J. Phil Thien's Projects

Alan -
Thanks again for your prompt, thoughtful insights and assistance. 

Your comments and suggestions have posed a provocative question:  Do I want to make the overall diameter as large or small as practical? 

• When you swing a weight on a string, the longer the string, the greater the linear velocity around the larger circle.  So bigger would seem to mean faster (better?) 
• The larger the space, the greater the volume of air and the greater force needed to get that air mass rotating.  Can it get so big that the air flow moves directly from the peripheral intake to the center output? (without creating a circular motion)
• Smaller diameters force greater angular changes in the air flow.  Does this redirection make the particulates hit the outside perimeter and then drop out?
• Conventional cyclones are quite small compared to their duct diameters.  This seems true for large 10,000cfm Torit/Donaldson units as well as Dust Deputy units for shop vacuums.  Why is this?
• If I have a large airspace, do I need as much centrifugal force for separation?  (Imagine if I had a sealed box as big as my garage.  In one corner, I had a 5" duct coming from my table saw.  In the opposite corner, I had another 5" duct going to me DC.  How much dust would make it through the 4000cu ft to get caught in my final filter?  Bizarre thought, I know - but an interesting exercise... ) 

I will look forward to the comments and answers.  If possible, I may build both a 2.5D and a 4D unit.  Depending on results, I can simply alter the In/Out fittings to change to the better performing design.  I don't know if I can justify extra testing attempts to my boss, but we may just build multiple heights at 1.25, 1.75 and 2.5D heights...  If I design the parts cleverly, I can just swap out different outer bands at alternate heights...

I will look forward to everyone's comments and posting my results...
- Jim

Alan -
The diameters you are suggesting seem counter-intuitive (but I am often wrong in my assumptions...).

The sander is 'fines only' - so I would assume that it would be the smaller diameter.  Making tighter "spins" to force the dust particles centrifugally against the outside wall.   

The planer creates the larger chips - with greater mass that requires less 'turning' to remove it from the airstream.     

I don't think I want to use the separator as the transition point for the ducting.  If I starve the 12" line with an 8" intake, I will reduce the airstream velocity too much.  Currently, I have just over 5500fps through my 12" line = >4300cfm.  If I choke that with an 8" intake, that same airspeed, is only 1900cfm.  The blower will be able to draw more, but even if it can get 2500cfm through the 8"pipe, once the air gets to the 12" line, the air speed is less than 3200fps - not high enough to keep the debris in the airstream.   I will accumulate dust inside the duct and that is unacceptable. 

Whatever airflow I can't get through the 8" line I will have to supplement with an additional port(s) to keep the airspeed in the trunk line over 4000fps.    I realize that is an uncommon situation for most readers of this website - most of us are  starved for every cfm we can squeeze through their system.  But we can only allow dust in three places: 1) on the floor or worktable; 2) in the bottom of the separator; 3) in the final bag/filter.   Anywhere else presents a hazard that is costly in fines or dangerous in the workplace. 

I will look forward replies about the separator diameter!
Thanks.
Jim

Hey 'Guy...
Running a commercial shop, we are always struggling with 'when to empty'...   

We have cut 'windows' into containers, with mixed results.  Often they get too dirty to notice if it is empty or full.

Big 55 gallon drums mean you don't have to stop and empty, but requires a forklift to handle and dump - not too mention the mess and 'dust cloud' when dumping. 

Also, big drums mean that you can create a lot of waste and walk away leaving it for the next guy (who may only have to make 3 cuts...). 

We are moving to much smaller containers.  Requiring everyone to 'clean up their own mess' and making it convenient to handle because it isn't too heavy (or messy) for one man to handle. 

Thinking about it, that isn't such a bad idea for a garage-shop, either... 

Regarding the lift the separator/raise the drum issue...
We have given a lot of thought of how to plumb the separator solid for maximum efficiency.  The gimmicks, or hardware, or mechanisms do move the drum got to be much more work that what it was worth.  However, now that we are going to much smaller containers, we may revisit it (again & again). 

Our best working idea has been do make a round separator to match the drums diameter.  Rigidly mount the separator a fraction of an inch above the drum on a dolly.  Create a metal band lined with thick, closed cell foam (neoprene).  Add a cam-over, draw latch to snug it around the separator and drum.  You will get a small amount of dust that will accumulate in the gap.  But it will be easy and convenient.

Hope this helps!
Jim

We are pretty well committed to improvising a separator over the wide belt sander.  I will include pictures when it is completed. 

As I lay-out the design, I'd like some experienced input of overall diameter...
Separator #1 is on a Planer - generating healthier chips and very few fines.  It has a 6" duct.  A stand alone DC attached to it works rather well.  The only mod we have made is to add a row of long bristle brushes across the from to keep chip 'spray' from exiting the front of the machine.  I expect my slot to be 1.25 - 1.63" wide to allow curly chips to fall through.  I am also planning on making the separator about 10" tall for a 6" duct.  It will sit on the floor adjacent to the planer and be a conventional top-hat-over-a-barrel design.

Separator #2 is on the Sander.  It does only finish sanding - so everything is fines.  It has a hood fir each belt and a vent for the interior cabinet that goes to a 8" duct.  Since it will all be overhead, I can make the separator any practical vertical height.  With an 8" duct, is there any advantage to a three-story 'Top Hat' design?  This will have a 8-12" high ring under the baffle and then a cone tapering to a hose to drop into a barrel on the floor.

So... my question remains, what is the optimum diameter for these separators?  I don't worry too much about loading the DC, I have a 12" trunk line and plenty of horsepower.  (I will have to add a third port to the trunk line to keep the 6" and 8" lines from starving the airflow down the 12" trunk)  I am looking for optimal separation to prevent as much material as possible from reaching the bag-house. 

I will welcome any recommendations and the ensuing discussion!
- 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

"D" is diameter. 

A "1D" bend turns within its diameter. 
ie:  If you made a 180 degree turn, the two pipes would be next to each other.  Or, 4" pipes would be 4" OC apart. 

A 1.5D U-turn would put 4" pipes 2" between them (6" on center).   To make things worse, most of these small radius fitting shrink the circumference (pinching down the size) at the apex of the bend.  So you are penalized for a small radius, and penalized again for the smaller size... 

Keep the bend radii as large as possible.  That is why Retired2 was explaining why large radius flex hoses aren't always so bad... 

Hope this helps!

I have been tied up with a number of other projects and have been following threads 'from a distance'... 

I have a few quick suggestions about taking some measurements on a Separator. 
There are three empirical tests that will judge the actual performance of your Separator.
1. Manometer.  Attach a manometer across the ducts leading into and out of your Separator.  The actual number is not as important as reducing the amount of vacuum across the Separator.  The greater the number, the greater the load to your DC.  Power lost in the Separator is power lost sucking dust. 
2. Weight Measurements.  Using a scale that measures in 0.1grams, weigh a small board.  Also, weigh your final filter.  Note these weights.  Saw or sand (or ?) the  board so that a significant portion of it has disappeared into your DC (not on the floor).  Re-weigh the board and filter.  The differences show your practical efficiency.  I don't care if there is dust inside my ducts, or even in the bottom of my filter can.  I don't want it to get to my filter.  Efficiencies will vary greatly between fine sanding MDF and planing doug-fir.  The important number is the improvement. 
3. Electrical.  Put an ammeter on your DC's motor.  This is counter-intuitive.  If you plug your DC inlet, it whines like you whipped your dog, but the current drops because there is no air to move.  Remove the inlet duct and it may make less air noise but the current goes up because it is doing more work.  Similarly, plugging the outlet stops the air flow and the work the blower can do.  Note the readings with zero and 'full' air flow.  (Blowers are purposely designed with restrictions so the motor stays within its safe operating range.)  Your attached Separator will show a current drop due to its restriction to air flow.  Making a more efficient Separator means the motor can pull more air through and hence work harder. 

By paying attention to these empirical numbers, I have been able to judge what improvements have made a difference... 

If we make these tests 'Before and After', we can judge our relative improvements! 

Hope this helps!
- 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

I wouldn't give up so quick... 

Being able to suck 'everything' up and then drop it into separating sieves is a great place to start. 

All of the current Separator designs assume that the debris will not impinge the Separator itself (other than eventually scratching the plexiglas exterior ring).  Your application will have to be seriously beefy to handle rocks and 'hard' debris. 

While very different than our 'sawdust' designs, I think you could scale it to work - with a fair amount of Trial-and-Error attempts.  You have one major advantage - the mass differential between separating gravel from air is MUCH easier than separating sawdust.  I think your design challenges will be: 

• Determining how big of 'rocks/gravel' you will pull through the system.
• What pre-screening you will use to prevent 'boulders' from entering. 
• What 'compromise' of separation you will accept to let grass or other 'lightweight' debris to pass through to allow 'rocks' to drop out.

I think that Phil's design has many applications beyond what we originally needed in our woodworking shops. 
I will look forward to hearing how your attempts are succeeding. 

If you pursue it, I'd look forward to sharing some additional ideas with you.
- Jim

I think it is important to distinguish between the recent comments about getting shocked and the thread's original topic of a dust explosion. 

Any grounding of ductwork, tools, benches, etc. can make immediate and significant reductions of the nasty jolt from static charges.  Although you cannot ground your PVC ducts, grounding the wires inside the flex tubing allows a path to dissipate the charges generated at either end.  They don't eliminate the static generation, but it can greatly reduce its toll on me when I touch them.

I have had fun replicating some of the Myth-Buster events - igniting sawdust, flour, even non-dairy creamers.  Even one package of creamer and a Bunsen burner is surprisingly 'big'.  If you contained it within a 4" PCV pipe, it would make a decent flame-thrower.  However, ignition still becomes the tricky part. 

I can't speak for Loren's experience.  There are lots of chances for combustion.  Loren's description of a 'woof' instead of a 'bang' is accurate for sawdust combustion.  However, a real dust explosion would have scorched bags and filters at one end and spewed a few flames out the tool ports.  My hunch is that is was not a spark induced explosion, but possibly some other source/form of combustion.   

I would definitely recommend all practical forms of grounding the DC and ductwork.  However, the purpose is our own increased protection from static shocks - NOT safety from explosions. 

Hope this helps!
Jim

Retired -
Thanks for re-stating the realities of our systems. 
Dust explosions are spectacular events for the MythBusters, but they won't happen in our workshops. 
Even the 'grain elevator explosions' that everyone fears had an external ignition source. 

Fire is a possible risk in any woodworking shop - you have lots and lots of combustible material.  Dust and chips and shavings can flare up in seconds.  But they all require an external ignition source.  Spontaneous explosions are for the movies 
and special effects. 

I recently built a burner system with several 200,000btu propane torches for charring wood.  Trying to install a BBQ spark igniter to a 'weed-burner' torch is NOT simple.  I had continuous sparking and lots of propane flooding the area - but it is amazing how difficult it is to get ignition.  Fuel-air and exact positioning is critical. 

If it is that hard to ignite propane, I will never worry about dust flying by a spark at 4000fps. 

Sleep easy, woodworkers.  Your DC will not explode from static!
- Jim

Impeller designs are quite unique.  Sometimes the vanes appear to go 'backwards' and other times 'forward'. 

They share one common feature though... 
If you reverse them, they still blow air in the same direction.   
This is particularly important with 3phase motors since the phasing controls the direction of rotation. 

If you think that the impeller is designed to go the 'other' way, open the motor connections.  There is almost always a schematic to show you what wires to change to reverse direction.  Take measurements, first, then reverse and compare.  The impeller's 'correct' direction will be 20-30% more efficient than 'backwards'. 

Hope this helps!
Jim

Retired -
I agree the compound miter saw can spray dust all over... 

Here are some solutions that I found - I have made my variation and they contain almost everything.  Some small fines can blow back out.  But that is a combination of needing more CFM to suck it in and a deeper hood to trap the dust.  It seems that having more volume in the hood (deeper box) allows the 150mph dust to decelerate instead of bounce out of the hood. 

I can tell you that it works VERY well! 
http://www.youtube.com/watch?v=mRCgwTqJhqM
http://www.youtube.com/watch?v=8AIITfs51PE
http://www.youtube.com/watch?v=W9Ll10MZMmg

Hope this helps!
Jim

I agree with Dave. 

My first attempt had a fitting centered in the lid.  At first start-up, I forgot to install the short piece of pipe to extend into the separator space.  It hardly worked at all.  It seems that when the air at the top is allowed to escape through the exit, it prohibits the circular motion that is needed to separate the debris. 

A few pictures would help explain a lot to us.  If it isn't convenient to post pics, how tall is the space between the top and the baffle?  And, how far down does the exit pipe extend into that space? 

Don't give up on your build - I think it can be salvaged! 

- Jim

Rick -
You are right!  33 gallons of sawdust too much heft to dump.  ...I guess that is why I try to keep my teenage sons around for 'chores'! 

My first 'Rubbermaid Separator' was a 33 gal Baffle-Inside-Design.  I even used the lid - just added backing plates for the inlet & outlet fittings.  The baffle sits down on the ledge at the handle height.  It works quite well - especially as my first attempt. 

However, the reduced interior volume is not a real problem - it keeps it from getting too heavy to dump.  The real issue is the lid has to be raised up several inches to clear the can.  Since I wanted a short run of hose to the DC, it was a real pain to flex it up and out of the way.  Top Hat designs only have to be raised high enough to break the sela and clear the lip - a huge advantage! 

Hope this helps!
Jim