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Thien Baffle Drop Slot getting plugged

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Forum topic by tengallonhat posted 345 days ago 1834 views 1 time favorited 21 replies Add to Favorites Watch
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tengallonhat

79 posts in 388 days


345 days ago

Topic tags/keywords: question

I recently finished a build of a thien separator. My table saw, jointer and planer all end up plugging my new separator’s drop slot. You can hear the whole system sort of bog down and then the shavings end up getting sucked through into the bag. Is this normal? Do I need to make the drop slot bigger?

Here you can see the width of the slot.

And the configuration of the 90 degree elbow.


21 replies so far

View rum's profile

rum

148 posts in 1218 days


#1 posted 345 days ago

Pretty unusual for the table saw to plug it. I did have some problems with my Jointer/planer plugging it up badly until I did some mods.

First make sure everything is as smooth as possible. Any rough spots are places where things will catch. Since you used MDF I might coat the edge with water putty and then sand back (but before you do read on).

Second I think your baffle is kinda thick. Thinner yields better separation and less places for things to get hung up. I started with 3/4” plywood and tried to be clever by beveling the edge – that worked better than just 3/4” plywood but not nearly as well as when I took it down to ~1/4” and also beveled the edge.

I’m also suspicious as to whether things might be getting hung up on the intake but I’m not familiar enough with that design to comment meaningfully.

Phil and crew also frequent his discussion board over at http://www.jpthien.com/smf/ – there are a lot of builds and information in the archives there worth looking and you can get some helpful data from folks who’ve spent an inordinate amount of time on this.

View HorizontalMike's profile

HorizontalMike

6925 posts in 1546 days


#2 posted 345 days ago

IMO, here are my thoughts:

  • Baffle supports are too thick. Too much air drag that can be minimized
  • The elbow diameter is too big/wide for the diameter of the can. And that means that you are minimizing the relative dead air space in the center column of air.
  • The center (exit) port fails to stick down into the can. This helps force the dust laden’d air to rotate more, losing speed and ability to carry the dust. Dust drops and flow to outside perimeter. Without this exit tube protruding into the can, the air will just shortcut directly between the in/out. I put the end of the exit tube half way to the baffle.
  • UPDATE Notice that there is a maybe 2in gap from the bottom of the elbow and the baffle. You need this in order to keep the rotation going. Your very large elbow is currently blocking 80-90% of this area and that stops any rotation from forming.

Here is my thien project on his website:
http://www.jpthien.com/smf/index.php?topic=339.msg1839#msg1839

-- HorizontalMike -- "Woodpeckers understand..."

View johnstoneb's profile

johnstoneb

656 posts in 805 days


#3 posted 345 days ago

It looks like your inlet elbow needs turned 180 degrees.

-- Bruce, Boise, ID

View HorizontalMike's profile

HorizontalMike

6925 posts in 1546 days


#4 posted 345 days ago

Sorry Bruce, but tengallonhat’s elbow IS oriented correctly in relation to the baffle.

-- HorizontalMike -- "Woodpeckers understand..."

View jonah's profile

jonah

452 posts in 1931 days


#5 posted 345 days ago

Are those supports square? It’s hard to tell from the picture.

View johnstoneb's profile

johnstoneb

656 posts in 805 days


#6 posted 345 days ago

His inlet elbow is pointed just opposite to yours and mine. I don’t know if that makes a difference or not. My exit port does not protrude into the lid at all and my 4”inlet elbow comes down tight against the baffle.. I used 1/2” plywood for my baffle. I am getting nothing into my dust collector bag. It a jet 1100 with 4” pvc for the main and 4”flex drops to the planer, jointer, and table saw.

What size dust colletor are you using? Maybe there is not enough velocity on the airflow.

-- Bruce, Boise, ID

View HorizontalMike's profile

HorizontalMike

6925 posts in 1546 days


#7 posted 345 days ago

The overall rotation does not really matter. Mine started out the other way and ended up at 180 original because after cutting down and trimming my elbow for least wind resistance it fit be that way.

FWIW, I suspect that the larger inlet elbow may be the problem. The inner wall of that elbow is as far in as the outlet tube wall. IMO, it is taking up too much cross-sectional real estate and preventing any circular flow, making it just too easy to skip the can and just from tube to tube directly.

-- HorizontalMike -- "Woodpeckers understand..."

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tengallonhat

79 posts in 388 days


#8 posted 345 days ago

Thanks everyone. I have a 2hp harbor freight dust collector and a Wynn 35a dust cartridge. The supports are 3/4 oak round dowels. I will have to start making some of the suggested tweaks and see what works. I want to stick with the 5” elbow and outlet if possible. Extending the outlet into the can should be easy enough. And using thinner longer supports would increase the gap and make more airspace.

View rum's profile

rum

148 posts in 1218 days


#9 posted 344 days ago

Good call on the inlet Mike – I’d bet a donut that that is a large part of the problem as I look closer.

I didn’t even notice the exit port not protruding – that would definitely break the system as well.

You might be able to deform the inlet a bit to give you some space under it but that will reduce the cross section and thus airflow. Better might be to add another inch or two to the supports..

I agree that 5” is about optimal for the HF unit.

View HorizontalMike's profile

HorizontalMike

6925 posts in 1546 days


#10 posted 344 days ago

If you are going to stick with the 5in elbow and outlet, then I would definitely lower the baffle, aka lengthen the support rods, as Rum suggests. I suggest ADDING at least 2-1/2 to 3in. I think you need a longer than normal adjustment because of larger cross-sectional area of the 5in tubing inside of the lid.

Also the outlet extension, in your case, should extend to at least bottom of the elbow.

Just my 2-cents…

-- HorizontalMike -- "Woodpeckers understand..."

View jonah's profile

jonah

452 posts in 1931 days


#11 posted 344 days ago

I think Mike is onto it there. The baffle seems very small and cramped. You need space there, especially with a 5” inlet there. I would split the difference with the outlet. You don’t necessarily want it that low, but yours is definitely too short.

Any particular reason you’re using a 5” inlet?

View HorizontalMike's profile

HorizontalMike

6925 posts in 1546 days


#12 posted 344 days ago

Rum: ”...I agree that 5” is about optimal for the HF unit….”

The more I thought about this, the more I started to conditionally agree with you. However, I think the 5in is best suited for the Top-Hat Design that has the in-port on the side of the Thien system and NOT protruding into the centrifuge portion of the system.

On the other side of the coin, the Lid Design does NOT really have the room for anything over the 4in tubing when used on a 20 or 31gal can without blocking a large portion of air column.

@tengallonhat, you have not mentioned the size of can you are using. The size of the can(diameter) is a limiting factor on what size of tubing you can/should use for your Thien LID Separator. Larger tubing means lower flow speed and means less centrifugal force inside the can. Something to consider.

FWI, Inside Diameters:
  • Behrens 20gal = 17.4in wide = 76.56 sq.in. area
  • Behrens 31gal = 20.5in wide = 105 sq.in. area
  • SteelDrum 55gal = 22.5in wide = 126.56 sq.in.

Bottom line is that a Top Hat Design would eliminate this blockage of air flow. If that is not possible, then limiting the size of your tubing is better/best.

-- HorizontalMike -- "Woodpeckers understand..."

View tengallonhat's profile

tengallonhat

79 posts in 388 days


#13 posted 344 days ago

Thanks everyone for the advice. I have a Behrens 31 gallon can. It seems like there are some good incremental optimizations I can make here. My goal is to eventually build a top hat, but until then I am thinking I can definitely make some good low-cost improvements and see what happens.
I’m going to
1) Extend the outlet into the can. I read on the Thien forum to have it sit 1/2 the diameter from the baffle so I will set it to be 2.5” from the baffle.
2) Then I will replace the supports with something much narrower and lengthen them to provide some room under the inlet elbow (and be about 2.5” from the outlet).

I appreciate all the help. It sounds like the smalll-ish can size is going to be the limiting factor beyond these optimizations. I’ll see how it works before jumping the shark and building a whole new setup (top hat next).

View rum's profile

rum

148 posts in 1218 days


#14 posted 344 days ago

HorizontalMike: Yeah I went straight to a top hat. for various reasons (primarily space as I flipped the impeller on its side on top of the top hat so it doesn’t take any more room than the original cart – plenty of others have done the same so I can’t claim any stroke of genius – but it was an idea worth borrowing). The 5” definitely gave me better airflow with the HF unit and I can pickup the chips from some of my larger machines where it was struggling/failing at 4”. I tried 6” but while there was more “flow” it was leaving stuff in the hose cause the air wasn’t moving fast enough.

One other option here might be to make a “half hat” and move the inlet into the side of the can. The main challenge there would be structural integrity as the can isn’t exactly going to like having a big hole cut into the side of it :D

View HorizontalMike's profile

HorizontalMike

6925 posts in 1546 days


#15 posted 344 days ago

If my Lid separator didn’t work so well over the last +3yr, I would have gone ahead and built a top hat. I still need to flip my DC motor on it’s side and make those adjustments/improvements, but my HF just keeps plugging along.

BTW, I just move the hose machine to machine. Nearly all of my machines can be fed by one 10ft section. Only my planer and horizontal mortising machine need 20ft, though on occasion I have managed to use just the 10ft’r on the mortiser.

-- HorizontalMike -- "Woodpeckers understand..."

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