Thien Separator?

  • Advertise with us

« back to Power Tools, Hardware and Accessories forum

Forum topic by Joekwon80 posted 06-19-2012 01:25 PM 4154 views 0 times favorited 14 replies Add to Favorites Watch
View Joekwon80's profile


87 posts in 2498 days

06-19-2012 01:25 PM

Now, I understand what a Thien separator is supposed to do but when I watch the video he has on his site I don’t understand one thing. Shouldn’t the dust form a thien separator make it to the DC or shop vac in his case? I thought these separators just remove the big chunks so all that goes to the DC is the saw dust. Am I wrong?

-- Joe Kwon

14 replies so far

View Bill White's profile

Bill White

5148 posts in 4196 days

#1 posted 06-19-2012 01:28 PM

Ah, the mysterious world of aerodynamics…...
Only the very finest dust will get to the actual filter medium.


View Tenfingers58's profile


96 posts in 2913 days

#2 posted 06-19-2012 01:32 PM

As I understand it, the Thein Seperator (or any seperator/cyclone etc.) is there to catch as much dust/chips as possible to keep the filter in the vacuume or dust collector clean so the flow stays high.

You can’t flow air through a dirty filter.

View Ripthorn's profile


1459 posts in 3221 days

#3 posted 06-19-2012 01:39 PM

Separators typically create a cyclone, which have been used for several years in military applications as very low maintenance air filters because they are extremely effective with particles of all sizes. Very fine dust will still make it to the shop vac, but only a portion of it. I just whipped up a quick and dirty one and some stuff still makes it to the shop vac, but that is because there were a couple of things I did not do correctly (so I will make another one sometime).

-- Brian T. - Exact science is not an exact science

View Tennessee's profile


2893 posts in 2750 days

#4 posted 06-19-2012 01:44 PM

It would appear that what he has done is to make a cyclonic airstream inside the can. The 240’ of “drop zone” is where the wood can fall off before being sucked into the vacuum cleaner. The trick is to get a single circle of air the diameter of the can above the baffle, and keep the air noise fairly quiet below the baffle so the wood can fall.

I think the pile on the floor did not have many fines in it, so the vacuum cleaner looked clean when he finished picking it up. Note, though, he did have the blue HEPA filter on the vacuum that Rigid sells, so at some point, fines probably would not fall into the can, but get sucked up by the vacuum hose, which is mounted in the center of the can lid. If you have to keep a standard vacuum in the system, seems to me using the can is redundant save you get more capacity. And you could fill the can, because the wood chips and fines would then just go to the vacuum. And I don’t see how he could use it on multiple machines, since the CFM is fixed on the vacuum, and it will drop dramatically if you add a second hose to the input of the steel can.

-- Tsunami Guitars and Custom Woodworking, Cleveland, TN

View Joekwon80's profile


87 posts in 2498 days

#5 posted 06-19-2012 01:44 PM

I see! That makes a little more sense. I thought a separator did just that, separate chips and dust. I didn’t realize it was supposed to separate dust and fine dust as well.

This still leaves me one more question. If it picks up the fine dust and the fine dust is what clogs or makes it through the filter isn’t that just making the filter less effective? Or does the regular sized dust also clog the filters of DC as well?

I have a fluid dynamics buddy that I want to reference when designing one of these things is why I ask. I want to go to him with as much detail as I can.

-- Joe Kwon

View Joekwon80's profile


87 posts in 2498 days

#6 posted 06-19-2012 01:47 PM

^^I see what you mean. And I’m impressed that more of the sawdust didn’t make it’s way into the shopvac as well.

I’m thinking of adding one of these to my floor sweep intake rather than my TS intake. I want to save the impeller blades from imminent failure from nails and such that inevitably make their way into the DC!

-- Joe Kwon

View dbhost's profile


5767 posts in 3467 days

#7 posted 06-19-2012 02:09 PM

I have never run my DC hooked up to any dust generating equipment without a Thien separator / baffle since day 1. What I can tell you is that in the I guess 3 years now since I got the DC setup, I have had to empty the 55 gallon separator drum 4 times, I have a grand total of about 2 cups of fine wood flour in the lower bag on my DC, and the inside of my filter has a thin layer / dusting on it.

Something more abusive to a separator like a drum sander, which I am building one of, will give it much more of a workout. In my shop vac thien rig, I get less spectacular results, mostly due to air flow problems caused by too small dust ports on my hand held sanders.. But still, I get good separation there as well…

The point to a Thien, or a traditional cyclone is picking the air stream up in the middle of the separation chamber. Air comes in, swirls around the outside of the chamber, and slows down enough to drop its dust / debris load, air then makes its way to the center of the separation chamber where the air is slowest, and gets picked up and passed on to the DC. The Thien baffle has the baffle in place specifically to prevent that center air flow from picking material up from the collection vessel and passing it onto the DC, or “scrubbing”.

Does that help the Thien baffle make sense?

-- Please like and subscribe to my YouTube Channel

View Joekwon80's profile


87 posts in 2498 days

#8 posted 06-19-2012 02:13 PM

Definitely, all these posts are a tremendous help for helping me understand it all better.

Thanks all!

-- Joe Kwon

View crank49's profile


4032 posts in 3206 days

#9 posted 06-19-2012 03:07 PM

Actually, in a traditional cyclone the flow does not slow down as it spins around the vortex. It speeds up to the point that the dust particles, being heavier than air, are thrown out of the air stream. As the circle cets smaller in the cone it increases speed, like a figure skater spins faster when they pull their arms closer to their body, the center of rotation.

There are all kinds of separation being done with cyclones. It’s possible to even separate an air stream into hot and cold due to the difference in density of hot and cold air. Carried to the most extreme limits you can enrich uranium by going through thousands of ultra high efficiency cyclone stages.

Back to the real world, the more efficient a cyclone is at separating fine particles, the more energy it requires. The energy used is in the form of pressure drop. A fan/collector that has 10” of available static pressure and is connected to a thein or cyclone might only have 7” or 8” of pressure available.

View JollyGreen67's profile


1676 posts in 2998 days

#10 posted 06-21-2012 12:54 AM


I also had my doubts of the Thien separation thingee. Built one, and it works! Only thing that gets past the can is very fine dust. Revalation!

-- When I was a kid I wanted to be older . . . . . this CRAP is not what I expected ! RIP 09/08/2018

View jmos's profile


905 posts in 2605 days

#11 posted 06-21-2012 11:58 AM

There are a lot of ways to separate solids from gas streams. One of the simplest ways is to slow down the gas stream and let the heavier particles drop out (Stokes Law). The more you can slow the gas stream the more will drop out. This is really what your typical home built Thein is doing. That’s why the designs that use a box on top of the can work too (these have a right angle turn into the can and a right angle turn out of the can, they don’t even try to spin the gas.)

Other Thein designs will impart some spin on the gas, and this will help knock out particles as they are heavier and go crashing into the walls of the can instead of following the gas around. A separate cyclone, like the Dust Deputy, is doing its separation like Michael described above; cyclones can give better separation with less volume (don’t need a big can).

You can also look up the wok modification for a DC; it’s supposed to work pretty well and doesn’t require a separate can. This works by causing the gas stream to change direction, which makes a lot of the particles drop out.

Like Michael said, all these designs require energy in the form of pressure drop. If you don’t change anything else on your DC, you may notice a reduction in suction; I did on mine.

As far a dust on the filter, more dust piling up on the filter actually makes it filter better. The caked dust acts like additional filter medium, trapping more dust. The down side is that the flow through the filter gets lower and lower to the point suction will suffer. The pre-separator helps reduce the loading on the filter and extends periods between cleanings. If you’re making dust finer that can be knocked out with your separator, you’re filter will load up and you’ll have to stop more often to clean it.

-- John

View Milo's profile


869 posts in 3555 days

#12 posted 06-21-2012 12:53 PM

Joe, if you look at my projects you can see an original Thein system hooked up to a standard dust collector.


-- Beer, Beer, Thank God for Beer. It's my way of keeping my mind fresh and clear...

View lieutenantdan's profile


176 posts in 2541 days

#13 posted 06-21-2012 01:03 PM

Just set the dust switch on your table saw from fine to coarse.

-- "Of all the things I have lost in life, I miss my mind the most."

View Joekwon80's profile


87 posts in 2498 days

#14 posted 06-21-2012 02:40 PM

Wait what’s a dust switch? Can I just turn it off? ;)

This thread made me truly understand how these cyclone systems work! Not. Completely just more than I did previously and definitely enough to see its merits.

-- Joe Kwon

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics