Dust Piping Reality

[David Kumm]

I think where the rubber hits the road here is the effectiveness of the shrouding at the machine. In designing a system you can't just look at the types of machines but the effectiveness within the type of machine at corralling the dust and chips. I run primarily old stuff, although the slider and shapers are euro. Old stuff has lousy dust collection and even with serious modification it is less than perfect. Even the types of chips from a spiral head pick up differently from those of a straight knife unit. I had a planer the made strings about 2" long- they were tough to pick up. Spiral heads make shorter, thicker chips. You need to think about the machinery you will use and how much capacity it will need. We tend to buy based on price more than quality of dust pickup, bearing, motor, and cast iron quality so manufacturers don't present that info to help with the decisions. Don't even get me started on edge sanders. Dave

[Alan Schaffter]

This issue is not black and white- it is a matter of degree with a lot of variables. It is not 6" is good and 4" bad or 800 CFM Ok and 450 CFM not, but I suggest you shoot for the higher numbers. A Dylos may tell you if you have enough collection or at least where your system falls on the good vs bad line. If you are going to err, do it on the side of bigger is better. There are almost no negatives going too big, other than money and maybe noise, though there are things you can do about the noise. I would like to use a Dylos sometime just to confirm what I already suspect, but will not pay good money for one of my own. I learned as much as I could from available information and devoted considerable thought, analysis and design work before I built the best DC system my wallet and desire would allow. I will not wear a mask- I had to do that in the cockpit for too many years, so I will live with what I have, and a Dylos will not likely result in my making major changes. If I had respiratory problems I would have a Dylos and the best DC money can buy, and likely wear a mask..

After reading many, many DC posts here and on other forums, I am concerned that there are legions of woodworkers out there who do not have even a basic understanding of what is happening, what the dangers are, and what is needed in dust collection. If they understand the numbers, maybe a Dylos will encourage them to learn more and strive for better systems. It can be a tough problem. With good shrouds and a well designed DC system with good CFM you can do a decent job collecting dust from many machines, but with others it is not so easy. Some of the tough situations include- dust collection from above the blade on a tablesaw, from belt sanders, OSS, ROS, etc. Also, compare how much time you typically spend doing other dust generating operations compared to the amount of time spent sanding! - a good case for smoothing planes and card scrapers!!

[Dick Thomas]

I think where the rubber hits the road here is the effectiveness of the shrouding at the machine. In designing a system you can't just look at the types of machines but the effectiveness within the type of machine at corralling the dust and chips. . . .

David has hit the nail on the head! You can install a 10hp DC and 12 inch duct, but if the shrouds at the machine aren't well designed, you've wasted your efforts. Those really interested in doing an effective job at dust collection are advised to go to your public library and browsing a copy of "Industrial Ventilation", put out by the Americabn Conference of Industrial Hygenists. It is the manual used in commercial situations, and they put out a new edition every couple years (my copy is over 30 yrs old, so its just a 'little' over the hill - like it's owner). It gets pretty deep into theory, etc., but has numerous illustrations of specific type machines, with guides on shroud locations and recommended airflows. It clears up a lot of confusion.

DickT

[David Kumm]

Dick, When I'm running the Oliver 299 or the big oakley sander I wish i had the 10hp collector. Would go a long way to curing their problems. While not practical my my world I really feel that anyone with 10 drops or more and some bigger machinery should look at a 2000 cfm system. By the time you get to the port, because of the way DC impellers are designed, you will have dropped down considerably. If you have the amps and are using a cyclone, 5hp 15-16" impeller gives you a system that can be dialed in for any home shop application. It is really hard to get the shrouding good on many machines. And then there is a balancing act in allowing enough air into the machine at the right place to feed the DC. I am looking at the dylos because as an accountant in real life I tend to want to put numbers to everything and judge performance relative to those numbers. Doesn't make it right- just my way. Dave

[Randy Dutkiewicz]

(1) When you're collecting chips, you're absolutely also getting fine dust. The notion that a 4" pipe gets the chips but not the fine dust is all marketing, IMHO.

(2) Some marketers will contend that you should spend all your money on your DC and ducting, that getting an ambient air cleaner is admitting defeat. I have never found a shop where their DC with 6" pipes was able to accommodate all the tooling they had. Some operations (even if hand sanding with sandpaper and a block of wood) almost demand some sort of ambient air filter.

(3) If we learned anything from the Great Dylos Group Buy, it was that dollars are not a substitute for clever when it comes to collecting dust. There are guys out there with 4" ducting that are doing great, better than some others with 6".

Completely agree with you on all accounts Phil

[Tim Davis 1947]

To get the CFM thru the line you have to have enough leakage inside the machine that the CFM will flow that amount. The 4 inch system with the correct leakage will work better than a six inch system with not enough leakage or motive air. If you have such a tight system inside the machine that you do no get enough motive air flow the system will not perform.

[Dan Hintz]

Define "leakage". I don't want a system with any "leakage", I want one that passes all air through (eventually) a filter. If you have to "leak" the air past a filter to get the CFM up, you need to rethink your filtering.

[Alan Schaffter]

I'm hoping he means take-up air.

[David Kumm]

Take up air or what I call make up air. Old machines have so many gaps that it becomes a balancing act to plug enough of them to allow enough air in to feed the collector but not so much as to negate it's ability to pull dust. My rockwell 12-14 saw has a 6" port going directly into the 3'x3' base with huge gaps between the table and base, bevel adjustment, and ventilation in the door. You have to plug the right amount and the Dc works surprisingly well. The Knapp saw on the other hand runs a 5" port into a 2.5" hose and shroud making the cfm in the 5" hose kind of irrelevant. Almost any system works with the new saw. Only a large system works on the old stuff. Dave

[Tim Davis 1947]

If you have your equipment as closed up as you can thinking that will help dust collection it is just the opposite of what you should do. Most machines have enough leakage to supply the needed motive air (air that transports the dust to the DC). If you had no leakage you would pull a vacuum on your machine and no dust collection would occur or not enough leakage and your line velocity would be lower than needed and dust collection would be poor and the line could plug. This depends on the length and turns in the line (resistance of system).

[Alan Schaffter]

If you have your equipment as closed up as you can thinking that will help dust collection it is just the opposite of what you should do. Most machines have enough leakage to supply the needed motive air (air that transports the dust to the DC). If you had no leakage you would pull a vacuum on your machine and no dust collection would occur or not enough leakage and your line velocity would be lower than needed and dust collection would be poor and the line could plug. This depends on the length and turns in the line (resistance of system).

Some machines like a cabinet tablesaw or bandsaw, barely have enough "leakage." If the user has blocked off the elevation and tilt slots or under table gaps, and is using a ZCI it can be really bad. Also, it is more than just the total cross-section of the openings, but how they are configured. Not all openings are created equal. An opening that is partially obstructed or makes some bends, essentially anything that creates turbulence and static pressure resistance will affect dust collection efficiency too. The ideal cabinet saw should have one or two large inlet ducts whose cross sectional area equals or exceeds the DC/cabinet outlet and which blow incoming air past the blade towards dust outlet.

But think about it, with just a minimal amount of suction on the cabinet, any dust down there isn't going to escape. It will settle in the cabinet or eventually be sucked out by the DC. The toughest place to collect dust from a tablesaw is above the blade. No amount of suction in the cabinet is going to capture the dust caught in the blade gullets which is often hurled at the operator! A tight, above-blade shroud, which is nearly impossible to achieve, will have some of the same problems as blocking the cabinet openings. That is one reason I went with a bristle dust shroud like used on many CNC machines. The bristles stop the dust from be hurled outward, conform better to the wood, and let more air in than a hard sided blade guard. It is still not perfect but works pretty well, but I can't use it all the time.

[Tim Davis 1947]

What he said......

[Mike Cruz]

Darrell, I have run all 6" pipe to each machine. If I can't get 6" to the machine itself (can't alter the port), I split it off into 2 4" pipes (like for band saws...one over one under). Works great.

[Greg Portland]

(2) Some marketers will contend that you should spend all your money on your DC and ducting, that getting an ambient air cleaner is admitting defeat. I have never found a shop where their DC with 6" pipes was able to accommodate all the tooling they had. Some operations (even if hand sanding with sandpaper and a block of wood) almost demand some sort of ambient air filter.

The air cleaner is not an instant fix if there is dust in the air (it will take 15-20m on average to scrub the air in an entire shop). As long as someone recognizes this then there isn't a problem. A downdraft table is easy to build and greatly reduces the fine dust when you are working on small tasks (hand sanding, routing, etc.).

[jim gossage]

However, if dust is allowed to escape due to low CFM or lack of a kinetic barrier, it will quickly spread out in all directions, in an ever expanding sphere. Even a sphere 6" in diameter has many times the volume of a 6" long 6" diam. DC pipe (pi r sqrd L vs 4/3 pi r cubed.) That is where CFM comes in. Unless you have sufficient CFM it is nearly impossible to collect the fine dust once it is only an inch or so from the machine.

It may not make a big difference, but I think your comparison might be incorrect. I think a 6" in diameter sphere would fit into a 6" diameter cylinder. According to your formulae, a "sphere 6" in diameter" has a volume of 113 cu in, while a "6" long 6" diam DC pipe" has a volume of 170 cu in. Now, if you are talking about the dust sphere expanding 1" on all sides to 8", then the 8" sphere has more volume (267 cu in) than the 6" cylinder.