Thread: Dust Collection - It often don't make sense?

Originally Posted by Gunnaduit

Meantime, looks like there is absolutely no point whatsoever in buying a conventional DC as personal protective gear, i.e. for your lungs' benefit. Totally misguided waste of money. Clearly they only work to keep the chips and coarse dust from collecting on the floor, that's all. So I wonder what to do, this has really been a big learning session for me. The only thing I can think of is to use a respirated mask while working.

The purchase of even a 1HP unit is not a waste of money - what is a waste of money is where it is located. If it is located inside a shed it is a waste of time, if it is located outside your shed it is of some benefit. A 2HP is better still since it moves more air. Next comes using larger ducting, Next would be going to a bigger DC.

Another thing I was thinking, if anyone reading cares to pick this up, I seem to remember years ago, 1980s maybe, there was some kind of room air ionizer sold by KTel or someone like that, which was supposed to precipitate fine particles in the room by ionization or static electricity or whatever. Was it a gimmick? Or would a big one of those work to drop out the <1 micron dust?

Electrostatic precipitators are in fairly widespread use in industrial situations but the large size and high voltages used means they are unlikely to see DIY use.

Yeah well I'm going to have to put serious thought into how to get this all happening at my place, either put a weatherproofed DC outside or else somehow squeeze that 2.4m high cyclone collector inside. Nothing's going to be easy about that, at all. At the other end of the system, I'm looking at my Felder combo machine and wondering if its own dust extraction is sufficient in terms of Bill Pentz's ideas about shrouding at the tool.
I'd missed that the Forums even have a dust extraction sub-forum, tucked away under what I thought was stuff about hand tools. Never much liked the way the Forums was split up so much a few years ago. At least the home page needs to be like a map instead of a visually confusing list -- anyhow that's off topic. Thanks, gents, for all the good stuff here.

Originally Posted by Gunnaduit

Yeah well I'm going to have to put serious thought into how to get this all happening at my place, either put a weatherproofed DC outside.

The DC does not have to be weather proof , all you have to do is build a weather proof enclosure for it. Mine is detailed in my shed fit out thread starts from post 127 here. My enclosure is also fairly sound proof so it gets rid of the noise as well for both me inside the shed and my neighbours outside.

Vey useful to see your mini-shed/enclosure, Bob. It gives me an idea. Has anyone on the forum discussed much about calculating the length of a duct run versus pressure loss, to feed to the DC? My best placement option for an enclosure like yours would require a 12m long duct. If that's possible I can start visualising what to do. Maybe I'll start a thread in the dust collection sub-forum and get some help on this, its all new territory for me.

Originally Posted by Gunnaduit

Vey useful to see your mini-shed/enclosure, Bob. It gives me an idea. Has anyone on the forum discussed much about calculating the length of a duct run versus pressure loss, to feed to the DC? My best placement option for an enclosure like yours would require a 12m long duct. If that's possible I can start visualising what to do. Maybe I'll start a thread in the dust collection sub-forum and get some help on this, its all new territory for me.

The pressure loss depends on the flow rate which in turn depends on the pressure loss.

At 600 cfm (which is about all you can expect from a 2HP unit with 4" pipe) the pressure loss is about 0.1"/m so for 12 m you will lose 1.2" of pressure. 600 cfm is pretty hopeless and just not enough air flow to grab fine dust at source.

To get 1000 cfm (that's the Bill Pentz figure of merit) through a 4" straight PVC pipe will require a 4 - 5 HP impeller. The P losses will around 1.25"/m so 12 m will lose 15" (which is more than most DCs can generate) which is useless.

The critical thing here is to use 6" diam pipe. At 1000 cfm the total pressure losses over 12 m will be 2" which is doable.

You can calculate these for yourself here http://www.pressure-drop.com/Online-...tor/index.html

One thing I must point out and you need to be aware of before planning starts. The losses build up as things like bends, blast gates etc are added. In your case you will be designing a system with a dust extractor that is marginal to start with, not your fault but that is the way it is so it needs to be kept in mind. If it were a more capable unit you could get away with a bit of a short cut here or there so to speak but your ducting will have to be spot on and the machines connecting it will have to be also. You need to run 150mm all the way to the machines preferably with no flex; it can be done but requires a lot of thinking about before starting and the mindset that cutting a few holes in machines is not the end of the world. The machines might require extra ports in them to allow air entry into cabinets as no air in equals no air out, cabinet table saws and band saws are very poor in this regard. My band saw for instance would not pick up the dust from the lower cabinet until I vented the cabinet to allow air entry, now it picks up nearly all the dust. This illustrates the lack of design thought that goes into most machines. It is not a five minute job to do all this stuff but the benefits of a clean work place make it worthwhile.

Originally Posted by BobL

The critical thing here is to use 6" diam pipe. At 1000 cfm the total pressure losses over 12 m will be 2" which is doable.

So is that doable with a 2HP motor, say that Major Woodworking Equipment (Sydney) model MWE-DU02S 2HP 1600cfm or are we really talking about a bigger DC than that? Care to suggest one?

Also, I might be looking at 2" pressure loss on 12m of 6" pipe (more probably, after elbows, gates and some flex), but what is the kind of negative pressure realistically occuring at the impeller intake of a 2HP DC? And on a 3HP DC? (Given that the specs on these machines are just so vague, we're probably talking ballpark figures with a bit of educated guessing thrown in). How much negative pressure do you need? In other words, how much pressure can you afford to lose in the ductwork before the suction is just too weak?

I started a thread under the dust collection sub-forum, as I've virtually hijacked this thread, which is not good form, many apologies to the original posters.

Originally Posted by Gunnaduit

So is that doable with a 2HP motor, say that Major Woodworking Equipment (Sydney) model MWE-DU02S 2HP 1600cfm or are we really talking about a bigger DC than that? Care to suggest one?

Also, I might be looking at 2" pressure loss on 12m of 6" pipe (more probably, after elbows, gates and some flex), but what is the kind of negative pressure realistically occuring at the impeller intake of a 2HP DC? And on a 3HP DC? (Given that the specs on these machines are just so vague, we're probably talking ballpark figures with a bit of educated guessing thrown in). How much negative pressure do you need? In other words, how much pressure can you afford to lose in the ductwork before the suction is just too weak?

I started a thread under the dust collection sub-forum, as I've virtually hijacked this thread, which is not good form, many apologies to the original posters.

See my post in the other forum.

Originally Posted by Gunnaduit

So is that doable with a 2HP motor, say that Major Woodworking Equipment (Sydney) model

Why settle for 2HP when you can have a Rolls Royce Olympus?

BAC TSR2 RAF Aircraft Olympus 320 Jet Engine TSR-2. UNIQUE Oportunity | eBay

If you can't get the dust going supersonic at some point, you're not trying hard enough.

Experience has taught me one thing about venting the DC outside either by placing it outside or venting it from a housing inside as I have done. Not a problem in a tin shed or unlined structure. My workshop is a brick garage with timber beams on piers supporting a truss roof with a AC sheet ceiling. Unfortunately there is a (ventilation) gap between brick wall and timber beam which is open to the ceiling space. Keeping the garage doors and windows closed to prevent ingress of the exhaust dust created enough negative pressure to suck goodness knows what from in the ceiling space into the workshop. I first twigged something was up when a bit of insulation puffed into the room. I'm currently sealing off all of this and will keep the door on the opposite side of the workshop to the exhaust open if I find flow is compromised. Best check all the nooks and crannies where you might inadvertently suck bad stuff into the room. Haven't seen this potential problem reported before...