Two dust collectors in-line for added velocity?

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Forum topic by MikeMcK posted 01-17-2013 04:49 AM 4286 views 0 times favorited 30 replies Add to Favorites Watch
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21 posts in 1967 days

01-17-2013 04:49 AM

Topic tags/keywords: dust collection table saw 2 stage

Would (2) dust collectors on the same main line (one feeding the other) increase velocity? I have an existing 1200cfm 220v Reliant from Woodworkers Warehouse. My contractors table saw is at the end of a 25’ 4” run. I’ve closed up the back and bottom of the saw to help with creating more suction but my existing dust collector with a 2-stage infront of the motor doesn’t seem to have enough velocity to pull chips & dust from the blade. I still get an awful lot of dust when cutting.

I saw a coupon in Wood Magazine this month for a Harbor Freight 2HP collector for $149. I’m considering installing it the end of line near the table saw to add velocity to the line. I just wonder if that will introduce too much turbulence and mess up the 2-stage infront of the original collector. Any advice or comments would be appreciated.

30 replies so far

View DIYaholic's profile


19620 posts in 2674 days

#1 posted 01-17-2013 04:57 AM

Stumpy Nubs of Blue Collar Wood Working is doing a blog on this very topic.

-- Randy-- I may not be good...but I am slow! If good things come to those who wait.... Why is procrastination a bad thing?

View GT350's profile


368 posts in 1981 days

#2 posted 01-17-2013 05:10 AM

I think I would check your filter. I have a 1.5 hp cyclone that I built that is pulling through 15 or 18’ of 4” line that goes across the ceiling and drops down to the table saw without any problems.

View MikeMcK's profile


21 posts in 1967 days

#3 posted 01-17-2013 05:34 AM

@GT350 the filter is one of those Micron bags. The single line is schedule 40 PVC with 3 Rockler dust ports and all fittings glued. I’ve checked closely and don’t find any leaks.

View GT350's profile


368 posts in 1981 days

#4 posted 01-17-2013 05:43 AM

I’m guessing you already checked to make sure nothing is clogged and the fan is ok? My joints aren’t glued but your runs are a bit longer. Could the inside of the bag be completely coated?

View Fred Hargis's profile

Fred Hargis

4986 posts in 2493 days

#5 posted 01-17-2013 12:16 PM

With 4” ductwork, you will only move maybe 400 CFM, and that won’t change with more power. My guess is you need to upsize the ducting.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Cosmicsniper's profile


2202 posts in 3158 days

#6 posted 01-17-2013 02:01 PM

You need 5” ducting, though at 1200 cfm (actual, not advertised) and 25’ you might not have the power to do 5” ducting.

-- jay,

View Cosmicsniper's profile


2202 posts in 3158 days

#7 posted 01-17-2013 02:10 PM

BTW, as you make the duct bigger, you gain the ability to pull in smaller dust farther away from end of the duct, but you will be trading off velocity in the pipe…you lose the ability to pull in bigger chips and run the risk of clogging the duct. It’s a trade off and you need to find the happy medium for your given DC and shop situation.

-- jay,

View Cole Tallerman's profile

Cole Tallerman

392 posts in 2184 days

#8 posted 01-17-2013 04:34 PM

Try upgrading to a wynn filter. I did that and added a baffle (Chinese wok) inside the dust collector and suction greatly increased. Also, it is very hard to fully capture all the dust from a table saw.

wynn filter:

Wok idea:

View crashn's profile


528 posts in 2465 days

#9 posted 01-17-2013 06:33 PM

I have often thought of adding another blower downstream from the main impeller.

This is a bit different from the current stumpy design, as his blowers are back-to-back.

My idea was to add another HF unit to the end of a very long run. That way the debri is pushed by the first impeller into the ducting and sucked out at the end by the main dc impeller.

Did not test this before I sold my HF unit.

I think for the price the HF will add some much needed CFM at the end of your very long run. You could change the TS port to 5”, run the 5” to the first HF unit, then maybe even 4” all the way back to your original DC unit.

-- Crashn - the only thing I make more of than sawdust is mistakes

View Ironwing_1's profile


11 posts in 1954 days

#10 posted 01-18-2013 03:26 AM

I haven’t tried this personally, but I don’t think it will be very effective and here’s why:
Ideally, you have two DC’s pulling air at exactly the same rate/velocity; in this case, the power of the two DC’s will help each other and effectively double your suction power, but not your velocity. Since they’re basically pulling the same volume of air at the same speed, each only has to work half as hard. Now if you reduce the diameter of your duct, you would then see an increase in velocity.
In theory. Now for the but:
But in execution, if you have two inline DC’s like this, the blowers will almost certainly be operating at different speeds (even identical DCs may have minor variations in motor speed), and you are going to have a power loss as the faster motor will be spending part of its power trying to speed up the slower one, which won’t work well since the motor has a specific speed it wants to run at and doesn’t want to turn any faster or slower than that. If you were really invested in this idea, you could start messing around with motor speeds and ducting diameter to get them power-matched.
Or, you could hook them up side-by-side instead. This way each motor can run optimally at its own preferred speed and you get the full power amplification of both motors running simultaneously. Your velocity will also go up, since when you duct the two DC’s together you’re effectively reducing the hydraulic diameter of your ducts by half. The downside is that you’d have to have two separate filter apparatus, although you could get by with only one cyclone separator.

View MikeMcK's profile


21 posts in 1967 days

#11 posted 01-18-2013 03:44 AM

Thanks for all the comments. I’m going to install a wok in the DC this weekend and wash the filter bags as was recommended. I’ve had the unit 12+ yrs and have only shaken the filter bag. I considered a 5” mainline but opted for a 4” because the Rockler Dust Right┬« 4’’ Dust Separators are 4” fittings. Hopefully after I wash the bag I’ll see an improvement.

View Cole Tallerman's profile

Cole Tallerman

392 posts in 2184 days

#12 posted 01-18-2013 04:09 AM

I see a big problem!! Check out your first picture, that is way to sharp of a turn! That could easily be taking 200 CFM out of your system right at the blower!

View MikeMcK's profile


21 posts in 1967 days

#13 posted 01-18-2013 04:37 AM

Cole, do mean from the DC to 2-stage? I was thinking about mounting the DC directly above the 2-stage so it would be directly inline.

View sprucegum's profile


324 posts in 1997 days

#14 posted 01-18-2013 12:44 PM

I had the same problem with my table saw. I had a old 1hp foley belsaw dust collector on hand that I bought used years ago for my planer but it was totally useless for that purpose. I just hooked it directly to the table saw with the discharge hooked to the line from my jet dust collector. It works great, but it seems like the old Belsaw blower is doing most of the work. my next step will be to buy a bag for it and wire it to come on when the saw is turned on. I will then become a dedicated collector for the table saw.

-- A tube of calk and a gallon of paint will make a carpenter what he ain't

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Paul Stoops

348 posts in 2560 days

#15 posted 01-18-2013 04:56 PM

As has been mentioned, try to eliminate any sharp 90┬║ bends. Also, it is a good idea to minimize the amount of flex hose in your system. Flex hose has about 3 times the air resistance of smooth walled duct for the same diameter.

-- Paul, Auburn, WA

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