. What are the rules to maintain this kind of impeller? Although I provided a ducting resistance calculator, the bottom line here is you need to follow a few rules to ensure the safety and longevity of your impeller and motor:

       1. Use an efficient cyclone placed before the impeller. Placing the impeller before will let the sawdust go through the impeller and these were never designed to handle hits nor are they self cleaning;

       2. Use all large 6" ducting and ducting runs with minimal resistance;

       3. Use at least one five foot long straight duct run before the cyclone. This will steady the airflow for better cyclonic separation and add enough resistance so the blower does not try to move too much air;

       4. Keep the equivalent of at least one 6" duct open at all times;

       5. Use large minimal resistance filters;

       6. Keep your filters clean enough that they don't create too much back pressure;

       7. Keep an eye on the overall pressure/amperage of your system to make sure it is working efficiently.

   15. Will this blower support multiple blast gates open at once? I only built it for one, but depending upon the size of your ducting, what you want to do, on and on, you might be able to get enough airflow to run two blast gates at once. In fact, if you only have a small one open, you really should open a larger one at the same time to make sure you keep up ample airflow. Otherwise you can have plugging and piles in your duct. These pose a serious fire danger.

   16. From my perspective, your blower looks good, but will it work with a real system in my larger three-car garage sized shop? No. Even the larger airfoil will not be able to overcome the static pressure in such a large shop. Also, there is a lot more to a system than just the blower. For this blower to work, it needs a very efficient cyclone, minimal resistance air filters, good hoods, and a sound ducting design. I think my system using my cyclone, all large 7" ducts, only 7" flex hoses, and a set of Torit filters keeps my personal system well under the 7" to 8" of static pressure that will cause problems with this blower. This gives me the ability to take care of the dust collection at the machine sources in a pretty good sized shop (large 3 car garage). It gives me the 800+ CFM at each of my large machines and 4000+ FPM airspeed needed to get rid of that dust.

   17. Which filters did you use in your setup? I used the larger impeller and very large ducts, so could filter. Most cannot filter with an airfoil impeller. The filters I purchased were from directly from the Donaldson-Torit retail outlet on line. I bought four 120 square foot 0.2-micron Donaldson-Torit filters. Mine are all polyester, but cost me double what the poly paper blended filters cost. These all poly filters need a minimum of 250 square feet but are recommended to be a full 500 square feet for my 1000 CFM airflow. The blended filters need a minimum of 500 square feet, but the engineering notes say they really should be at least twice that in area. Two of mine were ordered with metal caps and two with plastic caps. The plastic was easier to work with. All had both ends open. The cost on these filters was high and they were reluctant to do business with me because I was not a commercial firm buying multiple filters. They simply boxed these filters and sent them via expensive carrier resulting in some shipping damage and high shipping costs. Donaldson-Torit has since worked through those issues.
       
       Meanwhile, when it came time to replace my filters I shifted over to another supplier. I've had great service and support with excellent prices on filters, flex hose and hose clamps from Wynn Environmental that Jack Diemer found and referred me to. Also, make sure you check out your local suppliers. Many are now using a single 300 square Farr compatible filter from Wynn Environmental instead of the two Torit compatible units. I think that if you can afford it, you should do like me and buy a pair of the Farr compatibles filters would give far more life, better filtering, and be an overall better value.
       
       I've also recently heard of good service and pricing from Filter Mart on the all poly Torit compatible filters like I first used. You name your own price, but they will not accept your order at the prices Wynn charges.

   18. 

       Money is tight and I would like to use just one Farr filter as some of the guys have been doing instead of the two Torit units you used. Would that work equally well, and do you know which Farr filter to buy? Do you have any other suggestions?

       1. My friend Alan used a single pleated Farr cartridge filter and it works well for him, but I recommend a pair of these sized filters to minimize cleaning and how often you must replace. The more you clean the shorter the filter life. He bought the Farr model 125154-005 from MPW Filtration (pictured above) which has since been sold to CLARCOR Inc. Similar filters are available from a variety of sources. The dimensions are: 12.75 in. O.D.; 8.375 in. I.D.; 34 in. long; 284 sq. ft. area; 80/20 blend filter, and 0.5 micron filtering. You can order Farr compatible filters from Wynn Environmental for less cost. I personally use the Wynn "nano" filters because they provide much better protection for not much more cost.

       2. Another option is MSC Direct carries the Donaldson Torit dust collector cartridge filters for similar pricing and reasonable shipping.
          
          The filters MSC sells are made by Filtration Group of Joliet, Illinois, model number is 80002.

       3. A few wrote and said they got nice sub 1 micron filters for free or almost no cost from large truck depots. Many reported back after using these solutions, they had problems. What those with particle meters report is the blended poly paper truck filters fail quickly. Those lucky enough to find the all spun bond polyester truck air filters report these can be washed up to four times and they work fairly well but because they are not coated with release agents our heavy wood dust volumes rapidly cause them to plug and need far more cleaning that those who get filters made for the heavy wood dust loads.

       4. Finally, a few have written that they used a bank of shop vacuum filters such as those made by Clean Stream. These are very good filters, but it takes a lot of them to give the real 500 minimum square feet we need for maximum filter life. When I add up the cost to get the same square feet, these actually cost more. What most are doing is using far fewer filters, but our particle counters show that using too little filter area results in the filters quickly failing.

   19. Do you have a simple drawing giving a cross section through the center of the assembled blower? Maybe, this picture might help. It shows how I mounted the blower on a separate board that then mounts on top of the top of the blower shroud. I did this to get the sizing/spacing right and to let me make the blower-housing mount separately from the motor and impeller.
       

       

   20. Ok now you have confused me but good. First, you said the bottom of your blower is going to mount on the cyclone outlet. The cyclone outlet from your plan is D/2 or 9" for an 18" cyclone. Why did you make the blower opening only 6" large? In terms of the bottom of my blower, meaning the part opposite the motor that mounts on the cyclone, you need to remember that my goal was to quickly get something ready for testing. I wanted to be able to mate to a 6" ID piece of S&D PVC. To use my Dwyer magnehelic gauge I needed a piece that was at least 60" long with a hole 9" from the face of the blower. From my measurements, I concluded that as long as you have at least a 60" long piece of pipe holding the airflow from getting out of control, you can make that opening as large or small as you would like. Mine ended up being the size of 6" ID S&D PVC that I let hang out about 4" to mate with my test pipe. I will change that sizing if I decide to actually mount that blower on a cyclone. I may make a little smaller metal based case, simply because I have a room problem where that big blower will be in the way of my garage door.

   21. Assuming there is some good reason for your having only a 6" blower inlet, what size blower inlet should I make for my blower? My 6" inlet was to fit on a test pipe to check out the blower to make sure it worked before recommending it for others to try. I think the easiest and best thing to do would be to make the blower inlet a nicely flared entry that reduces down from the 9" (or 10" if you build a 20" diameter cyclone). Working over a $5 tapered HVAC reducer that goes from 10" to 8" to make it a 9" to 8" would work and not be too difficult to do. I might use my roller to create the flare.

   22. You say you made the steel for the blower sides from metal that was 6" tall. I bought an airfoil impeller from that same firm for my 3 hp motor and 6" is too short. Why? My impeller is not a full height and with each of these units being custom made, there are bound to be some small differences in sizing. Plus, if you told them you were using a 3 hp motor, they probably made you a full height impeller. Since I can't tell the exact sizes for your impeller, you need to take the time to figure out what will work best for yourself. Wish I could help more, but that is just not possible from here.

   23. I am confused by one of your photos. You clearly show one of the sandwich pieces with a 3" hole yet later I see one with a big hole and the other with about a 6" hole for PVC. Why did you make the 3" hole? I did that so the impeller would sit down flush instead of being held up on its tall arbor. I wanted to use the actual impeller to draw the sized hole I needed to make the blower shroud removable. That saved having to measure and guess, plus let me set my 1/8" clearance right on. Also, I wanted my actual result to be dead on for both the top and bottom so I could hold the 1/8" clearance on the inlet.

   24. I like the idea of mounting the motor and impeller, then being able to remove the blower housing and cyclone without having to lift up that heavy motor. What kind of vibration dampeners are you using to support that weight? I found some nice rubber dampeners at a surplus store, four for $3. I'm going to try and make them do. If not, on my previous cyclone I used four I got from Granger's sized to hold about 1/3 of the weight of the motor, blower, and cyclone combined.

   25. I've been banging my head into the wall for an hour. How did you ever come up with the calculation to get your inlet to sit exactly 1/8" inside your airfoil impeller? I had that same problem and was not able to figure that out by measuring as I had too many variables including a little dampness that had swelled portions of my Melamine backer. So what I did was cheat by making the inlet hole a very tight fit on the PVC and putting the flared piece of PVC through before I bolted the sandwich together. Once it was bolted together I gently worked the PVC down and by feeling through the hole was able to get it positioned just right, then locked it in place with hot melt glue to hold it still and seal the joint. Had I not made that sacrifice 3" hole you asked about earlier, I would never had gotten the inlet centered to within 1/8".

   26. I see your Cyclone Plan page lets you use an Excel spreadsheet to build the size cyclone you want. What size would be best with this sized impeller? Although you could use an 18" diameter cyclone, you would be better off to use either a 20" or 22" diameter unit and end up with just a tiny bit worse separation but with even less resistance. I built an 18" because that is all the room I have with enough clearance for my garage door.

   27. I have planed on using 8" diameter pipe connected to the cartridge filters and the blower outlet. Is there any problem with this? Nope, but you would have less noise if you followed Larry Adcock's (WoodSucker designer) suggestion and used insulated HVAC ducting instead. Plus that would be much easier to install.

   28. I see that you used regular steel for your blower instead of the galvanized stuff you recommend on the cyclone. Does it matter? Yes. I also have to watch my pennies, so buy my metal from Blue Collar Supply, a great surplus shop in Sacramento. They did not have anything galvanized in the size and thickness I wanted, so I got metal that was not plated and plan on doing some serious painting with epoxy appliance finish because the wood coming in hits hard enough that it releases water and generates heat. Instant rust!

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