Dust extractor: convert to cyclone?

[Eric The Viking]

You can tell what I'm up to from the questions I ask

I've now got a conventional two-bag extractor. It presently has cloth bags and I'd prefer a plastic bag underneath, both for convenience, and to trap small particles better.

It looks like it could be adapted to have a cyclone inside fairly easily, but I'm not sure of the theory: will it trap smaller particles as well as larger ones, and if it's blown rather than sucked, will that still work?

I'm hoping to do something like this:

But I don't know if the shape of the cone is critical, nor the size of the central tube.

I'd love to know if anyone else has tried this and how you got on.

Cheers, E

 

[Recky33]

I think you may find that the cyclone has to be on the machine side of the extractor so that stuff seperates before it hits the fan, also unless your using at least 2hp its not going to seperate any more than its already doing, it will appear to be doing something in as far as big bits will drop out, but it hasnt got the spin volocity to keep dust at the walls and out of the flow long enough for them to drop.

HTH

Allan

 

[Eric The Viking]

I think you may find that the cyclone has to be on the machine side of the extractor so that stuff seperates before it hits the fan, also unless your using at least 2hp its not going to seperate any more than its already doing, it will appear to be doing something in as far as big bits will drop out, but it hasnt got the spin volocity to keep dust at the walls and out of the flow long enough for them to drop.

HTH

Allan

Thank you: yes, it does help.

The extractor already does spin the air on the output, obviously, which might be useful, I don't know. The motor is only about 1.5hp, which may not be enough.

I think I can make it so that there's no alterations to the extractor itself (the design lets me sandwich the new bits in between the two halves of the metal shell), but it may not work. I'm also not sure what to make the cone from - galvanised sheet would be nice, but it would need a big-ish piece. I might try lino as an experiment, as I've got some decent-sized offcuts.

You've made me think, certainly.

 

[dsk]

Eric just read your post ,might be useful to have a look at http://www.billpentz.com/woodworking/cy ... nekits.cfm everything you need to know about dust collection cyclones etc is there in detail. Hope this helps...........Des

 

[Eric The Viking]

Eric just read your post ,might be useful to have a look at http://www.billpentz.com/woodworking/cy ... nekits.cfm everything you need to know about dust collection cyclones etc is there in detail. Hope this helps...........Des

Thanks,

I'd heard about him but hadn't seen the site. It's interesting stuff, but he does go on a bit though! There's also rather a lot of opinion (for example, hobby woodworkers should use 6-inch piping), which isn't obviously backed by research (it may be, but it's not obvious).

I like the idea of using aluminium tape as an earth inside plastic pipe. It's fairly easy to do and should work well. I'm toying with the idea of using a mop or perhaps a children's small football along the inside to tamp the foil down, but the runs I need aren't very long so I might be able to reach in.

Thanks once again - good link.

E.

 

[sometimewoodworker]

Eric just read your post ,might be useful to have a look at http://www.billpentz.com/woodworking/cy ... nekits.cfm everything you need to know about dust collection cyclones etc is there in detail. Hope this helps...........Des

Thanks,

I'd heard about him but hadn't seen the site. It's interesting stuff, but he does go on a bit though! There's also rather a lot of opinion (for example, hobby woodworkers should use 6-inch piping), which isn't obviously backed by research (it may be, but it's not obvious).
E.

I think that you must have skimmed the site. To be fair it is not written in a way that groups all the vital information in a small area. However it is all there.

http://www.billpentz.com/woodworking/cyclone/DCBasics.cfm#DuctingSize[/url]":2fo32glx]The resistance of our ducting pipe and hoses is so high that a 1 hp dust collector will only give us a real 195 CFM with a 3” pipe, 350 CFM with a 4” pipe, and 550 CFM with a 5” pipe. Dividing CFM/FPM gives ducting area in square feet which converted to a diameter shows we need 6” pipe to get our needed 800 CFM airflow and 4000 FPM duct speed.

http://www.billpentz.com/woodworking/cyclone/DCBasics.cfm#Airspeed[/url]":2fo32glx]For wood dust and chips, careful testing shows airspeed of between 3700 to 3800 FPM is needed to pull in the chips and heavier sawdust from our machine hoods. We then need about 2500 FPM to keep our horizontal ducting runs clear and about 3700 FPM to keep our vertical ducting runs from plugging.

http://www.billpentz.com/woodworking/cyclone/DCBasics.cfm#AirVolume[/url]":2fo32glx]We also need to know how big of a volume of air is needed to be moved at each machine to collect the dust. Knowing that FPM = CFM/Area where Area is the area to be collected from in square feet, we can calculate this volume. A little algebra shows CFM = FPM*Area. We can then measure the area of each machine that needs collection, convert to square feet and then multiply by FPM to get the required CFM. This theory approach works fairly well and shows most large hobbyist stationary tools need between 350 to 450 CFM of air volume for good chip collection. Verifying these calculations with testing is expensive and takes lots of work. We need to test each different type and size of woodworking machine working a variety of materials. Fortunately, almost all of this work was done for us and published ages ago. Since larger hobbyist vendor tools are the same as smaller commercial tools, we can use these same test results. Good chip collection on almost all hobbyist larger stationary tools requires between 350 to 450 CFM just as calculated.

http://www.billpentz.com/woodworking/cyclone/DCBasics.cfm#AirVolume[/url]":2fo32glx]To comply with 1989 government standards to also provide good fine dust collection, these same large equipment vendors and university staff went back to work. Their testing showed that airspeed of at least 50 FPM effectively moves airborne dust. This makes sense because we all know from watching dust particles in a beam of sunlight that it takes very little air to move the airborne particles. With tools designed and built from the ground up to protect and control that fine dust for collection, the prior “chip collection” air volumes work well. Festool and a few other brands have shown with their special tools engineered from the ground up with good fine dust collection built in that totally controls the airflow around where the wood is being machined actually get good fine dust collection with an oversized shop vacuum. Unfortunately, most of us use tools with minimal or no “chip collection” built in. Our tools and their open cutting areas allow the airstreams from our blades, bits, cutters, belts, motors, etc. to blow the fine dust away before it can be collected. Almost all air engineers say the only way to provide good fine dust collection for most hobbyist and older tool designs requires us to replace the hoods, sometimes remake the tools and provide nearly double the air volume to collect the finest dust as it did to collect the heavier chips and sawdust. The calculations show the same thing because collecting the finest dust at most current tool designs requires delivering our airflow over a much larger area than just at the port at the end of a hood. Both the math and testing show we need to provide close to 800 CFM air volume movement to get good fine dust collection.

 

[Ron Rutter]

Eric. The Pentz info is the best you can get. I have built two cyclones for our seniors WW shop. One of his design & one from Wood magazine. The Wood job is not as good but is better for low ceiling situations. You can modify the Pentz design. I built a drop box for both & we haven't had to empty the bags at all after 1 1/2 years!! With 6" pipe (use metal not plastic) I increased the cyclone outlet to 8" (Wood)( 2HP unit) & 10" (pentz)( 3HP unit) This lowers the outlet velocity & leaves the fines behind better. Hope this helps. Ron.

 

[beech1948]

There are always alternates.

I have seen, but not built, a Thien Separator into a conventional two bag dust sucker just like your diagram but it does not use the cyclone funnel. Quite a cheap approach as well.

Have a look at Phil Thiens web site.

regards
Alan

 

[Leo]

I have just made one of these cyclones, it works great, but my bin implodes, I was surprised by how much suction is in the bin itself :? . I am only using a normal vac. 1800 watts and 40 mm. pipes.....it's only for dust, not shavings. Is this usual?, thus getting a stronger bin will solve the problem ?? Or does it mean that my pipes are blocked in some way ??.

Any advice would be good, thanks. ( ps. new, larger pipes, good shop vac. etc. are out of my budget ).....A bin maybe..??.

 

[Bongodrummer]

Leo, I have a similar setup. The static pressure of little shop vacs is quite surprising. It is a lot higher than your average dust collector. So if there is a restriction of airflow at the hose (and there will inevitably be at some points when you connect it up to power tools) you need your collection barrel to be strong enough not to crumple in on itself.
I had to make reinforcements for mine :wink:

Agreed about The Pentz info being the best - that site is awesome if you have the time to sift through. But I don't think he considers a cyclone after the blower as Eric is proposing. I don't know if having the air pushed through, rather than sucked through would make any difference to the airflow dynamics?
Interestingly I got an e-mail from Axminster just the other day, with a new Jet DC that seems to be along similar lines (cyclone is after the blower). The marketing description is predictably useless though, with arrows pointing all over the place and not explaining how it works at all - other than it relying on the word 'cyclone' to sell it. All 'cyclones' are most definitely not equal...

 

[Leo]

Thanks Bongo,

I have since found, after buying another bin of course , that I did have an obstruction in the pipes :mrgreen: , but it forced me to buy a better bin anyway, it works like a dream now. need to adjust it a little, as it does let through a little of the dust, but that's a minor defect.

Leo

 

[Eric The Viking]

I've got a funny feeling, yet to be tested, that the pull-or-push thing is arbitrary. After all, the air moves from high pressure to lower pressure, and as long as that difference is created, why should it matter very much where in the system the fan goes?

The big advantage, if 'fan first' works, is that I don't need a big solid can, as the bag can't collapse (although it might burst!). Severe lack of round tuits at the moment, but I'll get back to it eventually...

 

[Leo]

I am no engineer by any stretch of the imagination :!: , but how can the push method work at all ?? as the suction through the tub is before my hoover, thus stopping stuff getting to my hoover. Wouldn't the fan being first, just make all the debris hit the fan, prior to it being seperated ??? or are the fan fins outside of the tubing carrying the air and rubbish stuff.

I did say that I ain't an Engineer :!: !!!! just curious really :mrgreen:

 

[Eric The Viking]

Wouldn't the fan being first, just make all the debris hit the fan, prior to it being seperated ??? or are the fan fins outside of the tubing carrying the air and rubbish stuff.

Yes you're right, and no, they're in the debris path. That's how the majority of small workshop extractors work.

Mine is a Delta and has metal blades with a 4" inlet and a 2HP motor (IIRC). All the chippings pass through it.

Regards,

E.

 

[Joiner Jim]

Hi
I am thinking of doing the same but I have a home-made extractor powered by an 3phase 380mm diameter in-line fan, the type used for spray booths. The reason I am writing is that I think that you have to have a sealed debris tank ie solid, not plastic extractor bags which may float up the cyclone extract before any waste is in to hold them down.
I am still thinking of building one but using one and a half oil drums connected vertically as I have 1500mm deep bags. I would intend to use the sealing lid to make the airtight connection and already have a huge number of bags that would fit in this. I would intend to put castors on the bottom and cut vertically through the drum, with the lid off, hinge one side and clip the other side in order to open it to let the bag out. I have not worked out the fine dust filtering yet but am looking at doing something like a huge sock with paper or cloth filter. I hope to do all this other than the drum bases at overhead level to free up floor space. Has anyone already done anything like this?

 

[beech1948]

An alternative would be to convert your two bag system to an upper cartridge instead of the upper bag and simply buy some plastic bags for the lower bag.

Then on a large plastic fruit drum 200 liters( ebay) build a Thien separator . The Thien device is before the DC so it is sucked not blown.

see http://www.jpthien.com/cy.htm

see http://www.jpthien.com/smf/index.php?PHPSESSID=g2op3q4fvuhrpk349f5bvddih2&board=1.0

The Thien device can be built into the 2 bag DC in just the way you proposed in an earlier message.

Advantages:-
1) There must be well over 5000 of these built now
2) Problems are few and far between them
3) Its cheap and certainly cheaper than the cost of the cartridge replacing the bag
4) You can build it yourself even using scraps left over from other projects
5) there are numerous blogs and Youtube descriptions about how to do it
6) its free info and a darn site easier to comprehend than Bill pentz mega ramble site
7) It has a cyclone like action

Disadvantages:-

1) Its cheap so many do not believe it and ignore the Thien separator
2) You are 50% on your own..so do the research

Have a look at woodbloke messages one of his later ones discussed something similar.

Al

 

[Deejay]

Morning all

Leo

Pressure relief valves, if you still want one ...

http://www.cyclonecentral.co.uk/PressureProtection/

Cheers

Dave

 

[Eric The Viking]

The issue has always been the bag(s) clogging. They are blown out by the fan (they don't/can't collapse), but too much of the dust clogs the fabric of the upper bag.

I like the idea of a cyclone, because if I can remove most of the dust that way, the filters won't clog as fast, and the air path will have less resistance and more of the fan's power will be used for actually sucking the dust and shavings, rather than overcoming the cloth bags.

I know it's a while but I haven't had time to get to it yet. After looking at Phil Thien's site, etc. I'm fairly convinced it will work, as long as I make the cone a good shape and slippery enough, too (without inducing too much static). It's important the dust can fall rather than stick to the cone.

I now have some galv. sheet and a nibbler. If it's wide enough (not certain yet!), I can construct something and give it a try.

E.

 

[Deejay]

Afternoon Eric

If you have the space available, have a look at Doorframe's thread ...

dust-extraction-and-thien-separators-my-efforts-t60232.html

I built a similar one and it works a treat, sitting on the lathe side of a Camvac extractor.

I used a plastic drum which held pottery slip, similar to these ...

http://www.ampulla.co.uk/prodtype.asp?CAT_ID=114

When it's full the lid seals it up for transport to the tip.

Cheers

Dave