I am building another Separator lid to be used just for my down draft portable sanding table and router and plan on making the drop slot 3/4" wide instead of 1 1/4". Would that increase collection of fines, or be too small? I know 3/4" is small but there will never be anything large going in this one, just sanding dust and chips from router.
It will improve separation but I'll just warn that the flour we get from sanding is a challenge, even with conventional cyclones.
Yep, familiar with the flour problem as I already have 2 of the Thien style separators, but have a
1 1/4" drop slot on those. Wanted to try a smaller one on this one, in fact I made it today and if I don't like it I can always widen it.
I guess this is more of a question than a statement. It seems the high air velocities required to keep coarse waste entrained for conveying becomes your enemy when you are trying to separate fines. So, I would be experimenting with ways to reduce the air velocity in the separator. The most obvious way is a larger than normal diameter. Another idea is one or two strategically placed baffles perpendicular to the drop slot to intentionally create turbulance.
Quote from: retired2 on February 04, 2015, 05:34:00 PM
I guess this is more of a question than a statement. It seems the high air velocities required to keep coarse waste entrained for conveying becomes your enemy when you are trying to separate fines. So, I would be experimenting with ways to reduce the air velocity in the separator. The most obvious way is a larger than normal diameter. Another idea is one or two strategically placed baffles perpendicular to the drop slot to intentionally create turbulance.
We need high enough velocity to keep the stuff against the wall, but we need a transition to a low enough velocity for it to fall. Tough combo.
Maybe borrowing that baffle concept from the Department of Energy is the smart move. This would force the airstream (and whatever is in it) down into the bucket. So imagine a baffle that is tight to the wall nearly the entire circumference, but has a 1" or 2" notch and a ramp that hooks whatever is meandering against the wall. You wouldn't want the hook to be too high, otherwise you'll get siphoning.
Thoughts?
Quote from: phil (admin) on February 05, 2015, 07:44:04 AM
Quote from: retired2 on February 04, 2015, 05:34:00 PM
I guess this is more of a question than a statement. It seems the high air velocities required to keep coarse waste entrained for conveying becomes your enemy when you are trying to separate fines. So, I would be experimenting with ways to reduce the air velocity in the separator. The most obvious way is a larger than normal diameter. Another idea is one or two strategically placed baffles perpendicular to the drop slot to intentionally create turbulance.
We need high enough velocity to keep the stuff against the wall, but we need a transition to a low enough velocity for it to fall. Tough combo.
Maybe borrowing that baffle concept from the Department of Energy is the smart move. This would force the airstream (and whatever is in it) down into the bucket. So imagine a baffle that is tight to the wall nearly the entire circumference, but has a 1" or 2" notch and a ramp that hooks whatever is meandering against the wall. You wouldn't want the hook to be too high, otherwise you'll get siphoning.
Thoughts?
That's another idea worth trying, and it might be worth trying the hooks with and without the current continuous slot. My baffle idea was just some verticle obstructions, not too high, placed at several locations around the slot.
I'm not sure if those obstructions would behave like your hook idea, or whether they would act more like a snow fence and dump the powder on the leeward side of the obstruction. To extend the snow fence thinking, my obstructions could be perforated to allow some air passage at a slower speed.
I guess the difficulty with advancing these ideas is that, even if they hold promise, they are only of use in a separator that will be used exclusively for fines. If you even accidentally sucked up some chips, you would have a very quick plug.
It's fun to "think out of the box", but you quickly get to the point where you gotta build a prototype to see if t holds promise, or if it is a complete failure. Are there any drywallers here?
Hmmm....just had another thought Phil. Your hook concept is going to push more air into the waste drum than with a conventional baffle. For that air to go into the drum, there must be a place for it to return. It would seem the place to vent the drum would be in the center of the baffle where the air is cleanest. I'm not sure what the vent should look like, one large hole, or a bunch of small holes intentionally sized to somewhat restrict airflow, and control waste bypass.
My Thien is a crude lash-up with the baffle pushed down into a plastic waste bin. The baffle is held in place by the slight downward taper and the spring in the walls. This bin has a series of indentations down the side to stiffen the thin and otherwise flexible plastic walls. Hence the air stream is forced against the wall and bumps along againsts this "rough" surface.
I have noticed that very fine dust ends up in the bottom of the collector. I have been so ashamed of my lazy build that I not mentioned this before. I checked today and indeed the very fine dust has been extracted. It looks as though this unintended structure might work for your sanding dust. The indentation are about an inch wide and 3/16 of an inch deep separated by a 1" wide smooth wall.
Quote from: BernardNaish on February 05, 2015, 11:52:25 AM
My Thien is a crude lash-up with the baffle pushed down into a plastic waste bin. The baffle is held in place by the slight downward taper and the spring in the walls. This bin has a series of indentations down the side to stiffen the thin and otherwise flexible plastic walls. Hence the air stream is forced against the wall and bumps along againsts this "rough" surface.
I have noticed that very fine dust ends up in the bottom of the collector. I have been so ashamed of my lazy build that I not mentioned this before. I checked today and indeed the very fine dust has been extracted. It looks as though this unintended structure might work for your sanding dust. The indentation are about an inch wide and 3/16 of an inch deep separated by a 1" wide smooth wall.
It would be pretty easy to take that a step further and simply build a separator whose inside wall is a washboard. In fact if the washboard were angled down toward the drop slot that would incorporate Phil's idea of a hook. However, that would complicate the fabrication.
I would love to see a picture or drawing of the added baffle you all are talking about, as I cannot quiet wrap my head around the idea.
Quote from: tvman44 on February 05, 2015, 04:29:11 PM
I would love to see a picture or drawing of the added baffle you all are talking about, as I cannot quiet wrap my head around the idea.
Without going to the trouble of mocking-up these ideas, let me try to describe what I think each of us was thinking, and for the sake of this description forget how each baffle would be installed or attached. Here goes:
1) Phil's concept: Imagine a sheet metal baffle - a full circle with no drop slot. Draw a circle on the baffle 1" in from the outer edge. That is arbritary, maybe it should be 3/4", maybe it should be 1-1/2". Who knows? We are in uncharted waters! At some yet to be determined number of places, cut into the baffle radially from the edge until you reach the circular line. Then continue the cut following the circular line. Cut along the circular line in the direction of the air flow. Stop the cut on the circular line when it is approximately 1" long (maybe 2") Now, bend this tab up 45 degrees. So what you have is something that looks a little like a fin on a turbine. How many fins are needed? Who knows?
2) My idea: Similar to Phil's, but the baffle would have a drop slot much like the current practice, but at some yet to be determined number of places, there would be a vertical tab. I have no idea how high or how many, but I'd guess maybe three of four tabs 2"-3" high. The tabs would be perforated with 1/4" diameter holes to allow air to pass through, but to be slowed down. This is the principle that causes snow to drift on the leeward side of a snow fence.
3) Bernard's discovery: He found that the ribs on his waste container partially produces the effect we are trying to achieve in the two ideas above. So, I just built on the idea by suggesting that the ribs be exaggerated somewhat to improve the effect. Here's one possibility. Imagine a conventional top hat design with a normal width drop slot. Now, cut wooden dowels to the height of the separator chamber. Cut these dowels in half down their length, so that you have half circle dowels. Attach the flat side of these dowels to the wall of the chamber directly over the drop slot so that you have a washboard. Maybe, the dowels need to be shoulder to shoulder, or maybe they could be spaced apart at regular intervals.
Now the ultimate variation on this idea is if that washboard effect, instead of being vertical, were angled 30 or 45 degrees in the direction of the air flow. That incorporates Phil's thinking from #1 above. It slows the air, but also directs it into the waste bin. The question of course is how in the devil do you fabricate something like that - vertical is easy, rotate it even a degree or two, and you have a real challenge.
Ok, now I am beginning to get the drift. Thanks.
Anything such as corrugated roofing cut at an angle would work.
Quote from: tvman44 on February 05, 2015, 06:17:26 PM
Ok, now I am beginning to get the drift. Thanks.
O.K. Now go build one of each and tell us how they work. If they don't perform as advertised, I'm sure we can come up with some mods for you to try! ;D
Thanks.
I think I will try working on the air velocity first combined with a narrower slot. While trying some things there, I will likely work up a "fin" design as it sounds like the one that would be easiest for me to execute.
Quote from: jnug on February 21, 2015, 05:03:17 PM
Thanks.
I think I will try working on the air velocity first combined with a narrower slot. While trying some things there, I will likely work up a "fin" design as it sounds like the one that would be easiest for me to execute.
Keep us posted!
As an experiment , I temporarily stuck some 1/4 in thick ply strips on my pail wall in the drop zone with double sided tape . The length of the strips bridge the top of the cover to the baffle and approx 3/4 inch wide. I am happy to observe that it improved the fine dust collection tremendously. It seems that these "turbulators" work very well. See attachment .
A useful experiment. It looks as though you are on to something here. I wonder what would happen if yours strips were angled down towards the slot? Again what would happen if the strips were thicker? Sorry - my mind is racing ahead of my concern for your work load.
Quote from: BernardNaish on March 15, 2015, 12:43:05 PM
A useful experiment. It looks as though you are on to something here. I wonder what would happen if yours strips were angled down towards the slot? Again what would happen if the strips were thicker? Sorry - my mind is racing ahead of my concern for your work load.
"angled down towards the slot " Do you mean for example angled at 70 degrees in the direction of air flow instead of my 90 degrees or you mean thick at the top and thinner at the bottom or both.
Quote from: sportflyer on March 15, 2015, 02:43:44 PM
Quote from: BernardNaish on March 15, 2015, 12:43:05 PM
A useful experiment. It looks as though you are on to something here. I wonder what would happen if yours strips were angled down towards the slot? Again what would happen if the strips were thicker? Sorry - my mind is racing ahead of my concern for your work load.
"angled down towards the slot " Do you mean for example angled at 70 degrees in the direction of air flow instead of my 90 degrees or you mean thick at the top and thinner at the bottom or both.
I'm pretty sure he means angled the way I described it in my earlier post in thiis thread. In that post I suggested the ribs be angled in the direction of the airflow. So instead of your ribs being vertical they would be rotated, say 30 degrees. Now as I pointed out in my post that creates a real fabrication challenge because they can't be flat because they need to follow the curvature of the drum.
Quote from: retired2 on March 15, 2015, 04:08:07 PM
Quote from: sportflyer on March 15, 2015, 02:43:44 PM
Quote from: BernardNaish on March 15, 2015, 12:43:05 PM
A useful experiment. It looks as though you are on to something here. I wonder what would happen if yours strips were angled down towards the slot? Again what would happen if the strips were thicker? Sorry - my mind is racing ahead of my concern for your work load.
"angled down towards the slot " Do you mean for example angled at 70 degrees in the direction of air flow instead of my 90 degrees or you mean thick at the top and thinner at the bottom or both.
I'm pretty sure he means angled the way I described it in my earlier post in thiis thread. In that post I suggested the ribs be angled in the direction of the airflow. So instead of your ribs being vertical they would be rotated, say 30 degrees. Now as I pointed out in my post that creates a real fabrication challenge because they can't be flat because they need to follow the curvature of the drum.
Yeah , that would be difficult to machine properly due to changing curvature :( . I wonder whether it necessary to follow the drum surface that accurately . Perhaps a little slop is OK ? I will see how much slop there is . Also now we are deflecting some of the sir directly into the slot and could possibly churn up the stuff below the baffle .
well after watching the dust in my can i can see it swirling around circumference down to the bottom. i like retired2 half a dowel idea maybe it could be steamed into shape
First I tried beads of silicone glue. You can do any angle you like and follow the contour of the can. It didn't help. I figured maybe it wasn't sticking up high enough or wasn't slick enough, so I switched to a rubber weather strip called I think a round seal or something like that. McMaster sells it, it is self-adhesive. Still didn't help.
While I was doing this testing I had my 16-32 drum sander. You really need fairly large volumes of dust, and you need a way to accurately measure the bypass (I used a kitchen scale set to grams, and was measuring my vac bag).
Eyeballing better/worse for fine dust isn't going to get you anywhere.
Most of the fine dust that bypasses never makes it to the wall, it simply short-circuits the entire thing. So I'm a bit dubious that anything you do to the wall is going to make a big difference where the finest dust is involved.
Quote from: phil (admin) on March 15, 2015, 05:55:48 PM
First I tried beads of silicone glue. You can do any angle you like and follow the contour of the can. It didn't help. I figured maybe it wasn't sticking up high enough or wasn't slick enough, so I switched to a rubber weather strip called I think a round seal or something like that. McMaster sells it, it is self-adhesive. Still didn't help.
While I was doing this testing I had my 16-32 drum sander. You really need fairly large volumes of dust, and you need a way to accurately measure the bypass (I used a kitchen scale set to grams, and was measuring my vac bag).
Eyeballing better/worse for fine dust isn't going to get you anywhere.
Most of the fine dust that bypasses never makes it to the wall, it simply short-circuits the entire thing. So I'm a bit dubious that anything you do to the wall is going to make a big difference where the finest dust is involved.
That's disappointing Phil, but thanks for all that testing. If you are right about the by-passing talc never making it to the outside wall, my guess is a bellmouth outlet pipe simply makes matters worse.
Another thing that I was starting to worry about is the frictional losses that might accompany a washboard separator wall.
Back to the drawing board!
I am not aiming for perfection . My main interest is balsa dust since that is what I generate the most . Those vertical strips seem to help .
I mean angled at 70 degrees in the direction of air flow. I was thinking the dust would be "screwed" downwards. I would have thought thin battens were flexible enough to twist and follow the curved wall. You might even be able to use balsa wood if it were coated with a hard finish. If this proves impossible then changes in the width, thickness and spacing of the vertical battens may be the only variables that can be tried.
I think the rectangular section of your battens could be why you are getting different results from Phil. Washboard ripples are quite different from an abrupt castellation. There are all sorts of possible turbulent flows around the "square" edges. My "lash up" bin has quite acute changes in angle of the stiffening indents around its circumference. Not at all like corrugated roofing. This does remove fine dust. Cannot say how much because I have not measured it but a significant layer of fine dust sits in the bottom of my bin every time I empty it.
What we are trying to do is slow up the very fine dust so that it will fall downwards through the slot. It has little mass so are we trying to "draw" the energy out somehow? The micro turbulent flows across abrupt changes in section might do this. Of course r2 is right to remind us that this will be at the cost of air velocity.
Another thought! Are these particles so small as to be attracted to electricaly charged plates. The words electrical precipitators floated slowly in so I searched and found: "An electrostatic precipitator (ESP) is a filtration device that removes fine particles, like dust and smoke, from a flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit." Just a thought.
Electronic postage or kitchen scales are remarkable accurate – not laboratory standard but good enough particularly if comparing before and after.
The difference in results being reported may have more to do with the particle size than separator design. Sanding dust from one wood species can be different than from another. Is it dust or is it talc, like drywall dust? Is there a technical difference between the two or is it just our individual perception?
Yes r2 is right about standardisation. However sportflyer has a specific need and has found an improvement, albeit subjective. Some quick weighing with and without the ply strips should quickly establish if he is on the right path for his application.
Quote from: retired2 on March 16, 2015, 06:50:40 AM
The difference in results being reported may have more to do with the particle size than separator design. Sanding dust from one wood species can be different than from another. Is it dust or is it talc, like drywall dust? Is there a technical difference between the two or is it just our individual perception?
That is a good point.
I'm not convinced that fines separation can be improved by doing anything at the wall. I don't even care much about what is at the wall. It is the stuff that is so fine that it won't hug the wall, or which bypasses altogether (never enters rotation) that is plugging the filters. You can't even see it at the concentrations that exist in the separator or pipe, but it is there.
When I was working on trying to improve fines separation by various additional baffles and modifications to the wall, at my darkest hour of frustration, I reached out to Steve Knight who uses his ClearVue for his CNC operation. I asked what kind of separation he was experiencing. He tired of plugged cart. filters, he said, and built a bag house.
More research (talking to manufacturers of industrial gear and also users of hobbyist cyclones) made it abundantly clear that my notions about what conventional cyclones could accomplish were way off. Most of those ideas were based on what I had read in woodworking forums. I later realized much of that stuff was posted by guys that barely used their shops, or may even have been sock puppets.
But the reality is, sanding generates enough "sanding smoke" that cart. filters plug pretty quickly.
So far I haven't figured out a way to improve things. People ask me if I have something up my sleeve, that I haven't told anyone about. Nope, I've got nothing. I've tried all sorts of stuff, more than you can imagine, and found nothing.
That's a pretty discouraging report Phil, and even if you had "something up your sleeve" I worry that it might be so specialized that it would only work well for powdered waste. If it didn't also handle planer shavings, it would be of no interest to me. And I could not afford to give up even a few more CFM's to a separator that creates additional losses in order to capture powder.
There may be a few people who work exclusively in powder producing tasks, but my guess is the vast majority of us hobbyists jump from one machine task to another; one minute we are producing big shavings and the next we are sending sanding dust into the air.
I couldn't justify the time or cost of setting up multiple specialized dust collection systems. I need a single system that is a "jack of all trades", if it is a "master of none" then so be it.
And everytime I think I should buy a Wynn filter for my setup, I think about how easy it is to clean my bag filter when it gets too much cake.