Thien Baffle vs. Cyclone: Efficiency Comparison


Which keeps more CFM, a Thein baffle or Dust Deputy? That’s what I wanted to know too!

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A few months ago when I decided to convert my single stage Harbor Freight dust collector into a two stage system I discovered there were three basic approaches:

  1. Buy or make a lid to go on top of a bucket for chip separation. The problem here is that the cyclone created inside the bucket keeps the dust stirred up so a lot of dust that goes into the bucket ends up being sucked back out.

  2. Make a Thien baffle. This is similar to the first option, but includes a bottom layer that separates the cyclone effect from the collected dust, preventing it from getting trapped and then sucked back out.

  3. Buy or make an after market cyclone. This does not have the issues of just a chip separator lid, but is a lot more complicated to build than a Thien baffle, and fairly expensive to buy aftermarket.

One of the things I learned during my research is that all of these techniques reduce the airflow of your dust collector because they introduced a lot of extra air resistance. Why go to a two stage system if it reduces your airflow? A few reasons.

Your motor lasts longer because everything being collector does not pass through the collector. That loud "clunk" when a chip hits your expensive impeller does not feel good. Also, your filter lasts a lot longer because most of the trips and a majority of the dust are separated before they reach the filter. Or it allows you to exhaust directly outside like I do and bypass a filter entirely. Blowing some fine dust out of my roof is okay, blowing every particle my dust collector picks up would not be.

But, what I could not find is a side by side comparison of each solution to figure out which is the most efficient. My intuition thought that a molded cyclone would be the most efficient, but they contain a lot more volume than a Thien baffle... and this is a new area of research for me so I did not trust my gut. The only information I could find was that just a chip collection lid is definitely the worst of the three, but still an improvement over a single stage.

For cost reasons, I decided to make a Thien baffle because I could do that with material I had on hand. Then I received an Oneida Super Dust Deputy as a gift and I realized I had the opportunity to generate the information I could not find and share it; a side by side comparison of a Thien baffle and cyclone. So I bought an anemometer and decided to find out for myself.

The bottom line is the cyclone is the most efficient. I walk through all the steps in the video, but below is how I did the math to come up with each calculation.

The formula: A * S = VA = Area of the opening in square feet

S = Airspeed in feet per minute

V = Volume of air moved in cubic feet per minute (CFM)

Area of a circle: πr²There are 144 square inches in a square foot.

No separator/straight from the motor:

  • Pipe diameter: 5.25" / radius = 2.625"

  • Airspeed: 5571 ft/min

  • Pipe diameter to area: 3.1415 * 2.625² = 21.64

  • Square inches to square feet: 21.64 / 144 = .15 sq.ft.

  • Area to volume: .15 sq.ft. * 5571 ft/min = 837 CFM

Thien Baffle:

  • Pipe diameter: 4.75" / radius = 2.375"

  • Airspeed: 3573 ft/min

  • Pipe diameter to area: 3.1415 * 2.375² = 17.72

  • Square inches to square feet: 17.72 / 144 = .123 sq.ft.

  • Area to volume: .123 sq.ft. * 3573 ft/min = 439 CFM

Oneida Super Dust Deputy:

  • Pipe diameter: 4.75" / radius = 2.375"

  • Airspeed: 5157 ft/min

  • Pipe diameter to area: 3.1415 * 2.375² = 17.72

  • Square inches to square feet: 17.72 / 144 = .123 sq.ft.

  • Area to volume: .123 sq.ft. * 5157 ft/min = 634 CFM

Efficiency Ratings:

  • Thien Baffle: 439 CFM/837 CFM = 52% (or 48% loss of airflow)

  • Cyclone: 634 CFM/837 CFM = 76% (or 24% loss of airflow)

So as you can see the Oneida Super Dust Deputy is about 50% more efficient than the Thien baffle (52% to 76%) and only has half of the efficiency loss as the Thien baffle. I am really glad it won, because it would have been a pain to put my Thien baffle back together.Help support me by using affiliate links!

Dust Deputy:

Super Dust Deputy: