J. Phil Thien's Projects

We have a wide belt sander with a vacuum hold down under the belt. 
Needless to say, the vacuum sucks a significant portion of the dust fines being generated. 
It has a large filter bag attached, but it needs a separator in the system. 

The vacuum has a 5" duct (120mm).  Velocity is good: 4500fpm when fully covered, to ~6500fpm when open.    The specs on the vacuum rate it at >800cfm which seems about right. 

Question #1 is: Is there an optimal diameter for the separator? 
Since it is a sander, it only has fines, no chips. 
I am planning on at least a 2x Top Hat with a bell mouth port. 

Due to the configuration of the machinery, it is quite practical to place the separator after the blower. 
So, Question #2: Are the other considerations for having a 'positive pressure separator vs. the conventional negative pressure designs? 

I'll look forward to any suggestions the 'collective wisdom' can provide.

Thanks!
Jim

This may be a topic for Phil, but perhaps others have had experience with this... 

Does the amount of volume below the baffle matter?  If not, what about shape? 

I have a wide belt sander that exhausts out the top (as most do).  My large DC does a pretty job job exhausting the dust out of the machine - we have minimal fines inside or around the machine after extensive use. 

However, I want to prevent as much dust as possible from going to the bags.  I also don't want to climb on top of the machine to empty trashcans.  My idea is to place the separator inline  from the machine's exhaust and our overhead pipe to the DC.  Then, under the baffle place a tapered cone to a pipe that drops to a trash can on the floor. 

Has anyone else tried something as unusual as this?  Does it work?

I will look forward to any replies!
Jim

I am considering building a separator to go under my large out-feed table for my Table Saw.  Therefore, I am trying to collapse my vertical height as much as possible.  The large sweep elbows take up too much elevation.  I am concerned that a small radius elbow will be too constrictive.  I 'could' put an engineered plenum on top, but at the least, I am looking at giving up my 6" duct diameter... 

So, after looking at this again, I am thinking "Why does the air have to go UP?"  Why can't I duct it DOWN through the center of the Baffle and then out the side of the container? 
a) The baffle isolates the rotation inside from the 'dead air' of the collection bin;
b) The 120deg section of the baffle provides ample room to duct under the baffle without being under the drop-slot. 

Obviously, taking the duct out the 'top' makes using pails, cans and drums very easy and economical to connect and use.    But since I am going under the table, I am considering building a wheeled dump cart that rolls under the separator.  This could easily have a cut-out in the end to accommodate the exiting duct...   

Am I missing something that would prevent this from working as well as the 'normal' upflow? 
I will look forward to everyone's suggestions and critiques! 
- Jim

Has anyone made any measurements or calculations for the 'extra' load of using the separator? 
There has to be a change in the static pressure between using the separator or not... 

Practically speaking, separating the chips out of the airstream increases the the overall performance of the system so the load of the separator itself is rarely noticed.  Only passing the 'fines' and not heavier chips permits the system to operate at a lower level and still work extremely well. 

However, my woodworking shop is re-organizing and we are trying to make one 10hp DC cover as many machines as possible.  In the old layout, it handled (10) 5" ports on sanders pretty well.  However, we are hoping to enlarge some ports on some different machines.  On paper, the numbers calculate VERY close to working.  If the Separators are a net gain/load it may tip the scales. 

Any measurements or calculations anyone has made would be greatly appreciated!

Thanks!
- Jim

Phil (or others) -
Have you experimented or tested a conical baffle?
(Where the center 'point' is higher and slopes down towards the cutout area) 

I was wondering if this would improve separation by working like an inverse-cyclone... 

Just wondering!