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I'm planning on a new TS, and wanted to clean up my exhaust system first.  I have a small Dust Collector (Griz 1 HP), so I wanted to make the most of it.  I have two "runs" of duct; the long one to the TS is about 18'; I originally used all 4" flex duct (with the spiral wire).  It did OK.  I had a kluge connection at the DC, with a Tee connector; I knew the Tee was hurtful.  In the end, I put in a 10' section of 4" ABS, with two formed 45's, replaced the Tee with a Wye.  I did the calcs on duct loss and flow change, and was a bit disappointed that the volume would only increase by 10%.  The actual performance seemed more than that; then I realized that dust collection works by the SQUARE of the air flow change (the force on a particle is proportional to the square of the air velocity).  So, 1.1 x 1.1 = 1.21:  I actually was getting 20% better dust collection, and the performance I observed was consistent with that.  So, swapping 10' of ABS for flex made a very nice difference.

     Along the way, I did some checking on fan inlet effects of duct.  If you connect an elbow right at the fan inlet, you lose about 2.4" pressure (most DC's run about 5--6"); if you put a 6" straight piece at the fan inlet, then elbow, the loss is only 1.6".  Using formed smooth elbows near the fan can really help a lot, too; bended flex has very high loss.

     If your DC has a wye connector at the fan inlet, put in 6" of straight duct between the wye and fan.  The wye will give unbalanced air flow, and the fan hates that.

Edited by Ron Dudelston
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Pete, your correct about airflow when it comes to what you use to flow it through. But from what I understand in the reading that I've done about dust collection is that for a ducted system the starting point is no less then a 2 hp dust collector for a small ducted system, anything lower then 2 hp is basically a portable DC that you would wheel from one machine to another, and keeping the dust hose short, especially with a 1 hp DC. I just acquired a used 1 hp DC that I'm going to use in a small shop, and I'm in the planing stage of how I'm going to add a onboard dust separator to it. It will probably take some CFM's from the equation, so I plan on making the dust hose as short as possible. 

Edited by CharlieL

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My system is 1.5 HP and it does work as a ducked system. I do use 4 inch PVC and wish I had started the trunk line with 6 but with the drop box on the floor it does remove a lot of dust. Something else you may want to look into is to add at least one air cleaner to catch fines and clear shop air. I have one and thinking now of adding another to improve air quality.

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Gerald, in my larger summer time wood shop I have a 1.5 hp DC as well where I also added a onboard dust separator too, but I use the DC as a portable unit. I believe in air filtration units as well, both shops I have a air filtration unit in them.

Edited by CharlieL

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No matter what size fan/motor, the principles are the same.  You can successfully employ a small (mine = 1 HP) DC as a stationary unit so you don't have to wheel it around.  The larger units have one convenience:  you don't have to be as efficient in duct and fittings because the extra HP overcomes wasteful installation.  My small unit actually serves 3 rooms and about 8 machines.  But I set it up for just one at a time.  NO blast gates.  The TS branch 4" gets a yogurt container as a cap; the scoop opening I cover with a fiberboard blank when using the TS.  Small tool DC (ROS):  I have a small hose that fits into the scoop throat, and that's enough to capture the dust.  The clear plastic hood fits over several tools and serves the three principles of DC:  capture, capture, capture.  A very important modification:  I got an after-market upper bag (that's the outlet bag) that's rated 1 micron (which is as explicit in filtration as "three season" is in sleeping bags, campers!).  So I don't need additional air cleaning:  the fines stay in the bag.  Going to 6" will increase air flow a little, but will reduce velocity, and velocity is what captures the particles.  [350 cfm at 4" is 4000 fpm -- feet per minute; 6" duct would give me maybe 400 cfm, but that's 2000 fpm;  woodworking LIKES about 4000 fpm to keep things moving]   This is why making sure a tool has inlet air as well as suction is important:  restricted inlet means lower velocity, and capture is all about velocity.

     My next project is figuring a simple capture for a bandsaw.  I've seen a couple videos, but they're more complicated than needed.  Just have to get the suction in the right neighborhood....I shall report in.

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I would  have to state that there is a difference between velocity and volume. With a shop vac there is velocity, but with a dust collector there is volume and volume is what you want to collect dust. No matter how good your system is there will still be fines in the air because with what we do there is no hood or syatem which will catch it all. It is the stuff that you do not see w/o a sunbeam that will give you problems.

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The real truth about good dust collection is a good dust catcher at the source of the dust.  With a contractors TS, dust collection is almost useless, unless you provide a means to close up the open area behind the saw . Same is true with a CMS or SCMS.. A means of capturing  the dust is needed. But even with these issues taken care of, the fine dust that floats in the air is the real problem . An air cleaner is the only thing that will catch these fine particles that you inhale whenever you're making dust. I believe a dust collector does more to keep the shop floor clean than it does to clean the air.

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I must respectfully disagree.  For a given duct size:  velocity and volume are the same thing (common measurements are feet per minute and cubic feet per minute; but in a duct the difference is a constant).  Velocity is what moves particulates, either in the open air or in a duct.  But to get velocity, you have to have volume.  Joined at the hip.  No system gives 100% capture, but in the under-5 micron size (which is what you worry about in the lungs), the particles go with the flow pretty well because they lose the tool-induced velocity almost immediately.

 

Fines are actually much easier to collect than hunks.  Large particle mass is not easily turned from its trajectory; small particles get sucked in pretty easy.  I have a contractor saw:  I took the closure off the back and the capture improved because the air flow increased (I use a retro kit that closes the bottom, with an air intake scoop; the back is open). 

 

You also have to consider air flow versus room volume when thinking "clean".  My bench area is 5'x8'x13' = 520 cubic feet.  DC is rated about 350 cfm, so (520/350) the air turns over every 1.5 minutes.  I try to do all "dust ops" close to the bench scoop, and brush toward the scoop, etc. 

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12 hours ago, It Was Al B said:

The real truth about good dust collection is a good dust catcher at the source of the dust.  With a contractors TS, dust collection is almost useless, unless you provide a means to close up the open area behind the saw . Same is true with a CMS or SCMS.. A means of capturing  the dust is needed. But even with these issues taken care of, the fine dust that floats in the air is the real problem . An air cleaner is the only thing that will catch these fine particles that you inhale whenever you're making dust. I believe a dust collector does more to keep the shop floor clean than it does to clean the air.

Al, I've got a good handle on the dust collection for the Contractor's table saw that I have, in a efficient and user friendly manner, which does include a good dust hood. I do agree with you that a dust collector does more to keep the shop floor clean than it does to keep the air clean, plus I'll add that there is less dust settleing on everything. A DC and air filtration unit reduces clean up time at the end of the day. If your concerned about your health, buy a good dust mask. 

Edited by CharlieL

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30 minutes ago, PeteM said:

Fines are actually much easier to collect than hunks.  Large particle mass is not easily turned from its trajectory; small particles get sucked in pretty easy.  I have a contractor saw:  I took the closure off the back and the capture improved because the air flow increased. 

 

 Pete, most of the back of my saw is open for that reason also. To improve dust capture a little further I put a dust deflector behind the blade to prevent the blade from throwing the dust out the back. The deflector moves with the blade when tilting.

 

Edited by CharlieL

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On 5/12/2017 at 8:16 PM, It Was Al B said:

  With a contractors TS, dust collection is almost useless. 

 Typical cabinet saw sales pitch that doesn't hold much dust. It's not that hard to do it in a useful manner.

Edited by CharlieL

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6 hours ago, It Was Al B said:

CharlieL, Can you post photos of your set-up to help those who own contractor type TS's?

Al, I had a website for several years with pictures of it and was offering the dust hood in two sizes until recently when I decided to delete the website. The industry doesn't care about dust collection on these saws, it doesn't sell new cabinet saws, and woodworkers will try to make one before they will buy one, no matter how reasonably priced they are. I've been mostly a hobbyist woodworker for about 30 years, and I'm about wore out having to practically to give everything away and takin advantage of. I've lost the passion and the pride that I had for it for many years and don't do much of it anymore, unless we need something done at our home.

Edited by CharlieL

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There are several ideas on the link below.  I think the basic idea is a TS blade throws most of the dust down (inside the cabinet) and somewhat to the rear.  If the back is open (and the cabinet is 3-sided), then air coming in the back will force most of the dust down to the collection point.  It's not perfect, but it's a lot better than nothing.  If you're using a shop vac (low volume), consider closing off the lower third of the back opening (often, that won't interfere with the motor/trunion structures).  Even with my little DC, the 4" connection pulls enough air that the completely open back is good for air intake.  Nothing succeeds like excess.

https://www.infinitytools.com/tablesaw-dust-collector?gclid=Cj0KEQjwo-XIBRCOycL7hsuI_NoBEiQAuS6HtM1PANDibFbjuhMRDs0Q3-2bcphc2igaTjsDyaAy93UaAmv-8P8HAQ

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3 hours ago, PeteM said:

 I think the basic idea is a TS blade throws most of the dust down (inside the cabinet) and somewhat to the rear.  If the back is open (and the cabinet is 3-sided), then air coming in the back will force most of the dust down to the collection point.  

 

 And if you want the most suction coming in from the partially open back then you will want to block air coming into the cabinet between the cast iron top and the top of the cabinet. Fill the gaps with dense foam sheeting cut to fit, and double sided tape it to the top lip of the cabinet. 

Edited by CharlieL

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On ‎5‎/‎15‎/‎2017 at 8:44 AM, CharlieL said:

Pete, out of curiosity what brand and model number is the table saw that you have now ? and what are you looking at to replace it ? 

Delta 36-675; it's been fine for about 12 years, and a friend will accept the gift.  I'm going to get a StopSaw 1.75.  I'm 70, would like to continue WW for a decade, don't do it quite enough to build in good reflexes, and the money comes from my night job (forensic engineering).

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On ‎5‎/‎15‎/‎2017 at 8:28 AM, CharlieL said:

 And if you want the most suction coming in from the partially open back then you will want to block air coming into the cabinet between the cast iron top and the top of the cabinet. Fill the gaps with dense foam sheeting cut to fit, and double sided tape it to the top lip of the cabinet. 

I have a guide for areas:  on the basis of 4000 fpm* in a duct (the usual design target for sawdust), and 100 fpm over open areas to capture fines, take the square inches of duct, multiply by 40, and that's the largest cumulative square inches of open spaces around the contractor saw.  Note that's ALL open spaces, including the slots for the adjusting handles, etc.  The lower end of that is maybe multiplying by 15, which increases the velocity through the open spaces, but doesn't put too much drag on the fan.  Realize that velocity above 100 in the open spaces doesn't capture much more than 100.  Anything you don't get at 100 fpm probably ignores any air flow below about 500--1000 velocity.

 

 

*feet per minute

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