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

[bennybmn]

For your table saw... With a shark guard and blade shroud, are you really getting much, if any, dust from the belly pan? You could put a plast gate inline with the bely pan split and manipulate the flow. Partially close it, and get more suck thru the blade and shark?

[dbhost]

Not sure... Haven't tried hooking up the shroud / shark and not the belly pan. The ports are there, I figured I'd use them...

[AllanJ]

Ahhh...thanks for the pics.  It looks like the router table fence might be best served with a shop vac.  Tiny ports = shop vac.

Thanks for the info about the revised HF 2HP DC.  If you get bored one day can you please remove the blower cover and measure the fan for me?  I'm curious how much this has grown.  Ideally, a 2HP DC would have a 12" fan so I'll keep my fingers crossed for you.

Too bad you didn't get the shark guard with a 4" port.  I've tested that one and compared it to my Excalibur and it performs very well.  Maybe it works just as well with a shop vac?

I have the Ridgid OSS so I know what you mean.  Right now I use my shop vac with it.  I'm hoping to build a custom hood for it, especially when I use the belt sanding attachment.  I'd use the factory port in addition to a hood at the side of the belt sander.  I'm debating a movable one for the spindle sander too.  If it can move easily and be suspended in the air, then maybe it can go above the spindle if you are sanding inside a shape.

The big tools requiring a DC rather than a shop vac would always benefit from larger ducting.  4" just doesn't cut it, except for the drill press.

Cheers,
Allan

[bennybmn]

Ahhh...thanks for the pics.  It looks like the router table fence might be best served with a shop vac.  Tiny ports = shop vac.

My router table fence has a small port too, but I have the DC split with a 4" Y, then it necks down to 3" PVC to the cabinet, and down to the 2.5" hose to the fence. IT sucks REALLY well from the fence I have to say. Maybe reducing the entire DC flow down to 2.5" would be bad, but dividing it up then reducing it seems to work well.

[dbhost]

Well,

Since I have the hose, blast gates, and fittings, only thing I am missing is the pipe, and honestly, getting everything in 6" would be a pure and simple PITA at this stage, the system, at least for now, is going together with 4" S&D pipe...

FWIW, this is a temporary setup at best. I am working on permitting and budget considerations for a new 12x16 gambrel roof barn / shed for a workshop. Yeah I know, not the biggest footprint, maybe not even big enough, but as big as I can go on my lot. Depending on air quality readings with the 4", I may go to 6" in the new shop... So in the space of about 2 years, I may be selling some 4" self cleaning blast gates, some 4" to 2.5" wyes, and a fist full of clamps...

[AllanJ]

I hear ya.   ;)

Like most things, something is definitely better than nothing.  I ordered a Dylos particle counter so one of these days I'll try some tests to see what the difference may be in a situation like yours.  I'm curious.   ;D

Cheers,
Allan

[dbhost]

I am doing what I can to maximize air flow. I wish money and time weren't the rare commodities that they are...

Bill does have some very valid points though that pretty much most tool dust collection ports need a LOT of improvement...

I can say that the high static lift of the shop vac setup does work well on top of the saw / router table. But below is a different story... Too big of a space involved LOTS of air needs to be moved to replace the lots of air that gets quickly filled with dust...

Where possible, I want to keep flexible hose to less than 2.5', but I know that won't always be possible...

So I continue with the odyssey and plod forward...

With the pending shed / workshop layout, I will likely START off with 4", but I found a company called KenCraft that seems to offer 5" DC ducting and fittings. Lee Valley has 5" blast gates, now I just need to find 5" hose, and a way to connect that to the tools / improve the dust hoods there and I think I am good...

Just like the shop, the dust collection is a work in progress...

[AllanJ]

I am doing what I can to maximize air flow. I wish money and time weren't the rare commodities that they are...

You and me both!

I can say that the high static lift of the shop vac setup does work well on top of the saw / router table. But below is a different story... Too big of a space involved LOTS of air needs to be moved to replace the lots of air that gets quickly filled with dust...

That's a good way to look at it.  Big space requires a big DC.  Small space requires a shop vac.

Where possible, I want to keep flexible hose to less than 2.5', but I know that won't always be possible...

Yes, keep the hose short, but don't mess up your shop because of it.  Woodworking is a hobby for most of us and a hobby should be fun.  It shouldn't be a PITA.  Do what you need to in order to reduce the length and turns in your ducting, but don't piss yourself off because of it.  It's all about balance.

With the pending shed / workshop layout, I will likely START off with 4", but I found a company called KenCraft that seems to offer 5" DC ducting and fittings. Lee Valley has 5" blast gates, now I just need to find 5" hose, and a way to connect that to the tools / improve the dust hoods there and I think I am good...

Just like the shop, the dust collection is a work in progress...

You can make your own blast gates too.   ;)  I made my own 7" blast gates.  Lee Valley sells 5" flex hose, same with Grizzly.  Three local woodworking stores within 40 mins from me sell 5" hose too.  If you live near a big city, it's probably available right there.  I use HVAC fittings (elbows, reducers, wyes) available at Home Depot and seal all the seams.  Sure there are better parts available elsewhere but I'm not interested in mail ordering expensive parts.  Sizing the duct diameter properly and using crummy HVAC parts will flow way more air than 1" smaller diameter pipe with fancy welded long radius elbows, extra long tapered reducers and nicely flowing wye branches.

For hoods, I'll remind you about my blog on Wood Magazine's site about making new hoods utilizing HVAC parts.  They are a major time saver and are really cheap at a few bucks each...and it's kinda fun to find a close-fitting HVAC part and make it work.   ;D

http://tinyurl.com/cjwa9f

Good luck with this!

Cheers,
Allan

[dbhost]

Yeah. I am very happy with the shop vac system, mostly. It works GREAT on the planer (Ryobi AP1301), jointer (Sunhill SM-150B), and did work as well as anything could on my old Ryobi BTS-21 table saw... It also works exceedingly well with handheld sanders. Where it falls flat is with my Ridgid OSS, 14" band saw, and table saw. We aren't even going to talk about the drill press... I will check your blog later. Maybe you have some ideas how to collect the dust off my Ridgid OSS that actually, oh I dunno, works...

I agree with you about the balance thing. I am an unrepentant cheapskate and tinkerer. I am actually having fun fooling with this setup. I am aware there are some of my locations that need more flex line than that.

Not sure I am quite willing to make my own blast gates when the Lee Valley self cleaning ones are quite affordable. While not as cheap as a DIY approach, this is one of those what is your time worth issues... I was not aware they had 5" flex hose...

Are there any special things to consider when using HVAC ducting?

Just curious. I have seen more than a couple of guys upsize to 6" on the HF 2HP DC inlet before the impeller. Won't the 5" between the impeller and the inlet ring be a problem with that setup?

[Bill Pentz]

I fully agree with Alan and a few others here.

Yes, my web pages grew from incorporating well meaning help from simple without explanations to so complex I can?t even find things. To make repair I am doing another rewrite to separate off the cream and move the technical into its own areas.

Also, as Alan shared, the CFM numbers I advocate remain the industry standard which our small shop vendors continue to ignore. Not me, but instead the top commercial dust collection firms that guarantee their customer air quality built the following table. This table includes more than twenty years of refinement to set the minimum airflow we need at each tool for each different level of dust collection.


Also Alan was correct with his summary about blower horsepower and air moved  and he accurately touched on the major problem with our small shop vendors. These ?bendors? remain trapped in an exaggeration game they created and now don?t know how to escape with their often just plain fictitious CFM and filtering claims. Based on tests that dozens of us did all over the country, most vendors advertize maximum airflow that is roughly double what their systems provide in real use. Many, especially vacuum vendors exaggerate maximum horsepower when the reality is none provide more than about 1.5 hp when connected to a 120 V outlet.

Alan also touched on our biggest problem in getting good fine dust collection today. Almost all small shop dust collector and cyclone filtering claims are badly exaggerated. Our tests found all mainstream small shop dust collector and cyclone makers freely passed ten to twenty times larger particles than claimed on their ads. Their rationale is they use outdoor testing versus indoor which requires testing the filters when clean and new. The result is the fine filters we buy to protect our health leave a clean looking shop while freely passing the fine invisible unhealthiest dust particles sized 10-microns and smaller. Worse, these filters become dust stores so every time we turn on our dust collector or cyclone they blow dangerously unhealthy amounts of fine invisible dust all over our shops.

You would not believe the numbers of people who have bought http://www.DylosProducts.com Dylos 0.5 and other air quality meters that found their expensive top magazine rated dust collectors and cyclones made their shop air outright dangerous. Additionally, you would not believe the hundreds who have written over this past nine years who said they had no problem with wood dust, then suddenly they ended up getting ill, some with life threatening problems. Folks, many woods are sensitizer so just like me you can go for decades with no problem the suddenly find yourself with a minor problem up to being rushed to the hospital.

Let me summarize all the physics, engineering and medical concerns together. The only way to avoid the fine dust is not to breathe it. You can work outside, collect the fine dust as it is made or use a strong fan blows that dust away from us as it is made then out of our shop. Air cleaners are great to help with finishing, but they work so slowly we end up with our lungs doing the filtering. To collect the dust at the source we either need tools that totally trap the dust or the airflows shown in the above table plus upgraded hoods and tool ports. For tools with un-modifiable 2.25? ports always use a big shop vacuum with fine filter. To move the air we need for good fine dust collection either use an oversized blower with smaller pipe or an appropriate sized blower and the right size pipe. For my cyclone solutions I do a little of both because we really should be using 7? diameter pipe for 1000 CFM, but I recommend 6? diameter pipe and compensate by using an oversized blower wheel to increase pressure and duct air speed. This lets me move the real 1000 CFM that our table shows we need at most larger tools with all 6? duct. To move this much air in an average shop with ducting and a good set of fine filters such as the MERV-15?s I get from Wynn Environmental http://www.wynnenv.com/cartridge_filters.htm  we need at least a 3 hp dust collector turning a 14? diameter impeller or 3.5 hp cyclone turning a 15? diameter impeller. That is pretty much it in a nut shell except you still need to address your tool ports and hoods.

[dbhost]

Bill...

Okay so for example, for those of us cheap skates here that went with the cheapo HF 2HP DC (yeah right I know overrated but it is what it is..) and Wynn 35A cartridge (your recommendation) how are we to get the 5" port, and connection hose between the impeller housing and inlet ring to play nice with 6" (or bigger) duct?

I quote your Cartridge Conversion page subsection G...http://www.billpentz.com/woodworking/cyclone/DCConversion.cfm
"They make this filter in the same paper poly blend that most other makers offer, and offer it in the far superior all poly version."

And I in turn quote from the Wynn Environmental product description page for the 35A cartridge kit.
"99.995% efficient at 1.0 micron and above"

You recommend .5 micron filtration, yet you tout the 1 micron spun bond poly as being far superior. Why is that?

And YES I understand you state that as a lesser solution, but if it is what we have to work with.

I'm mostly trying to get my head around this. You do recommend the 6" pipe pretty clearly in your writings, so I am just itching to figure out how that works when not all, but most single stage dust collectors use 5" fittings like the Central Machinery does... Is necking the port down from 6" to 5" at the DC an option? If not then how does that work? On most of these machines, you CAN make a custom flange to go into the impeller housing, but it would require a LOT of sheet metal work to adapt the inlet ring and outlet of the impeller housing to accept 6" hose...

And with a great quantity of woodworking equipment being fitted with 2.5" ports injection molded in to fragile plastic housings, it would seem to be a less than simple matter to upgrade those to 6" duct.

[Bill Pentz]

dbhost...

Okay so for example, for those of us cheap skates here that went with the cheapo HF 2HP DC (yeah right I know overrated but it is what it is..) and Wynn 35A cartridge (your recommendation) how are we to get the 5" port, and connection hose between the impeller housing and inlet ring to play nice with 6" (or bigger) duct? You don?t, the HF only has ample capacity to support 5? duct.

I quote your Cartridge Conversion page subsection G...http://www.billpentz.com/woodworking/cyclone/DCConversion.cfm
"They make this filter in the same paper poly blend that most other makers offer, and offer it in the far superior all poly version."

And I in turn quote from the Wynn Environmental product description page for the 35A cartridge kit.
"99.995% efficient at 1.0 micron and above" So step up to the newer Wynn MERV 15 filter and get your real 0.5-micron filtering.

You recommend .5 micron filtration, yet you tout the 1 micron spun bond poly as being far superior. Why is that? Let?s discuss apples and oranges separately:

1. I recommend spun bond poly filters over paper poly blends because the spun bond lasts four times longer, can be washed, and for the same CFM requires half the overall filter area. They cost twice as much but are worth it.

2. In terms of filtering level the EPA, European Union, and medical experts all consistently recommend HEPA level filtering for dust control. HEPA is the old radiation breathing mask standard where every single filter is individually tested and certified as 99.9% efficient on particles sized 0.3 microns and larger. When I first put up my web pages only one vendor, Donaldson Torit, offered a fine woodworking filter, their 0.5-micron filters. All other affordable filters were 1-micron. Since then manufacturing efficiencies have improved and we can now get good 0.5-micron filters for about what I had to pay for poly blended filters ten years ago. Today I personally use on my Jet DC a single and on my cyclone a set of the Wynn Environmental MERV-15 rated filters.

And YES I understand you state that as a lesser solution, but if it is what we have to work with. I tire of hearing this same argument. For decades I used a ceiling mounted air cleaner, nice set of dust collectors, and a large doorway fan that kept my shop well ventilated and often too hot or cold to enjoy. I saved diligently and finally bought the top magazine rated cyclone system with vendor designed and supplied ducting plus vendor recommended filter upgrade. Less than a month later I found myself rushed to the hospital with an apparent heart attack. That cyclone created a bad false sense of security because it left a clean looking shop while building up dangerously high invisible dust levels. Three months after I went to the hospital an air quality test showed my shop and home badly contaminated. Worse, that cyclone was a dust store as just turning it on with no woodworking pushed the fine invisible dust level over 10,000 times higher than the maximum airborne invisible dust that EPA considers safe. Because I worked many toxic woods the considerable invisible dust that built in my clean looking shop and home caused me to rapidly sensitize with a bad allergic reaction. My Cyclone and Dust Collection Research web pages and dust collection efforts are dedicated to try and help others avoid this same problem. I would gladly pay ten times what I spent on that expensive POS cyclone with ducting and fine filter to have not had to live on an oxygen hose for the last ten years. So you will never convince me that compromise on our dust collection is wise.

I'm mostly trying to get my head around this. You do recommend the 6" pipe pretty clearly in your writings, Yes, you need 7? duct to move the 1000 CFM or 6? duct and oversized blower wheel. so I am just itching to figure out how that works when not all, but most single stage dust collectors use 5" fittings like the Central Machinery does... Is necking the port down from 6" to 5" at the DC an option? If not then how does that work? On most of these machines, you CAN make a custom flange to go into the impeller housing, but it would require a LOT of sheet metal work to adapt the inlet ring and outlet of the impeller housing to accept 6" hose... Although it is an easy fix to install a 6? flange on the face of the HF blower, upgrading a HF to 6? pipe is a waste of time and money. That blower and impeller do not move ample air to support 6? duct, so you will end up with clogging in the vertical runs and piles in the horizontal runs unless you use minimum duct and keep very clean open filters.

And with a great quantity of woodworking equipment being fitted with 2.5" ports injection molded in to fragile plastic housings, it would seem to be a less than simple matter to upgrade those to 6" duct. Agreed, I quit buying tools from makers who continue to give us 2.5? diameter ports on machines that need up to 1000 CFM for good fine dust collection. For those tools that I already own and use these small ports I forget my DC and instead use a good shop vacuum. An okay shop vacuum pulls about 50? of working vacuum versus a HF dust collector at about 5?. My high end shop vacuum pulls over 100". That ten to twenty fold difference in pressure is the only way to get good chip collection from tools with these tiny ports. To get them to also have good fine dust collection you need to use in addition to your vacuum a hood going to your dust collector which pulls in as much air as possible from around the working area of your tool.

[aqengineer]

I tire of hearing this same argument. For decades I used a ceiling mounted air cleaner, nice set of dust collectors, and a large doorway fan that kept my shop well ventilated and often too hot or cold to enjoy. I saved diligently and finally bought the top magazine rated cyclone system with vendor designed and supplied ducting plus vendor recommended filter upgrade. Less than a month later I found myself rushed to the hospital with an apparent heart attack. That cyclone created a bad false sense of security because it left a clean looking shop while building up dangerously high invisible dust levels. Three months after I went to the hospital an air quality test showed my shop and home badly contaminated.

Oh common, that is B.S.  Unless you had a hole in your filter stage, no such thing was happening.  Anyone with a Dylos meter can tell you those types of assertions are bogus.

And there is no way your shop/home air quality was "contaminated" three months after running any machines.  That is preposterous.

[dbhost]

I'm mostly trying to get my head around this. You do recommend the 6" pipe pretty clearly in your writings, Yes, you need 7? duct to move the 1000 CFM or 6? duct and oversized blower wheel. so I am just itching to figure out how that works when not all, but most single stage dust collectors use 5" fittings like the Central Machinery does... Is necking the port down from 6" to 5" at the DC an option? If not then how does that work? On most of these machines, you CAN make a custom flange to go into the impeller housing, but it would require a LOT of sheet metal work to adapt the inlet ring and outlet of the impeller housing to accept 6" hose... Although it is an easy fix to install a 6? flange on the face of the HF blower, upgrading a HF to 6? pipe is a waste of time and money. That blower and impeller do not move ample air to support 6? duct, so you will end up with clogging in the vertical runs and piles in the horizontal runs unless you use minimum duct and keep very clean open filters.

This begs the inevitable question then. If, in your opinion, after all of the research you have done, the HF DC and similar models are not workable dust collection solutions, why list them at all in your writings other than to say DO NOT DO THIS?

Your assertions on pleated filtration versus a simple bag are certainly based on solid, well established engineering principles (Look at an automotive air filter for an example of using pleated media to expand the amount of surface area available to filter through, thus increasing air flow for a given filtration level).

A cursory Googling of duct size / cfm charts shows a WIDE array of highly conflicting data. Most of this data is aimed at negligible static lift systems (HVAC) and nearly useless, there are the charts you seem to quote, and other charts showing, well vastly different data. Going back to the automobile analogy, while I am certain the amount of static lift has to be somewhat higher, typical carburetor fitted big block V-8 engines were frequently fitted with 650 to 850 CFM 4BBL carburetors, which pulled air through an enclosed can type air cleaner housing with an approximately 3" intake hole for fresh air. From a "Feel of the hand" perspective, a Pontiac 455 CID V-8 Holley 750CFM 4BBL intake pulls with a perceptably lower feeling of suction than my Harbor Freight 2HP Dust collector. This is however a mere pereception issue, and has no basis is scientific method or measurement.

This leaves us to ponder, what setups were tested, and were air quality samples taken before / after the dust collection system was run, and before / after dust producing events took place?

[servant74]

If you really want to know the CFM of your system at the dust ports, contact your friendly neighborhood HVAC person that has an air velocity gauge (or google to find how to DIY a pitot tube like used in airplanes to measure air speed). 

The air velocity gauge will tell you the speed of the air in feet per minute.  Here is the basic math: given you have the feet per minute (FPM) now multiply that times the cross sectional area you are pulling the air from (change it from square inches of cross section to square feet by dividing by 144).  So a 6" pipe is  29.27 sq inches or .196 sq feet.  So to get 1000 CFM you need an air velocity of 1000/0.196 = 5093 feet per minute in air velocity.  That is almost a mile a minute or 60 MPH (88 KPH).


So if you have a 6" duct, if you don't have 5093FPM, or about a 60MPH breeze, you don't have 1000CFM.

And for some popular ducts to give 1000CFM:

Duct Size	Feet Per Minute	Or roughly Miles Per Hour
2.5"	29,333 FPM	333 MPH
4"	11,459 FPM	130 MPH
6"	5093 FPM	57.8 MPH
7"	3742 FPM	42.5 MPH

So the size of motor/impeller/duct(diameter, length, curves, and smoothness inside) combination you use still needs those air speeds applied at the tools to fulfill the air quality needs.  I think it is easy to see why a good system requires big motors!  And why using to much flex tubing will cause lots of friction in the air especially if there is much of it at lower sizes.

Now in defense of Bill... He is addressing what it takes to keep us healthy.  He has been effected by poor dust management in his own shop and this is what he has come up with to keep him healthy. ... If you are superman, well, this may not apply to you. ... All of us must make our own choices.

In short, more air removed from the work area, the fewer fine particles you will breath in.  If you must recycle the collected air back into the shop, you need to filter it.  A poor filter will let the 'bad stuff' on through, and to small a filter will clog a lot faster.   

In what I see in Bills documents, chip collection is a good thing (and helps keep the filters clean) but secondary to keeping the fine particles picked out of our breathing space. 

Bill has made his decision for him, and is just trying to let us know what he has found to be reasonable solutions in his eyes.



On duct work, not all HVAC type ducting will stand up to the vacuum pressure that a good dust collection system will generate.  If you close all the 'blast gates' it can starve the blower and the low pressure will cause the air to collapse the ducts.


If I am wrong, please correct me.  This discussion is to help us all.