Experienced Thien user planning to build a 3HP 6" version with fine dust in mind

[Coalsmoke]

Hi all, I wanted to first thank Phil Thien and his team for all of the work they have put in to sharing their wealth of knowledge. A year or two ago I built a 2.5" inlet and outlet Thien cyclone on a garbage can that works really well for everything but fine dust. Table saw dust is captured, but sanding dust is generally not. I'm a 5 days a week woodworker and am installing a 3HP dust collector in my shop. I want to build a new Thien cyclone with a 6" inlet and 6" outlet, both through the top (I guess?) and set it on a 45 gallon drum. Now, what I'm wondering, is if I build the cyclone larger than the barrel, say 40" in diameter and have a cone or funnel connect the cyclone to the barrel, will that extra large cyclone diameter help slow down the fine dust so that it will drop out of the airstream easier? Is it going to have other adverse side affects to the system performance that I am not thinking of at the moment?

Thanks you guys for all of your wealth of knowledge.
Stephan

[alan m]

hi there welcome.

i am  not certain but i think increasing the diameter will slow down the air spining around and reduce seperation (increasing bypass). it depends on your extracter. maybe it can get the air moving fast enough. i doubt it. all the seperaters iv seen are around the size of the barrel. althow there would be less performance drop for the larger diameter.
where that sweet spot is im not sure

i would consider going to a side inlet. there are less bends to sap away your cfm

[Bulldog8]

I've never tried what you are describing, but due to the cone being below the baffle it seems like you wouldn't get a noticeable increase in fine separation. It would seem to be that the baffle has already got what it will get and the remaining fines will have already passed to the filter.

Have you considered raising the height of the chamber? Drum sanding fines are what brought me to this forum in the first place. I use a standard tophat with a 2 HP blower and have had good results. If/when I build tophat version 2.0 I will use a round to rectangular inlet, with the inlet being high in the chamber and the outlet deeper in the chamber than the standard 1/2 D of the outlet tube. (I will increase the outlet depth by the same amount of distance that I have added below the inlet, plus the 1/2 D and see what I get)

Steve

[Coalsmoke]

Thanks guys for that info, I figure that just saved me about 5 hours of cutting apart my 6" design and rebuilding it  ;)  I never gave thought to the idea that the cyclone needs a certain airspeed to keep the dust particles against the outer walls and out of the airstream heading back to the DC. I'll try what you guys suggested with making a taller unit the same diameter of the barrel and using a little longer outlet tube.

Thank you again,
Stephan

[Contemporarycraft]

Coalsmoke

I think I have done what you are now going to do.  I have a separator 20" diameter and 16" tall.  Ill post a pic at some point-not really pretty.  It is essentially like the top part of a cyclone with rectangle inlet and air ramp.  Instead of the cyclone cone at the bottom I put a baffle on it because I need something portable.  I roll the whole thing outside to use it-its life started as a 5HP Grizzly double bag unit.  I dont think you will achieve your objective of good fine separation with this sort of scheme.  As I said Ill post more later but for true fine separation I think you really have to go for the full cyclone.  And if you look at the Pentz plans, they arent really very hard to build and dont take up so much floor space.  It was simply too tall for me to wheel around or I would have built it.  When I post pics, Ill add details and perhaps others can give me ideas to try and improve the fine separation.  The user Retired2 seems to be on the ball and Id read his posts/Bill Pentz site before attempting a build to capture fines.

[Contemporarycraft]

Here are a couple pics of what I built.  The baffle detail cant be seen but I did use about a 3" slot.  The blower inlet is 9" diameter and extends to within about 3" of the baffle.  Given the dims of everything, it means the slot to "blower pipe" is about 2.5" on the horizontal plane.

The separator inlet is 5"x7" and has a "straightener" down the middle (making 2 effective 2.5"x7" inlets)-have no clue if it helps or hurts.  The inlet total area is roughly a 7" round equivalent.  I did watch it pull in some dust as I held a can in front of the inlet...it may favor taking the dust in on the inside half of the inlet which would be the smallest effective inside radius. 

Basically need to put a view window in this thing and see whats going on.  Im sure there are improvements to be made by tuning the slot position and working with the blower inlet pipe distance to baffle.  The bell end and straightener in the blower inlet appeal to me as experiments.  Also thinking to use some items from the grocery store to see if I can get any objective idea about separation that would be easily duplicated by others.  I tried sugar which it captures easily and flour which it doesnt.  Maybe look at some other things like hot chocolate mix etc.

But the bottom line is that I dont think you can get to the really fine stuff with this sort of a setup.  Ultimately small particles are still able to follow airflow in these sort of separators and wont fall out.  Large particles experience sufficient centrifugal force even with relatively large diameter separators that they fall out.  I think thats why the sloping sides of the cyclone cone are so critical and why the truly great designs like Pentz work where other off the shelf "cyclones" dont.  For me, I want to make this as good as I can and learn something new (the Thien baffle is clever and you can learn alot about fluid flow tinkering with it)-but I exhaust outside so its really not too critical.  The hoods for my gear are way more important. 

[Coalsmoke]

CCraft, thank you for sharing those photos and info. I'll take a gander over at bill pentz's website and see what is involved with building one of those cyclones. I guess the tapered cyclone is maybe inherently a better design for capturing fine dust.

[Contemporarycraft]

Thats correct.  His site is big but if you just go right to the build instructions you can see its really not hard.  Thin sheet metal like 24ga can be cut byhand.  Thats how i built my setup.  Sheet cost me $14 at a real metal supply.  Much cheaper than box stores!

You will also see that his full advice is a larger blower than you will have.  He comments that for the 3hp 13" impeller crowd it may be best to scale his cyclone to 20" dia as opposed to 18".  This will also increase height slightly.  He simply trys to reduce static pressure so the small blower can still move the CFM he think you need to move in the ducting.  Youll have to see how it feels to you...but the cyclone is way too easy not to try it.  Its rare to find something so well designed and easy to build... And free.

[phil (admin)]

But the bottom line is that I dont think you can get to the really fine stuff with this sort of a setup.

The reality is, conventional cyclones (including Oneida and Clearvue) miss a lot of the flour, too.

Anyone that works with a lot of MDF (like Steve Knight with his CNC connected to a ClearVue) or uses a drum sander (like Fred Hargis with his Oneida) tends to load the filters pretty darn fast.

There was a thread at SMC (interesting reading) where the guy had ganged Dust Deputies.  Still, flour was making it to the vac's filter:

http://www.sawmillcreek.org/showthread.php?184893-Serial-Cyclones-is-this-just-a-daft-idea&highlight=flour

There is a post there (#13) where I indicate my experience w/ flour.

[Coalsmoke]

Thank you Phil, I'm going to read that thread and see what I can gleam from it. It could be that we're approaching a point where I have to accept the limitations of fine woodworking dust and it's ability to suspend in air.

Contemporary craft, that sounds like something I wouldn't have much trouble building. I'll start reading over there and see what I come up with.

[rumwrks]

The slot width does matter as well.  The 3" (really? 3"? that seems pretty large) slot of CCrafts setup is pretty large and undoubtedly hurting his fines separation - although as he notes he doesn't care  ;D.

I ended up widening my slot to 2", which is still wider than normal, due to the behavior of the shavings off of my planer.  I noticed a difference in sucking up piles of sanding dust in my tests with that vs a smaller slow.  Basically I put a clean cloth  filter over the outlet and sucked up a big pile of sanding dust and saw how much made it to the filter.  At 1.25" it did better than at 2", but it was really the difference between practically invisible and fairly noticeable but still darn good.

I don't know if anyone has done any studies on slot width vs HP/CFM (vs all the other things that matter like: separator diameter - bigger separates more but hits your cfm more, inlet/outlet placement, etc... etc...) but more info is interesting.

Based on comparing reviews and observed performance at the low-mid range I'd say that Phils baffle works at least as well and in at least some cases better than a lot of the crappier cyclones and about as well as some of the better ones.  At the high end I haven't seen anyone who has done any sort of comparison so... for ease of build and straight up performance the baffle is still a huge win in my book and while a cyclone _may_ work better at fines separation it will also eat more CFM and is a lot harder/more expensive to build.

If I ever find a higher powered blower cheap I'm still planning on doing another one, hoping to find at least a 3HP or better a 5HP and see how it works  ;D

[sparkysmart]

Contemporarycraft, now that you've had some experience with your "experiment" what's the conclusion?  I've been thinking about all of the features that you built in to your separator and if you've done the experiment I'd hate to have to "reinvent the wheel".