why run 6# duct to tools with 4" ports?

[Tyler Davis]

Reading Bill Pentz's site and others, they all suggest running 6" duct to all machine, for both the main runs and all drops. But all my large tools (table saw, 8" jointer and soon-to-be planer) have 4" dust collection ports attached to them. If the max CFM through the branch is limited by the smallest opening on that branch, aren't the dust collection ports going to limit to the same flow as that of a 4" duct? Wouldn't 6" duct be overkill if you are reducing the flow right at the collection point? I have a Grizzly 1029 2 hp collector, if it matters. Thanks for your thoughts on this

[walter stellwagen]

if you read farther in penzes site you will find that you need a certain airflow to
adequetly clean the air in your shop and to remove sawdust from your tool. He suggests modifing undersised ports. On the other hand for a saw if you have two 4" ports on at your blade guard and one at the cabinet splitting the 6 into two fours gives you sufficient airflow .(32 pi cross section close to the 36 pi of the 6 inch pipe.) . For some odd reason
manufactures of home woodworking machines fastend on the undersised 4" ports. Possibly this was done in Ingorance of the effect that the undersised ports have on airflow.

Walt

[Rick Malloy]

This seems like a good place to add to this question. I have a new 1200CFM Steel City DC. It has 2 4" connections to it. When I use just one, the sucked in saw dust swirls around in the bottom section, when I open the second one just to let air in then it looks like a tornado in there. So this thing seems that it was designed to be fed by a 6 inch hose\duct. Simple math shows that 2 4" circles have almost the same area as a 6". So I can see running 6" duct work and plan to do that.

But if I run overhead duct work, will I be better running 4 inch to the machines? I will do some testing with opening a gate at the end of the line to add to the volume of air going thru the 6" duct, but if I run 6" to my saw, then I will have slower air flow than a 4". I'm getting a bandsaw with a 4" port on it but my contractors table saw only has a 2 1/2 so I want enough air flow to carry the chips and sawdust up to the main line.

[Jim O'Dell]

I agree. Change the port if possible. If not, either use a 4" drop, or do the 6" with a 6-4-4 wye so that you can have proper air flow in the 6" vertical run. Otherwise you could possibly not have enough CFM in the 6" to keep some of the chips moving. Use a second blast gate on the extra 4" to regulate air flow with out starving the tool. But best would be to change over to 6" at the tool if at all possible. Jim.

[David Parker]

Hi Tyler,

The ducts cause "resistance" (also known as static pressure loss) to the flow of air. The amount of resistance is dependent on both the diameter of the duct and the length of the duct. Thus a short segment of 4 inch duct provides less resistance than a long segment of 4 inch duct. To minimize your static pressure loss, use larger diameter ducts as much as possible. True, the 4 inch diameter port will introduce some resistance, but not as much as an entire 4 inch diameter duct.

The other factor that needs to be considered is the air velocity within the ducts. Your dust collector needs to be powerful enough to maintain at least 700 CFM through a 6 inch duct to keep the sawdust moving. For a 4 inch duct, this only needs to be 400 CFM. See my post here (http://www.sawmillcreek.org/showthread.php?p=779137#post779137) for more details.

I'm just starting out in all this, so I defer to those more experienced. It sure is interesting learning all this new information though.

Dave

[Anthony Whitesell]

If you look at it from the point of view of a single machine, the majority of the machines require 350-400 CFM which is just fine for a 4" line connected directly to/from the DC. Of course the manufacturer does not take into account that some users may utilize a whole shop DC system in which case the 4" port becomes too small and really needs to be 5" or 6" in diameter.

I have seen a picture of a cleverly designed system. They used microswitches on the gates to tell which gate was open to open a sacrificial gate at the end of the trunk to maintain the proper opening size. When 4" gate opens, then a 4" gate would open at the end of the main line to add in the "missing" air flow. If a 5" gate opened then a 3" airflow gate would open. If all gates were closed then a 6" gate would open to apply the correct amount of pressure to the system. The idea was to leave the DC running the whole time without working the motor too hard. I believe it was a cyclone and not a bagged system.

I wonder if the same principal would apply if the DC had a 4" inlet and everything was plumbed with 5" or 6" outlets? Could a 5" line work properly with a 4" inlet on the DC?

[Curt Harms]

I use 6" flex to connect to mobile tools. Even the better quality hoses have pretty rough insides which has to slow the airflow next to the walls. My thinking is that 6" hose should have somewhat more airflow than a smooth 4" duct. I do know that 6" hose with a 6 X 4 reducer on the end will still move a lot of air. I don't have any problem with chips falling out of the airstream that I can detect.

HTH

Curt

[Tom Veatch]

.... If the max CFM through the branch is limited by the smallest opening on that branch, ...

It isn't!

For a given motor/impeller system, the max CFM is limited by the total flow resistance in the system.

All other things being equal, large ducts have less flow resistance per unit length than small ducts. 10 feet of 4" duct offers more flow resistance than 10 feet of 6" duct.

Yes, the 4" port on the machine will introduce more resistance that a 6" port on that same machine. But it is the total resistance that counts. 6" ducts and 4" ports have less flow resistance than 4" ducts and 4" ports. Therefore, for a given system, 6" ducts with 4" ports will flow more CFM than will 4" ducts with 4" ports.

[Paul Johnstone]

Reading Bill Pentz's site and others, they all suggest running 6" duct to all machine, for both the main runs and all drops. But all my large tools (table saw, 8" jointer and soon-to-be planer)

It's pretty easy to modify the DC opening on the jointer. Most jointers have a plastic plate you can unscrew and replace with a piece of 1/4 plywood and a 6" fitting.

The planer is a little more involved, but I made one with a HVAC fitting.. It was basically a "funnel" piece with a 6" duct.

Hard to say on the tablesaw. My contractor's saw was easy, as I had to box it in anyhow. Depends on the saw, but certainly doable.

It's a PITA to convert the ducts when you much rather be playing in the woodshop.. I am not going to sugar coat it.. but it's time well spent.

[Bob Aquino]

Reading Bill Pentz's site and others, they all suggest running 6" duct to all machine, for both the main runs and all drops. But all my large tools (table saw, 8" jointer and soon-to-be planer) have 4" dust collection ports attached to them. If the max CFM through the branch is limited by the smallest opening on that branch, aren't the dust collection ports going to limit to the same flow as that of a 4" duct? Wouldn't 6" duct be overkill if you are reducing the flow right at the collection point? I have a Grizzly 1029 2 hp collector, if it matters. Thanks for your thoughts on this

Run your 6" duct as the mains and then branch off to 4" for the machines that only need 4 inches. I have (2) 6" blast gates, one for the mitersaw and one for the bandsaw that branches to (2) 4" lines for the two ports on that machine. For everything else, I only run a 4" port. If I need more flow, I already have it with the 6" pipe and can just change the fitting as necessary. I use PVC and nothing is glued, just taped up with aluminum foil tape. I previously had everything in 4" and changed it out when I went to the larger collector. If you can avoid having to upgrade, its cheaper in the long run. But don't we all know that...:rolleyes:

[Jim Becker]

There is also a bit of a venturi effect when you bring the larger 5" or 6" drop right to the tool and only reduce right at the port...it's not a huge increase in performance, but the brief acceleration of the air flow helps add a little CFM that you otherwise could not get with just a 4" drop to the tool. That said, increasing the size of the port to accommodate a 5" or 6" drop is ultimately the best performance boost you can do for most tools.

[Thom Sturgill]

One of the magazines recently reviewed several small DC systems. One of the things they did to improve the systems was to replace the machine ports with ones made with rounded edges so that the transition from the machine to the hose was as smooth as possible.

[Tyler Davis]

interesting comments - thanks all. I will definitely run 6" duct to all machines and then either expand the tool port sizes or just do 4" drops if that's not possible.

So basically the name of the game is to end up with cross-sectional area for dust collection at each tool equal to a 6" diameter duct - easy enough :cool:

[Anthony Whitesell]

You got it. Equal to the the main line, but no larger. You're better off to go slightly smaller to ensure that the airflow is kept up to snuff in each of the drops.

I spent last night with my 2HP DC playing around with various configurations of inlet port sizes feeding my 4" main to prove to myself that my calculations and intuition were correct.

[Chris Padilla]

I'm still waiting for these machine manufacturers to "get it" and start offering larger ports than 4 inches or at least provide an option to move to a larger port size. For now, we are all stuck modifying 4" openings to 5" and 6" openings.

If you must drop in size from say a 6" pipe to a 4" opening, do it through a tapered fitting so that the change in size is as gradual and you can stand to make it.

[Anthony Whitesell]

The real zinger is the fact that the opening to my DC is pointed at the floor and my ductwork is overhead, so there is a double 90 degree u-turn to get into the DC.

If I made a gradual change as you propose (which I have no problem doing) and before I make any other changes to the duct work, I'm trying to determine how large I can go and still make it work with the 4" inlet.

Is it going to be possible to get the airflow required to make 6" ducts work at all? Or in this situation, am I better off changing to 5" ducts to increase my chance of success?

[Chris Padilla]

Anthony,

My rule of thumb is to carry the largest diameter possible as far as possible to the inlet of the machine. For your case, flex line is the way to go most likely. Don't make life too complicated for yourself. :)

[Anthony Whitesell]

By "inlet to the machine", do you mean inlet to the DC or to the work equipment (TS, BS, etc)? My shop is currently plumbed with 100% 4" flex line. I think I hear Mr. Pentz grumbling already, and don't worry I have learned much since then. I have no problem running the largest diameter I can to the work equipment 5" or 6", that's obvious (now).

I'm actually trying to uncomplicate myself right now. I have purchased a drum sander and this fall (or the next time there's a special) getting a bandsaw, so I was thinking of upgrading to solid 4" PVC to get some more performance from my current system, but then I thought 'why buy 4" now just to have to upgrade to 5" or 6" later?'

My hope is that someone can confirm that I can successfully use 5" line, or better yet 6" line, with the caviat that it must be reduced to 4" at the DC. My intuition tells me 5" might not be a problem, but that 6" is probably too big with too much cross-sectional area and the dust will collect in the line.

[Chris Padilla]

Anthony,

Yes, "inlet to the machine" is the device requiring evacuation of dust. :) I guess that is an incorrect term to use: "outlet" would be better. My apologies. :D

6" is the defacto recommendation but it will depend on your DC as well. What size impeller...what is the size of its inlet (correct term here)? Is it a cyclone?

Simply telling you to install 6" and your worries are over without considering the whole system would be, well, INconsiderate. :)

With a "good cyclone" (basically, what is out on the market from most manufacturers probably fits this bill decently, more or less), 6" should serve you very well.

[Jim Becker]

6" is "defacto" only for systems that the blower system is suited optimally for a 6" or slightly larger input...but it's true that at the typical FPM velocity generated by an acceptable blower, you will be able to fit enough air in the 6" duct to be able to move about 800 CFM or so. That's the real goal... ;)

[Anthony Whitesell]

I have a (according to the manual) a 2HP 120VAC 17amp non-cyclone two bag (one up-one down) Rigid DC with one non-expandable (no special ring I can cut free) 4" port.

Actually, I didn't expect an exact answer, just more information to ponder. Based on the OP got me to thinking of the reverse situation (my current situation) and was wondering if the proximity of the 4" restriction so close to the motor would give me some extra CFM if I had 5" or 6" ducts run through the shop? And subsequently, would there be enough CFMs to support running 5" or 6" ducts?

I am also working on procuring a magnehelic gauge for better performance testing of any changes. Any idea where I would attach it to the ducting? Do I just attach it through the side of the port at the DC impeller?

[Samuel Brooks]

What I did, After reading allot here, I went with a 6" main trunk that branches to 4" before going to each machine. Before I was using the twin 4" connectors with the stock 30 micro bag which would fill up taunt when the DC was running. I have the Jet DC1100a 1.5HP unit. I changed the bags to the Penn State 1 micron bags and when I turned on the DC the top bag did not fill up. I was told this was normal because their was not enough air flow to fill up the bag. After running the 6" main duct, I removed the twin 4" from the Jet and connected directly to the 6", I had to crimp a standard 6" to get it to fit because it was a little big. When I turned the unit on for the first time the Penn State 1 micro bag puffed out to it's max size. It now stays that way all of the time when it's running so I can see a difference in air flow even with 4" connects at the end of the runs.

85026

I then ran 6" along the main run across my shop. I am planing on converting to 6" all the way to my Table Saw but for now it transitions to a 4" I used strips of wood that were attached to my studs that were 2" x 3/4" thick. I then used metal banding to connect the duct work to the ceiling and walls. It worked out pretty well. I am now going back though and removing all of the duct tape which did not hold up well and replacing it with the duct work tape that is very adhesive and does a much better job of sealing.

85025


Pricing Issue. I went with Penn State for the two y's the 6" in / out with the two 4" and the one 6" in / out with the 6" branch. They were around $40.00 each. All of the rest of the stuff, 6" 90 degree elbows and straight pipe, I purchased at my local HD and Menard's. It was around $4.00 - $5.00 per 5' section when Penn State wanted $15.00 per 5' section plus shipping. They were both made out of 26 gage so I did not see any difference. I also had purchased a long 90 degree turn from Penn State and a couple of 6" to 4" conversion fittings because the ones at HD were not very smooth. I found the 90 degree turn from Penn State to be of not good quality because I had it pull apart at one of the seams and I had to put it back together and re-crimp :confused:. In all I have about $250 dollars in the duct work alone, but I feel that it is very worth the investment after operating for 4 years without it.


Good luck with whatever you come up with, it will be worth it. Now I just have to figure out how I can add over the top dust collection to my table saw with something that looks decent without breaking the bank. :D

Sam Brooks
Woodhacker

[Jim Becker]

I have a (according to the manual) a 2HP 120VAC 17amp non-cyclone two bag (one up-one down) Rigid DC with one non-expandable (no special ring I can cut free) 4" port.

Actually, I didn't expect an exact answer, just more information to ponder. Based on the OP got me to thinking of the reverse situation (my current situation) and was wondering if the proximity of the 4" restriction so close to the motor would give me some extra CFM if I had 5" or 6" ducts run through the shop? And subsequently, would there be enough CFMs to support running 5" or 6" ducts?

Your particular current DC will not support 5" or 6" duct based on your description. Ratcheting down at the hood is one thing, but the velocity drop with that on both ends would be quite undesirable.

[Buddy Clark]

With a cabinet table saw and a zero clearance blade throat, where is the sufficient air flow to feed a 6" (or even 4") dust collection system?

[Chris Friesen]

With a cabinet table saw and a zero clearance blade throat, where is the sufficient air flow to feed a 6" (or even 4") dust collection system?

On my saw at least, there is a finger hole in the throat plate and the cabinet does not seal tightly to the bottom of the table all the way around (ribs get in the way). Normally there would also be a gap at the depth control wheel but I've covered that to prevent sawdust from escaping through there.

Also, for best dust collection you want to divert close to half of the total airflow to the blade guard so that the dust above the table is captured as well.

[Dave Lessley]

So how does that apply to my oneida which I believe is an 8" inlet. Do I run 8" as far as I can and then neck down to my machine port or should I be converting from 8" to 6"?

[Chris Padilla]

Dave, I would convert down to 6" and then carry the 6" to your machines. Use a tapered fitting that drops the 8" to 6" over a foot or two. I think Oneida carries these or they can whip one up for you.

[David Giles]

Simply telling you to install 6" and your worries are over ....

I don't know, Chris, it sounds like pretty good advice. I bet it would solve lots of DC problems.