Thien Type Pre-separator

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Project by Vincent Nocito posted 06-29-2011 07:37 PM 6242 views 31 times favorited 12 comments Add to Favorites Watch

Like many others, I found myself constantly cleaning my dust collector because the cartridge was plugged with sawdust and chips.

I purchased a cyclone separator lid (photo 2) at a woodworking show and placed it on a 30 gallon metal trash can. While it did reduce the amount of debris getting to the dust collector, it was far from optimum. If the can was more than about 25% full, the turbulence would scrub the can and carry more material and fines to the collector.

The first improvement that I made was to add a pair of 90 degree elbows (photo 3). The inlet side elbow was angled toward the wall of the trash can and the outlet side elbow was oriented so that it was near the center of the lid. The thought was that the inlet would create a swirling effect and allow the dust and chips to settle. The outlet was in the center in a region of minimum turbulence. I saw an immediate improvement but there was still too much material getting to the collector. The loss to the dc became very pronounced if the can was more than half full.

The next stage was to add a Thien baffle. The height of the elbows was 6.25 inches so I measured the diameter of the trash can 6.25” below the lip. That dimension turned out to be 19.5”. The next step was to cut the circular baffle (photo 4). I used a circle cutting jig and a router to get the circle from 3/4” plywood. The next step was to cut the inner surface across 240 degrees of the disk. Photo 5 shows the cut out collector disk. The disk is reduced by 1.25” across 2/3 of the lid. The disk was then mounted to the collector lid using 1” hardwood dowels and 2.5” screws (photo 6).

I reconnected the hoses and ran through a large pile of sawdust and chips. Over 99% of the material ended up in the can and only a small amounts was in the dc bag. Overall impression is if you either don’t have the space or the budget for a cyclone separator this is a viable solution. Total time invested was about 2.5 hours and about $40 for the lid, trash can and elbows. The plywood and dowels were leftovers from prior projects.

12 comments so far

View Darell's profile


436 posts in 4106 days

#1 posted 06-29-2011 08:27 PM

Never thought about adding the Thien baffle to my current plastic seperator lid. Sweet. Great idea!

-- Darell, Norman, Ok.

View TheDane's profile


5690 posts in 4175 days

#2 posted 06-29-2011 08:57 PM

Good idea, Vincent! I was never satisfied with the lid I bought from Rockler, which led to the purchase of my Oneida. Wish I would have thought of this!


-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View Dusty56's profile


11852 posts in 4200 days

#3 posted 06-29-2011 09:32 PM

I’m going to try adding this to mine as well . Thank you : )

-- I'm absolutely positive that I couldn't be more uncertain!

View dustysawyer's profile


112 posts in 3141 days

#4 posted 06-29-2011 10:04 PM

Ingenuity at it’s finest! You must be from the South. I bought a HF collector and was going down the same path. You just saved me a step. Thanks

View scarpenter002's profile


617 posts in 4417 days

#5 posted 06-29-2011 11:29 PM

Nice writeup and instructions. Thanks for the inspiration. How full can the get now before dust is sucked into your DC?

-- Scott in Texas

View Vincent Nocito's profile

Vincent Nocito

485 posts in 3876 days

#6 posted 06-30-2011 12:29 AM

I filled the can until it was about 3 inches below the baffle. The amount of dust in the DC bag was about a handful. The DC cartridge looked clean. There was no apparent reduction in suction as the can filled.

View WilsonCreations's profile


105 posts in 3043 days

#7 posted 06-30-2011 12:33 AM

I use the Thien baffle in a 35 gallon metal can with just the original top, the inlet is as close to horizontal as I could get it and the outlet is straight up from the center. Originally I tried a small gap between the top and the baffle, it was better than nothing but not great. Then I changed the space equal to the diameter of my inlet hose, 4 inches inlet and 6 inch outlet, and the improvment is incredible. I just started using it about a month ago, this week I can hear movement while it’s running. It’s about a third full and I still see only very fine dust in the DC bag.

-- Wilson

View phil619's profile


35 posts in 3963 days

#8 posted 06-30-2011 01:37 AM

I’ve been using the Thien baffle plate for some time now and works fantastic.

-- Building fine furniture in my driveway.

View bigike's profile


4057 posts in 3801 days

#9 posted 06-30-2011 01:53 AM

Nice I was thinking of doin the samething thanks for the help. Now to get the parts!

-- Ike, Big Daddies Woodshop, http://[email protected]

View TopamaxSurvivor's profile


18672 posts in 4188 days

#10 posted 06-30-2011 06:44 AM

Good one!! looks like one of the easiest, simplest ones yet ;-)

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View David Grimes's profile

David Grimes

2078 posts in 3152 days

#11 posted 06-30-2011 06:50 AM

Very similar to mine. I hope yours works as well.

-- If you're going to stir the pot, think BIG spoon or SMALL boat paddle. David Grimes, Georgia

View ScotttheSurveyor's profile


31 posts in 2863 days

#12 posted 01-03-2012 01:23 PM

What about the tiny micron size. Does the shopvac catch this? Or am I way off base/

-- Angular error is proportionate to the distance run

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