Replies

1. 
   AntzyClancy | Apr 06, 2006 07:38pm | #1

   Fred,

   Bill is the real expert on this, but I will give it a go.

   1-Though reading it made me realise that fine particules are not trapped by my collector, it also made me realise that almost any DC will let the finest ones that get trapped go througt the filter anyway.  Chip collection seems satisfactory to me with the setup I have.

   You are right if you say that most ("almost any") hobbiest dust collectors do not adequately capture the fine partials that are most dangerous to our heath.  Be aware that there are good options if you have the resources.

   My question: It seems that a 4'' duct will not carry more than 400 cfm. If I upgrade my collector to a 2 or 3 HP good quality cyclone but leave my ducting as it is, will I get any improvement in my overall dust collection performances (supposing same size particule filtration on both units)?

   I larger HP collector with a larger diameter impeller and a very good cartridge filter, will improve your performance considerably.  It is quite possible that your current setup collects chips very well, but in essence is a dust pump that circulates dangerous fine dust throughout your shop.

   Can a monster 3HP cyclone move more air than a smaller one in the same ducts?

   Not sure what you are asking here.  Increasing HP will mover more air in the same ducts, to a point.  Bill recommends: "most small shop woodworkers that use a cyclone separator with fine large cartridge filters need at least a 13? impeller turned by a 3 hp motor"

   Can a unit with higher SP rating improve things in small ducting?

   Although not entirely true, SP (static pressure) is more a function of your ducting and machine dust port size, than it is a function of the cyclone itself.  Your current ducting setup has a very high SP due to its length, the 4 inch diam, the use of flex hose, and the small machine dust ports.  The best cyclone in the world won't change that.  You really need to go to 6 inch ducting and larger ports.

   Maybe I can only buy a bigger (say 1?-2 HP)single stage unit with a canister type filter just to make shure there is really 400 cfm or air moving in my ducts, invest the extra money in proper radiant heating and move air out the window with a big size blower. In other words, use the DC as a chip collector and ventilate the dust outside, providing an even healthier environnement with less investment???

   I am confused.  You want to heat the shop and then blow the air outside?

   Its all just cutting corners.  There are only 2 methods I know of for good dust collection in the shop.  A top notch cyclone with cartridge filters and good ducting.  Or a single stage canister type that you wheel around to every machine.  All of this assumes 6 inch ducting and machine ports.  I wouldn't invest in anything less.

   Was that post too long?

   Not at all.

   Todd

1. 
   jeff100 | Apr 06, 2006 09:41pm | #2

   In all these DC posts I've never seen this issue brought up.  Sharpness of cutters.  Back in the day when I ran a chainsaw a lot, I learned that a sharp chain produced CHIPS.  A dull chain produces DUST.  In my workshop, I keep my planer knives, tablesaw blades, jointer knives, router bits, etc, etc, anything that is supposed to CUT wood SHARP!  I don't see DUST except when I'm sanding, which I try hard to avoid.  My machines cut CHIPS, and lots of them.  Therefore, IMHO, part of the battle to control dust is keeping your cutting tools as sharp as you can.  I can appreciate that there may be a insignificant amout of wood dust created no matter how sharp my cutters are, I don't have any data on that, but I'd bet a beer that the dust created is insignificant....

   I CAN say that I don't see any residual dust collecting on the surfaces of my machines after I've been working.  That should be anecdotal evidence of my claims.  Not to say you don't need chip/dust collection, I have a simple DC system installed and used religiously.  Just stating that it helps a great deal to keep your cutters sharp to keep the wood in a larger form e.g. chips.  Enjoy.

   Jeff

1. 
   AntzyClancy | Apr 06, 2006 11:54pm | #3

   Jeff,Anecdotal evidence is by definition unreliable, and no basis for make any kind of claims.  Your supposition that sharp tools produce little to no dust belies years of study and expert analysis.  I respectfully disagree.Todd

2. 
   Fred | Apr 07, 2006 01:51am | #6

   Thanks for your opinion.

   It is quite possible that your current setup collects chips very well, but in essence is a dust pump that circulates dangerous fine dust throughout your shop.If I understood well the things I've read, a cartrige filter will not be a lot more efficient as of the size of particules it traps compared to a caked bag type filter, will it? The problem is more of the airflow loss because of the obstructed filter. In my case, I dont have sufficient airflow at the tools anyway, so my concerns about the DC are more about  collecting chips and not re-circulating fine dust. But the more I inquire, the more confused I get. I might be wrong...

   Concerning heating, it is my understanding that radiant heating will heat the objects in the shop, not the air. It then becomes less of a problem to ventilate large volumes of air outside the building.

   Fred

    

1. 
   AntzyClancy | Apr 07, 2006 02:16am | #7

   Fed,Whatever your current bag is rated for, you can bet that its a blatant lie.  Put simply, the DC companies use clean filters when rating the CMF (dust pumps), and then they clog them up so that barely any air moves when the rate them for particle size filtering (no air moves).  I is all a big scam, and there are no standards, so companies get away with it. You can get cartridge filters that have been independently tested and certified to perform as advertised.  Bag filters have very little surface area when compared to cartridge filters, which means they restrict air flow and clog up much faster.  By design, cartridge filters pack huge amounts of surface area into small volumes.  Cartridge filters will however clog up at some point if in a single stage DC.  Thus, frequent filter cleaning will be necessary to maintain air flow.  Only an efficient cyclone can prevent this and currently I know of only one proven design: the Clearvue based on Bill Pentz.I am not an expert in heating, but I would think that if you constantly replace ambient air, with new unheated air, you are not going to be able to heat your shop very well.Todd

2. 
   AlanWS | Apr 06, 2006 11:56pm | #4

   I'll try to say what Bob Dodge might, and once he gets here, he can clarify or correct me.

   Venting your DC outside will certainly get rid of the small dust, but you need to find out whether it's allowed in your area, and to know what the consequences will be with respect to A/C, heat and combustion exhaust that can be pulled into the shop. If you do vent outside, it's probably worth it to have the DC on only when needed, perhaps by sensing when blast gates are open, or machines are turned on.

   As far as using more power to pull air through smaller ducts: yes it can be done, but it's not practical because of the very rapid increase in power needed to move the same air through smaller ducts. For instance, 800 CFM is considered an appropriate maximum flow needed for small woodworking machines. Static pressure (SP) is just a measure of how hard we need to push to get the air to flow. If we consider 100' of straight galvanized pipe 100' long, and ignore the very real resistance to getting the air in one end and out the other -- we are only considering flow over that distance -- it would take an SP of 4.3" of water. That means if we filled a vertical section of pipe 4.3" deep with water, the water would be pushing down as hard as we need to push the air to get 800 CFM to go through the pipe.

   How much power would 800 CFM through 100' of 6" round galvanized duct need from the blower? If we assume a 100% efficient blower (nonsense, but OK for comparison) it would take 0.55 HP. In actuality, we'd use a considerably larger motor, something like 3-5 HP in this application, because of efficiency and safety factors.

   How much power would it take to push the same amount of airflow (800 CFM) through 100' of 4" diameter galvanized duct? It would take about 40" of SP, and that would mean about 5.8 HP, assuming 100% fan efficiency, meaning to actually do this would take a lot more. That's more than 10 times as much power required for the same airflow. If we consider using only half the flow, 400 CFM, through 4" duct, it would require a 9.2" SP, corresponding to 0.58 HP at 100% efficiency. In other words, it takes a bit more power to run 400 CFM through 4" duct than to run 800 CFM through 6" duct, and the power requirement goes up very rapidly with increased flow (10 times the power is needed to double the flow).

   That last sentence is what people mean when they say it's
   "impractical".

   I got my numbers from the duct friction loss calculator here: http://www.freecalc.com/ductfram.htm
   and the "fan laws" link at the top of that page.

   
   

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   Edited 4/6/2006 4:57 pm by AlanWS

1. 
   Fred | Apr 07, 2006 01:42am | #5

   Thank you. This is the information I hadn't found elsewhere.

   Your numbers give me a rough idea of power requirements for 100' of pipe. In my shop, there is only 10' of main pipe (I measured it this afternoon, not 20' as I first mentionned), galvanised and straight. Does the 40'' of SP for a 100' pipe fall to 4'' of SP in a 10' pipe? This would mean I don't need a monster collector???

   I guess I'm just talking theory here. I really lean towards a cyclone. But I like to fully understand things before meeting salesmen! And I might wait some more before buying if I find out my situation is not as bad as I see it now.

   Thank you.

   Fred

    

1. 
   AlanWS | Apr 16, 2006 07:09pm | #9

   I'll try to answer, even though it means resurrecting this aging post. The reorganization of Knots made it so the email link did not work, and most of the ways I tried to search for it didn't either. I found the thread now.I think your conclusions would in general be quite similar if you analyzed the real system. My real point was that resistance goes up very rapidly as duct diameter diminishes. The way most small shops are set up, the actual straight line distances matter much less than the duct diameter, the number and types of elbows, and the shapes of the intakes at the tools. A convenient way to summarize all this is to say it's equivalent to some length of straight duct. Of course, blower size, configuration and outlet, filter size, type, and cleanliness, and presence of cyclone, also matter a lot, but I would categorize those as parts of the DC, rather than the duct. To work well, it all needs to be chosen to work together.If you want a decent estimate, try the static calculator on Bill Pentz's site. He has made some simplifying assumptions there. If you want to make your best estimate for your duct runs, the link I gave above is good. If you plug in Pentz's assumptions, it will give your the same result as does his spreadsheet. But it allows you to change those things too, to see how that affects the results.To add to the confusion, while cartridges can be certified to filter small stuff, apparently high quality filter bags can too.

3. 
   DonStephan | Apr 07, 2006 05:04am | #8

   Most or all of your questions are addressed on Bill Pentz' web site. It is not easy reading, but I would recommend the effort. Venting outside will create significant air volume change rates in your shop which are very undesirable. They will significantly increase heating costs, even with radiant heat, because moving cold air will draw heat from warm objects inside. The moving air will also make you feel colder. Air change in many areas increase the humidity level in the shop. ...

   Portable units will collect chips rather well. Permanent duct runs need a minimum velocity of moving air (FPM - feet per minute) to avoid buildup of chips in the pipe. 800 CFM of air is needed to capture small particles at machines. I just purchased an 8" Powermatic jointer, and the owner's guide says "a minimum of 800 CFM is needed" for it. See Pentz materials.

   I agree with others' comments that cartridge filters are necessary, and that woodworking tools all produce some fine dust, even with sharp edges. Jointers and planers will produce much less fine dust than chips, but table saws produce a lot of fine dust.

   You can try various work arounds, but in the end you'll probably have spent just as much money, with poorer results.

   
   

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   Edited 4/6/2006 10:06 pm ET by DonStephan