Dust Collection AKA pain in the ass

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Blog entry by Manitario posted 11-12-2010 03:09 AM 9091 reads 1 time favorited 9 comments Add to Favorites Watch

So, in my continual quest to squeeze every inch of space out of my shop I moved my DC to a far corner. Rather than have 15ft runs of 4inch flex duct, I thought I’d upgrade and have a short run of 6 inch metal duct and then take off 4 inch flex duct for each machine. In theory, this sounded perfect. I’ve heard a lot about the advantages to using larger ducting to keep from choking the CFM of the DC, so I hooked it all up and prepared to bask in the mighty suction power…. What I got though was a major pain in the ass. Strangely, the suction seemed less at the end of the run, and the DC was not able to keep up with the output of shavings from my jointer, which didn’t make sense as the DC is 1.5HP rated at 1100CFM. The highlight (or lowlight) was the suction dropping to zero, and me finding a huge section of the 6 inch pipe plugged with shavings. Something was clearly wrong with my setup…
The pics are of the setup…The ducting is 26g HVAC with 4” stepdowns.

So, with trepidation, I waded into the treasure trove of information on Bill Pentz’s website. To my surprise, a lot of the information was simple and not as highly technical as I expected. Very quickly I realized several things: a)stepping down from 6 inch to 4 inch ducting is a bad idea. The drop in air velocity going from 4 inch to 6 inch is not enough to keep the shavings moving up the pipe into the DC. A much better way of designing my “system” would have been to limit the drop to 1 inch ie. 6 to 5 inch. b)Bill makes a big deal of calculating feet/minute which is CFM/duct size. A certain FPM is needed to keep my shavings moving. Basically, regardless of the rated 1100CFM that my DC boasts of, the actual CFM at the end of my runs is around 550. Therefore, by going up to 6 inch duct, despite the gain in CFM I got, the increased duct diameter decreased my FPM below the needed velocity to keep my shavings moving, thus allowing the blockages. c)A chip separater would keep me from having to empty my bag as often, but would drastically increase the total resistance of my DC system, which has a major impact on CFM. Couple of other silly things I did, like use a T connector instead of a wye, not having a straight run into the DC, etc. To make a long story short, once again, I’m spending my evening fiddling with my DC rather than woodworking. I’m tempted to tear it all apart and go down to 5” ducting as Bill suggests, ideally running 5” right to my machines. Unfortunately, this means buying new 5” metal ducting, and ordering 5” flex hose (no-one in town carries over 4”). Anyways, this is a massive pain in the ass. Any advice from the LJ’s community would be greatly appreciated! If it wasn’t so cold out, I’d drag my machines onto my lawn, and let the chips fall where they may…

-- Sometimes the creative process requires foul language. -- Charles Neil

9 comments so far

View DrAllred's profile


137 posts in 4067 days

#1 posted 11-12-2010 04:34 AM

I would also look at the filter on the DC. From the pictures I see that you have a canister filter, similar to the one I have on my Jet DC-1100. I found that the fine dust particles were clogging up my filter and the CFM would drop in the lines causing chips and other items to clog the lines.

Here is what I did and it improved everything on the DC. Less dust and chips in the filter. Dust Issues. I have 6” line going into the DC as it has a 6” connector, about 2/3 of the way down the shop I go to 4” pipe and at this point it only services the table saw, band saw, and miter saw. The 6” services the planner, drill press and all the sanders I have.

Good Luck.

-- David, Mesa Arizona

View BigTiny's profile


1721 posts in 4132 days

#2 posted 11-12-2010 06:56 AM

Just in case you haven’t done this already, I’d suggest two things.

1- Make sure all your joints are tight and duct taped. You’d be surprised how much loss a loose joint will give.

2- Make sure the “valves” at each machine close tightly. Just one left part way open will slaughter your FPM levels.

-- The nicer the nice, the higher the price!

View Manitario's profile


2818 posts in 4127 days

#3 posted 11-12-2010 07:19 AM

Thanks guys for the suggestions.
David; I’d seen the idea for a Thein separator in the DC before, but forgot about it, thanks for reminding me of the mod. The inside of my DC ring certainly looks a lot like yours did pre-Thein, I’ll have to try adding that.
BigTiny; funny you mention the “valves”, I was puttering around with them after I posted this blog, and noticed that indeed, one of them doesn’t close fully. I guess that’s what I get for buying $4 plastic gates.

-- Sometimes the creative process requires foul language. -- Charles Neil

View Bob #2's profile

Bob #2

3810 posts in 5265 days

#4 posted 11-12-2010 08:00 AM

I notice that one of your gates near the blower is pointed down to the floor. That’s probably not the best situation as debris will fall in there and create a problem. The other thing that concerns me is that you used an HVAC Wye to get 2 outlets in your main. I think you may be better off buying some saddle type take offs and mount them 45 degrees. as shown here:

They are available as most plumbing supply houses.
p.s. yours is mounted against the flow of air to your DC.
Also check for leaks – they are killer.
You want to keep your shut off gates as close to the main line as possible to prevent dead air space and turbulence in the pie too.

-- A mind, like a home, is furnished by its owner

View Sarit's profile


552 posts in 4384 days

#5 posted 11-12-2010 08:00 AM

Why is your metal “wye” (no pun intended) pointed in the wrong direction?

View Dez's profile


1176 posts in 5321 days

#6 posted 11-12-2010 08:23 AM

Those plastic blast gates are not self cleaning and tend to build up stuff in the corners where it gets packed in tight every time you close the gate.
I “fixed” the problem by making a small “cut out in the corners so that the crud gets pushed out letting the gate close all the way.

-- Folly ever comes cloaked in opportunity!

View Manitario's profile


2818 posts in 4127 days

#7 posted 11-14-2010 07:13 AM

So I tore out the old line and tried as much as I could to simplify the layout, changing the “T” takeoff to a wye and re-arranging the shop layout so that the flex duct is short and relatively straight. Immediately I’ve notice a huge improvement in suction, as well, no chip clogging when using the jointer. I’ll keep my fingers crossed!

-- Sometimes the creative process requires foul language. -- Charles Neil

View mikeberry's profile


59 posts in 4331 days

#8 posted 12-15-2010 11:31 PM

you might try 4 inch pvc pipe & get a filter for the top

-- It's hard to plane a door when you have to use the crack of your ass for a vise

View Bob #2's profile

Bob #2

3810 posts in 5265 days

#9 posted 12-16-2010 01:35 AM

Much better now. It will do the job for you.
The next thing to think abot is a pre separater at or near where you have that 45° elbow in the line to drop your shavings before they hit your filter and bag.
I just saw another impellor clobbered by a piece of wood that escaped into the suction and lodged in the fan cage.
You don’t need that plus your filter will stay almost clean if you put one on.

-- A mind, like a home, is furnished by its owner

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