|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
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
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