J. Phil Thien's Projects

How did you get the HF unit for $139?  They sell them for $199 here and the best coupon I've found so far is 25% off.

Scanning through this post I'm wondering why while everyone is trying to save money but no one is considering the life span of the motor.  Replacing the impeller to a larger, heavier one will make the motor works harder, which will shorten its life span.  Not to mention possibility of decrease in performance or trip the circuit if the impeller is much heavier than the original.  Imagine using a motorcycle motor to run a car.  I'm exaggerating but the idea is the same.

Quote from: retired2 on March 12, 2013, 12:45:00 PM

Quote from: Rick T on March 12, 2013, 12:00:45 PM
What Wilburpan is proposing s what I had in mind basically for my Delta 50-760. http://www.jpthien.com/smf/index.php?topic=845.msg0#new
It has a 5" dia inlet so I should be in the 6-8" dia hole or chimney to filter.

It's been a while since I looked inside my 50-760, but as I recall the outlet from the fan doesn't enter the separation area in the fashion you might expect.  It might need some internal baffles to direct the incoming air in a more conventional manner.  This is probably the reason you don't seem many, if any, implementation of a Thien baffle in the 50-760.

The most unique setup I've seen just recently are people installing a Super Dust Deputy cyclone under the 50-760 so that the outlet of the SDD ports directly to the inlet of the 50-760.  But the $64K questions are 1) does it separate any better than the Thien separator, and 2) does it result in more or less CFM losses.

Rick,
I have a Delta 50-760 as well and have been trying figure out how to improve the dust separation and your top hat build and retired2's are great.  I'm in the process of building a top hat and would like to shed of light on some of the topics discussed here.

   1. Being an HVAC engineer, I know a little bit about airflow, fans and pressure drop.  I disagree with your thinking that having the baffle on the outlet side doesn't hinder the airflow.  All fans have associated fan curve which show the correlation between airflow and total system pressure drop.  More pressure drop = less airflow, and vice versa.  Notice I said total system pressure drop.  The fan sees both inlet and outlet pressure drop.  Adding a baffle to the outlet will add pressure drop to the system.  Thus the fan has to work harder to push air out, meaning it has less power to pull air in, thus less airflow.  How much cfm loss will depend on the baffle design but there will definitely loss in airflow.
   2. I believe the idea behind the Thien baffle/top hat is that air and dust enter the separation chamber (I'm using top hat as example) and its velocity slows down because of the larger chamber compare with the duct.  The "mostly clean" air gets suck out of the chamber while the heavier dust particles spin around the chamber wall and eventually slow down and drop through the slot.  That's why it's important to have the outer radius of the slot to be flushed with the chamber wall so the dust can drop through easier.  It's also important to have a chamber roof to prevent heavier dust to get suck out of the chamber (more on this later).  Of course all this adds pressure drop to the fan system.
      2a. If you look at most dust collection, Harbor Freight's for example, the outlet is built very similar to a top hat design: a cylindrical chamber, a chamber roof with small opening to the filter in the middle to prevent larger dust particles to be pushed into the filter.  Note that the roof is sloping downward from the outside in. This is similar to the Thien baffle idea that the outlet opening has to be 1/3 of the way into the chamber and not flushed with roof.  This makes a better dust separation.  Because of the similarity, it's easy to add a baffle to the outlet of a typical DC.  The 50-760 design is different from most DC that I think just adding a baffle to the outlet will make dust separation worse.  Here's why:
   1.  The outlet chamber is not cyclindrical.   The air and dust will still spin in circle but because the chamber is not round, this will cause some turbulence, and we don't want that if we want good separation.
   2.  The opening to the collection bag is smaller than the chamber wall.  There's a "lip" between the chamber wall and and the collection bag opening.  If you install a baffle, most dust won't drop through the slot but rather settle on the lip, which bring me to my next point.
   3.  There's essentially no "roof".  The opening to the filter is almost as large as the chamber wall.  Air tends to find the path of least resistance, which is to the filter, carrying with it new dust and and dust that settled on the lips, then caking the filter wall, adding pressure drop to the system, reducing air flow.

As I'm writing this, I'm wondering why I trusted the woodworking magazine reviews and bought this Delta 50-760 in the first place.  If I am to build a dust separator in the outlet of this DC, this is what I would do.
  1. First reduce the opening to the filter by building a "roof" to prevent heavier dust particles from getting pushed up.
  2. Build a wall around the collector bag opening from the "roof" down.  This eliminate the lip.  Of course this wall wouldn't be a complete circle, but rather 2/3 or 3/4 of the bag circumfence with opening toward the air outlet.
  3. Install the baffle at the bottom of the wall/top of the collector bag.

Again, all these add pressure drop and I doubt that it's any less than the top hat on the inlet.  Maybe just adding the roof will help with the separation, and that would add less pressure drop.

I hope some of this helps and I'm not just rambling.