Static pressure Calculation for Dust Collection systems

[jpitz31]

Been doing a lot of digging on the forum about the dust collection systems everyone has been building and I have been wondering about how the size of the inlet opening effects the FPM required to pick up find dust.

According to what I have been reading you need lots of FPM and CFM to pick up the dust. Optimum hose size has to be around 6" to get the FPM needed to pick up the dust.

Here is an excel spreadsheet I found that has some good information and has a built in calculator for hobby and commercial dust collection systems.

http://billpentz.com/woodworking/cyclone/StaticCalc.xls

Thanks

Joe

[DocWheeler]

Joe,

That spreadsheet scares the crap out of me. I bought a horse-and-a-half collector for my drum sander and was going to use it on my CC, but that spreadsheet indicates that I should have about a five horse power collector!

I'm going to have to think about this on my drive home.

[jpitz31]

Yes Doc,

It scares me as well. I was going to pick up the small dust collector at Harbor Freight Tools. But after looking at the calculations I am going to have to do some more digging.

Joe

[locovalley]

I didn't look at the calculator but I have a 1.5 HP collector hooked to my downdraft and it works like a champ. As a matter of fact I use the same system with my tablesaw, lathe, and router tables and It works fine for my purposes. I have the idea that the calculator is programmed by a dust collector salesman. I'll stick with what I got.

JM

[Pratyeka]

ahem, I have a cheap 1hp, 600cfm, with a 4" hose picking up everything inside my CW with a modified intake nozzle... pictures soon.

[fwharris]

ahem, I have a cheap 1hp, 600cfm, with a 4" hose picking up everything inside my CW with a modified intake nozzle... pictures soon.

Same here!!! (650 cfm) Top and bottom vents with a little air push...pictures soon too...

[mfdchief]

Bill Pentz is well known in the woodworking/dust collection arena for his efforts on buliding the best systems for the money. Without studing them, I am guessing that these specs are for a cyclone system with multiple ductwork runs and blast gates to several woodworking machines. I have a 2hp Grizzly cyclone that I have yet to hook to any of my machines and still use the old Craftsman shop vac every 15 minutes or so for the CW. Just my .02 worth.

Mark

[jpitz31]

I did go back and do a bit more reading on the spreadsheet.

On the table named "Hobbyist Fan table for shop ducting..."

There are two columns listed "For Shop with no ducting" I would imagine that most of us hobbyists are in this situation, I know that I am.

The HP and fan sizes are a bit more down to earth in size and price.

For example 1 1/2 HP and a fan size of 11.50 will give 716 CFM with a 10' 6" hose. (He gives this a blue rating, picks up chips)

Or at 2 HP and a fan size of 12" gives 1214 CFM (he gives a green rating, picks up fine dust)

I would image that this kind of setup is what most of us would be able to afford and have enough space available.

Thanks

Joe

[DocWheeler]

Joe,

Several of us made cabinets that contain blowers to pull air out of the bottom 17" X 2" slot. There is a great advantage to this - it is self-contained and can be used anywhere. I used a blower (to draw air out of the cabinet) that was only about 750 CFM and by the time I pulled the air through a "tight" filter, it is really not quite strong enough. Several other people used either a stronger blower and/or a more "open" filter and they work well.

The down-side of just drawing air out the bottom is that wider boards and sleds keep too much dust on the top, there needs to be more movement across the top of the board to move the debris. Several people use various methods of using positive pressure to direct dust to the back of the machine, and some have pulled air from the "back" of the machine by mounting a 2.5" - 4" duct port on that back surface (see Kenm810's pictures).

This is a summary of the many posts on the subject as I see it.

[Kenm810]

Hi Joe,

If you have some time, this it a pretty good thread of posts to read,
it covers loads of information, photos, and ideas about dust and chip control
in your new caving system. :wink:

Dust Collector (http://forum.carvewright.com/showthread.php?t=10145&highlight=Down+draft) (http://forum.carvewright.com/images/misc/multipage.gif 1 (http://forum.carvewright.com/showthread.php?t=10145&highlight=Down+draft) 2 (http://forum.carvewright.com/showthread.php?t=10145&page=2&highlight=Down+draft) 3 (http://forum.carvewright.com/showthread.php?t=10145&page=3&highlight=Down+draft) ... Last Page (http://forum.carvewright.com/showthread.php?t=10145&page=8&highlight=Down+draft))

[AskBud]

Joe,

Several of us made cabinets that contain blowers to pull air out of the bottom 17" X 2" slot. There is a great advantage to this - it is self-contained and can be used anywhere. I used a blower (to draw air out of the cabinet) that was only about 750 CFM and by the time I pulled the air through a "tight" filter, it is really not quite strong enough. Several other people used either a stronger blower and/or a more "open" filter and they work well.

The down-side of just drawing air out the bottom is that wider boards and sleds keep too much dust on the top, there needs to be more movement across the top of the board to move the debris. Several people use various methods of using positive pressure to direct dust to the back of the machine, and some have pulled air from the "back" of the machine by mounting a 2.5" - 4" duct port on that back surface (see Kenm810's pictures).

This is a summary of the many posts on the subject as I see it.
Like others, I have had limited success with some of the above methods. I have a feeling that some of our machine problems start with too much dust and chips on the board surface and moving parts.

I'm trying to develop a efficient, usable and easy to make, Dust/Vacuum Head.
I've played with a probe to place in the Flex slot, but that's not the answer.
I've designed take-offs on several store bought Vacuum heads and did not like the air-flow of my design as I could not easily sculpt the inside as they had.

I'm currently working on what may be my best attempt so far.
If it works well, I should be able to make pattern(s) for placement in the Pattern Store

I have modified the cover to accept the Vacuum Head and have made the attachment easy to place & remove. I'm also working on a good/possible way to use the muffler port to move the "Filtered" air back into the cutting area to "assist" the air flow.

I'm waiting on a new part (top bag) for my Shopsmith DC-3300. I want to see if I get better movement with that new bag. If not it may just be that the DC-3300 is not strong enough to do the job (it's rated at 360 CFM).
AskBud

[jpitz31]

Thanks Ken,

I have been going through that thread series presently.

The only reason I brought up the CFM and FPM idea, is I want to make sure I get the surface area of the collector big enough and wanted to feel out what size fan and HP everyone is using. I want to make sure that I do not under power the fan.

Bud, That is a way cool idea and nice images of your setup.

If you put a pattern out for sale I would be interested in seeing the design.

Thanks

Joe

[Jeff_Birt]

You must have enough CFM to remove all the really dangerous small particles, otherwise you just have a chip collector. Most of the least expensive units I looked at has really poor filters and would spew most of the really fine, really dangerous dust back into the work space.

As I recall the unit I got from Grizzly is about 2 hp and 1200 CFM. I don't have duct work as my shop is too small. There is one 4" hose 10' long that is hooked to the machine in operation and another 10' pieces hooked to a floor sweep that is gated (mostly) off when not in use.