Rules of Dust Collecting

[Steven Alford]

As stated in a previous post, I ended up with a new (used) dust collector because mine "bit the dust" (hehe).

I got a Jet DC-650. I realize it is probably only good for one machine, but what are the engineering possibilities of reducing the hose down to 2"?? Will this increase my air flow and allow for use on two machines, or is this a pipe dream??
My thought is that we are dealing mostly with fine dust, so there will not be chunks and chips of wood.

[fwharris]

As stated in a previous post, I ended up with a new (used) dust collector because mine "bit the dust" (hehe).

I got a Jet DC-650. I realize it is probably only good for one machine, but what are the engineering possibilities of reducing the hose down to 2"?? Will this increase my air flow and allow for use on two machines, or is this a pipe dream??
My thought is that we are dealing mostly with fine dust, so there will not be chunks and chips of wood.

Steve,

I think the answer to your question is, no. I found with my old version top mount (shop vac floor nozzle (sound familiar?) that my DC acted like it was starving for air.

I used a 4" to 2" reducer with about 4 foot of 2" hose to the nozzle and found that the amount of air movement at the nozzle was not adequate for picking up the dust.

I recall someone posting some good technical info in the dust collection thread about this.

[AskBud]

Half hour video on DC Air-Flow
http://www.shopsmithacademy.com/SS_A...Collection.htm
DC Chart
http://www.woodcraft.com/Articles/Ar...?articleid=657
AskBud

[Steven Alford]

Wow!
According to the math this man gives in the video, a 650 CFM machine will produce 13,374 FPM (feet per minute) which is enough to run three machines. One machine needs 4,000 FPM. I find that hard to believe. That is using a 3" pipe.

[lawrence]

I'm certainly no expert, but here's my .02

You want to keep your pipes as large as the input on your collector for as far as you can... don't constrict things at all as you are not trying to increase velocity (as you are probably thinking with the decreased dimension) but are trying to maintain as high a volume as possible... The basic rule here is keep your line to your machine as

1. Short as possible... I keep my lines for my 1100cfm machine around 10 feet and that works fine--it is usually the safest bet with the smaller dc's to take your dc to the tool.
2. as wide as the entry point on the machine.. if that is 4 inches use 4 inch line, if it is 5 or 6, try to use that width and only constrict at the last minute. I'm guessing your input will be 4 inches.
3. As smooth as possible-- flexible hose (with one or two expensive exceptions) has ridges on the inside-- this creates friction which decreases dust flow... I myself use flexible hose but will eventually switch to smooth. If your dc is going to be permenantly mounted you may want to consider going with a ridgid pipe system. (just remember to ground it)

If you have to use turns, use as gentle a turn as is possible... 2 gentle turns are better than one 90. It's amazing how much a tight bend will restrict dust flow.

Also, I highly recommend that for a 650 cfm machine you limit yourself to one line (or multiple lines with gates) I use gates and place them as close to the dust collector as possible while still being functional.

As for narrowing down to a 2 inch hose... this will restrict flow as has already been stated. I know it sounds counter-intuitive, but you want to keep your volume high with a single wide input.

Good luck and I hope this helps,
Lawrence

[fwharris]

Lawrence,

Great information and well worth the .02.

[sk8nmike]

Here's another 1/2 cent on the issue of grounding. If you are just building a DC system or yours is easy to disassemble run a bare copper wire from the blower case down the inside of each tube. If that's not possible wrap the wire around each tube with no more than 1 foot per turn as you go. This will cut down on the static build up on the tubes preventing clogs and nasty jolt

[HighTechOkie]

Wow!
According to the math this man gives in the video, a 650 CFM machine will produce 13,374 FPM (feet per minute) which is enough to run three machines. One machine needs 4,000 FPM. I find that hard to believe. That is using a 3" pipe.

The Jet DC650 is rated 650CFM @ 4". If you decrease the pipe diameter, CFM will decrease also. Running the numbers for 4" gives you ~7500FPM. After figuring static pressure drop from your ducting, it basically is enough for 1 high chip producing machine like a planer or drum sander, or two smaller machines like a band saw and table saw or CW in our case.

There are two things to look at when looking at vacuum, pressure and flow. Small shop-vac type machines use high pressure/low volume, while a dust collector is high volume/low pressure.

Rob

[Steven Alford]

Thanks guys, very good info.
I am going to stick with the 4" and run it through a hole in the garage wall into the work shed on the other side of the wall. I need to put it at about 7 feet up, over the rafters of the shed and down to the CW. That way the ducting is somewhat permanent and out of the way so I can move around in the shop. I am thinking that the total length of ducting should be around 14 feet. Is that too much??

I will have to rebuild the downdraft setup so that instead of the duct going to the underside of the CW (too many bends in the duct) I will have to build a box under the CW (5" high) that has a 4" connector on the side.

I ordered the front dust collector from Floyd so there will be a "Y" connection to that.

Getting a hole in the garage wall is my biggest challenge.

[Steven Alford]

Here's another 1/2 cent on the issue of grounding. If you are just building a DC system or yours is easy to disassemble run a bare copper wire from the blower case down the inside of each tube. If that's not possible wrap the wire around each tube with no more than 1 foot per turn as you go. This will cut down on the static build up on the tubes preventing clogs and nasty jolt

When you run the wire inside the ducting, do you just connect the wire to the metal of the dust collecting machine or do you actually have to have a grounding rod of some sort?? And at the other end (the PVC connected to the CW) what do you connect the wire to? Or can it just be attached to the PVC pipe??