Proper sizing for DC ducting. How right is Bill Pentz?

[dbhost]

Okay the question is a little arbitrary, but not meaningless.

I see time and time again folks with 4" ducted systems, with reasonably well designed ducting, and the typical 1.5 - 2 HP DC (the average Taiwan job like HF, Shop Fox, Grizzly etc...), and a Wynn type cartridge filter.

I fully agree with Bill on eliminating tight turns, and rough hose as much as physically possible. And for the most part the folks I see setting up their 4" dust collection networks use a pair of 45s and a piece of pipe to make a 90 degree bend, OR they use sweep elbows.

From reading what I can manage to get through on Bill's site, it sure seems like no way, no how, not gonna happen with 4" duct, but I am seeing well laid out 4" systems that people are posting on, using those fancy pants air quality gauges and reporting good results. So what gives?

My tool selection radically limits my options for dust collection, and some of it has been modified, or will be modified VERY soon to accept larger dust collector air volumes.

The tools and ports in question are... (And yes, there are Thien Cyclones in the system here...)

Ryobi BT3100. 1 Factory 2.5" blade shroud port. 1 added 4" belly pan, 1 2.5" shark guard port. The setup here will be 4"x4"x2.5" wye in line with a 4" hose to the belly pan, and a 2.5" line from the 2.5" on the wye to the blade shroud. That will be pulled by the HF DC. An overhead 2.5" to the shop vac.  The shark guard 2.5" will get moved to the router accessory dust collection port as needed.

HF 14" Band saw with 6" riser block. Factory dust port removed. sheet lower dust collection blade cover similar to Pentz' illustration in the works. The idea is to cover as much of the lower blade, while making effectively a... well sort of funnel from the table, down into the lower blade guard. A 4" dust port is in the works for the lower blade guard. A 4"x4"x2.5" wye will be in line with the hose, the 2.5" port will be run up to the upper blade guide shroud. Again like in the Pentz diagram.

Northern Industrial 16 speed floor model DP / table. A 4" port will be run here, and as soon as I figure out how to connect it to the fence will be a happy camper...

Ridgid EB4424 belt / spindle sander. With the spindle, the 2.5" seems to work fine, with the belt, it sprays dust everywhere. Can I use the 4" to correct this?

Ryobi AP1301 planer. 2.5" port on the machine. No real way to attach 4", no real fines being created anyway.

Sunhill SM-150B benchtop jointer. 2.5" port. No real way to attach 4" Might be possible to hack away plastic, but probably not a good idea...

ALL freehand routing done outside on a makeshift workbench.

All sanders (Ryobi Corner Cat, Ryobi Quarter Sheet, and Skil Orbital) have 1.25 (ish) inch ports which are hooked up to the shop vac via reducers. I want a downdraft table hooked to the 4" and keep the 2.5" connector to the machines.

Am I on the right track, or do I really need to carve up my equipment and figure out a way to get 6" duct in here?

Basically, can 4" be effective when combined with 2.5"

[bennybmn]

I've had great success with my 4" stuff. The only time my router table spits ANY chips out is of I'm routing a dado or something, so the fence can't catch stuff. Otherwise it's more like it's peeling away wood it's so good. My setup is 4x4x2.5 Y with the 4" to the cabinet reduced to 3" PVC. Seems to divide the suction quite nicely between the cabinet and fence. I think the key (to any system) is reducing the distance of tubing or hose. I have a bunch of my stuff plumbed directly to the DC, but with a flex connection so I only hook up one at a time. I may connect the TS and miter saw together with some blast gates... we'll see. But it works darn well like this. I think you'll be fine.

Your planer and jointer should mainly produce chips, not fines, so it's more a matter of cleaning up the mess...  Belt sanders are next to impossible to effectively collect from, so unless you have an air cleaner nearby, you've probably got the best setup you're gonna get.

[dbhost]

My "Air cleaner" is a 20" box fan with a 20x20x1 Filtrete HEPA rated filter attached. It doesn't pull through that tight filter as well as I would like...

I know I need to do something else to address this, but I am not sure what. The DIY fiend in me says build my own air cleaner, the lazy bum in me says wait a couple of pay periods and pick up one of those Steel City air scrubbers at Woodcraft... The lazier bum in me says forget it, just go grab a beer...

[phil (admin)]

My father had an old saying about automobile engines:  "There is no substitute for cubic inches."

I think the same thing can be said about dust collection.  The larger the pipe, the better.

Problem is, you get to a point of diminishing returns at some point.

And that point varies depending on tools, the size of your shops, etc.

Man, I'm absolutely no help.

[shrxfn]

I will have to look through my magazines but one had a good design using a squirrel blower and some house filters to use as an air cleaner. If I can find the project I will try to scan and post somewhere for use or will e-mail if someone wants. Wish me luck I have about 200 magazines to look through. :o

[bennybmn]

I will have to look through my magazines but one had a good design using a squirrel blower and some house filters to use as an air cleaner. If I can find the project I will try to scan and post somewhere for use or will e-mail if someone wants. Wish me luck I have about 200 magazines to look through. :o

I've seen a couple different versions of that, and I've helped build one. The trick is finding a squirrel cage blower that runs on 110... If anyone finds one, let me know!! I'm in the market :D

[shrxfn]

here is one on e-bay.
Blower

sorry did not see that it was sold or ended. Here is another one from everyones favorite hardware store.
HF Blower

or the big orange box
HD Blower

[JakesDad1]

I created an air filter from two fans left from a kitchen and bath remodel. A simple box to hold two stacked furnace filters (prefilter and then a better filter) with an exhaust port to allow a kitchen hood fan and a bathroom vent fan to draw air through the box. Works great but have no idea of how much air I am pushing.

[AllanJ]

Bill is definitely on the right track with his ducting advice, but there are a few things to keep in mind that help to explain the wide variety of opinions out there:

- People have different levels of sensitivity to wood dust (more sensitive people will notice problems before less sensitive people)
- Hood design is extremely important!  Often two hoods are way better than one (think tablesaw and cabinet/above table)
- Sometimes you want a small port at a tool (imagine 6" hose at a drill press or router table fence!)
- Sometimes a larger port won't do much like at a restrictive tool like a benchtop planer
- With a less restrictive tool like a big hood behind a CMS, a 6" port is much better than a 4" port and will definitely catch more dust
- 4" ducting is cheap and people often have no idea what they are missing with larger ducting
- etc

I used to have a 1HP DC and thought it was fine for a couple years...until I started coughing and sneezing after a day in the shop.  So I upgraded to a 2HP DC.  Ahhh!  Much better!  However, eventually the coughing/sneezing and now sinus headaches started arriving after a day in the shop.

Now I have a large Pentz cyclone with big ducting and have had that for several years now.  No problems.  Also, my wife has asthma and she's fine in the shop.  Bigger is definitely better for us.

When you look at those tool airflow tables you see in magazines that say a CMS only needs 350cfm to clear the debris, what you are really looking at is the theoretical amount of airflow required to remove that type of waste, assuming you have a perfect dust hood.  However, back in our shops in the land of reality, we don't have a perfect hood that will entirely contain all the dust spewed by these machines.  We have a hood that captures a portion of the dust.  If you can't contain all that dust, then you need to help make up for it and that's with a larger DC with properly sized ducting (not too big and not too small) with properly sized hoods.

At my DeWalt 12" SCMS, I have a full 1250cfm going to it via 7" pipe (airflow measured by me), yet I'm still not capturing all the dust.  I've measured the air outside the shroud with a Dylos particle counter and it slowly gets worse and worse with each cut.  Much, much better than not having the DC on though.

If I had smaller ducting with smaller ports, then the air quality would get worse much faster.

fyi, with my large cyclone and a 7" main duct, in one place in my shop I could flow about 1400cfm.  Add on a 6" reducer and the airflow dropped to about 1300cfm.  Add on a 5" reducer and the airflow dropped to just over 1000cfm.  Add on a 4" reducer and the airflow dropped to 730-ish cfm.

Why would I want to kill airflow with a small port?

However, with my benchtop planer, using 6" flex hose to the tool and its factory 4" port, I could flow 725 cfm.  With a shop made 6" port the airflow only went up to 779 cfm.  Not much of an improvement.  That's because the tool is so restrictive internally.  There is not much makeup airflow inside the machine around that cutterhead.

Always remember that hood design is the most important thing.  I'd rather have a 600cfm dust collector hooked up to a tablesaw with two 4" ports (cabinet and above table like a Shark or Excalibur) than 1000 cfm via a 6" port to the cabinet alone.  The more efficient your hoods are at containing the spewing dust and directing it to the ducting, then the less airflow you'll need at the tool.

Cheers,
Allan

[dbhost]

Allen, you just hit on the problem...

I do believe that Bill is on the right track, but his explainations are so detailed as to end up being plain and simple noise. Which leads me to wonder just how is the hobby woodworker supposed to deal with all they have to deal with in dust collection? Most of us aren't engineers... How do us mere mortals deal with this?

I mean honestly I would love a bucket of cash and to have Bill over on a consulting basis to set my system up... But that's just not going to happen in this lifetime unless I hit the lotto (hasn't happened yet...).

I hope I didn't come off as saying Bill is wrong, I don't think he is, I simply don't get it... I can only keep up with him so far before my head goes numb...

[bennybmn]

Even us engineers don't like too much detail sometimes... I like boiled down explanaitions a lot of times! Good thing for us, there's usually someone who LIKES reading the details, and is willing to do the boiling down for us!

[AllanJ]

I hear ya guys.  That's why I've been trying to help out folks on the WOOD Mag DC forum.  Testing how saw blades cut and explaining the info is very simple.  Going over DC theory stuff where it's hard to see the results in your shop is much more difficult.  Add on the fact each of us is different and reacts to wood dust in different manners just adds to the confusion.   ???

A simple way to think of dust collection is like this:

A dust collector is simply an air mover.  It moves dirty air at the tool through some pipe to the DC.  Then this dirty air gets sorted into two areas, bigger bits in the dust bin and fine dust in the filters.  Some tools are better at moving air and "sorting" the dust than others are.  The more concerned you are about dust collection and respiratory health, the better performing DC you should buy.

For ducting, you want to help make your DC purchase work well.  You don't want to hinder it.  A DC can only move air well if the airflow isn't restricted.  The more restrictive you make the path from the tool to the DC filter, the less air it will flow.  That will mean more dust in your shop and in your lungs.

You will restrict airflow and lower performance by using too much pipe, too many elbows, too much flex hose, as well as using pipe that is too skinny.  A poor filter that clogs easily is also a problem.  All these things will reduce airflow, so you want to minimize them.

- Keep the runs short
- Use long radius elbows or two 45 deg elbows instead of a sharp 90 deg bend
- Reduce the amount of flex hose you use
- Use properly sized ducting

*** Using ducting that is too large can also cause problems.  I'll skip the reasons for that at the moment.

I have a "duct size" ballpark rule of thumb that will give good performance for the majority of people out there with a modestly sized shop (2-car garage and smaller).

1HP DC = 4" ducting (really shouldn't use a duct network)
1.5HP DC = 5" ducting
2HP DC = 6" ducting

There are exceptions to this but I'll skip that for now.

Ideally, once you've decided on a duct size, you want to keep that size all the way from the tool to the DC.  So if you want 6" pipe for a 2HP DC, you'll need to make sure your DC inlet is sized to match the pipe and you also want a new 6" hood for the tool.

Visualize that for a moment....lots of airflow moving from around the blade, carrying the dirty air though an unrestricted hood, through a short run of 6" ducting and then through the DC inlet, all the way to the dust bin and filter and finally back into the shop air.

You don't want 4" drops on a 2HP DC with a 6" main duct.  It doesn't match.  You've choked the airflow down and are losing performance.  With some tools it won't matter because the tool itself is very restrictive internally and you can't move much air inside them.  Benchtop planers are like this because there is hardly any space around the cutterhead.  However, with tools like a CMS, TS, lathe, etc where you can have a large open hood, it can matter a lot.

Before I type a small novel, are we on the same page so far?   8)

Cheers,
Allan

[dbhost]

So far so good...

But let's use for example, a layout like mine...

Dust Collector #1. Wet Dry vac / Thien cyclone setup.
Dust Collector #2. Reasonably stock HF 2HP 20amp DC fitted with Wynn filter and Thien cyclone setup.

Table saw, 3 ports, 1 @ 4" belly pan, 1 @ 2.5" blade shroud and 1 @ 2.5" blade guard (Shark Guard). The DC will pull from the belly pan and blade shroud. I have a shop vac setup to pull from the shark guard.

Band Saw. Will be adding a 4" port to the lower wheel guard, and adding a 2.5" port to the upper blade guide area to pick up what is spewing off the blade. This will be serviced from a 4x4x2.5 Y fitting.

CMS, Need a bettter hood, seen some plans out there but not sure what to do honestly...

Jointer. Benchtop with 2.5" port.
Planer. Bencthop with 2.5" port.
Oscillating sander. Bencthop with 2.5" port.
Sanders etc... 2.5" to reducers to the tool.
Drill Press. Need to add SOME sort of dust collection port.
Router table accessory. 2.5" port on top, need a lower port of some kind...

My Dust collector, and almost every single one like it I have seen including the Jet, Delta, etc... models I have seen at Rockler, all have 2 @ 4" to a single 5" fitting for intake.

As far as I know, 5" ducting is all but non existent.

From what I understand from Bill's articles, and I could stand to be corrected, hence why I posted the questions... Going with 6", and reducing down is a bad thing....

The impeller housing to inlet ring connection size is 5"...

My plan, such as it was, was to make a single straight run down the wall the DC is located against, for all the dust collection aside from the drill press, which would be gotten to via 2 @ 45 deg bends and across 6 feet.

I KNOW I want to keep flex hose to an absolute minimum, and completely eliminate any sharp bends.

So the question remains. Do I figure out a way to adapt the inlet of my DC to 6", and live with the restriction between the impeller and inlet ring, or do I go with 4"?

Sorry about all the questions. This is not exactly an easy topic to fully grasp, and it is quite important...

[AllanJ]

So far so good...

But let's use for example, a layout like mine...

Dust Collector #1. Wet Dry vac / Thien cyclone setup.
Dust Collector #2. Reasonably stock HF 2HP 20amp DC fitted with Wynn filter and Thien cyclone setup.

Sounds good....but we have a "problem" right away.  The HF 2HP DC seems to have been designed by a marketing guy because its performance is nowhere near what a "normal" 2HP DC should be.  The fan is way too small so in this case I'd stick with 5" pipe....at least until I can see one of these in person and do some testing.  I live in Canada and HF isn't available here.

My Dust collector, and almost every single one like it I have seen including the Jet, Delta, etc... models I have seen at Rockler, all have 2 @ 4" to a single 5" fitting for intake.

If you had a different brand of dust collector, I'd recommend replacing the factory metal blower inlet cover (most are removable) with a shop made plywood version with whatever sized flange you want to use the pipe size you want.  Here's a pic of my friend's General International 2HP DC (very nice unit) and it came with a 2x 4" adapter on a 5" flange.  It's now gone and he has a plywood version in its place with a PVC coupler screwed in so he can use 6" PVC pipe.

You can also see the factory blower cover being used to hold up the 6" PVC pipe during some airflow testing I was doing.  That's all it's good for now.   ;D

As far as I know, 5" ducting is all but non existent.

It's only tough to find if you are looking for PVC.  Your local BORG or a local HVAC distributor has a ton of 5" metal HVAC parts.  Buy the heavier gauge stuff (26ga preferred) or buy 28ga spiral pipe (no need for 22ga spiral like some places recommend).  Avoid 30ga stuff.  You'll suck it flat.  You can use HVAC elbows, wyes and reducers too.

From what I understand from Bill's articles, and I could stand to be corrected, hence why I posted the questions... Going with 6", and reducing down is a bad thing....

The impeller housing to inlet ring connection size is 5"...

Yup.  Reducing pipe diameter reduces airflow.  It's as simple as that.  However, there are times when you want to do that and that's when your DC isn't strong enough to move enough air through the pipes.  You see, dirty air wants to move within a certain speed range though the pipes.  Too fast and it'll have too much resistance and will reduce airflow.  Too slow and the sawdust will fall out of suspension in the airstream and clogs may form.  It's like Goldilocks....you want the ducting to not be too small or too large.  You want it sized "just right".   ;D

An example for your shop...suppose you had a 24 foot long run on the ceiling to get to a restrictive tool.  I'd run 5" along the ceiling and 4" down to the tool.  The reason for this is because with a restrictive tool, the airflow will be reduced.  So 5" pipe would be too large going up the wall and sawdust would fall out of suspension and build up at floor level, making a clog over time.  So I'd stick with 4" pipe to keep the velocity higher and carry that sawdust up to the ceiling.  Then it can slow down a bit because the dirty air is moving horizontally and doesn't need to move as fast to get the sawdust to the DC.

...about that typical 5" flex hose joining the blower to the filter stand....  Want to see what my friends and I did to a friend's 2HP DC?  Click this link and read the blog called "Project Hotrod - how to modify a 2HP DC to flow more air".

http://tinyurl.com/7ghmax

I will never let a little sheet metal get in the way of better performance.   8)

My plan, such as it was, was to make a single straight run down the wall the DC is located against, for all the dust collection aside from the drill press, which would be gotten to via 2 @ 45 deg bends and across 6 feet.

Ignoring the drill press for now, how long is that wall?  Or are you saying the run to all the tools is only 6 feet long?  Would you have the ducting run along the floor?  4' high?  Ceiling?

So the question remains. Do I figure out a way to adapt the inlet of my DC to 6", and live with the restriction between the impeller and inlet ring, or do I go with 4"?

I'd do 5" pipe.

Table saw, 3 ports, 1 @ 4" belly pan, 1 @ 2.5" blade shroud and 1 @ 2.5" blade guard (Shark Guard). The DC will pull from the belly pan and blade shroud. I have a shop vac setup to pull from the shark guard.

I'd run 5" to the saw, then use a 5x5x5 wye with a 5x4 reducer for the belly pan and 5x3 (or 2.5) for the blade shroud. (I'd need to see the shroud)

Band Saw. Will be adding a 4" port to the lower wheel guard, and adding a 2.5" port to the upper blade guide area to pick up what is spewing off the blade. This will be serviced from a 4x4x2.5 Y fitting.

I'd run 5" to the BS, use a 5x5x5 wye with a 5x4 reducer for the door and another 5x4 reducer for a custom made under table port.  I just finished making my bandsaw DC hookup and here's a pic.  I used 5" for the under table port because I have a large DC.

CMS, Need a bettter hood, seen some plans out there but not sure what to do honestly...

Lots of styles to choose from, but most revolve around a large shroud covering the rear portion of the saw from the fence back.  Run 5" pipe to here and use a big port behind the saw.  I use HVAC parts for hoods like floor register pieces.  Cheap and saves a bunch of time.  Look at my blog again and read the one about making new hoods for some ideas.  I should probably add my SCMS and BS there now.

http://tinyurl.com/7ghmax

Jointer. Benchtop with 2.5" port.
Planer. Bencthop with 2.5" port.
Oscillating sander. Bencthop with 2.5" port.
Sanders etc... 2.5" to reducers to the tool.

Use your shop vac with these but use a good filter.  I use a HEPA filter in my shop vac.  Those tools you listed are very restrictive and a big DC doesn't like to move air through tiny ports.  4" minimum is my rule of thumb.

Drill Press. Need to add SOME sort of dust collection port.

A shop vac is good here or 4" hose from a DC.  Anything larger becomes unwieldy.

Router table accessory. 2.5" port on top, need a lower port of some kind...

Back to the DC.  Run 5" pipe, 5x5x5 wye with 5x3 and 5x4 reducers, 3" to the fence and 4" to the cabinet.  There is a chance you might get better performance by using your shop vac at the fence port.

Sorry about all the questions. This is not exactly an easy topic to fully grasp, and it is quite important...

No problem.

Cheers,
Allan

[dbhost]

I should have explained the TS here. I keep forgetting this isn't BT3Central...

I have a Ryobi BT3100 table saw with the router table wing and accessory kit that I modded to get a GREATLY improved fence. The factory ports on the blade shroud and router fence are 2.5". I have no clue how to hook up a different fence port since the router fence is based on the TS fence...

The saw. (Sorry, no pics of the shroud,)


The router fence setup.


Adapting to 6" S&D is NOT out of the question with the current 2HP HF DC... The older model, with the 14 amp motor / smaller impeller is reported to be a bit weak, the current model though, has a much stronger 20 amp motor, and a larger, I believe 11.5" impeller. (I may have read that wrong, and I haven't measured it myself).

I have seen at least 3 of these converted like your friends General International DC. I am / have considered it, but debate the usefulness of 6" in my small shop.

The DC plumbing will be run along the ceilling, down an 18' wall, and accross to meet up with the drill press. I believe tools needing the dust collector will be the table saw, the band saw, the compound miter saw, the drill press, and eventually a lathe. I am sure the Ridgid OSS could use improved dust collection, but how?