6" Top hat thien baffle

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Forum topic by UpstateNYdude posted 10-09-2013 03:17 AM 9367 views 3 times favorited 13 replies Add to Favorites Watch
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671 posts in 1404 days

10-09-2013 03:17 AM

So me and a friend from work have been talking about building a top hat thien for awhile to try it out.

Now for clarity I have 2hp Grizz DC and I am using 6” pipe everywhere up until the machine 4” ports, now we just went off the typical design of what everyone else has done using 4” pipe for the inlet and return.

The problem is it’s not separating well I’d say maybe 70% of the chips make it into the barrel the other 30-40% are in the bag I’ve tried adjusting the height of the return pipe up and down with minimal effect. I will get some pics up in a few minutes but off the top of your heads is there something we did wrong?

Does the top hat have to be taller for 6” pipe or a wider slot, does beginning of the slot need to start back farther…I’m at a loss.

Anyone with some knowledge on the subject please feel free to shed light on this for me.

-- Nick, "Choking to death on bacon is like getting murdered by your lover." - JG

13 replies so far

View HorizontalMike's profile


7064 posts in 2335 days

#1 posted 10-09-2013 03:31 AM

I personally believe that a 6in pipe in a 31gal can is too big and won’t work. I said as much in another thread. See if this answers some of your questions.

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

View WoodES's profile


35 posts in 1112 days

#2 posted 10-09-2013 03:59 AM

Had to weigh in on this topic as I just finished the same system. 2 Hp Grizzly, with 6” duct (pvc) with a Thien separator on a 48 gallon barrel. The system sucks, which is the intended result and very little gets past the separator.

My separator was based on the design from Sketchup

The Thien outside diameter size is driven by the barrel diameter and a groove was routed in the bottom of the separator for a better seal. Also the inside diameter is roughly 3 times the diameter of the pipe size to minimize the interference from the input and exhaust air.

The slot was routed about 1/4” or less from the inside face of the separator wall and is 1-1/8” wide. The slot is about 3/4 of the inside circumference of the separator.

If the image loads, you can see the separator on the left hand side.

Hope this helps

View UpstateNYdude's profile


671 posts in 1404 days

#3 posted 10-09-2013 04:04 AM


-- Nick, "Choking to death on bacon is like getting murdered by your lover." - JG

View UpstateNYdude's profile


671 posts in 1404 days

#4 posted 10-09-2013 04:08 AM

WoodES – any chance you can get a better pic of the separator itself, I am curious to see how big the slot is in yours. Also what would you say the ratio of chips in the can to chips in the bag is if any at all?

-- Nick, "Choking to death on bacon is like getting murdered by your lover." - JG

View WoodES's profile


35 posts in 1112 days

#5 posted 10-09-2013 04:49 AM

I’ll try to remember to take pics tommorrow. A couple more points, the exhaust side has 3” clearance from the bottom, I read someplace that this should be 1/2 the diameter to be effective. The inside height of the separator is 8”. While I haven’t used this with planer or jointer yet, I have run it with the table saw and test dustpans full of sawdust. Only about a cup of fine dust has made it through the collector.

What I see different in your separator is it appears taller and the diameter appears to smaller. The slot appears to much larger and appears to be about 1” to 1-1/2” away from the exterior wall. The slot maybe too close to the exhaust to allow the chips and dust to drop into the drum. You may be able to test this by creating a temporary cover for 1/2 of the slot width.

Good luck

View Bluepine38's profile


3336 posts in 2506 days

#6 posted 10-09-2013 02:59 PM

I think the slot needs to up against the inside edge of the barrel, the same as it would for the regular
separator, and it might help if you could cut the barrel so the top hat would be setting on the widest part
of the barrel instead of the narrower top giving you a larger diameter on your slot. Just my opinion, and I
have been known to be wrong once.

-- As ever, Gus-the 77 yr young apprentice carpenter

View rum's profile


148 posts in 2007 days

#7 posted 10-09-2013 05:20 PM

Yep so a few things:

As Gus said that lip between the slot and your sidewall will simply kill performance. Ideally its a smooth transition all the way to the bottom of the slot. Basically the material moves to the outside wall, swirls around and then drops down below the baffle. With the lip there you’re going to get more stuff staying up top and then cycling around to the outlet.

Your baffle itself is to thick. Think more like 1/4” hardboard. I started with 3/4” plywood skinned with metal and beveled on the underside edge with the hope that the bevel would allow the extra thickness to work – nope that was wrong. The thinner the better up until it starts to oscillate due to the suction. I ended up routing the underside of mine down to less than 1/4” thick because I didn’t want to rebuild the whole thing e_e.

Your slot is huge compared to the diameter. A thinner slot separates better (up until it glogs – I had to go with an almost 2” slot to get the longer shaving from my straight blade planer to go through but I snuck up it until it just worked and took a small hit on the the smaller stuff by doing so).

I can’t really tell for sure but I’m also wondering about your inlet. Ideally it feeds in right at the edge of the wall and feeds at a tangent to the side of the separator (if you drew a straight line 90deg from the side of the circle that is where you would ideally feed in). It sort of looks like you might be feeding in to far towards the center. Also (again can’t see for sure) but make sure that there are smooth transitions for material cycling around so it doesn’t bounce out off of the wall.

View bondogaposis's profile


3969 posts in 1772 days

#8 posted 10-09-2013 06:24 PM

I think that the diameter of the top of your barrel too small. A pickle barrel is not ideal, where a trash can that has tapered sides will work better. I also think that the outlet port is too close to the baffle.

-- Bondo Gaposis

View HorizontalMike's profile


7064 posts in 2335 days

#9 posted 10-09-2013 11:59 PM

I agree with you. PLUS, I feel that the intake is placed “too-late” in reference to the bottom plate.. It should start “right at” the bottom plate blockage, and not some “half-way” through it. Learned that from my own screw-ups…

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

View WoodES's profile


35 posts in 1112 days

#10 posted 10-10-2013 03:49 AM

Here are a few pictures of the separator and the collection bag

View Shawn Masterson's profile

Shawn Masterson

1294 posts in 1370 days

#11 posted 10-10-2013 02:32 PM

I think you are losing a lot of air speed by reducing to 4” at the machine. I have 6” pipe and when I use my 4” DR stretch hose to sweep, when I remove it at the blast gate there is a deposit of crap at the joint, and I can hear a rush of shavings through the pipe. If you are not going to modify your machines with 6” ports then it would be best to stay with 4” pipe. also flex pipe slows down airspeed drastically. I am no expert, but this is my experience.

View brtech's profile


883 posts in 2344 days

#12 posted 10-10-2013 03:34 PM

Shawn, a WHOLE lot of DC setups use 6” mains and 4” drops. There are many reports of poorly designed blast gates that have the problems you cite, so I’m inclined to think thats the problem you are seeing. Are you going from 6” to 4” at the blast gate?

There is no doubt you get an airspeed hit, but if you do 6 to 4 at the Wye, with a smooth transition, it’s not bad.

Very few pieces of equipment have, or can be modified to accept, a 6” port.

Flex is certainly bad for airspeed, no doubt about that.

View WoodES's profile


35 posts in 1112 days

#13 posted 10-11-2013 04:03 AM

The effect of the drop to a 4” connection at the tool can be easily tested disconnecting the 6” at the separator and taking a dustpan full of sawdust and see how much passes through the separator.

I suspect that the problem is related to the slot size and location. As the separator works by reducing the velocity of the air, thus allowing the dust to settle out. The slowest air is at the face of the separator wall (try flushing your toilet and watch the flow, testing material is optional). The slot placed too far inboard of the inside face, will not allow the settling dust to drop into the barrel.

As it appears there is sufficent material, the slot in the bottom of the separator could be widened to the outside and temporary hardboard or other suitable this scrap could be placed partially cover the slot. This would provide an opportunity to test solutions before deciding which way to go.

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