how to make a 4 inch duct flow like a 2
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You should see the 'dust-port' on my Rikon bandsaw. This literally has a rectangular plate WELDED over the 4" (?) port - covering >85% of the opening. Wow.
Sure, only dust will get past that - so no big damaging pieces hitting the impeller. Great - my impeller is safe and secure.
On the flip side, not much dust (or air) will get past that either. Defeats the purpose, does it not?
Exactlly. Nothing a Sawzall can't fix. Sure on a BS maybe a piece can get through but my ClearView would laugh at it. Fortunately on my Harvey BS, it was removeable by a couple of screws. Compare a flat hole with a hose on it to one with a 17 degree taper and 3/4 inch round over. You lose about 20% right off the bat. These things have been understood for a couple hundred years. Stamped sheet metal. NO excuse not to have a radius.
Doesn't convert the size. Scott's title implies this 'grate' impedes the airflow to something equivalent to a 2" instead of a 4" tube or opening.
Yes - way more complicated. Which is why the statement that this converts a 4 " to a 2" is likely an overstatement. It does in fact reduce airflow but not to the degree of a 2" outlet port would. The main impact a very short impedance (obstruction) has is to increase turbulence in the flow for about 2-3 diameters downstream (the distance depends on geometry, flow rate, viscosity of the fluid, expansibility factor, etc). This causes an effective back pressure that reduces flow and or pressure, depending on the system geometry. The text I used in school was Engineering Fluid Mechanics, Roberson and Crowe.
Yes and no. My aerometer says 2 inch properly executed ( radius and taper) is about the same as the 4 inch grill that has about 30 to 35% area obstruction with the turbulence you mention added in. Shape of the downstream port important too so a quick 90 out of a machine will drop a little more than if it was a foot or two away. Also reference Smith and Morrison. There is some modern CAD simulations that really expose the issues and take into account all the nasty details you studied. Out of my price range but should not be if you are designing machinery. In any case, this execution is just plain stupid. A drum sander is a high volume, low lift problem. My ROS is the opposite, high lift low volume.
One thing we agree on is the degree of difficulty here! The Navier-Stokes equation is not only mind-bogglingly difficult, it can't even be proven there IS a closed form solution, let alone what it is. That's why it's a millennial math problem. I have a copy of Smith and Morrison if you'd like to borrow it.
Its generally there to keep long, thin pieces (think tablesaw) or other random things out of your DC... could it be designed more aerodynamic? certainly, would we all want to pay for it?, probably not. All engineering is a trade off, quality, design, cost , features and most recently, sustainability (QDCFS).
Maybe your DC is undersized to allow for these losses?, looking at your mitersaw station and related piping (from your other post) Id say you have serious losses at your inlet piping using multiple HVAC duct piping and wyes a the head of your system.
Maybe your DC is undersized to allow for these losses?, looking at your mitersaw station and related piping (from your other post) Id say you have serious losses at your inlet piping using multiple HVAC duct piping and wyes a the head of your system.
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I'll chime in on the fun-On these kind of things do not over think it. The parts we use and the designs we employ make it really not worth the academic exercise.
May be fun, but calculating your flow minus static resistance minus the other factors is just mental fun. The inch column measurement along with feet per min are all the we need functionally for figure for sawdust extraction. Bottom line if it works, it works.
May be fun, but calculating your flow minus static resistance minus the other factors is just mental fun. The inch column measurement along with feet per min are all the we need functionally for figure for sawdust extraction. Bottom line if it works, it works.
So, why the post? Is your sander sucking sufficiently or not?
I suspect that, when deciding to manufacture such things as you've at hand, the entrepreneurs did hope to produce a product that buyers decided not to return to the store screaming "This (&&%%(( thing don't Suck, I want my money back!" Not sure how to say it in Chinese, but I suspect they can.
Then again, if we are talking about sucking 'dust' particles, how much air flow do we really need to move a dust particle along?
I do recall, years ago when they were adding all manner of tubes to improve mileage and reduce pollution by car, that gas station 'mechanics' would often 'fix' a rough idle by cutting this tube or that, then plugging the open ends with screws or a similar object. (Back when one set a GM point gap with a matchbook cover)
I refused to pay for such a 'repair,' upon the premise that it did not fix the problem with the system, but by-passed it absent any idea what the long term effects might be to 'the rest of the system.'
That's not to say that they're might well be another way to address the issue than that particular 'obstruction.' After all, look at the SawStop improvements to the table saw - think of all the hot dogs - but is it actually worth the expense?
And with respect to the drum sander, no it did not work very well. It went from some sawdust leakage to none when I cut out the grill. Drum sanders do not make chunks or slivers to be blocked. They produce fine sawdust which is the most dangerous and what we need to collect as efficiently as possible.
If you are an engineer designing a product, then it is NOT academic. It is your job! Expense? Many ducts are leaving a stamped panel. Easy to stamp a radius. If sometimes a tube welded to the sheet, bit of molded plastic is not expensive when we are talking 4 digit price machines. 5 cents maybe for the part, 5 more to install it, add margins through to delivery and maybe $5 retail. It could actually be cheaper to draw stamp a panel with the radius and enough flange that welding on a duct to connect the hose is not needed. We went over all kinds of things like that in the "Design for Manufacturability" program from Troy Institute.
Dust collection improved visibly on my band saw when I removed the grills. I have much more work to do as experimenting shows a focused cross-flow to do significantly better than the suck-what-you-can from open space below the table.
I changed the duct on my TS to a 6 inch. The cabinet is sufficiently large to drop out any chunks. No grill needed. It leaves about half as much in the base as it did originally. I have no lower shroud so somewhat limited what I can do without taking the table off and re-designing the whole thing.
Chris, all seams are taped. Yes, HVAC lines and elbows leak which is why they are taped. HVAC Y's are a disaster, again taped up. All branches have blast gates. 5 HP cyclone. I don't guess, I use a slack tube and an aerometer. When I say it flows like garbage, I fix it and the flow picks up, I know because I measure. I just re-did the branch that goes down to the TS ( right on the other side of the wall, and low duct where the sander, jointer and planer get plugged in. The upper branch with flex duct will get replaced with spiral duct and moved over on the wall by about 5 feet. It serves the band saw, router fence, and spindle sander. Soon probably the drill press. If you would like to gift me with a full Nordfab setup, I am sure it would be a few percent better for several thousand dollars. It would not fix badly designed machines.
How auto emission's were done in the short interval between the laws in 67 and the introduction of cat converters and full sensor ECU control, has NOTHING to do with the sloppy design in woodworking machines. FWIW, newest cars have far better performance and mileage. My '66 Mustang had about 200 HP, weighed 2200 Lbs and got 16 MPG. At 80K, it needed an overhaul. My GTI also has 200 HP, weighs 3600 Lbs and gets 29 MPG. At 160K, it is barely broken in. WAY better. Some may complain about emission and safety laws, but we have a lot better cars because of it. Our machine tools are stuck in the '60's but we pay 2024 prices anyway. Is the technology of a SawStop worth it? At least for now, you have a choice and in cabinet saws, they hold a majority of the market so it seems consumers are willing to pay the price. Especially those who have had close calls.
Many buyers are unaware how poor these things perform. They just assume it works as it should. You pay several grand for a machine, you expect it to be competently designed. I am highlighting they most often are not and we should make noise to the OEMs do their job and improve their machines. As an example, how many buy a HF or Jet bag type dust collector thinking it is actually collecting dust when it only collects chips and power feeds the dangerous fine dust that causes lung disease into the air most efficiently? They don't know and assume a "dust collector" is that.
I still have my copy of Scientific Design of Exhaust and Intake Systems. Dust collection should be a lot easier as it is a continuous flow.
If you are an engineer designing a product, then it is NOT academic. It is your job! Expense? Many ducts are leaving a stamped panel. Easy to stamp a radius. If sometimes a tube welded to the sheet, bit of molded plastic is not expensive when we are talking 4 digit price machines. 5 cents maybe for the part, 5 more to install it, add margins through to delivery and maybe $5 retail. It could actually be cheaper to draw stamp a panel with the radius and enough flange that welding on a duct to connect the hose is not needed. We went over all kinds of things like that in the "Design for Manufacturability" program from Troy Institute.
Dust collection improved visibly on my band saw when I removed the grills. I have much more work to do as experimenting shows a focused cross-flow to do significantly better than the suck-what-you-can from open space below the table.
I changed the duct on my TS to a 6 inch. The cabinet is sufficiently large to drop out any chunks. No grill needed. It leaves about half as much in the base as it did originally. I have no lower shroud so somewhat limited what I can do without taking the table off and re-designing the whole thing.
Chris, all seams are taped. Yes, HVAC lines and elbows leak which is why they are taped. HVAC Y's are a disaster, again taped up. All branches have blast gates. 5 HP cyclone. I don't guess, I use a slack tube and an aerometer. When I say it flows like garbage, I fix it and the flow picks up, I know because I measure. I just re-did the branch that goes down to the TS ( right on the other side of the wall, and low duct where the sander, jointer and planer get plugged in. The upper branch with flex duct will get replaced with spiral duct and moved over on the wall by about 5 feet. It serves the band saw, router fence, and spindle sander. Soon probably the drill press. If you would like to gift me with a full Nordfab setup, I am sure it would be a few percent better for several thousand dollars. It would not fix badly designed machines.
How auto emission's were done in the short interval between the laws in 67 and the introduction of cat converters and full sensor ECU control, has NOTHING to do with the sloppy design in woodworking machines. FWIW, newest cars have far better performance and mileage. My '66 Mustang had about 200 HP, weighed 2200 Lbs and got 16 MPG. At 80K, it needed an overhaul. My GTI also has 200 HP, weighs 3600 Lbs and gets 29 MPG. At 160K, it is barely broken in. WAY better. Some may complain about emission and safety laws, but we have a lot better cars because of it. Our machine tools are stuck in the '60's but we pay 2024 prices anyway. Is the technology of a SawStop worth it? At least for now, you have a choice and in cabinet saws, they hold a majority of the market so it seems consumers are willing to pay the price. Especially those who have had close calls.
Many buyers are unaware how poor these things perform. They just assume it works as it should. You pay several grand for a machine, you expect it to be competently designed. I am highlighting they most often are not and we should make noise to the OEMs do their job and improve their machines. As an example, how many buy a HF or Jet bag type dust collector thinking it is actually collecting dust when it only collects chips and power feeds the dangerous fine dust that causes lung disease into the air most efficiently? They don't know and assume a "dust collector" is that.
I still have my copy of Scientific Design of Exhaust and Intake Systems. Dust collection should be a lot easier as it is a continuous flow.
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You obviously have been away from design for a while..... nothing costs 5 cents anymore, nothing. Especially installation costs. Whenever an OEM adds any parts, one of the biggest costs is hard tooling costs. Now youre talking about an injection molded plastic part I guess here. And a fairly large one at that. Im not sure where you want to put a stamped radius on the DC outlet pipe. the attachment flange?. Something in the size of 5" diameter (at the mounting flange) x at least that in length. This is also low volume as compared to many consumer products. This dramatically impacts the piece part cost based on a tool that I would guess could be in the $250k or alot more range. Now lets add logistics to and from that new supplier of this part and lets not forget aftermarket support to maintain a new part for many, many years as weve come to expect. I guarantee now that its plastic warranty , think breakage , will certainly play in here as well, further adding heavy costs. Next, how will this "simple" plastic part attach the sheetmetal? snap in? (perceived quality plays heavy here) a screwing flange of some sort (more new parts) ? .
I personally would prefer a welded sheetmetal flange on my DC outlets for their inherent ruggedness, how many times have you leaned a board vertically against something and they invariably fall over or get knocked down and slam into something? I can picture this happening and shearing off countless 5 cent plastic DC flanges.
Im not sure what you mean by draw stamping a panel either or are you referring to a progressive stamping die of some sort?.
I was referring to bad flow geometry , like multiple 45 degree elbows and not using proper DC piping
Engineering is a compromise. It has to fit in the space available and one has to be able to pay for it. Not every shop can have a dust collector at machine level and a single strait 5 foot perfectlly smooth pipe connecting it. If you would like to spring for a Nordfasb setup, I'll take it but it would require multiple 180 degree turns to attach to my equipment and maintain the strait flow prior to bends and splits. I considered a large plenum floor to ceiling to eliminate the "Y"s and most angles, but the calculations are beyond me and a low pressure drop box is one more thing to clean out.
One only needs about an inch of flange to fit a duct or hose. A radius of only an inch is enough to recover almost all of the airflow necking problem.
I did not post this to generate an argument. It was only to highlight the really stupid and legacy design of many tools.
Cost: You can still buy a solar powered electronic calculator, delivered to your door for $3. Yes scale matters. So does assembly, packaging and shipping. Less tangible is the effect of advertising and customer satisfaction with a superior -preforming design. We are talking about machines that cost hundreds or thousands of dollars. Stamped, injection molded, fabricated, vacuum formed, blow molded? One can determine the total cost of production and choose the appropriate design. A good engineer understands manufacturing as well as function. Stamping a strip, rolling it, welding, and sealing it to a panel sounds like an expensive operation. I would probably look at Kydex vacuum formed and let the end user screw it on with a strip of double sided tape seal. SOP on many tools. "some assembly required" I was highlighting a drum sander that only produces fine dust. Remember, our tools come from only a handful of OEMs. Where one brand name may sell 100s of one model, the OEM is making tens of thousands of machines with common parts used by all the OEMs. One is of course able to be happy with the status quo and put up with inferior performance. Your choice.
Stupid conversation I once had:
Q: " Why do we do it this way."
A: "Because IBM does it that way."
Q: "But why don't we to this other thing this way."
A: "Because IBM does it that way."
Lazy engineers not doing their job and happy with the status quo. No wonder we went Chapter 11.
I want my dust collection to collect dust. It starts at the machine. I selected a grossly oversize collector to overcome the ducting as it was most economical. It can only work if a machine can feed it.
I did not reply to argue either, just to basically point out that I've never seen 100% dust extraction that costs me more money as a selling point, especially if I have to marry it with a cyclonic collector @ 5+HP even if we should all have such things. Luckily, I do and I'm OK with occasionally cleaning out cabinets of sawdust caught in machine eddies. Its woodworking, and you're going to have some air born dust, it's inevitable.
The difference is some vs a lot due to poor design.
As some companies do highlight dust collection so the marketing folks seem to think it is an issue. Table saws went from empty boxes ( like my Harvey C-30) to controlled airflow shrouds like on their newer ones so at least some of the engineers think it is important. I run the SawStop large tube overarm sold specifically as improved dust collection and it does pretty well unless an edge trim. I then have a hose with magnetic port I can drop right on the table where the stream shoots out. Not perfect, but pretty good. I also have a DIY MERV 18 ambient air filter and MERV 14's on my HVAC. Days like today, I open up and use the leaf blower to get all the settled dust out. I have a lot more work to do as I fins ( by measurement) what works and what does not.
My current conclusion is the big cyclone excels at things like the table saw, jointer, and planer but I would do far better with high lift vacuums for all the other tools. If I had a shroud on my TS, then a vacuum may be better there too. If that was true, I would not need the big dust collector as jointer and planer make chips you can sweep up, no dust.
If I was starting from scratch, I think I would go for the Oneida high lift machine or that green 3 motor job over the 5 HP clear view. Or maybe 3 or 4 cheap shop vacs, each with a Dust Deputy on it, all ported to a big WIN filter stack. Then depending on which machine, you could pick just lift, or volume.
In other words, we need to back off SOP and do the engineering. One of the next mods is to out in a 1/2 inch welded wire screen under the table saw so when I drop the spindle nut, I can reach it without sifting through the dust that drops out in the big empty box. I don't mind the dust there as it is collected. Actually, I have some foam board taped in there that directs the airflow to the port much better. Seeing where the dust settles gives me a hint where to add more.
As some companies do highlight dust collection so the marketing folks seem to think it is an issue. Table saws went from empty boxes ( like my Harvey C-30) to controlled airflow shrouds like on their newer ones so at least some of the engineers think it is important. I run the SawStop large tube overarm sold specifically as improved dust collection and it does pretty well unless an edge trim. I then have a hose with magnetic port I can drop right on the table where the stream shoots out. Not perfect, but pretty good. I also have a DIY MERV 18 ambient air filter and MERV 14's on my HVAC. Days like today, I open up and use the leaf blower to get all the settled dust out. I have a lot more work to do as I fins ( by measurement) what works and what does not.
My current conclusion is the big cyclone excels at things like the table saw, jointer, and planer but I would do far better with high lift vacuums for all the other tools. If I had a shroud on my TS, then a vacuum may be better there too. If that was true, I would not need the big dust collector as jointer and planer make chips you can sweep up, no dust.
If I was starting from scratch, I think I would go for the Oneida high lift machine or that green 3 motor job over the 5 HP clear view. Or maybe 3 or 4 cheap shop vacs, each with a Dust Deputy on it, all ported to a big WIN filter stack. Then depending on which machine, you could pick just lift, or volume.
In other words, we need to back off SOP and do the engineering. One of the next mods is to out in a 1/2 inch welded wire screen under the table saw so when I drop the spindle nut, I can reach it without sifting through the dust that drops out in the big empty box. I don't mind the dust there as it is collected. Actually, I have some foam board taped in there that directs the airflow to the port much better. Seeing where the dust settles gives me a hint where to add more.
