Industrial Sawdust Collection for Cheap
Terry Cain
| Twenty years ago when I started a millwork/cabinet shop, small import dust collectors were not yet available in this country. I am somewhat thankful that was the case because I may have been swayed to thinking that this was an acceptable route for a commercial venture. Sawdust collection for a shop that is going to attempt to profit from cutting wood all day is not real complicated. It amazes me how complicated people make sawdust collection for their garages and hobby shops, mathematics of design and execution can stymie the woodworker used to inches and feet. Pressures and velocities, psi and horsepower all make the world of suction far more complex than it really needs to be. While it is necessary to oblige the factors present in system design, you cannot let other design elements fall short of the goals of clean air and a clean shop. Does your system work? All you have to do is hold your hand up to the inlet to find out. |
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Interior of shop. Note handle for reching blast gate on planer. |
In the beginning, I had plenty of time to shovel out my saws and I let the planer spew chips everywhere. I was young and had important things to build, time was plenty and cleanup was fun. Nowadays the amount of chips my shop makes in a week would bury me knee deep from one end of the shop to the other. Also I have employees which means that OSHA and fire inspectors stop by and "want to get to know me better". Insurance people also have preferences to what kind of system you have. A couple of years ago my agent landed a memo about bag type units in commercial cabinet shops, the memo was to encourage the removal of these units "well away from structures" to the outside of the shop. The reason as we all know is fire safety. Basic thinking will yield the fact that sawdust explodes when confined in a container and ignited, you simply must decide not to put your sawdust collector inside but put your explosion outside. This way if and when your DC blows, you can walk outside and enjoy the view of a large fireball outside knowing you can walk back in to your shop and or home without getting that ugly black soot all over you and your project.
So we can see that the smaller bag type units and many other supposedly "industrial" units need to be outside of a structure for common sense and safety. Locating a unit near the outside wall under the eaves of a wooden structure doesn't quite measure up to fire code safety but you will have cleaner air. Locating a bag unit in a garage to catch planer shavings can actually make the air in the shop worse if the bag is not a fine filter bag. I have walked into many a shop with a tablesaw running and the DC spews dust into a bag that lets fines into the small shop making perhaps more mess than without the DC.
Locating the DC outside has drawbacks, mainly that heated air in the wintertime will be lost when the unit is running. This increases the expense of heating the structure and in extreme cases makes heating the shop very nearly impossible. You have to balance the expense and also try to eliminate the air-change effect by using blast gates at every machine and be sure to turn them off when using another machine.
The benefit of locating the sawdust collector outside, aside from the fire danger is the real benefit of much cleaner air than is possible by locating the unit inside. There are fine European systems designed to be placed indoors in smaller shops, Felder, Coral and Atlantic to name a few. They are designed with finer, flameproof filters and more powerful blowers and have hefty price tags compared to the very popular import two or four bag type units Grizzly, Sunhill and other importers sell.
Noise is another reason to place the unit outside. This can be a challenge because an outside collector needs to be larger to begin with because there presumably is more pipe to blow or suck through. Pipe itself is a major culprit in amplifying noise, acting like a pipe organ resonating the blower's howl louder than without the pipe. Wrapping the pipe with insulation can work to lower the sound level considerably.
| My own system I have now is unique in that I was inspired to take the "farmer" approach to designing and building a dust system. Farmers as you know "spread it around", you might not have known that they also "blow it around" when storing grain, feeding livestock or conveying bulk materials. It would be hard for me not to use the American farmer as a role model for a woodshop, mechanically speaking that is. Nearly every farm has great expense in machinery over a long term investment just like a woodshop has. The farmer also is efficient, so much more so than many industries can claim, so long ago I chose agriculture as an inspirational model for my business, oh yeah and Italian chairmakers. Which means I need the European standard for air, which is CLEAN and BREATHABLE, I'll take cooler over dustier anyday! Ever seen shops in Europe? Breakfast, on the floor with champagne! So I first began my system design for 10-20 machines, I have 16 at present and am taxing the suction to about the limit. Nothing settles in the pipes but I could use a little more suction at the thickness planer which needs the most velocity. All the sanders and saws are serviced just fine by the system. |
Wooden blast gate with long handle. Steel pipe meets pvc. |
| The blower (fig. a) is 34" diameter by 9" wide with a 1.5" shaft. I found this blower in an agricultural junkyard for 125 bucks, it is off of a Chisholm-Ryder pea combine. I had it modified with a longer shaft and inlet sized for my needs. The inlet is 12 and by way of the Grainger catalogue I was able to determine velocities and horsepower requirements by using similar sized blower data. I run ten HP via belt drive (two "b" belts) and run the unit at a conservative 1500 rpm for durability. It has been running daily now for eight years without interruption. The cyclone is off of a hay chopper. Every hay chopper has one. I paid $50 for it. Inside I bent an 1/8" steel plate into the mouth of the inlet for wear resistance as sawdust under pressure is highly abrasive. The bin under the cyclone is a seed or feed bin like you see everywhere farmers are. The stand was made by a local steel fab shop The dust pipe is all steel spiral pipe except for the drop to the machinery. The cyclone separates all but very fine sanderdust, nothing is visible but slight dust emissions when stroke sanding. |
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Blower with hinged cover |
| I use the pvc for drops because of the inner smoothness and ease of hanging. I get a kick of the worriers that swear using pvc will cause bodily harm if you use it. Well I used both steel and plastic. Is this a pillow tag removal arrest scare or what? By the way, when you have plastic dust pipe isn't it the same as "flexible PVC" ie. DUSTHOSE. I have a friend with a 30 person cut up shop and he has this wood hog/grinder for scrap that has PVC on the outflow. Something like 2-6 tpi (tons per hour). Static, sure it stands your hair up but he's not worried. There is too much dust going up his tube and no air for an explosion. Yes PVC creates static. So does walking on carpet. I could shuffle my feet across my mom's carpet and touch a full sander dust bag and I know it would blow. Will grounding help? In my case the pvc is connected to steel pipe on one end and a metal machine at the other, I feel safe. Blast gates are where I really saved some money. I now buy the metal ones and some of the larger branches I even splurge on quick change pipe couplings. I started out with homemade blast gates which I still use many of. They are easy to make and work very well with the PVC drop. |
Top of cyclone is 22ft. |
I make enough dust now I had a trailer with an opening in the top made just for sawdust. It also doubles as a tool shed on out of town jobs. The bin holds 1 unit or 1-2 weeks worth of chips and the trailer holds exactly one bin full giving me nearly a month not to worry about sawdust. This amount is also equal to a pickup truck with sidetracks full. Emptying the bin is where this particular unit has trouble. The cone shape packs in and in winter freezes up at the bottom making a quick 5 minute dump into 20 minutes of frozen sawdust battle from the small amount of water that creeps into the bin. This system could well cost upwards of $10-15grand or more engineered and installed but some dirt under my nails, some bathroom reading (ya know technical stuff) and a total investment including pipe, I farmer'd it together for $5k incl. trailer.. Times a wastin, got me a stack of boards to plow before it rains.
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