major woodworking cyclone dusty

[TP1]

There only ways I know of determining the effectiveness of a dusty have little to do with anything other than airflow (volume and velocity) and the size/effectiveness of the negative pressure bubble (or the effectiveness of airflow through the machine). This requires measurement and data that are meaningful. The fine dust that harms health cannot be seen, so observation is a poor guide. We need data.

As has been mentioned by several of the posters, the data provided by the manufacturers have largely proven to be meaningless. I often wonder if the quoted readings are taken with a naked impeller and the motor spinning at 60 Hz.

Even the motor and impeller size, whilst a guide, do not provide adequate data. If we add static pressure developed, we get better, but far from definitive data because some impellers are superior at overcoming resistance (duct and machines) and maintaining higher flows for a given static pressure. That's why the fan curve is important.

Because air is almost incompressible at the pressures/velocities we use, duct size is often an absolute limiting factor. To get 800-1,000 CFM through a duct and a machine with anything less than a 6" pipe is highly unlikely, regardless of motor and impeller size.

My data say that a 3 kW (4 HP) motor spinning at 60 Hz and driving a 15" impeller on a modern cyclone with 6" PVC ductwork draws about 900 CFM (plus or minus 50 CFM, depending on the machine). The research indicates we need 800 CFM, and good hoods/shrouds, to effectively capture the very fine dust.

Cheerio!

John

John, the problem I have with theories of ideal air flow, motor size etc is that despite the calculations, when you connect one machine directly to a smaller dusty the air flow easily takes care of the waste. I do not see dust extraction as a one size fits all solution. If I hooked up a 3 or 5 HP cyclone to a single machine it would make more noise but the same amount of dust will still end up in the bin like it does already.

There are possible exceptions like with the older style of cabinet saws where the saw dust just drops everywhere inside and you need the air flow of a tornado to have an impact. Modern saws with European style plumbing inside have more efficient dust extraction.

Most people still use the old style of dust extractor with a cloth bag which is a safety hazard. I think people should be encouraged in the first instance to buy dust extractors with pleated filters and cyclones over conventional bag types. Many blokes have a budget for purchases and I think it would be a great shame if people reading threads like this didn't end up buying a cyclone and pleated filter type because they could not afford to buy the theoretical ideal.

Cheers
Tasso

[John Samuel]

Tasso,

You're right. We all have a budget, and some have deeper pockets than others. One of the reasons I like BobL's optimised 2 HP dusty is that is puts reasonable (not great, but reasonable) dust collection within the economic reach of the great majority of woodies. But it was not for me. I did a dummy spit about the disgusting state of my shop and after some reading decided to both clean up my shop and to protect my health better.

Today my son and I started a set of bookshelves and made a coffee table. He was wearing his street clothes, but was clean at dinner time despite spending most of the day using the thicknesser, drum sander, linisher and table saw. More importantly, the air in the shop is clean. There was a time when it made my nose tingle. I could always smell the wood dust. But no more.

My drum sander looked almost as clean when operating with a 1 HP dusty as it does now with a 4 HP cyclone, but looks can be deceiving. The big chips can lie on the floor for all I care. I am not breathing them. It's the very fine, invisible particles that concern me. Back in the days when I used a 1 HP dusty, the drum sander looked clean ... until one looked carefully at the surfaces within several feet. They soon became covered in a superfine dust that was invisible at first, but which built up over time to become visible. This is the stuff I was breathing. I deliberately did not clean these surfaces for a while just to see what would show up. Plenty showed up. In another area of the shop the shop vac turned out to be even more effective at producing superfine dust than the drum sander.

So I hit the references. Dust collection is a mature science; it is well (but not perfectly) understood. The Cincinatti Fan folks alone have published a vast amount of material over many years. The different types of motors, impellers, cyclones and filters are all thoroughly tested and these data are available. These data have been published in peer reviewed journals, a world different to the demonstrable rubbish we see in WW magazines, which I do not trust. I recall some years ago a journo getting caught writing a nice review on a car after being paid a secret commission to do so. I simply don't trust the data in magazines. Every time I see a 2 HP dusty advertised as pulling 1,200 CFM I want to throw up. These claims are misleading if not dishonest, because they do not clearly state the conditions under which these figures were arrived at.

No two shops are alike, as are no two machines. However, the vast body of data available can be condensed into some pretty good rules of thumb to guide us. I used these rules to guide my solution selection.

1. We need an airspeed of at least 50 FPM at the machine to grab the fine dust. The airspeed of the negative pressure bubble drops off very quickly; dramatically quickly, as the bubble grows in size.
2. To get a decent sized negative pressure bubble and to capture fine dust at the machine we need to pull about 800 CFM at the duct/machine. (Some say 1,000 CFM.)
3. To do this we must have a 6" duct, and an impeller/motor combo that will pull that 800 CFM through the machine and ductwork.
4. To pull that much air through a 6" duct we need 4-5 HP and a quality impeller. A 3 HP motor is borderline, and sometimes on the wrong side of that border.
5. To effectively separate the dust out we need either a good filter or a modern, effective cyclone. Generally, the modern cyclones are easy to spot. They have a ramp which angles the airflow so it spins the air down the cyclone body in a spiral.
6. Finally we need to keep the dust moving in the duct at about 4,000 FPM, to avoid particles falling out of suspension.

Then we have personal preferences and needs. I needed a small footprint for my smallish shop. I badly wanted to vent outside to eliminate filters and leaks.

Only one machine offered 800-1,000 CFM (real CFM ... through the machine and duct) 4,000 FPS, a small footprint and venting outside. So I bought it. My only regret is not spending about $5-600 more to get a bigger impeller and 8" main line duct.

My recommendation has long been to sit down and prepare a wish list before a solution is purchased. This is similar to what you said when you wrote, "I think it would be a great shame if people reading threads like this didn't end up buying a cyclone and pleated filter type because they could not afford to buy the theoretical ideal". I know BobL agrees with you here. He has often recommended a cartridge filter to people seeking advice for the same reasons.
My wish list has been illustrated here. Others have different priorities and budgets, which is fine. But if we have, for example, a stated requirement for a minimum of 800 CFM through the machines and ducts, we will soon discover that very few dustys will provide this, and so our list becomes very short quite quickly. If, on the other hand, a woodie is happy to focus on collecting the visible dust and to keep his shop reasonably clean, that is his call alone, and he can do this much more economically than by doing what I did ... but the research data are clear ... he will likely be breathing fine dust that he can't see.

There are no right answers, just solutions to stated problems. All I am doing is suggesting we state the problem and the requirements clearly before moving to potential solutions. Sadly, it seems some buy a solution before stating the requirements in operational, objective terms.

Finally, here is one of the tests that convinced me to do a proper job. I glued the top of a piece of A4 paper weighted with a piece of dowel at the bottom to a bit of timber. I moved this paper towards the naked inlet of my old dusty until the deflection of the bottom of the sheet was 2" from vertical. Then I moved it back until that deflection halved to 1". Then I moved it back again until it halved again to 1/2" . The piece of paper only had to move a few inches before the deflection halved. This told me that no matter how good the suction felt at the inlet, that only a few inches from the inlet the airflow fell dramatically and was unlikely to give me good dust collection. High air speed collects fine dust. High volume gives us the bigger negative pressure bubble with enough residual air speed to do the job at hand. High volume requires power, a good impeller and big ducts.

Cheerio!

John

[John Samuel]

And dont forget, most machines dont have enough air inlets to allow for suction.


Goes and sits down after can of worms spilled . . .

Arghhhhh ...

That is likely the biggest can of worms of all!

When ronboult measured the airflow in my system it soon became clear that the biggest losses were the machines and their hoods/shrouds ... not the ductwork. My worst machine for dust collection is the thicknesser/jointer. I reckon I could put a 20 HP motor on a three foot impeller and not increase airflow ... the air simply can't get through the machine.

There are days when I wish I could meet the engineers who designed this machine ... in a dark alley.

Grumble, bitch, moan and complain!

John

[TP1]

Tasso,


There are no right answers, just solutions to stated problems. All I am doing is suggesting we state the problem and the requirements clearly before moving to potential solutions. Sadly, it seems some buy a solution before stating the requirements in operational, objective terms.

I very much disagree that smaller dusties cannot be used effectively connected to a single machine. There is no dust all over the workshop after machining either. We know more powerful dust extractors have greater airflow so there is no point repeating it.

I have heard it all before on this forum - You shouldn't have a table saw with less than 3HP -(5 HP is better). Bandsaw should be at least 3 HP - (5 HP is better), Dust collectors should be at least 3 hp- (5HP is better), Minimum shed size is 40 square metres or you have no hope, etc, etc. I shudder to think about the number of people who have been put off taking the hobby further with talk that they are wasting their time "unless you get a big muther of a machine machine just like mine"

I really think people with actual experience of the machine in question should chip in ( if there are any more here) because they have first hand information. I am afraid making assumptions at the best of time is fraught with danger and without a shred of experience with the machine in question, it is simply not valid. We know a 3HP motor will draw more air but the MW machine connected directly to the machine is also an excellent choice.

[John Samuel]

We know a 3HP motor will draw more air but the MW machine connected directly to the machine is also an excellent choice.

Indeed, a 1.5 to 2 HP dusty connected directly to the machine can do a reasonable job. BobL showed that with his optimisation of a generic 2 HP dusty.

All that matters in your shop is that you are happy with the result. It sounds as if you are.

I am happy with my result too.

Cheerio!

John

[Chris Parks]

I too regret John didn't buy the Max, I would have been $500 better off.

What is good to see is that during the initial conversations we had I assured him it would do what he needed and he is now enjoying his hobby far more than he did prior to buying the cyclone. My impression from talking to customers was that they thought I was overstating the effect it would have on their work environment when in actual fact I most probably didn't push it enough due to not wanting to appear pushy as sales people can be. One thing I can say with certainty is that I never tried to persuade anyone to buy a cyclone, they made that decision on the information provided and sometimes from their spouse believe it or not. I had one lady order one and then told her husband to install it as she was sick of hearing him cough and sneeze all the time. It really is good to see so much positive recommendation for the system and it all came about because I made a phone call to the right person at the right time.

[safari]

I certainly agree with Chris. He didn't push me into buying a cyclone but during our discussions he answered all my questions about the CV1800 and it's capabilities and continued to offer advice during the build after I had paid my money. So after I read the Bill Penz site and posts on this forum, and a bit of a shove from my wife, it was fairly easy to make the decision to buy. I have not regretted the decision because the dust extraction is fantastic by comparison to the Dust deputy and vacuum I had connected to my Triton gear and works heaps better than the usual 2hp systems I see in most workshops. I have overhead piping and you can run a hand along the top of the pipe and virtually no dust comes off. The lack of dust coating everything in the workshop makes it a pleasure to be there. While I agree that it more expensive than most other systems , after i experienced the results I consider it is more than worth it.