J. Phil Thien's Projects

I confessed, retired2, because I couldn't let you go around telling the world what a lousy designer I am.  ;)

Regarding the inlet design rawdawgs50 shows in his videos: It is lots easier to build, I suppose, but there are all sorts of cavities around that round pipe to cause unwanted turbulence.  If you look at interior pics of the top hat designs that use round inlets, and even some of the original in-can designs, you'll see random piles of dust in these cavities.  My original top hat, which I made for my Shop Vac, uses a round pipe. Even with the higher static pressure and faster air flow afforded by the Shop Vac, there is a build-up of dust inside that clearly shows the results of eddies.

Okay, it's not really a big deal, especially with the Shop Vac, since the build-up of dust doesn't seem to hamper its function. But I suspect that with the larger volume and slower velocity of air pulled through the separator by the dust collector blower, it could be an issue. That's why I take to heart the advice that forcing the dust-laden air against the outer circumference of the separator and to eliminate as much as possible any untoward turbulence, will bring the performance of an otherwise marginal machine (such as the HF "2 hp" unit) to acceptable levels.

First, I will take full blame for the error in the posted sketch: I am Thom Porterfield. My middle name is Peter. :)

Second, that sketch came from my original design that used 6"? duct and was otherwise full of flaws. When I resized my system to 5"?, I neglected to change the note on the inlet duct. In my current design the transition goes from 5"? to a 7.25" x 3" rectangle. I believe retired2's complaint is covered by this change. My apologies to the group.

Make a hatch in the middle of the baffle that you can reach your hand through. You could fasten it on the bottom side of the baffle with a hinge and toggle, that wouldn't interrupt the air flow inside the cyclone area.

I've even had hand plane shavings--those gorgeous long curls you get from a properly tuned plane--pack up at the end of the slot so that overall efficiency of the unit was compromised.

My first separator has a removable top. The one I have planned, which will have a blower close-coupled to the top, will have a removable bottom.

I don't know about clogging in a large-diameter duct system--my first Thien separator was made for my shop vac. The vac has such high static pressure that it sucks up all kinds of big things, even through the 2 1/2" hose. Such as baggies, pieces of cardboard, etc.
And some of these wrap around the support strut I provided to keep the middle of the baffle from flopping about.

Regardless, it seems to me to be poor planning to not provide some way to get inside a cavity in any vacuum system, because the alternative is disassembly!

I used aluminum flashing. Other than you can't see through it, it works fine.

I do recommend making some provision to easily open the separator to remove the occasional clog in the drop slot.

Can't wait to see your solution, Don.

I used a coil of 6" aluminum flashing I had left over from a remodel project.  A picture of my unit with the lid off is here. If you're interested, I can give you the SketchUp file I use. It's for my next build, but the concept is similar.

Quote from: Bruce Seidner on March 06, 2012, 02:04:26 PM
This is exactly what I want to build and I was wondering if there is some thought on the internal volume of the separator relative to static pressure/cfm. Then there is the issue of how to dimension the volume. The design seems to be incredible forgiving and people seem to design based on the size of the bucket and fittings they will be using. But x cubic inches of volume can be wide and short or skinny and tall. I have not seen the issue of volume relative to the static pressure/CFM digging through the archives or on the web. The slot size and percentage of the baffle to circumference has been discussed so I keep thinking I must be missing something.

Bruce:

Although there is no doubt some SP loss in the separator, I doubt it's enough to be a detriment when using a shop vac. When I made my first Thien separator, I had an interesting experience.  I was happily sucking up junk, including 1/2" hex nuts, when the hose picked up a small piece of plywood. I heard a "thunk." I removed the plywood and turned to see that my can had a big dent in the side. While pondering how that could even be possible, the hose picked up one of those plastic bags they put your stuff in at the store, and there was a big "KAFWUMP!" and my 30-gallon galvanized steel garbage can collapsed. Yep, it imploded.

Not wanting to buy a new can, I banged out the dents and installed some external ribs to prevent this from reoccurring. In so doing, I introduced some leaks into the system, but not enough to hamper the effectiveness of the overall assembly. I failed to take photos of the initial damage, but you can see my fix in reply #2 here.

I guess the internal diameter of my separator is about 19 inches, and it's about 5" high inside. If I remember correctly, the drop slot is 1" wide. I made the baffle out of 1/2" plywood, and after reading discussions here, beveled the inner circumference of it to about 1/8" thick. I don't see any improvement (or detriment) from doing that, but then, the thing works so damned well to begin with, I really don't care.

The issue of static pressure drop would be an issue, however, when installed in a large volume dust collection system. As has been discussed ad nauseum here and elsewhere.

Bruce:

I built a top hat style separator for my shop vac, (a real deal official ShopVac brand, big, noisy, red, awkward), and I put it atop a 30-gallon metal garbage can.  Other than the awkward bulk of the affair, it works GREAT. All the big gunk goes in the garbage can, only fine flour winds up in the shop vac and on the vac's pleated filter.

I wouldn't hesitate to make one again, to top a smaller container (it'd be LOTS easier to empty) and to put the whole thing on ONE cart (mine is on two: one for the can, and the shop vac itself). [ETA: see the post immediately above--a very cool solution!] If you're only interested in a 5-gallon sized affair, don't discount Phil's original design (available elsewhere here in these forums).

Shop Vacs work just fine coupled with a Thien separator, and it's fun to hear that long-lost brass wingnut go clank! in the bucket. :)

Most reducers are pretty abrupt.  I.e.: they have a transition angle of about 45?.  Since we worry about every little thing that might cause turbulence that will slow down FPMs, I'd worry that such would occur in that transition.

Y'know, if I had another $1000, I'd have a 5-hp cyclone and use 6" duct.

But I don't, so I'm gonna finesse the HF install.

First, though, I have to build storage cabinets to get all these miscellaneous tools off my floor so I can put a ladder in the shop to install the duct.

Does it sound like I'm procrastinating?
You be the judge. :)

Quote from: dmh on March 02, 2012, 04:06:47 PM
Where can one find out how to do these calculations?

Use this forum's search function and look for posts by retired2. Recent ones. Like in the last month or so.

Why not get a length of 5" duct, and cut it length-wise, 180? opposite the seam.  Then make the rectangle of mdf as you did, but with your desired dimensions. Place the duct over the form, just as you did, and pound the thing into shape.  This should leave you with two long triangular gaps...which you could easily patch with a piece of flashing and pop rivets.

That's what I plan to do. :)

I believe he means the condition in your side view.

Around here (Bend, Oregon) Home Depot sells 5" duct

But it's 30 gauge. To get 26 gauge, you have to order it from the HVAC guys.