re-purpose blower for dust collection

[Brendon_t]

hey guys I'm thinking out loud right now so please feel free to interrupt the train of thought. I have a few Granger supply bounce house blowers with two horsepower motors rated at 500 CFM. I was wondering if this would be adequate to use as a movable dust collection unit. My vision being to add some 6 inch hose to the intake port stepped down to a 4 inch port on all of my machines then attach a 5 micron bag to the blower side. I suppose I could also put a few wheels to make it easier to roll around the shop. This blower came from a store I used to work in that sould bounce house equipment I borrowed it one day to help drive some carpet after a flood and totally forgot I had it. The company has long since gone out of business so returning it is not really an option. Anyone have input as to whether this would satisfy my needs for collection from a table saw router table miter saw joint ur and planner

[Tpt life]

The motor is likely not sealed against so much dust. Instead of blowing through it will likely end up packing the motor.

[Raefco]

At a minium, I think you would want to incorporate a cyclone or mini "bag house" in the mix before the blower 

[Brendon_t]

The motor is likely not sealed against so much dust. Instead of blowing through it will likely end up packing the motor.

I'm not sure if dust would be An issue to the motor. It appears to be a sealed unit that works rain or shine. There is a 4 inch shaft that exits the motor housing and enters a stamped steel fan shroud. Where the aluminum fan is attached to the

[Bill Tarbell]

DC info always seemed a bit overly complex.  I say just slap a bit of hose on the inlet port and connect it to one of your machines to see how it does.  No need to buy a filter bag or enough hose for all of your machines yet.  Just see how well it works on a single machine that's easy to measure, such as a jointer.  If it works then you saved yourself around $250-300 for the cost of an equivalent powered store-bought unit.  At that point you can do more investing into the hoses, blast gates, filter bag, separator, etc.

[tim0625]

==>500 CFM

CFM is one thing; CFM at a usable inH2O is another… The issue is velocity: can you pull CFM/inH2O through the inlet to move fines down the pipe (between 3500-4000FPM, depending)… The last time I looked (years and years ago), Bill Pentz’s site has (had) a decent ‘basics’ section for DC, single-stage and cyclone-based collection… I’d start there: http://billpentz.com/woodworking/cyclone/dc_basics.cfm

 

As a starting-point, 2HP/500CFM could be in the right ballpark for a very basic single-stage bag unit... YMMV.

 

I forget where, but there is (was?) a dedicated DIY-DC community… I haven’t looked in years, but seem to remember it was pretty good – a little too much BP Kool-Aid, but useful…

 

Good luck.

Ummmmm....is the correct answer tater salad?.....sorry H....you're going to have to say that in English.

[tim0625]

So do you necessarily have to have the 5HP Oneita cyclone to get the fines?  Do the 2HP units have the FPM to collect the fines as well? Or are we just fooling ourselves into thinking we're ok with a bag of dust when we're really in danger from the small stuff?

[Tpt life]

Length of run. Do you park the machine and DC side by side? Notice the drop off occurs over the length of run. HHH dropped this out of the picture because most of us dream of a piped shop with a single location DC.

[Bill Tarbell]

So do you necessarily have to have the 5HP Oneita cyclone to get the fines?  Do the 2HP units have the FPM to collect the fines as well? Or are we just fooling ourselves into thinking we're ok with a bag of dust when we're really in danger from the small stuff?

 

I don't know all of the vac details like hhh, but it seems to me that if you wear a dust mask while you're working then it makes it more of a moot point.  I can't imagine any dust collection system being perfect, so you'll likely always have airborne dust to content with.  My goal with dust collection is to not have to sweep up piles of sawdust each time i'm done working.

[Raefco]

I have started to reply to this a few times but it gets messy in a hurry. Since reentering the wood game I have bought a Planer, Jointer, a band saw and a lathe and for the first time I am seriously considering clean up and dust as separate issues. The mountain of shavings and debris accumulation is a bigger problem and more time consuming than the particulate matter in the air, the filtered fans knock that down pretty quick.

 

I just hooked a shop vac up to the router table for the first time and I was amazed at the difference it made, I never realized how much time and energy I was spending on clean up, I am currently collecting pieces to put a small vac and cyclone at or under each large piece of equipment, that will save space, labor and it will only run on demand when that piece is turned on.

[Brendon_t]

Bill, I believe we are in the same boat, I have no problem wearing my camo respirator, I am more sick of cleaning up the whole shop from settling dust from even using one machine for a few minutes.

[Tpt life]

I don't know all of the vac details like hhh, but it seems to me that if you wear a dust mask while you're working then it makes it more of a moot point. I can't imagine any dust collection system being perfect, so you'll likely always have airborne dust to content with. My goal with dust collection is to not have to sweep up piles of sawdust each time i'm done working.

I don't know how to know if I am making too big a deal of this, so please be patient with me. Asbestos is an environmental concern because of the minuscule size of the fiber. This is not a part time concern because the fiber will remain airborn for a long time after it is lofted. For truly fine fines, the concern would be after the tool and DC have been powered down for awhile and you decide to unmask. This is some of what I have chewed on with my basement shop work.

[Raefco]

I don't know how to know if I am making too big a deal of this, so please be patient with me. Asbestos is an environmental concern because of the minuscule size of the fiber. This is not a part time concern because the fiber will remain airborn for a long time after it is lofted. For truly fine fines, the concern would be after the tool and DC have been powered down for awhile and you decide to unmask. This is some of what I have chewed on with my basement shop work.

 

 

The bigger issue with asbestos is the the shape and make up of the fiber, or particulate in question, asbestos is very resistant is decomposition and the fibers are shaped like a barb, think fish hook, once inhaled they imbed themselves in the soft tissue in the lung and create scare tissue and this is where the real problems start. not to minimize inhaling anything, but silica, asbestos and VOC's are different animals then most sawdust.

[RDavS]

HHH is almost spot on. But the issue is not velocity, but volume, or more precisely, volume per minute - rate of flow. CFM is not a velocity. It's related in a DC system, for in piping with a given cross sectional area velocity is the primary factor. But one can increase the CFM without increasing velocity by increasing the cross sectional area - going to a larger diameter tube.

 

This is also the case with regard to the idea that higher velocity (speed in a given direction) is needed to move the finest particles. The finest particles will remain suspended in the air for a long time even if the air is not moving at all. Most of the finest visible particles of dust will fall out in a matter of minutes; the invisible particles - the dangerous ones - will take hours to fall out of non-moving air. It is the larger particles that need fast moving air so that the force of drag on their surfaces will overcome inertia, friction, and gravity. 

 

The physics of collecting both large and small particles in DC systems is that you can increase the volume by increasing the diameter, but if the CFM remains constant, the velocity can drop below what is needed to move the larger particles and your tubing fills up with large chips, reducing its efficiency. Having small diameter tubing can keep the velocity high enough to move the larger particles, but can drop the CFM so that the system doesn't collect the finest particles. It's not that the finer particles won't be moved through the system, but that they will not be collected into the system.

 

The dust produced by most tools is not all directed toward the DC collection point. It is thrown in all directions. Hand-held tools generally have a small blower built in to pull air through the motor to keep it cool and that blower blows dust everywhere and most of those particles thrown in all directions are the finest. Moving sanding belts and saw blades throw particles tangent to their motion. Therefore the DC system needs to move enough air so that it pulls the dust-filled air not only directly from the cutting or sanding surfaces, but also from the whole area round about. That's why volume is so important. You need to pull air not only from the tool but also from the whole work space.

 

If you can get a powerful enough motor and blower assembly to pull 3500 to 4000 CFM through a 2" pipe, that will generally accomplish what is needed. But given the physics of moving that much air through a 2" pipe, that's going to have to be a really high powered and noisy motor and blower. To enable a reasonably sized motor/blower combination to pull adequate CFM one needs to have larger diameter tubing, yet not so large as to reduce the velocity to the point where large chips don't move through. (This is why many shops have chip collectors at each machine and leave the fine particles to the central system.)

 

At the collection end of the system it is again a matter of volume per time. Many (if not most) of the retail systems for small shops do a very good job for larger particles but not so well with the fine. The Pentz cyclone design is probably the best at finer particles, but is still not 100% effective and it is recommended to have some sort of filter after the cyclone. To keep up the volume of air flowing through the system it is important to have a large surface filter. The finest particles that are first collected will serve to filter out those that come later, as they build up on the inside surface of the filter. Eventually, however, the layer of fine particles becomes so thick that the volume of air moving through the filter is reduced, affecting the whole system. This is why pleated filters do better than bags, for they provide more surface area in a given volume of filter space. It takes longer for the layer of collected dust to reach the point of defeating the DC system.

[xxdabroxx]

HHH is almost spot on. But the issue is not velocity, but volume, or more precisely, volume per minute - rate of flow. CFM is not a velocity. It's related in a DC system, for in piping with a given cross sectional area velocity is the primary factor. But one can increase the CFM without increasing velocity by increasing the cross sectional area - going to a larger diameter tube.

 

This is also the case with regard to the idea that higher velocity (speed in a given direction) is needed to move the finest particles. The finest particles will remain suspended in the air for a long time even if the air is not moving at all. Most of the finest visible particles of dust will fall out in a matter of minutes; the invisible particles - the dangerous ones - will take hours to fall out of non-moving air. It is the larger particles that need fast moving air so that the force of drag on their surfaces will overcome inertia, friction, and gravity. 

 

The physics of collecting both large and small particles in DC systems is that you can increase the volume by increasing the diameter, but if the CFM remains constant, the velocity can drop below what is needed to move the larger particles and your tubing fills up with large chips, reducing its efficiency. Having small diameter tubing can keep the velocity high enough to move the larger particles, but can drop the CFM so that the system doesn't collect the finest particles. It's not that the finer particles won't be moved through the system, but that they will not be collected into the system.

 

The dust produced by most tools is not all directed toward the DC collection point. It is thrown in all directions. Hand-held tools generally have a small blower built in to pull air through the motor to keep it cool and that blower blows dust everywhere and most of those particles thrown in all directions are the finest. Moving sanding belts and saw blades throw particles tangent to their motion. Therefore the DC system needs to move enough air so that it pulls the dust-filled air not only directly from the cutting or sanding surfaces, but also from the whole area round about. That's why volume is so important. You need to pull air not only from the tool but also from the whole work space.

 

If you can get a powerful enough motor and blower assembly to pull 3500 to 4000 CFM through a 2" pipe, that will generally accomplish what is needed. But given the physics of moving that much air through a 2" pipe, that's going to have to be a really high powered and noisy motor and blower. To enable a reasonably sized motor/blower combination to pull adequate CFM one needs to have larger diameter tubing, yet not so large as to reduce the velocity to the point where large chips don't move through. (This is why many shops have chip collectors at each machine and leave the fine particles to the central system.)

 

At the collection end of the system it is again a matter of volume per time. Many (if not most) of the retail systems for small shops do a very good job for larger particles but not so well with the fine. The Pentz cyclone design is probably the best at finer particles, but is still not 100% effective and it is recommended to have some sort of filter after the cyclone. To keep up the volume of air flowing through the system it is important to have a large surface filter. The finest particles that are first collected will serve to filter out those that come later, as they build up on the inside surface of the filter. Eventually, however, the layer of fine particles becomes so thick that the volume of air moving through the filter is reduced, affecting the whole system. This is why pleated filters do better than bags, for they provide more surface area in a given volume of filter space. It takes longer for the layer of collected dust to reach the point of defeating the DC system.

I was thinking something very similar when I read that the fines needed more velocity.  They are suspended in the air, they should be easy to move.  For them it should be a more cfm is better, but like noted above, the heavier stuff would need more fps to stay airborne and moving down the line to the collector.  

[Brendon_t]

Since this is 7 months old, I'll report that this little home made dc worked great. I have my powermatic DC on most machines and this one tucked in under the drum sander and planer station. It keeps each running clearly.

[RDavS]

It seems we are talking about two different concepts. One where the fines are airborne, the other when they have settled or become attached to the inside surfaces of the DC system. When airborne it doesn't take much of either rate of flow (CFM) or speed (or velocity) (FPM) to keep 99% or more of the fines moving through the system. It's when they settle or become attached to the inner surfaces of the system that the comparison to leaves and grass clippings fits.

 

Various factors can cause dust particles to settle inside the system. If the air entering the system still has dust in it when the system is turned off, those particles will settle out; first the larger, then the finer. Even when the system is on, static electricity can create an attraction between the sides of the system and particles of dust and inertia can cause a buildup at turns and on blower blades. At a microscopic level almost no surface is perfectly smooth and especially the finest particles can find places to nestle. Once there, their shapes will catch still more. It takes something strong to dislodge this buildup and increasing the speed of the airflow might accomplish it; but it might be necessary to use mechanical means to remove it.

 

I doubt that any DC system, however speedily the air flows, can totally prevent the buildup of fines inside the system. But the purpose of a DC system is not to have a clean system, but to have a clean work space. It matters little if a small percentage of the fines collect inside the system, even if the system must be cleaned from time to time. What matters is that the system pulls them in and collects them either in the tubing, in the collection bin, or in the final filter. To do this it needs to bring in a sufficient volume of air per unit of time so that the airborne fines flow toward the collection point and don't escape into the rest of the work space.

 

In my earlier post I said that 4000 CFM would be adequate. I was confusing the abbreviations. I doubt that 4000 CFM would be possible in a small shop. If the DC system had 6" mains, that would mean an air flow speed of 20,382 feet per minute (231.59 mph, 339.7 fps). It was said that 3500 to 4000 FPM (feet per minute) should be the goal. With a 6" main, that would move 687 to 785 cubit feet of air per minute. It would appear, then, that the 500 CFM blower that was mentioned at the start of this string isn't too far off. So long as it isn't hampered by long runs or small diameter tubing, it might not be perfect, but certainly could be a plus.

[Trip]

Yea, taking collection and transport... But usable CFM at inlet burried in the CFM/FPM relationship... If you run the numbers for real (with a CAD program, not internet scripts), you find that it's very hard (read as impossible) to collect and transport fines in a system built around 6" mains - part of your 4K observation. It's one of those things that seems to work on the internet, but in the real world it falls over. It's the ugly little secret at the heart of the 6"-PVC universe... It's not the PVC, it's the 6"... It's also why HEPA systems tend to have 8"+ mains...

 

==>It was said that 3500 to 4000 FPM (feet per minute) should be the goal. With a 6" main, that would move 687 to 785 cubit feet of air per minute. It would appear, then, that the 500 CFM blower that was mentioned at the start of this string isn't too far off.

Again, one of those things that almost 'appears to work' on paper (although it falls a bit short even using ideal models), but not in the real world with real ductwork... I think that was the point of my first post... If you use an internet calculator, it kind of looks like it would work, but if you hooked this setup and used test equipment, the numbers would tell a diferent tale... There's a seperate thread on ideal-model SP calculators vs the 'real world' that covers this stuff in detail... As a side note: if you work for a large company, you can borrow all you need to perform measurements of your shop from the Environmental, Health and Safety department or perhaps the Facilities group -- just about every large company has both...

[rodger.]

So do you necessarily have to have the 5HP Oneita cyclone to get the fines? Do the 2HP units have the FPM to collect the fines as well? Or are we just fooling ourselves into thinking we're ok with a bag of dust when we're really in danger from the small stuff?

My understanding from reading Bill's site is that a single stage collector is fine as long as you treat it as such. Short run of hose (5' a min 5" diameter), 12" impeller (I believe), min 1.5 hp motor, etc.

[tim0625]

Well it's like this boys....I love a tool but....I watched my dad die from lung complications and it wasn't pretty.  I will take whatever steps necessary to avoid this. Having said that, I'm looking for a system that will get it all....all.....fines, chips, everything.  If it takes a large system or a creatively made smaller system, I'm looking for one that is so efficient I can cut exotics or anything else and I do not have to worry.  You just do not know who to believe.  Everyone is trying to sell something.  Oneita, jet, Laguna, everyone has an angle.  I've toyed with a building a system where a DC would collect chips at the tool and then I would have a sort of range hood over the table saw to collect the airborne fines.  The range hood would have a 12" or 14" metal duct hooked to it and would go into the attic of the shop, turn, and go to the rear and attach to a plywood box. Inside the box are 2 squirrel cages out of HVAC units that pull the air and exhaust it into the back yard - no filters. I'm not worried about replacing air.  Would THIS system pull enough air to draw out the fines?

[Brendon_t]

This conversation has gone way way above my ability to understand

[..Kev]

Trip is correct.  I'm considering 2 different manufacturers and will use their design service when I make my choice. I will let them tell me which machine is correct for my shop per the duct design.  I hate to use the term "money is no object" but, I want a system that is right.  Buy once and cry once. 

[andrew-in-austin]

Yea, taking collection and transport... But usable CFM at inlet burried in the CFM/FPM relationship... If you run the numbers for real (with a CAD program, not internet scripts), you find that it's very hard (read as impossible) to collect and transport fines in a system built around 6" mains - part of your 4K observation. It's one of those things that seems to work on the internet, but in the real world it falls over. It's the ugly little secret at the heart of the 6"-PVC universe... It's not the PVC, it's the 6"... It's also why HEPA systems tend to have 8"+ mains...

So why is this the case, other than "just because"?  Is it the collection part that fails, or the transport?  What is "bad" about 6" piping that prevents this?  Is it because the length of 6" pipe overall creates too much pressure drop?  If so, at what length is that a problem?

[Beechwood Chip]

Here's the way I think about it.  It may not be completely correct, but it's simple enough for me to understand.

 

There's cubic feet per minute (CFM), which is just the volume of air which passes through the filter every minute.  Then there's static suction.  I picture a vacuum cleaner trying to pick up a tennis ball, softball, basketball, bowling ball...  Static suction is the amount of weight that the suction can pick up when there's no air moving (because the ball has blocked the vacuum hose).

 

So, the spectrum goes like this:

• air cleaner, 2 sq ft or more: highest CFM, lowest suction.  Moves lots of cubic feet through the filter, but can't move sawdust.
• dust collector, 8": pretty good cfm, can move sawdust.  Can move chips if with a powerful motor.
• dust collector, 4": moves sawdust, chips, some heavier stuff.  CFM is beginning to suffer.
• shop vac, 2": picks up water, small rocks, nuts and bolts, etc.  Low CFM.
• dust extractor, 1": great suction, tiny CFM.
• air compressor: cleans the crud out from under your fingernails.  A cubic foot will last a long time.

The microscopic dust particles that are worst for your lungs are essentially part of the air.  The only way to get rid of them is to collect the air and put it through a filter or put it outside.  So, you want high CFM.  You don't need any suction, because the dust goes wherever the air goes.  So, air cleaners work well.

 

But, releasing clouds of dust into the air and breathing it while it's waiting it's turn through the air cleaner isn't great.  If something is producing toxic dust, you want something that will collect all the air near the source of the dust and move it away from your face and through a filter.  So, that's a high CFM low suction dust collector.  Big pipe.  Essentially, a powerful air cleaner mounted a few inches away from the source of the dust.

 

If you want to pick up sawdust, shavings, and other stuff that will settle out of the air, then  you need suction to pick it up, and you need to keep the air moving fast enough to keep it moving along with the air.  So, smaller pipes.

 

If you want suction to pick up shavings and high CFM to get all the dust, you're going to need a big motor and fan (impeller).

 

So, dust collection systems are trade offs between price (motor, impeller), convenience (ducts, blast gates, bends), fine dust collection, and picking up heavier stuff.

[andrew-in-austin]

Thanks for the reply, TripleH and Beechwood.  I was asking primarily because I just spent $1500 on ducting, and mostly 6" and some 5"

 

Hopefully mine will come out OK.  I'll be taking CFM measurements at several points, from just fan housing, to adding cyclone, to adding filters, to adding ductwork, then finally with machines connected.  Should be interesting to see how it all comes out.  Ducting is Nordfab and cyclone is Clear Vue, with shop only 22 x 22.