Thien Separator Lid

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Forum topic by deadherring posted 02-14-2014 12:16 AM 2809 views 0 times favorited 14 replies Add to Favorites Watch
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77 posts in 1849 days

02-14-2014 12:16 AM

Hey all,

My 2HP Grizzly DC is coming tomorrow. I’m running 6” PVC ducting and am going to introduce a separator in the middle. All of the retailers (Woodcraft, etc) carry seperator lids with ports that accept 4” hose. The advice I’ve previously gotten here and elsewhere is that I will lose a lot of velocity if I reduce down from 6” to 4” at the seperator so as far as I can tell that means I have to make my own lid (does anyone know of anyone that carries a seperator lid with 6” I can buy?)

Everyone recommends making a Thien lid and I found a thread that has some textual plans:

but I’m still a bit of a beginner although I’ve had some success with some projects and am a bit intimidated by both the process described there and the fact that there are not visuals that accompany the process (I’m more of a visual learner). I imagine that you’ve got to have a tight seal on the lid for it to function well so I’m guessing there’s not much margin for error.

I’m looking for some suggestions for how to proceed. I don’t want to go the store bought 4” route and lose the benefit of the 6” PVC to begin with but I’m a little intimidated to try the Thien plans. Maybe someone has some really good step by step visual plans for the Thien or a simpler way to try a lid with 6” ports?

14 replies so far

View lew's profile


12446 posts in 3961 days

#1 posted 02-14-2014 12:22 AM

Foam tape on the inside of the lid will go a long way in creating a seal.

Check this video-

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View Kwit's profile


104 posts in 2165 days

#2 posted 02-14-2014 01:09 AM

just my opinion -

I have a 2hp Grizzly DC – and I run it with 4” hose all around; most of my tools have 4” ports on them anyway
I don’t think you will gain a whole lot from keeping everything at 6” (If you had an industrial strength 5hp DC then that would be a different story)

I added a Thein baffle to the inside support ring of my DC setup and replaced the upper bag with a Wynn nano filter; I’ve been really happy with my results so far.

Try to spend more time on your woodworking – it’s easy to get carried away with tweaking your tools and shop – but when it all comes down to it – you got into woodworking to build stuff – so build stuff!

-- don't talk about it - be about it

View changeoffocus's profile


467 posts in 1823 days

#3 posted 02-14-2014 01:43 AM

I can attest to Kwit’s sound advice, both sizing and focus, sooner or later I’ve got to get some projects posted. Being ready can only go so far, then you must execute. (This is self criticism based on his reminder)
My DC setup is very similar to Kwit’s.

View ynathans's profile


55 posts in 1923 days

#4 posted 02-14-2014 03:55 AM

Thanks for the advice. I think, therefore what you are saying, is not to worry too much about it and roll with the 4” separator and spend my time working in actual projects? :-)

View deadherring's profile


77 posts in 1849 days

#5 posted 02-14-2014 06:19 PM

I might have stumbled across a solution. Check out 8:45 in this video:

He makes a thien seperator but uses the trash can lid itself as the cover. That seems a lot more doable than the instructions in the post above.

View b2rtch's profile


4868 posts in 3254 days

#6 posted 02-14-2014 06:50 PM

You do not want 6” withe kind of Dc you have.
You need to find a balance between flow-rate and velocity to get a good dust/chip pick up.
If your velocity is too low then the chips and dust will deposit in you pipes/flex-hoses.
The larger the hose the lower the velocity.
You need to keep the velocity as high as possible but too small a hose/pipe will starve the DC and create cavitation.
You better stay with what the DC came with = 4”.

-- Bert

View changeoffocus's profile


467 posts in 1823 days

#7 posted 02-14-2014 08:09 PM

Amen, to b2rtch he is right on target.

View Ocelot's profile


2115 posts in 2844 days

#8 posted 02-14-2014 08:18 PM

In my shop, the highest chip volume comes from the planer. My 20” planer has a 5” outlet. A very experienced man told me that I should go up to 6” instead of down to 4”. I’ve been running the planer fine with 4” hose and a 5 to 4 reducer at the planer. I think a spriral planer (which I have) produces smaller chips than a straight blade, so my friend might be right that you need 6” if you have a large straight-blade planer.

The velocity argument makes sense to me too.


View mds2's profile


310 posts in 2150 days

#9 posted 02-14-2014 08:58 PM

The HF dust collector has a 6” port that immediately Y’s into two 4” ports right?

If so I’d ditch the 4” Y and run 6” for as long as possible. Especially though the thein separator.

View deadherring's profile


77 posts in 1849 days

#10 posted 02-14-2014 09:12 PM

@MDS2: Correct. That is my plan (although it seems like there are those that disagree above).

View bbc557ci's profile


595 posts in 2280 days

#11 posted 02-14-2014 10:11 PM

What Bert said. I said/typed something similar in another thread about DC and there was no comment/s before or after regarding velocity vs volume. 5 or 6 inch pipe will increase volume, but will likely decrease velocity. Gotta be a balance there. FWIW I have the 2 hp (alleged) HF DC and with a cyclone and 4 inch to the machines, and it seems to work well.

You could easily forget the math, and just try it with a 5 0r 6 inch hose and then a 4 inch, and see which works best. And of course report back here so your brother LJ’s will have fewer questions and more info !! :o)

mds2 think my HF 2 hp DC has a 5 inch port. Maybe do the newer versions have 6 inch? I don’t know…..

-- Bill, central where near the "big apple"

View b2rtch's profile


4868 posts in 3254 days

#12 posted 02-14-2014 10:52 PM

The HF dust collector has a 6” port that immediately Y’s into two 4” ports right?
The large port is 5” not 6”.

-- Bert

View brtech's profile


1052 posts in 3128 days

#13 posted 02-14-2014 11:05 PM

There are two ways to use the Thien baffle with the HF DC. You can put the baffle in the ring, or you can put the baffle in an outboard container that sits on top of a barrel of some sort. The in-the-ring version is much simpler, although you have to deal with the odd angles the supports that hold the baffle need when they meet with the ring.
It also forces the chips through the impeller, which the outboard version doesn’t.

Although the inlet and housing of an off-board solution can provide a somewhat better airodynamics situation than the baffle in the ring, the losses through the connection to the DC more than make up for that, so the in-ring solution probably provides more suction. This is almost certainly true if you use several feet of flex hose between the off board separator and the DC.

You did not mention a filter upgrade. All the Thein baffle does is improve separation of chips and dust from the airstream. Less goes up to the filter. The stock filter bag is 5 micron and its no where near good enough for your health. You really want .5 micron filtering. The recommended solution is the Wynn Engineering canister filter which is more efficient than the bag, and thus GAINs suction as well as improves air quality.

As several LJs note, the inlet before the Y on the HF DC is 5”, not 6”. 5” ducting is hard to come by and/or expensive. I agree with b2rtch that you are better off with 4” duct on an HF DC than 6”. It’s not even clear that you can get enough velocity if you did try a 5” main.

Remember to not use ANY 90 degree elbows or Ts. Use only 45s with a straight section between them, and use Ys (or wide sweep 90s if you can find and afford them). Minimize use of flex. Seal joints tight.

But it’s the most bang you can get for your buck in DCs. Well done.

View b2rtch's profile


4868 posts in 3254 days

#14 posted 02-14-2014 11:34 PM

This is how I modified mine, I sold it.
I had Thein baffle in the trashcan.
I bought a CLlear View

-- Bert

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