Thinking bigger

[Rick Potter]

I am trying to figure out the best way to hook up the baffle idea to my 3 HP Powermatic DC.  It has an 8" inlet and a double bag setup.  The mounting hoop where the bags attach has a downward slanting flange about 2" wide which helps keep the dust headed down into the clear plastic bags, and not up to the fabric bags.

My thought is to make a baffle a few inches below this flange and put a plywood top on the hoop instead of the fabric bags.  Each one would have a 6" pipe coming out of the center and out the side of the shop.....no filter bags (California).  If it saves 90% or so, I can vent the really fine stuff outside. 

The Wynn filter site shows a setup somewhat like this, but the baffle would make it even better.

Any ideas??

One more question....Why does one bag on my dual bag setup have about 5 times as much dust in it than the other?  One side has about 3" and the other has about 15" full.

Rick Potter

[windmill]

Sounds like it would work. Venting outside is best of course, no clogging of bags/ filters and no particles escaping. Of course, living in California helps...I wouldn't want to do this in Vermont!

The only downside I see is that you're still putting dust into bags. Those need to be emptied/ replaced, which is cumbersome and can get expensive. Have you considered getting rid of the bags completely, and instead using a large 55 gallon fiber drum? I don't know if you can combine the two exhausts into one (to feed into the drum), but it might be possible to make a baffle with two inlets and one outlet.

BTW, if you this route, you've just built a "real" cyclone system, not a trash can separator..... Since you already have the motor/ impeller (which is the expensive part), you may want to consider getting a real cyclone. 3HP should be plenty for that.

One more question....Why does one bag on my dual bag setup have about 5 times as much dust in it than the other?  One side has about 3" and the other has about 15" full.
That's bizarre. Is it possible the cloth bag on top of the "full" plastic bag is cleaner, and is letting more air through? More dust/ air would flow to that side then. It could also indicate you have a leak. Try swapping the top bags and see if it makes a difference.

[D Romano]

I also have a DC, a Jet 1200 that I'd like to make this modification to. I have installed a neutral vane with a little deflector mounted behind the vane to ease the path of the air around the vane rather than having it collide with the back of it. The neutral vane is 4" in diameter and is tangent to the separator ring of the DC and extends to the center line of diameter. I also have the paper Wynn canister filter. I installed a flapper to the inside of the canister as most have done. I run 6" ducts from it and when I do alot of face jointing or planing, the pleats really clog up with shavings.

My question is regarding the small diameter of the baffle. In the trash can separator with shop vac sized inlets, the gap around the perimeter is 1.125". I wonder if Mr. Thien has any advice regarding this gap for a 1200 cfm DC.  The large diameter is about 19" or 20".

Also, I think there was a comment somewhere about using greater than 120 degrees for the large radius. What do you recommend?

Thanks and nice job on this design!

David

[windmill]

I made a baffle for the HF unit, which is about 1.5HP. The CFM ratings on dust collectors are generally worthless, but the amount of air it moves is more or less comparable to the JET unit. The trash can I used has a diameter of 19.5". 4" hoses, Wynn filter.

I used the same size for the "gap" as Phil used for the shopvac baffle. The inner circle has a radius 1 1/8" smaller than the outer circle. It works really well. But, I do have about 1/4" gap around the outer edge of the baffle. This makes it easier to put the lid back on without scraping the sides. I have no idea whether this gap size is optimal. The slot has to be wide enough for the chips to pass, but not so wide the dust gets sucked out. In addition to the system's power (CFM/ SP), the diameter of the trash can is also a factor.

I placed the intake elbow about 1/3 inset from the start of the radius, so I'm probably using only 90 degrees. Again, it seems to work really well. This is also an interesting variable to experiment with.

I think the design is very forgiving. I hope Phil has some real information he can supply rather than my speculations, but I wouldn't be overly concerned with the measurements.

[phil (admin)]

I am trying to figure out the best way to hook up the baffle idea to my 3 HP Powermatic DC.  It has an 8" inlet and a double bag setup.  The mounting hoop where the bags attach has a downward slanting flange about 2" wide which helps keep the dust headed down into the clear plastic bags, and not up to the fabric bags.

My thought is to make a baffle a few inches below this flange and put a plywood top on the hoop instead of the fabric bags.  Each one would have a 6" pipe coming out of the center and out the side of the shop.....no filter bags (California).  If it saves 90% or so, I can vent the really fine stuff outside. 

The Wynn filter site shows a setup somewhat like this, but the baffle would make it even better.

Any ideas??

One more question....Why does one bag on my dual bag setup have about 5 times as much dust in it than the other?  One side has about 3" and the other has about 15" full.

Rick Potter

That will probably work better than you'd think.  The very fines that are exhausted through the wall will dissipate quickly.  The only evidence you'll have is the wooshing noise of the moving air.

On the 2nd question, some (I guess newer) four baggers have an adjustment to control the amount of airflow into each compartment.  I take it your model doesn't offer this?  The reason one bag gets more chips has gotta be that side getting more air.

[phil (admin)]

My question is regarding the small diameter of the baffle. In the trash can separator with shop vac sized inlets, the gap around the perimeter is 1.125". I wonder if Mr. Thien has any advice regarding this gap for a 1200 cfm DC.  The large diameter is about 19" or 20".

Also, I think there was a comment somewhere about using greater than 120 degrees for the large radius. What do you recommend?

Thanks and nice job on this design!

David

The 1.25" was arrived at via testing.  I discovered that making it smaller than 1" increased the # of above-baffle clogs (clumps of debris that wouldn't break-up and wouldn't drop through the slot).  1" seemed to allow everything to break-up and fall through, and I added another 1/8" just to make sure.

For your application, 240-degrees of drop (120-degrees of full baffle) has worked great.

[D Romano]

Thanks for the suggestions. I think I'll mount the baffle permanently inside the DC. Seems no reason to ever remove it. Along the large diameter, I'll attach it right to the DC separator ring with 2 or 3 screws, then 1 more on the the other side for support. I think I'll be able to mount it right above the lower collection bag. Maybe use MDF or 1/4" hardboard. I wonder how much stress will be on the baffle and if a screw will rip out of the hardboard. 1/2" plywood wound be ideal. Hmm...  Maybe I'll glue some small blocks to the underside of the hardboard to screw into. If it all works well, I'll include pictures later on.

David

[D Romano]

I haven't tested it yet, but I made a baffle out of 3/4" MDF and mounted it permanently inside the DC separtor ring. It is attached with 3 screws along the large diameter section with one extra for support in the middle of the smaller diameter section. Finding the "diameter" of the separator ring is trial and error since these things are not very round. I first made the large diameter a little too big, then checked the fit, reducing the radius little by little. I located it by installing the collection back which has a flexible plastic ring the snaps into the inside of the DC, then registered the baffle up against it. This way the baffle is as low as it can be to help airflow and helped keep the baffle level during installation. I positioned the baffle so that the air inlet is just after the beginning of the large diameter.

Also, while looking at the assembly, I began to rethink the use of the neutral vane. The neutral vane is said to increase airflow, presumably by reducing turbulence and therefore SP when the air enters the separator ring. But, does anyone know if it helps separation?

It appears to me the the dust would circle around the outside of the ring, hit the back of the neutral vane (4" pipe) where it would be deflected into the center of the ring and drawn up through the large hole towards the filter. What force would be driving it down to the collection bag? It would take the path of least resistance. I had tried to address this by putting a ramp on the back of the vane, but especially with the baffle in there now, it seems like it would hurt the separation.

After having the thing assembled, I realized that I could not mount the canister filter because the mounting holes are inaccessible. Oops. Instead I bought 4 rubber straps (like bungee cords) and used them to hold the canister down, hoking them to the axle of my flapper. They actually worked quite nice, and are way more convenient than the bolt method recommended by Wynn. 

I didn't take any pictures because time was running short and I had to cook dinner. I'd like to test it out and report the results and if all goes well, I'll take the photos.

David

[D Romano]

Had another thought- In a DC, the separator ring is a doughnut with about an 8" hole in the center. Anyone have any thoughts on making that smaller? I'd guess that smaller gives better separation but at the cost of reduced airflow.

[phil (admin)]

Also, while looking at the assembly, I began to rethink the use of the neutral vane. The neutral vane is said to increase airflow, presumably by reducing turbulence and therefore SP when the air enters the separator ring. But, does anyone know if it helps separation?

It appears to me the the dust would circle around the outside of the ring, hit the back of the neutral vane (4" pipe) where it would be deflected into the center of the ring and drawn up through the large hole towards the filter. What force would be driving it down to the collection bag? It would take the path of least resistance. I had tried to address this by putting a ramp on the back of the vane, but especially with the baffle in there now, it seems like it would hurt the separation.

By the time the air makes a single revolution the chips that are going to settle will have done so.  Gravity is foolproof in this regard.   ;D

So as the airstream circles once and then hits the neutral vane it will hopefully be pretty clean.  However, if there is one thing I've learned with baffle use, it is that turbulence is your enemy.  My concern is that the turbulence will cause problems for new air entering the chamber, and any particles that do get picked-up again from the bag.

My advice would be to try with and without the neutral vane, but I suspect that removing the neutral vane will improve overall performance.

In terms of the roundness of the ring, yeah, these aren't perfect.  It can take some trial and error when fitting them.  Getting the larger diameter as close to the side of the can (or ring) is important to prevent turbulence in the bin (or bag).

Looking forward to your report (and pics).

[phil (admin)]

Had another thought- In a DC, the separator ring is a doughnut with about an 8" hole in the center. Anyone have any thoughts on making that smaller? I'd guess that smaller gives better separation but at the cost of reduced airflow.

Yep.  You may be able to choke it down a little w/o impacting the overall CFM (especially if you're using 4" ducting).  But I'd try leaving it as-is for now.  8" should still leave a 5" or so ledge at the edges, which should be plenty.

[D Romano]

By the time the air makes a single revolution the chips that are going to settle will have done so.  Gravity is foolproof in this regard.   ;D

So as the airstream circles once and then hits the neutral vane it will hopefully be pretty clean.  However, if there is one thing I've learned with baffle use, it is that turbulence is your enemy.  My concern is that the turbulence will cause problems for new air entering the chamber, and any particles that do get picked-up again from the bag.

[/quote]

So are you saying that even at those velocities, the first revolution will make most of the dust settle? Is that the case only with your baffle, or would this happen with no baffle. I agree that it seems that when using the baffle, that it is better to not use the neutral vane. I'm unclear as to why the neutral vane helps at all anyways. The incoming air is going to collide with either the back of the vane, or the circulating air. The only thing that would mitigate this would be an air ramp. I must be missing something I guess.

David

[D Romano]

Had another thought- In a DC, the separator ring is a doughnut with about an 8" hole in the center. Anyone have any thoughts on making that smaller? I'd guess that smaller gives better separation but at the cost of reduced airflow.

Yep.  You may be able to choke it down a little w/o impacting the overall CFM (especially if you're using 4" ducting).  But I'd try leaving it as-is for now.  8" should still leave a 5" or so ledge at the edges, which should be plenty.

I use 6" ducting, but after the impeller, there is a 4" duct leading to the separator ring. That step down in size must really increase the velocity. Seems like it would be better to increase the diameter after the impeller, not decrease it.

[phil (admin)]

I use 6" ducting, but after the impeller, there is a 4" duct leading to the separator ring. That step down in size must really increase the velocity. Seems like it would be better to increase the diameter after the impeller, not decrease it.

I can't disagree with that!  Perhaps they (original designers) did it as a way to prevent the blower motor from overworking (the more air the impeller moves, the more current the motor draws)?  I donno.

[Ken45140]

David:  I am intregued by your comments but have a hard time visualizing your system from the description.  Is there any way you can post pictures of the details of your design/implementation.

I am very interested in learning more.  I have built Phils design for a 10gal garbage can with a shop vac.  Here is a pic of the cart I made for the collection.  Note the raised platform for the ShopVac so I could keep the inlet hose to the ShopVac as short and straight as possible.

I was able to purchase a used, high vol (700cfm/1.5hp) "barrel-top" dust collector.  The motor sits on the top with the impeller shaft vertical, and the inlet port at the center of the top.  The inlet is at the outer edge and has a built-in 90 turn to the exit within the drum is horizontal.  It is exactly like the upper plate in Phil's design.  It sits on top of a 55 gal drum and is ripe for having a larger baffle plate attached to hang below the plate.  I found a picture (crude and small) of this design and it is attached.   

I sort of gather from other posts that you all think that the baffle design will work with the higher flow rates of these larger blowers.  Is that right?

Thanks,
Ken