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.

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