"you don't want to buy a cyclone separator"

[Chris Friesen]

I don't know the velocity of your DC, but for argument's sake, let's say it is at least 4000 fpm, a typical velocity for material handling blowers. Inlet area (in sq. ft.) times velocity (4000 fpm) = CFM through the filter. The SDD has a 5" dia. inlet. so cross-sectional area = pi X 2.5² sq. in. = 19.63 sq. in. To convert to sq. ft. we must divide by 144 = .136 sq. ft. Multiply that times 4000 fpm and you get 545.4 CFM. Now you need to ask yourself what happens to that ASRAE rating when you try to push 545 CFM through a filter media that is rated at 11 fpm (amd what happens to CFM when you try to push it through that filter). I don't know the answer, but am also certain no salesman will either. I doubt the rating will be as good as claimed!

Again, while not rocket science, dust collection is physics and can be complicated.

You're comparing different units. You need to factor in the area of the filter material. Looking at the website the 39" filter has 110 sq. ft. of media, which at 11 FPM would let you push 1210 CFM through the filter.

[Bradley Potts]

One way to avoid the long runs (and thus the drop in CFM and SP) is to cluster tools around the DC. This particular configuration has always impressed me:
http://www.finewoodworking.com/works...-workshop.aspx

Joe, thanks for the link, that's an admirable setup, although I am inclined to go to a galley arrangement that minimizes my steps.

-- Bradley

[Bradley Potts]

Thought about this a little,
You are correct because of what is available commercially. Technically, just because your duct run is longer, does not mean you need a bigger collector. It means you may need a different fan/motor to overcome the extra system losses. The cyclone and filters do not need to be any bigger because you do not need to increase the flow, only the SP capability to pull that volume through the system.

However, with pre-packaged commodity hobby systems, you do not have a choice to buy a larger fan/motor only. For example, I don't think you can buy a DC-1100 with a 1.5, 2, or 3HP motor. As you go up in motor size, you go to the larger system.

Right, and Michael, another couple of thoughts:

* Mathias Wandel has an interesting vid on his WoodGears.ca about an impeller he designed and built from wood. It took me quite a while to find the small one that this links to, but I recall seeing a YouTube vid of a somewhat taller one that he hooked up to his fancy-pants commercially produced DC, and it out sucked it. The key here is that he is running a somewhat delicate impeller only because he has an inline separator ahead of the fan section, and this brings up an interesting point: Simply by using a DIY improved impeller, we can effectively super-charge our existing DC's just because the factory designs are very inefficient shapes and sizes in order to safely allow the digestion of larger damaging debris that our separators remove.

* If we want the benefits of separation, then we should reap all the benefits by juicing up our impellers IMHO. This mod is worthwhile because it it gets more air movement with the same motor and the same power consumption -- that's the point of efficiency improvements.

* I recently went to the trouble of looking at the guts of a number of Made in China/Taiwan DC's, because my local HF and Rockler are just 2 doors apart in the same strip mall. Not too surprisingly, the only real differences I could see between the motors, the fans, the fan housings, the bags, the collector rings, the darn plastic hose fittings and blast gates, even the mobile bases on the mobile ones, and the hoses themselves boiled down to paint-job, and differences in the diameter of the collector rings! Certain of the spring straps were nicer, the Jet has a "window" in the collection bag, etc.


-- Bradley

[Bradley Potts]

My shop is a bit bigger than yours but still not huge and I started out with the theory that move around was more space efficient than ducting. Having live with it for ~3 years now I'm not as convinced. You have to have space to move it and it seems that that starts to add up to more space than it would take to just have it in place. In the end I ended up with a tool cluster and don't really move the DC much (unless I need to roll the BS to the front of the shop to do longer resawing in which case the DC follows). YMMV but walk though the workflow a few times and see how much space is saved or taken as the case may be.

Ryan, thanks for that insight. Right now, I have the privilege of using my mobile unit as I work in my driveway -- yes, it sucks. For new proper shop, I'm inclined to go w/ my stationary tools installed into a common height 1-wall or galley style or L-shaped bench arrangement. It will be interesting to see what I settle on.

-- Bradley