# HF dust collector and 6" duct



## cburdick1

*HF dust collector and 5" duct (Updated with photos)*

Hi everyone. I'm am finalizing my DC system design and have one final question before I start building.

I am going to run DC in my small shop using a HF dust collector, Thein Baffle seperator and a Wynn filter. I'll be using 6" metal HVAC duct for all lines. All turns will be gradual. Right now it will be pulling from my router table, table saw, band saw, planer, downdraft sanding table and miter saw, each with gates close to the tool.

I'd like to use 6" duct as 4" doesn't see to be viewed as efficient enough to capture fine dust. My concern is if the HF dust collector has enough "oomph" to pull 6" duct. If you are using the HF dust collector with 6" ducting, please let me know how it works.

Thanks.


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## dbhost

I am not running in that manner, but a lot of folks do. You will need to make a replacement impeller housing intake port piece. 

My rig is run with 5" ducting instead of 6, it works fine.


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## cburdick1

my plan is to run the 6" duct to the Thein baffle, then have the HF impeller pulling from the top of the baffle, so no need for an adapter.


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## Dave Paine

Any blower will pull air through a system. The larger the duct, the easier it is for the blower to pull.

Normally the bigger the duct diameter, the lower the pressure drop so you get better static pressure throughout the system.

Also the bigger the duct diameter, the lower the velocity. Velocity is proportional to the area.

6in duct will have area e.g., approx 28.2 sq in. (9 * Pi)
4in duct will have area e.g. approx 12.5 sq in (4 * Pi)

So 6 in duct will be less than 1/2 the velocity of 4 in duct.

Ideally you would need the manufacturers curves of pressure vs flow to determine what this means for your dust collector.


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## rrbrown

It will probably work. The biggest problem with the HF 2 HP DC is the impeller is smaller then it should be and or the motor is not a true 2 HP. Personally I have a Shop Fox 1.5 Hp DC that has and works with a 6" ducts. So I believe that the 5" port on the HF DC is based on the smaller impeller or maybe a poorly designed impeller. 

With that said I would try it with the 6" duct because you could upgrade later to a new DC if needed without needing to replace the duct also. That's provided it's not a extremely long run because the longer the run the slower the air will move. My system has 6" through the Thien Baffle/separator and all the may to each tool. It gives you better efficiency, especially when some tools like the TS and BS use a 4" port as well as a smaller 2" port. For those pieces I use a splitter or Wye after a 6" blast gate.

Your Wynn canister filter should have already improved the efficiency of the system by around 50%. I also got another 50% increase in effiency from changing to the 6" duct. However not sure how that will work with the HF DC but I would think it should help and not hurt. just my .02


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## rrbrown

cburdick1 said:


> my plan is to run the 6" duct to the Thein baffle, then have the HF impeller pulling from the top of the baffle, so no need for an adapter.


You may want to think about emptying the can. If the blower is on top of the Baffle which is on top of the can that will be a real difficult situation for emptying the can.


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## cburdick1

That's a good point, however I will be mounting the impeller housing and the Thein baffle to the wall and have a little platform that raises the can underneath the baffle.


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## rrbrown

cburdick1 said:


> That's a good point, however I will be mounting the impeller housing and the Thein baffle to the wall and have a little platform that raises the can underneath the baffle.


So your Baffle fit's inside or on top of the can. If it goes inside you need about a 10"-12" clearance because that's how much will sit inside of the can. In this case i would suggest a 55 gallon drum.

Actually you will probably need a 55 gallon drum because of the diameter needed to accommodate two 6" ports. It was tight even using the drum and mine sits inside. The top is a little smaller then the actual barrel so I need to tilt mine to start off when removing and or installing the baffle. 

I'm just trying to give you the benefit of my experience with this. If you have a better idea then please share it because I fought with all these things in my design and I'm sure someone else will be after you.


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## cburdick1

I see exactly what you are saying. However, the plan is for the Thein baffle to sit on top of the can, not inside of it.


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## rrbrown

You will still have the diameter issue and then some do to the outside wall of the baffle add that to how the debris needs to spin up against the sides then fall. 

How about some pictures then? I'm interested in how it will work. Knowledge is good.:thumbsup:


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## Icutone2

*D/C Lines*

Yes pictures please very interested in this set up.
Lee


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## cburdick1

I dint have it built up yet, but will post sketchup drawings, probably tomorrow.


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## cburdick1

Okay, here's a mock-up drawing of the planned collector. This is not a construction drawing, mounting of the blower isn't specified, connections aren't detailed etc. This was merely a study into how the whole thing would be put together to figure out what footprint it would take up so I could figure out where to put it in my shop.

The flow goes like this Dust > 6" Ducting > Thein Baffle > HF Motor/impeller > HF Seperator > then either Wynn Environmental filter or plastic collection bag.










I've designed the system this way for two reasons:

1: It puts the Thein Baffle before the Impeller reducing the chance of debris hitting and damaging the impeller. 
2: It will provide suction to help seal the trash can to the bottom of the Thein Baffle (instead of blowing into it).

I'll start building the system tomorrow or Thursday. I ordered my Wynn filter today and it should be here on Monday.


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## Shop Dad

That's exactly what I've been thinking about doing. Look forward to seeing how it goes together.


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## rrbrown

Those Brute Trash Cans are plastic and may very well get sucked in to colapse. I'm thinking it may not because of the Thien Baffle but be prepared.


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## dbhost

Provide yourself a bit of space, maybe 6" of exposed flex hose between your separator and the bottom of your impeller housing to allow you to slightly lift the separator to remove the can. You will want some means of supporting the separator while it isn't resting on the can...

It is entirely possible, if not likely you will suck the trash can in on itself until the seal breaks, and then repeat the cycle... You really ought to consider a much stronger vessel... I am using a 55 gallon drum with side inlet no problem (I was willing to sacrifice some volume for not having to build a top hat...)

The more of these I see, the more I want to wall mount mine... If for no other reason than to save space...

How would you support the bag ring?



cburdick1 said:


> Okay, here's a mock-up drawing of the planned collector. This is not a construction drawing, mounting of the blower isn't specified, connections aren't detailed etc. This was merely a study into how the whole thing would be put together to figure out what footprint it would take up so I could figure out where to put it in my shop.
> 
> The flow goes like this Dust > 6" Ducting > Thein Baffle > HF Motor/impeller > HF Seperator > then either Wynn Environmental filter or plastic collection bag.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> I've designed the system this way for two reasons:
> 
> 1: It puts the Thein Baffle before the Impeller reducing the chance of debris hitting and damaging the impeller.
> 2: It will provide suction to help seal the trash can to the bottom of the Thein Baffle (instead of blowing into it).
> 
> I'll start building the system tomorrow or Thursday. I ordered my Wynn filter today and it should be here on Monday.


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## haugerm

Here you go, maybe this link could help you.
http://lumberjocks.com/projects/29578
--Matt


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## PSDkevin

There is a youtube video out there where a guy builds this exact setup using this exact can. It didn't appear that he had any collapse problems. I intend to build this set up too. I just have to decide how I want to do the can change out. I like the idea of a small piece of flex between the separator and the impeller. I was going to fab a new cart of some kind as a project for my welding class. I HATE the cheap a$% cart HF put this thing on. (I know what can you expect for HF and the price) and since right now I wheel it around it makes a difference.


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## dgoodyear

Does your HF DC have 4" port? Most DC manufacturers purposely make the ports smallers to air starve the DC. This prevents the DC from drawing too much amperage under load if the DC is ran without the ducts connected. To have effective fine dust collection with 6" duct you will need to move about 800-1000 CFM at the tool port. If you are afraid that you will burn up your motor. Get a clamp on ammeter, run the DC with a sizeable (8'-10') 6" duct connected to a modified inlet that supports 6" and measure the current. If its substantially more that the motor plate current, you risk burning up the motor. Keep in mind that once you system is in place the situation will not be the same as the test. ie More duct means more static pressure. More static pressure means less CFM and less amperage draw.


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## cburdick1

*Update on DC system*

So in the past two weeks I've done the following:

- Switched the plan to 5" duct as the low ceiling in my basement shop would cause me to whack my head on 6" duct.
- Built the Thein Baffle seperator that now sits on a steel trash can. 

This is the bottom of the baffle. Dust/air enters at the upper left corner.









Gluing up the interior wall. I used 1/2" birch ply, relief cuts every 1". Much to my dismay the ply slid off my workbench and broke at one of the relief cuts, but I managed to use some bracing to piece it together.








Here is the interior glued up and some steel sheeting added in to prevent the ply from getting worn down from all the particles smacking into it. I used 77 spray adhesive to laminate it, worked like a charm.








The completed baffle.








More to come in the next week.


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## Scot H

I used the HF 2 hp dc for about 5 years and it great until I got the new Unisaw. I had to upgrade to a 3 hp (Grizzly) to get the cfm's up. The new Unisaw is an air hog, so unless you have a new unisaw the HF works fine. 
BTW my DC system uses a cyclone separator and 6" ducting and no flex hose except on portable equip. (router, planer). All of my ducting is hard piped in and reduced at each equipment connection.


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## cburdick1

Okay, here's the almost-done system:









The collection trunk line pipe feeds into the top of a Wye, with the other half of the wye being fed by a length of 5" flex hose, which I use to connect to the table saw, router, mortiser and downdraft table (to be built). The Wye then goes into a 9" piece of flex tube, then into the Thein. A piece of flex tube then exits the top of the Thein and goes into the HF blower. Eventually I'll mount the Filter/Bag support ring on the wall, but I'm too busy building cribs and such to do that right now. NOTE: I had to rotate the impeller housing on the HF blower so that I could mount it this way. IN it's original configuration, air exited the blower UP, which would have made the exit blow straight out into the room once wall mounted. I took the impeller housing and impeller off, removed some screws, rotated the housing and put it all back together, without any problems. 









Here's a better look at the intake side of the Thein. I don't have a gate on the top part of the Wye because each tool has a gate on that run of pipe. The Wye is held up by two bungee hangars that I made (see the next picture) and by a brace which holds up the blast gate.








I made these hangars from 7" wide strips of 3/4" ply about 8" long. I routed a 5-1/8" hole in the middle and cut the strip in half. I then drilled pocket screw holes to anchor the hangar to ceiling joists. The bungee is attached to the hangar by driving a 1-1/2" drywall screw into the hangar and tying the bungee to the screw. The bungee wraps around the cleat on this side as shown. I got the bungee pieces from a pickup truck hold-down thing that I bought at Home Depot for about $15.00. These hangars work like a charm and are awesome for putting the system together as it's easy to test fit pieces.


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## dmh

So the impeller housing rotated and bolted back up with no problems? Nice to know. I have one I need to do that to also.

The whole setup is looking great. Thanks for sharing.


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## dbhost

If you can, get a jumper of 5" duct, and pick up your bag ring / inlet ring, and make a smooth short connection between the impeller outlet and the ring inlet to get rid of that hose... Other than the top hat type, which I probably should have built that is the sort of arrangement I am aiming for... 

I have my DC system, actually my whole shop torn apart right now... This will be one of my reconstruction projects...


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## ChipperOfWood

dbhost said:


> I am not running in that manner, but a lot of folks do. You will need to make a replacement impeller housing intake port piece.
> 
> My rig is run with 5" ducting instead of 6, it works fine.


Hi Dave, New here and am in the process of doing about what you are. My question is will there be a problem with air leaking at the seams of the AVAC piping? I was thinking of running 4" PVC because of cost. 6" seems a bit too much for a HF dust collector.

C


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## ChipperOfWood

Impressive. I like what I see here. I am wondering about the wisdom of quarter turning the HF dust collector. I wonder the bearings might wear out fast. I was thinking of just running the DC with a Thein collector attached just ahead of the HF DC. Any one have any thoughts on that.


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## rrbrown

ChipperOfWood said:


> Hi Dave, New here and am in the process of doing about what you are. My question is will there be a problem with air leaking at the seams of the AVAC piping? I was thinking of running 4" PVC because of cost. 6" seems a bit too much for a HF dust collector.
> 
> C


the benefit of running larger pipe is increased volume which creates increased velocity when reduced back down. The HF collector has a lightly smaller impeller but supposedly a 1 /2 hp more motor than my Shop Fox. Mine came with the 6" inlet. I think if you could open that inlet up some it would probably support 6" line ok.



ChipperOfWood said:


> Impressive. I like what I see here. I am wondering about the wisdom of quarter turning the HF dust collector. I wonder the bearings might wear out fast. I was thinking of just running the DC with a Thein collector attached just ahead of the HF DC. Any one have any thoughts on that.


I out turning that blower would have any effect on the bearings.


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## SteveEl

How about raising it all up just a little bit.... fixing the thien to the wall.... setting the can on a movable shelf..... when its time to empty, let gravity be your friend and lower the shelf (with the can). This will eliminate both flex duct and slackness down stream of the thien, both of which will help reduce pressure loss.... but will it be enough to matter? Beats me. When I get that far, the idea of a lever-operated shelf to handle the can has some appeal just for ease of operation.


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## Shop Dad

SteveEl said:


> How about raising it all up just a little bit.... fixing the thien to the wall.... setting the can on a movable shelf..... when its time to empty, let gravity be your friend and lower the shelf (with the can). This will eliminate both flex duct and slackness down stream of the thien, both of which will help reduce pressure loss.... but will it be enough to matter? Beats me. When I get that far, the idea of a lever-operated shelf to handle the can has some appeal just for ease of operation.


That's exactly what I want to do.


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## ChipperOfWood

cburdick1 said:


> So in the past two weeks I've done the following:
> 
> - Switched the plan to 5" duct as the low ceiling in my basement shop would cause me to whack my head on 6" duct.
> - Built the Thein Baffle seperator that now sits on a steel trash can.
> 
> This is the bottom of the baffle. Dust/air enters at the upper left corner.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Gluing up the interior wall. I used 1/2" birch ply, relief cuts every 1". Much to my dismay the ply slid off my workbench and broke at one of the relief cuts, but I managed to use some bracing to piece it together.
> 
> 
> 
> 
> 
> 
> 
> 
> Here is the interior glued up and some steel sheeting added in to prevent the ply from getting worn down from all the particles smacking into it. I used 77 spray adhesive to laminate it, worked like a charm.
> 
> 
> 
> 
> 
> 
> 
> 
> The completed baffle.
> 
> 
> 
> 
> 
> 
> 
> 
> More to come in the next week.



I want to build one of these exactly like this. Is there any place that complete directions or videos can be seen? This looks like a great piece.


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## Upstate

ChipperOfWood said:


> I want to build one of these exactly like this. Is there any place that complete directions or videos can be seen? This looks like a great piece.


This should get you started http://webpages.charter.net/pjbolin...eparator - cyclone and thien baffle plans.pdf


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## ChipperOfWood

cburdick1 said:


> So in the past two weeks I've done the following:
> 
> - Switched the plan to 5" duct as the low ceiling in my basement shop would cause me to whack my head on 6" duct.
> - Built the Thein Baffle seperator that now sits on a steel trash can.
> 
> This is the bottom of the baffle. Dust/air enters at the upper left corner.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Gluing up the interior wall. I used 1/2" birch ply, relief cuts every 1". Much to my dismay the ply slid off my workbench and broke at one of the relief cuts, but I managed to use some bracing to piece it together.
> 
> 
> 
> 
> 
> 
> 
> 
> Here is the interior glued up and some steel sheeting added in to prevent the ply from getting worn down from all the particles smacking into it. I used 77 spray adhesive to laminate it, worked like a charm.
> 
> 
> 
> 
> 
> 
> 
> 
> The completed baffle.
> 
> 
> 
> 
> 
> 
> 
> 
> More to come in the next week.



I like your design and wonder if there are any actual plans or video on this set up.


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## ChipperOfWood

*Thein baffle*



cburdick1 said:


> So in the past two weeks I've done the following:
> 
> - Switched the plan to 5" duct as the low ceiling in my basement shop would cause me to whack my head on 6" duct.
> - Built the Thein Baffle seperator that now sits on a steel trash can.
> 
> This is the bottom of the baffle. Dust/air enters at the upper left corner.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Gluing up the interior wall. I used 1/2" birch ply, relief cuts every 1". Much to my dismay the ply slid off my workbench and broke at one of the relief cuts, but I managed to use some bracing to piece it together.
> 
> 
> 
> 
> 
> 
> 
> 
> Here is the interior glued up and some steel sheeting added in to prevent the ply from getting worn down from all the particles smacking into it. I used 77 spray adhesive to laminate it, worked like a charm.
> 
> 
> 
> 
> 
> 
> 
> 
> The completed baffle.
> 
> 
> 
> 
> 
> 
> 
> 
> More to come in the next week.



I like your design and wonder if there are any actual plans or video on this set up.


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## Fred Hargis

ChipperOfWood said:


> I like your design and wonder if there are any actual plans or video on this set up.


If you google "thein separator" you get a lot of choices, here is a link to his site.


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## ChipperOfWood

dbhost said:


> I am not running in that manner, but a lot of folks do. You will need to make a replacement impeller housing intake port piece.
> 
> My rig is run with 5" ducting instead of 6, it works fine.



I would like to run 5" also but I can't find the fittings. Where did you get yours? I have been asking around here but so far no one has replied.


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## Shop Dad

Penn state industries has the 5" fittings. However, if you keep all the paths 6" or greater at the DC end you should be able to run 6" in a garage sized shop. I had planned to go with 5" too but have reassessed and now plan to put the blower directly on the Thein baffle as above. This will reduce drag and support more airflow.


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## ChipperOfWood

Shop Dad said:


> Penn state industries has the 5" fittings. However, if you keep all the paths 6" or greater at the DC end you should be able to run 6" in a garage sized shop. I had planned to go with 5" too but have reassessed and now plan to put the blower directly on the Thein baffle as above. This will reduce drag and support more airflow.


Thanks. I have been reading posts on this subject and there seems to be a lot of resistance to anything small than 6". Probably comes from the posters years of experience. :yes:

I just wonder if my HF DC will have what it takes to use the 6". I guess my thing is I only want to do this once. :laughing: So I would like to do what is going to work better for me.


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## cburdick1

Regarding a few comments:

- I plan on lifting the plastic bag/filter support ring and mounting it on the wall so the blower feeds straight into it without flex hose.

- I entertained the idea of building a raising/lowering platform that the garbage can would ride on, but figured that 1' of flex hose isn't a big deal in my system, especially as it's not curved.

- Right now, the system works REALLY well. I have about a 20' run to my miter saw, through multiple (gradual) 90 degree turns and it sucks almost all the dust up. I could probably improve the amount captured by building a better shroud.

- After filling the can for the first time, I had less than a handful of dust in the plastic bag under the filter. Thein baffles WORK!

- 5" fittings are available from Oneida. They are EXPENSIVE though. 6" HVAC duct from Home Depot is the way to go, but I have low ceilings in my shop and couldn't fit 6" (without whacking my head all the time).


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## ChipperOfWood

cburdick1 said:


> Regarding a few comments:
> 
> - 5" fittings are available from Oneida. They are EXPENSIVE though. 6" HVAC duct from Home Depot is the way to go, but I have low ceilings in my shop and couldn't fit 6" (without whacking my head all the time).


Thanks for that reply. I have finally made the decision that I am going to go with 6" HVAC ducting. I checked Home Depot and they do have or can get the fittings I need. They were out of the 6x6x6 and 6x6x4 wye fittings. Going the check with Lowes today and /or Menards.


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## ChipperOfWood

cburdick1 said:


> Okay, here's the almost-done system:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> a


Did you do anything special to seal the seperater against the metal trash can. I am in the build process right now and am using a metal can too.


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## cburdick1

ChipperOfWood said:


> Did you do anything special to seal the seperater against the metal trash can. I am in the build process right now and am using a metal can too.


All I did was rout a 3/16 (I think) wide circular groove in the bottom of the baffle for the lip of the can to fit into. its snug enough that the empty can holds on to the baffle when I pick it up. Seems to work well enough.


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## ChipperOfWood

cburdick1 said:


> All I did was rout a 3/16 (I think) wide circular groove in the bottom of the baffle for the lip of the can to fit into. its snug enough that the empty can holds on to the baffle when I pick it up. Seems to work well enough.



Thanks. That's about what I did. I am not at the point of trying it out yet but I did wonder about the seal. My groove might be a tad more than 3/16 but it still seems to be snug. If it does leak I'll put some thin weather stip around the bottom of the groove.


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## ChipperOfWood

dbhost said:


> I am not running in that manner, but a lot of folks do. You will need to make a replacement impeller housing intake port piece.
> 
> My rig is run with 5" ducting instead of 6, it works fine.


Unfortunately I had my system just a little short of done when I started reading these message s. I have my system all in 4" PVC. Eventually I now want to convert that to 5" HVAC but that will be down the road.

My question now is where do you guys that run 5" get your fittings. 5" wyes etc. And how do you get back down to 4" where most power tool ports are?


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## troyd1976

i am presently using the 5" only for my main run lines, than dropping down to 4" and flex where i need to run a wye or a blast gate. my setup works well, but i really need to get into it and improve its efficiency factor..finding some 5" wyes that are reasonable in price, getting rid of those damned home-center adjustable elbows that leak like a sieve. i tried at the time to use two of them to elongate the curve, but i do hear air escaping through the adjustment ribs.
as far as making reductions to 4" the home centers have a reducer that goes from 5" down to 4"


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## Shop Dad

Penn State Industries has 5" ducting, flex and fittings. 
http://www.pennstateind.com/


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## ChipperOfWood

troyd1976 said:


> i am presently using the 5" only for my main run lines, than dropping down to 4" and flex where i need to run a wye or a blast gate. my setup works well, but i really need to get into it and improve its efficiency factor..finding some 5" wyes that are reasonable in price, getting rid of those damned home-center adjustable elbows that leak like a sieve. i tried at the time to use two of them to elongate the curve, but i do hear air escaping through the adjustment ribs.
> as far as making reductions to 4" the home centers have a reducer that goes from 5" down to 4"


That is pretty much what I had in mind too. Main line in 5". I used a couple of the adjustable elbows in 5" to mod my HF DC. I did tape all of the joints and seems. Seems to be working ok.


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## ChipperOfWood

Shop Dad said:


> Penn State Industries has 5" ducting, flex and fittings.
> http://www.pennstateind.com/


They are not inexpensive but might be worth it.


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## dbhost

On the 5" duct thing. The Split Lock Ducting itself is available at Home Depot, as are the 5" to 4" bell mouth reducers. For the wyes, and long radius elbows etc... take a look at







, they are reasonably priced for decent stuff. Just run your main, branch it off with a 5x5x4 wye, throw a 45 in there, and some straight pipe to your blast gate, and repeat as neccesary.

Mind you, ducting with metal is substantially costlier than ducting with thinwall PVC, which is why I went with just running 5" through my separator, THEN using the stock HF wye and branching to 2 4" circuits. MUCH less expensive, and it offers me great flexibility in my configuration.


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## mrkozmic

dgoodyear said:


> Does your HF DC have 4" port? Most DC manufacturers purposely make the ports smallers to air starve the DC. This prevents the DC from drawing too much amperage under load if the DC is ran without the ducts connected. To have effective fine dust collection with 6" duct you will need to move about 800-1000 CFM at the tool port. If you are afraid that you will burn up your motor. Get a clamp on ammeter, run the DC with a sizeable (8'-10') 6" duct connected to a modified inlet that supports 6" and measure the current. If its substantially more that the motor plate current, you risk burning up the motor. Keep in mind that once you system is in place the situation will not be the same as the test. ie More duct means more static pressure. More static pressure means less CFM and less amperage draw.


 
This is not correct!

It's true that the manufacturers makes the port smaller, but not to lower amperage. Acctually the opposite is true. A smaller port gives higher load, thus higher current. AC motors tend to run away at no/low load. The electric parts of the motor should handle this, but the machanical parts may overheat.

The higher the load the higher the current. A electric motor has a constant power output. Higher speed/lower torque. Higher torque/lower speed. When a motor is loaded it has to produce more torque to overcome the external force, thus the speed dicrease. It will also draw more current due to lower back-EMF. Imagine what happens when the motor stalls due to some external mechanical force, say a huge piece of wood stack in the impeller. According to your theory the current whould be 0. The opposite is true. If the motor wan't blow then the circuit breaker will. 

There is however a situation when lower speed will result in lower current (acctually lower current gives lower speed), that is at constant load and variable voltage. But that is not the case you are describing.

Take a toy motor and a ampmeter and play with it. Let it spinn free or under load. Remember that the voltage will drop at heavy load if run from a battery. That's the nature of batteries and has nothing to do with the motor. 
Thanks God we are not running our DCs and TSs from batteries 

So the conclution is: as long as the DC has some load to work with 6'' port or larger should be fine. Assuming that this is efficient from the impeller and aerodynamical point of view.


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